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# LIFE PROCESSES

### INTRODUCTION

• Living organisms require oxygen, water and food in every cell of their various tissues to sustain life.
• Living organisms require oxygen, water and food in every cell of their various tissues to sustain life.
• The various processes essential for maintenance of life are called life processes, which are nutrition,    respiration, transportation and excretion.
• Energy is continuously required by living organisms to carry out various life processes. This energy is   liberated due to intake as well as utilisation of nutrients and also by respiration of an organism.
• Organisms can be classified into two groups – autotrophic and heterotrophic.
• Respiration is the process in which food is oxidised to release energy, which can be aerobic or   anaerobic. The first step in respiration is called breathing.
• Animals have evolved different organs for the uptake of oxygen from the surroundings and for release   of carbon dioxide.
• In human beings, the transport of materials like oxygen, carbon dioxide, food and excretory products   is a function of the circulatory system.
• The circulatory system consists of heart, blood and blood tissues.
• In higher plants, transport of water, minerals, food and other materials is a function of the vascular   tissue which consists of conducting tissues, xylem and phloem.
• All plants and animals produce harmful substances due to a number of metabolic activities occurring   in their body tissues. These substances are to be eliminated from the body as they are toxic in   nature.
• In human beings, excretory products in the form of soluble nitrogen compounds are removed by the   nephrons in the kidneys. Plants use a variety of techniques to get rid of waste material; which are   stored in the cell-vacuoles, removed in the falling leaves or excreted into the surrounding soil.

### NUTRITION

The whole process by which an organism obtains its food is referred to as nutrition.

#### NUTRITION

Nutrition It is the method of obtaining nutrients from the environment. It can be defined as the process by which the organism ingests, digests, absorbs, transports and utilises nutrients and disposes off their end products.

#### NUTRIENT

Nutrient The different component of food that have distinct functions like providing energy. materials for body building, maintenance & regulation of metabolism are called nutrient. For exmple-Proteins, Minerals, Vitamin, Carbohydrates, fats.

#### Modes of Nutrition

(a) Autotrophic Nutrition

In this type of nutrition, organisms synthesise the organic materials they require from inorganic sources. All green plants are autotrophic and use light as a source of energy for the synthesis.
Autotrophs

The organisms which make their own food from carbon dioxide and water in the presence of sunlight and chlorophyll are called autotrophs. These organisms are also called producers and include green plants and some bacteria.

### PHOTOSYNTHESIS

It is the process by which green parts of the plant synthesise organic food in the form of carbohydrates from CO2 and water in the presence of sunlight.

$6C{O_2} + 6{H_2}O\mathrel{\mathop{\kern0pt\longrightarrow}\limits_{chlorophyll}^{light}} {C_6}{H_{12}}{O_6} + 6{O_2}$

In plants and most algae it occurs in the chloroplasts and there are two principal reactions:

(i) Light reaction (light-dependent) requires the presence of light energy from sunlight which is obtained by photosynthetic pigments, i.e., chlorophyll and used to bring about the photolysis of water.

${H_2}O \to 2{H^ + } + 2{e^ - }$

(ii) Dark reaction (light-independent) i.e., this reaction is not dependent on light and during this reaction carbon dioxide is reduced to carbohydrate in a metabolic pathway known as the Calvin cycle.Difference between light and dark reactions

### Various Components of Photosynthesis

Various components necessary for the process of photosynthesis are :

1.Chlorophyll
2. Carbon dioxide
3. Sunlight
4. Water
This can be demonstrated with the help of various experiments.

#### 1. Chlorophyll

Chlorophyll is green pigment present in the green leaves.

#### 2. Carbon-Dioxide

• Photosynthesis has been found to takes place in a very wide range of CO2 concentration.
• Within the range the rate of photosynthesis will decrease or increase with decrease or increase in CO2 concentration, provided other factors are not limiting.
• Relatively high concentration of CO2, reduces the rate of photosynthesis and if given for a considerable period of time, has detrimental effect on the process itself.

#### 4. Water

• Plants absorb water from the soil with the help of root system. The effect of water deficiency on the rate of photosynthesis is indirect one.
• Decrease in H2O content of the leaves may cause partial or complete closure of stomatal opening, and hence a reduction in the rate of diffusion of CO2.
• A partial drying of the cell walls cause decrease in its permeability to CO2, Another indirect effect of water deficiency is that the accumulation of sugar within the cells increases the rate of respiration and thus decreases apparent photosynthesis

(b) Heterotrophic Nutrition

The type of nutrition in which organisms derive their food (nutrients) from other living organisms. In heterotrophic nutrition, the energy is derived from the intake and digestion of the organic substances, normally of plant or animal tissue. Heterotrophic mode of nutrition are of different types :

(i) Saprotrophic Nutrition
It refers to the mode of nutrition in which organisms obtain nutrients from the dead and decaying organic matter, e.g., fungi, yeast and bacteria are called saprophytes.

(ii) Parasitic Nutrition
It refers to the mode of obtaining food synthesised by others. The organism which obtains food is called the ‘parasite’ and the organism from which food is absorbed is called the ‘host’. This nutrition is observed in fungi, bacteria, a few plants like Cuscata and some animals like Plasmodium and roundworm.

(iii) Holozoic Nutrition  It refers to the mode of nutrition in which the complex organic matter in the form of solid food is ingested, digested and then absorbed into the cells and utilised, e.g. amoeba, frog, human beings.

#### Heterotrophs

The organisms which cannot make their food and depend directly or indirectly on autotrophs for their survival are called heterotrophs. These organisms include animals and fungi.

### Type of Heterotrophic Nutrition

1. Saprophytic or Saprotrophic Nutrition:  It is a mode of heterotrophic nutrition in which food is obtained from organic remains like dead organisms, excreta, fallen leaves, broken twigs, food articles, etc. Organisms performing saprophytic nutrition are called saprophytes.

2. Parasitic Nutrition :  · It is a mode of hetrotrophic nutrition in which a living organisms flourishes by obtaining food from another living organism. The lving organisms which obtains food and shelter from another organism is called parasite. The organism which provides food and shelter to a parasite is known as host. An external plant parasite is Cuscuta (Amarbel). It is a non-green plant that sends haustroria or sucking roots into host plant for obtaining food and water.

3. Holozoic Nutrition : It is a mode of heterotrophic nutrition which involves intake of solid pieces of food. Since solid food is taken in, holozoic nutrition  is also called ingestive nutrition. The food may consist of another animal, plant or its parts. Depending upon the source of food, holozoic organisms are of three types – Herbivores, carnivores, omnivores.

Herbivores :

(L.herba-plant, vorare-to eat) They are holozoic organisms which feed on plants or plant parts, e.g., Cow, Buffalo, Deer, Goat, Rabbit, Grasshopper, Elephant, Squirrel, Hippopotamus.

Carnivores :

They are animals which feed on other animals. Carnivores are also called predators they hunt, kill and feed on their preys, e.g. Lion, Tiger, Leopard, Snake, Hawk.

Omnivores :
(L.omnis-all, vorare-to eat)
They are holozoic organisms which feed on both plant and animal materials, e.g. Cockroach, Ant, Pig, Crow, Rat, Bear, Dog, Humans.

#### Nutrition in Amoeba

Protozoan protests carry out holozoic nutrition through intracellular digestion.

Fig. – 4 Nutrition in Amoeba

Some protests can ingest food particle from any point on the surface (e.g., Amoeba) while others have fixed points for the same (e.g., Paramoecium). Protozoans like Amoeba capture food with the help of temporary finger-like processes called pseudopodia. Protozoans like (Paramoecium have small hair-like processes called cilia.) Beating of cilia creates current in water  that pushes food particle through cytostome or cell mouth. The process of ingestion of solid food  particle by a cell or unicellular organism is called  phagocytosis.  As soon as Amoeba comes in contact with a food particle or prey, it throws pseudopodia all around the same. The tips of encircling pseudopodia fuse and the prey comes to lie in a vesicle or phagosome. This method of intake of food is called circumvallation. Amoeba can also ingest food by other methods like import, circumfluence and invagination.

### Digestive system of human

The organs which are responsible for ingestion, digestion, absorption, assimilation and egestion constitute the digestive system. The digestive system comprises of the alimentary canal and associated digestive glands.

#### (A) Alimentary canal

The alimentary canal is basically a long tube extending from the mouth to the anus. It is differentiated into following parts.

(i) Mouth
It is a transverse slit bounded by movable lips. The lips serve to close and open mouth. holding the food in between and also help in speaking. The floor of the buccal cavity has a tongue bearing taste buds. Man possess teeth on both the jaws. There are 32 teeth of four different types, namely incisors, canines, premolars and molars. ·

• Digestion may be intracellular (Paramoecium) or extracellular (multicellular animals).
• The process of digestion starts in the mouth cavity and continues upto the intestine.
• In the mouth, food gets mixed up with saliva secreted by salivary glands.
• Saliva contains an enzyme ptyalin which breaks polysaccharide starch into disaccharide maltose.$Starch\mathrel{\mathop{\kern0pt\longrightarrow}\limits_{(Sali{\mathop{\rm varyAmylase}\nolimits} )}^{Ptyalin}} Maltose$
• The food from the mouth cavity passes into the stomach through the oesophagus.

(ii) Pharynx
It is a short, conical region that lies after the mouth cavity. The pharynx are divided into two parts — the nasopharynx which lies behind the nasal cavities and the oropharynx which lies behind the mouth.

(iii) Oesophagus (food pipe)
It is a long, narrow, muscular tube which leads to the stomach, The oesophagus is a collapsible muscular tube leading from pharynx to stomach. There are no digestive glands but mucus glands are present.

(iv) Stomach
It is a thick, muscular and J shaped sac present on the left side of upper part of abdomen. Gastric glands are present in the wall of stomach. These releases gestric juice or digestive juice, which contains mucus. hydrochloric acid and a protein digesting enzyme called pepsin. Mucus lubricated the food and protects the inner linning of the stomach from the action of HCl. HCl creates an acidic medium, which facilitates the action of enzyme pepsin and kills the bacteria present in food. Pepsin breaks down proteins into peptides. Sphincter muscles regulate the exit of food from stomach into intestine due to peristaltic waves of stomach.

Fig. -5 Human alimentary canal

(v) Intestine
It is the largest part of alimentary canal which is fitted into a compact space because of extensive coiling. It is distingushed into small intestine and large intestine.

•  Small intestine
The small intestine is the site of the complete digestion of carbohydrates. proteins and fats. It receives the secretions of the liver and pancrease for digestion. Food is mixed with three digestive juices (bile juice, pancreatic juice and intestinal juice)
Bile juice (from the liver) provide alkaline medium and emulsifies fats (conversion of larger fat globules into smaller fat droplets) but it is non enzymatic digestive juice so has no chemical action on food.
Pancreatic juice (from the pancreas) contains trypsin, pancreatic amylase and pancreatic lipase enzymes which digest the peptons, starch and fats into peptides, maltose and fatty acids and glycerol respectively.
The wall of intestine secretes intestinal juice which contains enzymes for complete digestion of proteins into amino acids, carbohydrates into glucose and fat into fatty acid and glycerol.
The inner lining of the small intestine has numerous finger like projections called villi which increase the surface area for absorbtion of digested food.
These are richly supplied with blood vesseles.
• Large Intestine
It is much shorter and wider than small intestine and is differentiated into three regions viz., caecum, which is small rounded blind sac from which vermiform appendix arises; colon is the inverted U-shaped tube and the rectum opens to exterior through anus.(vi) Anus
The rest of the material is removed from the body via anus. The exit of waste material is regulated by anal sphincter.

#### (B) Digestive Glands

Various glands associated with alimentary canal are :

Fig. -6 Salivary glands of man

(i)  Salivary Glands
The salivary glands secrete the first of the digestive juices, the saliva. There are three pairs of salivary glands, namely the parotids, sub-maxillary and sublingual glands.

(ii) Gastric Glands
They are branched tubular glands which lie in the mucus membranes of the stomach. They secrete gastric juice, which is clear, acidic containing HCl, enzymes and mucus.

(iii) Liver
It is the largest gland in man and lies below diaphragm in the right upper part of abdomen. Liver comprises of two lobes, right and left, where the right lobe is much larger than the left lobe. The cells of liver, i.e., hepatic cells produce bile juice which flows out of liver through hepatic ducts forming common bile duct and opens into duodenum. Bile juice then flows into gall bladder through the cystic ducts.

Fig. -7 Liver and Pancreas and their ducts

(iv) Pancreas
It is a soft lobulated gland present in between the loops of duodenum. It secretes pancreatic juice containing enzymes which is poured into duodenum with the help of pancreatic duct.

Table: Summary of the digestive enzymes of various glands with their secretions and end products of Digestion in Man

## RESPIRATION

Respiration is essential for life because it provides energy for carrying out all the life processes which are necessary to keep the organisms alive.

#### INTRODUCTION

All living cells need a constant supply of oxygen to enable them to carry out the essential biochemical reactions of their metabolism. This oxygen supply is provided by the blood which also removes the CO2 and other waste products. Where does the blood get the oxygen, and what does it do with the CO2 ? The oxygen comes from the outside air, into which also the CO2 is discharged. The respiratory system provides the means of doing this.

Anabolism
It is the synthetic or constructive metabolism. In this case smaller molecules unite to form larger molecules. e.g., photosynthesis.

Catabolism
It is the destructive metabolism which involves the breaking down of large organic molecules. This is of ten accompanied with the liberation of energy e.g., respiration.

Metabolism
The sum total of the constructive (anabolism) and the destructive (catabolism) chemical  changes occurring in living beings.

Breathing
The process involving inspiration (intake of air or oxygen) and expiration (removal of air or carbon dioxide) is called breathing. No enzymes are involved in this process.

Respiration
The process of releasing energy from food is called respiration.
ATP. It refers to a nitrogenous compound, Adenosine Tri-Phosphate. The energy released during cellular respiration is immediately used to synthesise a molecule called ATP from ADP and inorganic phosphate as

ATP is used to fuel all other activities in the cell. Therefore, it is said to be the energy currency for most cellular processes.

#### Type of RespirationType of Respiration

1. AEROBIC RESPIRATION
It is a type of respiration which occurs in the presence of oxygen. The organisms showing aerobic respiration are called aerobes.

${C_6}{H_{12}}{O_6} + 6{O_2} - \to 6C{O_2} + 6{H_2}O + 2830kj(686Kcal)$

Break down of glucose occurs in various steps which can be summarized as :

#### 2. ANAEROBIC RESPIRATION

When food is oxidized without using oxygen is called anaerobic respiration.

(a) Fermentation
Anaerobic respiration is also called fermentation. It is found in lower organisms like anaerobic bacteria and yeasts :

${C_6}{H_{12}}{O_6}\buildrel {Bacteria} \over\longrightarrow 2{C_2}{H_5}OH + 2C{O_2} + 2ATP$

$SugarSoluion\buildrel {Yeast} \over\longrightarrow Ethanol + C{O_2} + Energy$

(b) Temporary anaerobic respiration
may occur even in our own body in the fast working skeletal muscles, as in fast running, walking, swimming etc. The fatigue experience is due to lactic acid accumulated in the muscles in the shortage of oxygen, a condition which may be called Oxygen debt. When one rests after the exercise the lactic acid gets slowly oxidized by the oxygen later available and then the “debt” is cleared.

${C_6}{H_{12}}{O_6}\mathrel{\mathop{\kern0pt\longrightarrow}\limits_{Cytoplasm}^{Glycolysis}} PyruvicAcid\buildrel {AB{O_2}} \over\longrightarrow LacticAcid + 2ATP$

Differences between Aerobic and Anaerobic respiration

#### RESPIRATION IN PLANTS

Respiration in plants is simpler than the respiration in animals. Gaseous exchange occurs through:
(i) Stomata in leaves
(ii) Lenticels in stems
(iii) General surface of the roots

(i) Respiration through stomata :

• Stomata are small apertures found on the surface of leaf.
• For the process of respiration, oxygen enters stomata by the process of diffusion and then into other cells of the leaf.
• This oxygen is utilized in the break down of glucose to carbon dioxide and water.
• This does not occur in a single step but in a series of steps.
• When concentration of CO2 increases inside the cells, it is diffused out through stomata.

(ii) Respiration through lenticels :
Lenticels are the openings in the bark of woody stems.

(iii) Respiration through general surface of the roots :

• Exchange of gases in roots take place by the process of diffusion, when oxygen diffuses into the root hairs and passes into the root cells, from where carbon dioxide moves out into the soil.
• In older roots there are no root hairs present. Instead they have layer of dead cells which is protective in nature and encloses small openings. These are used for gaseous exchange between soil and inner living cells.

Difference between Respiration and Photosynthesis

#### Respiration in AnimalsRespiration in Animals’

It takes place with the help of some specific respiratory organs  which differs in different animal groups, according to their habitat. Aquatic animals like fish, prawns and mussels have gills as respiratory organs ; land animals like lizard, bird, human have lungs, frogs breathe both by skin and lungs and insects like grasshopper, housefly or cockroach have air lubes or trachea as their respiratory organs.

Fig. 4 Respiration in amoeba

Fig. 5 Respiration in fish

#### HUMAN RESPIRATORY SYSTEM

This kind of respiration, where lungs are the main structures is called pulmonary respiration. Respiratory system communicates wilh the outside atmosphere through external nostrils which draw air into nasal cavities.

Respiratory organs in human beings consists of :

1. Nostrils and nasal cavity
2. Nasopharynx
3. Larynx
4. Trachea
5. Bronchi
6. Alveoli
7. Lungs
8. Diaphragm

1. NOSTRILS AND NASAL CAVITY
Nostrils are two nasal openings which serve like the gateway of the respiratory system. The nasal cavity has one central septum that divides the whole cavity into two parts.  The nasal cavity secretes mucus which helps to remove the dust particles from the air and air also normalizes the air while swallowing food.

2. NASOPHARYNX2. NASOPHARYNX
It is the junction between the nasal cavity and the larynx. It is guarded by epiglottis which closes the passage of air to body temperature.

3. LARYNX (Also known voicebox)
It is the voice box which is interposed to prevent the entry of food material in the trachea. While swallowing this part rises and falls. Larynx contains two ligamentous folds called vocal cords. Air expelled between the vocal cords vibrates them producing sound.

4. TRACHEA
Trachea is about four inches longt. It is composed of 16-20 incomplete cartilagenous rings. These cartiligenous rings ensure that trachea does not collapse even when there is very less air in it. The oesophagus is situated on the back of the trachea.

5. BRONCHI
The bronchi are formed by the bilateral bifurcation of trachea. Further divide into bronchioles which end into alveoli inside the lungs.

6. Alveoli
Alveloli are lined by a layer of epithelial cells and surrounded by a network of blood capillaries. Alveoli covers about area of 80 metre square when spread out. This large surface area helps in efficient exchange of gases.

7. LUNGS
These are two spongy elastic organs formed of alveoli bronchioles, blood vessels etc. The right lung has three lobes and the left lung has two lobes.
Lung is covered by a double membran known as ‘pleura’. The visceral layer of the pleura is closely attached to the lungs. The free layer on the thoracic wall is known as parietal layer. Between two pleural layers, there is a fluid which lubricates the surface and prevents friction between the lungs and the chest wall during respiration.

8. DIAPHRAGM
It is a large dome shaped sheath of muscle which separates the thoracic cavity from the abdominal cavity. The contraction of diaphragm brings about it’s downward movement which decreases the intrathoracic pressure and increases the intra-abdominal pressure.

Fig. 7 Human Respiratory System

Mechanism of Breathing
Lungs cannot expand or contract of their own. The contraction and expansion of lungs is brought about by diaphragm muscles and external intercostal muscles.

BREATHING DEFINATION

(A) Inspiration

It is also known as inhalation. It is as a result of combined action of the ribs and the diaphragm.

• Ribs move upward and outward by a set of muscles known as intercostal muscles thus enlarging the thoracic cavity.
• Diaphragm, which normally remains arched upward like a dome, towards the base of the lungs, flattens to an almost horizontal plane and thus enlarging thoracic cavity lengthwise.

As a result of above two actions of ribs and diaphragm, thoracic cavity increases in size. It leads to the decrease in pressure in the lungs as compared to the atmospheric pressure. Therefore, the atmospheric air which is at a greater pressure rushes into the lungs.

(B) Expiration
It is also known as exhalation. It is the reverse of inspiration. It again involves the action of ribs and diaphragm.

Fig. 8 Diaphragm Depressed During Inspiration

• Ribs move downward and inward by the action of other set of intercostal muscles.
• Diaphragm moves upwards to form a dome shape thus, putting pressure on lungs.

As a result, there is increase in pressure in the thoracic cavity as compared to the atmospheric pressure. Lungs are therefore compressed forcing the air out into the atmosphere.

Gas Exchange in Alveoli

• Blood rich in carbon dioxide, i.e., the deoxygenated blood enters the capillary network of alveolus.
• CO2 diffuses into the alveolar cavity because of its higher concentration in the blood.
• Alveolus has a higher concentration of oxygen as compared to the blood in capillaries.
• Therefore, O2 diffuses into the capillaries and combines with haemoglobin of red blood cells to form oxyhaemoglobin to be transported throughout the body.

Gas Exchange in Tissues.

• In the cells, continuous metabolism of glucose and other substances results in the production of CO2 and utilisation of O2.
• The concentration of oxygen in the cells and tissue fluid decreases while the concentration of CO2 is higher than in the capillaries.
• Therefore, oxyhaemoglobin breaks down releasing  O2 diffuses  out from the capillaries into the tissue fluid and then into each and every cell.

#### Lung volumes and capacities

Spirometer is the instrument used to measure lung volume & capacities.

(1) Tidal volume
Amount of air inhaled and exhaled during quiet breathing = 500 ml.
air : A small amount of air breathed in respiratory tract that does not take part in gaseous exhange.
(b) Alveolar
air : Part of tidal air takes part in gaseous exhange. It occurs at alveoli is called alveolar air. It is about = 350 ml.

(2) Inspiratory reserve volume (IRV) :
(Complemental air) Maximum amount of air that can be inhaled forcibly following normal expiration (Tidal expiration).
It is about = 3000 ml.

(3) Expiratory reserve volume (ERV) :
(Supplemental air) Maximum amount of air that can be expired forcefully after a tidal inspiration.

(4) Residualvolume :
Volume of air that remains in
lung after maximal expiration.

(5) Vital capacity : Maximum volume of air that can be takes in or expelled by maximum inspiration and expiration = 4500ml ; V. C. = T. V. + I. R. V. + E. R. V.

(6) Total lung capacity : Maximum air which can at any time be taken in two lunge = 6000 ml.
TLC = V.C. + R.V.
Gas exchange occurs in alveoli. Fresh air has
high concentration of oxygen and very low concentration of carbondioxide. As a result oxygen diffuses from alveolar air to blood present in capillaries around the alveoli. Carbon dioxide diffuses from blood in to alveolar air.

• Respiratory cycle-inspiration, expiration and respiration pause.
• In adults respiratory rate is 12-14 breaths/min.
• In Newborn respiratory rate is 18-22 breaths/min.
• Increase % of CO2 in blood leads to increase respiration.
• Slow and shallow breathing least to inadequate supply of oxygen.
• At altitudes above 5,000 m above sea level, one could easily suffer from dizziness, blackouts accompanied by impaired vision.
• As the altitudes increases, the pressure decreases resulting in decreases supply of oxygen.
• Respiratory rate and cycle is maintained by respiratory centres present in Pons & Medulla.

## TRANSPORTATION

Transportation whether in plants or animals is the key to the efficient assimilation of the nutrients that the organisms synthesise, get from their environment or digest

#### INTRODUCTION

Every living organism whether big or small, unicellular or multicellular, needs a regular supply of energy for its proper functioning. This energy is supplied to the body in the from of nutrients obtained from food. Moreover, the wastes generated are also to be removed from the body in order to maintain a proper equilibrium in the body. So, an arrangement is set up in every living orgainsm to carry out the process of transports substances from one part to other part is called transport system or circulatory system.

Transportation in living beings is process through which nutrients (obtained during digestion), respiratory gases (obtained during respiration), excretory products, hormones, etc., are carried from one part to another part of the body. Transportation occurs in all organisms-microscopic to large ones. Depending upon the complexity of organisms, the method of transportantion varies. Diffusion is a major method of transportation in unicellular organisms like protozoans (Amoeba and Paramecium) and also in simple multicellular organisms like cnidarians and spongs.

#### Significance of transport system

(i) It transports food from the leaves in plants and small intestine (alimentary canal) in animals to each cell of the body.
(ii) It transports oxygen from lungs to all body cells and carbon dioxide from all body cells to the lungs.
(iii) It carries waste products to kidneys for elimination.
(iv) The water absorbed by the plants is circulated to all parts through the transport system.
(v) Hormones are formed in a particular area of the body. It is transported to the area of function via transport system.

##### Transportation in humans

The process of transporting the absorbed food, water and waste products from one place to another in the body is called circulation
In human beings,
circulatary (transport) system comprises two system

##### (A) Blood Vascular System

A system in which fluid is transported from one part of the body to the other through tubes is called vascular system. Blood vascular system or circulatory system is a system used for transportation of blood between various organs of the body and the heart. The system is a complex network of hollow tubes called blood vessels. Blood vessels carry blood and connect heart to all other organs of the body.

The circulatory system has three different parts –
(1) Pulmonary circulation (lungs)
(2) Coronary circulation (Heart)
(3) Systemic circulation (The rest of the systemics processes)

There are three major components of blood vascular system
(i) Blood (fluid)
(ii) Blood vessels (tubes)
(iii) Heart

(i) Blood
Blood is a fluid connective tissue. It is red, sticky and viscous fluid flowing in blood vessels. It forms 6-10% of total body weight. An adult human contains approximately 5-6 litres of blood. Blood is composed of two parts
(i) Blood plasma (fluid part)
(ii) Blood corpuscles (Solid or cellular part)

• Properties of blood
(i) In all chordates and in annelids amongst the non-chordates, blood is a bright red fluid of salty taste and peculiar smell.
(ii) Blood flows in a continuous circuit of blood vessels.
• Composition of blood Blood
consists of four parts, each with its own job in the body.
(i) Plasma
(ii) Red Blood cells (erythrocytes)
(iii) White Blood cells
(iv) Platelets

Fig. 1 Different types of blood cells in man

(v) Regulation of Body Temperature
The blood flows in all parts of the body, so it equalises the body temperature. It carries heat produced from one place to another place of the body.

(vi) Maintenance of pH
The plasma proteins act as buffer system and maintain required pH of the body tissues.

(vii) Transport of Hormones
The plasma of blood transports various hormones from one region to another and bring about the co-ordination in the working of the body.

(viii) Water Balance
The blood maintains water balance to constant level by distributing uniformly over the body.

(ix)  Protection from Diseases
The WBC (eosinophils, neutrophils, monocytes) engulf the bacteria and other disease causing organisms by phagocytosis. The lymphocytes produce antibodies against the invading antigens.

(x)  Clotting of Blood
Blood forms a clot at the site of injury, thus preventing further loss of blood. Blood helps in rapid healing of wounds.

#### Mechanism of blood clotting (Coagulation)

Sealing off a leaking blood vessel to stop bleeding is called blood clotting or haemostatic mechanism. A small leakage is sealed by blood platelets which adhere together to form a sticky plug called thrombus and the complete process is called the agglutination of the platelets. This process was discovered by physiologist Howell. He suggested that this mechanism is a complex process conststing of three steps which are as follows.

Step-1 Formation of enzyme thrombokinase (or thromboplastin) by the injured tissue cells and platelets Step-2 The enzyme deactivates heparin (natural anti-coagulant found in blood) in the presence of calcium ions (Ca2+). Heparin changes blood into ‘sol’. Thrombokinase converts plasma protein prothrombin (formed in liver) into thrombin.
Step-3 Thrombin acts as an enzyme and converts souble fibrinogen into insoluble fibrin which undergoes quick polymerisation and forms long fibrin threads. The fibrin threads form the clot which entraps RBCs.

This process takes 2 to 8 minutes and produces a ‘red clot’ at the wound site. After clot formation, bleeding stops. Now, the clot begins to contract and produces a pale-yellow fluid (serum) which is blood plasma without corpuscles and fibrinogen.

Fig. 2 Mechanism of blood clotting

(ii) Blood Vessels
Blood vessels are the network of hollow muscular tubes that transport blood throughout the body. They are mainly of three types

The major differences between various blood vessels have been given in Table.

##### (iii) Heart

Fig. 4 External View of Human Heart

Fig. 5 Internal structure of the human heart

Size – 5 × 3.5 inches
Colour – Pink
Shape – Conical shape
Weight – 300 gm.

Structure of heart

The basic structure of the heart (illustrated below) may be described as follows:
The Heart is divided into separate right and left sections by the interventricular septum, or “septum” when the context is clearly that of the heart. Each of these (right and left) sections is also divided into upper and lower compartment known as atria and ventricles, respectively. The four main chambers of the heart are : Right Atrium
Right Ventricle
Left Atrium
Left Ventricle
It is essential that blood flows in the correct direction through the heart so the structure of the heart includes a series of valves The Tricuspid valve separates the right atrium from the right ventricle.

The Pulmonic/Pulmonary valve separates the right ventricle from the pulmonary artery.

The Mitral (also known as the Bicuspid) valve separates the left atrium from the left ventricle.

The Aortic valve separates the right ventricle from the ascending aorta.

#### Working of Heart/ Physiology of Heart

Heart does not work throughout the day. It rests double the time it works. It rests between every beat. The resting period is called diastole, its duration is twice as long as that of systole, which is the period of muscular contraction. The series of events which occur during one complete beat of the heart is known as cardiac cycle. Cardiac cycle mainly consists of three steps, i.e., Auricular systole, Ventricular systole and Joint diastole.
Contration of the two auricles is simultaneous and is called auricular systole, relaxation of the auricles is called auricular diastole. Similary ventricular systole is the simultaneous contration of two ventricles and ventricular diastole is their relaxation. Cardiac cycle occurs in the following steps:

1. In the beginning, both auricles and ventricles are in a joint diastole.

2. Blood flows into the left auricle from the pulmonary veins and from superior and inferior vena cavae in the right auricle.

3. Next step is of auricular systole in which both auricles contract simultaneously which drives most of their blood into their respective. At this stage ventricles are in diastole i.e., they are relaxed.

4. Ventricular systole follows immediately. Pressure of the blood in the ventricles forces to close the bicuspid and tricuspid valves.

Fig. 6 Working of heart

5. The first sound “Lubb” is produced when the auriculo-ventricular valves get closed at the start of ventricular systole.

6. Pressure in the ventricles leads to the pressing of the semi-lunar valves of the great arteries  (i.e., aorta and pulmonary artery), and thus driving the blood into them. The second sound “Dupp” is produced when the semi-lunar values of aorta and pulmonary artery get closed.

7. After this ventricles get relaxed or there is ventricular diastole. The auricles are still undergoing diastole. Thus we can say, all chambers are in diastole or relaxed. One cardiac cycle is completed in 0.8 second.

Fig. 7 Route of blood circulation

Single Circulation· Single Circulation In fishes, the blood flows through the heart only once while completing the full circuit of the body. It is called single circulation. The heart receives and pumps only venous blood. It reaches to heart on deoxygenation.

Fig. 8 Single circulation in fish

• Double Circulation
It is passage of the same blood twice through the heart first one the right side, then on the left side in order to complete one cycle. Double circulation has two components, pulmonary circulation and systemic circulation.

Fig. 9 Double circulation in mammals and birds

(i) Pulmonary circulation
It is movement of blood from heart to the lunge and back. Deoxygenated blood of the body enters the right auricle, passes into right ventricle which pumps it into pulmonary arch. With the help of two separate pulmonary arteries the blood passes into the lungs. Here, it is oxygenated. Oxygenated blood comes back to left auricle of heart through four pulmonary veins, two from each lung.

(ii) Systemic Circulation
It is the circulation of blood between heart and different parts of the body except lungs. Oxygenated blood received by left auricle passes into left ventricle. The left ventricle pumps it into aorta for supply to different body part including walls of the heart by means of arteries. Inside the organs the blood loses oxygen and nutrients. It picks up carbon dioxide and waste products. This deoxygenated blood is drained by veins and sent to the right auricle of heart.

Differences between Pulmonary circulation and Systemic Circulation

### Blood Pressure

Fig. 11 Measurement of Blood Pressure

Blood pressure is the pressure exerted by the blood on the walls of vessels (arteries). The blood pressure is always expressed in form of two values called systolic pressure and diastolic pressure. The temporary rise in blood pressure during contration of the heart is called systolic pressure. The temporary fall in blood pressure during relaxation of the heart is called diastolic pressure. The blood pressure inside the arteries is much more in comparison to that inside veins.

In humans, the systolic pressure is about 120 mm of Hg whereas diastolic pressure is about 80 mm of Hg. The blood pressure under normal conditions is thus 120/80 mm of Hg. It varies from person to person and from time to time. It also varies with age.

A persistent increase in blood pressure is called hypertension or high blood pressure. It is caused by narrowing of arteries which results in increased resistance to blood flow. A lower systolic or diastolic pressure is known as hypotension (low blood pressure). Blood pressure is measured by using an instrument called sphygmomanometer.

•  Pulse
Due to beating of heart, the blood enters into the arteries forcefully due to which artery expands a little. Pulse is the expansion of an artery each time the blood enters into it. Each heartbeat produces one pulse. Thus, the pulse rate is similar to heartbeats/minute, i.e., the pulse rate of a person in 70-72 per minute while resting.  During exercise or any physical activity the pulse rate increases. Due to deeply-seated arteries, pulse cannot be felt everywhere except certain places like wrists, temple and neck where they are close to skin.

### The Lymphatic System

Lymphatic system is another circulatory system in human body which transports materials through circulating fluid called lymph. The lymphatic system consists of the following parts.

(i) Lymph
(ii) Lymph capillaries
(iii) Lymph vessels
(iv) Lymph nodes (or glands)

(i) Lymph
Lymph is a straw-coloured or light yellow coloured fluid connective tissue. It is translucent alkaline fluid present in the lymph vessels. It is formed of two parts, i.e., plasma and lymphocytes.

(ii) Lymph capillaries
Lymph drains into lymphatic capillaries (or lymph capillaries) which are thin-walled, highly permeable tubes that form a network in every organ except nervous system.

(iii) Lymph vessels
The lymphatic capillaries unite to form lymph vessels which are small vessels with numerous values. The lymph vessels are like veins but they have comparatively thin wall and numerous valves.

(iv) Lymph nodes
At places, lymph vessels bear swellings called lymph nodes or lymph glands. They are the site where lymphocytes accumulate and produce antibodies. As lymph nodes are rich in lymphocytes, they filter out germs and foreign particles from lymph. Lymph nodes are abundant in the regions of neck, armpit and groin. Tonsils and adenoides are masses of lymphatic tissues.

Fig. 12 Lymphatic System in human

• Functions of lymphatic system
(i) The volume of blood decreases due to filtration of blood plasma from blood capillaries. Lymph collects this excess fluid and drains it back into the blood, thus, maintains the volume of blood.
(ii) It acts as a connecting link between blood and the body cells and helps in exchange of materials between them.
(iii) Lymph capillaries (lacteals) of intestinal villi help in absorption of fat and transport of the same to the blood.
(iv) It protects the body by killing the germs with the help of lymphocytes. Thus, develops immunity of the body.
(v) Various tissue secretions like hormones, macromolecules, plasma proteins are first added to lymph which passes it to the blood.
(vi) It collects carbon dioxide, waste products and metabolites from tissues via tissue fluid and passes to blood.

##### Transportation in Plants

Unlike animals, some materials pass in and out of plants through diffusion. For gaseous diffusion to occur, the plants possess stomata and lenticels. During the daytime the photosynthetic organs obtain carbon dioxide from outside by diffusion. The same is used for synthesis of food. Oxygen is released as a by-product. It passes out of me plant by diffusion. Simultaneously, a lot of water vapours pass out.
Other materials required for building plant body are obtained from soil, e.g., nitrogen, phosphorus, other minerals, water .They are sent to chlorophyll containing organs where food is manufactured. The manufactured food is passed to all parts for utilisation and storage. If the distance between the two is small, the materials reach there by diffusion.  If the distance is large, as in most plants, they have to be transported through a proper system of transportation. However, plants have a large proportion of dead cells. They do not move. Therefore, they have low energy needs. The transport systems are slow. Further, there are two independent pathways having conducting tubes.  One is xylem that moves water and minerals from soil to aerial parts. The other is phloem which carries food and hormones from the region of availability (e.g., leaves, storage organs) to the areas of utilisation (all living cells, growing points, storage organs, developing fruits).

•  XYLEM It is a complex tissue which transports sap (water and minerals). Xylem has four types of cells.1. Xylem fibres
2. Xylem parenchyma
3. Tracheids
4. Vessels
Only xylem parenchyma are living cells. Others are dead, empty and lignified. Vessels and tracheids are called tracheary elements because they take part in transport of sap (water + minerals). Vessels are long multicellular tubes which are formed by end to end union of several cells in which cross walls have broken down. Tracheids are elongated cells with pointed ends. Both the tracheary elements have pits or other thin unlignified areas for element to element movement of water. Xylem parenchyma takes part in lateral flow of water.

Fig. 13 Xylem and phloem elements

• Phloem
It is complex tissue which takes part in transport of food. Phloem has four types of cells —
1. Sieve tubes
2. Companion cells
3. Phloem parenchyma
4. Phloem fibres.
Only phloem fibres are dead cells. Others are living cells. Sieve tubes are conducting channels of phloem. They are elongated multicellular tubular channels formed by end to end union of numerous sieve tube elements. The end walls or septa between adjacent sieve tube elements are bulged out and have pores. They are calied sieve plates. Sieve tube elements do not have a nucleus. Their functioning is controlled by adjacent nucleated companion cells.

#### Transpiration

(L. trans-across, spirate-to breathe) Transptiration is loss of water in vapour form from the exposed parts of a plant. Aerial parts of the  plants are always losing water through transpiration.

• Functions of transpiration
(i) Cooling
Evaporation of water from the aerial parts results in lowering of their temperature which will otherwise rise due to exposure to sun.
(ii) Concentration of Minerals
Transpiration helps in increasing concentration of minerals present in rising water.
(iii) Transport
It helps in transport of water and minerals.

#### Transport of Water and Minerals

There is a continuous system of dead conducting channels (vessels and tracheids) from near the root tips to leaves and shoot tips. It transports water and minerals. The two are obtained from soil by the roots. The various steps involved in transport of water and minerals are as follows :

1. Mineral absorption
It occurs in the growing parts of the root. Both the surface or epiblema cells as well as root hairs take part in mineral absorption. Mineral absorption is an active process which involves expenditure of energy. Active absorption creates a higher concentration of minerals in the root as compared to soil solution.

2. Absorption of water
Root hair zone is the region of water absorption. The inside of the root has higher osmotic concentration than the soil solution. Root hairs are in contact with soil interspaces having capillary water. The root hairs pick up water which is ransferred inwardly due to still higher osmotic concentration. It reaches the cells surrounding the xylem channel. Salts accumulated in the basal part of xylem channel cause osmotic entry of water into xylem and form column of water. It also creates a positive pressure known as root pressure. This is, however, unable to push water to any great height. Root pressure is often absent, atleast during the day time. Its effect becomes important at night.

3. Ascent of sap
It is upward movement of absorbed water or sap from root to the top of the plant. The mechanism of ascent of sap was given by Dixon and Joly (1894). It is called transpiration pull or cohesion-tension theory of ascent of sap. The force for ascent of sap lies in the aerial parts. Here mesophyll and other cells lose water to outside air through transpiration which produces a negative pressure.

Fig. 17 diagrammatic representation of ascent of sap

Development of Negative Pressure
Loss of water by mesophyll cells increases their suction pressure. They withdraw water from the xylem channels. As there are billions of mesophyll cells withdrawing water from xylem channels, water column present in the xylem comes under tension or negative pressure.  Its value is 10-20 atmospheres. Water column does not break due to two forces:

(a) Cohesion force among the water molecules.
(b) Adhesion force between water molecules and wall of the xylem channels.

Rise of Water
Tension or negative pressure of the water column results in its upward pull just as cold drink is sucked with the help of a straw pire. Since it develops due to transpiration, it is called transpiration pull.

Translocation or Transport of Food and Other Substances
Food materials are translocated from the region of their manufacture or storage to the region of their utilisation.

Fig. 18 Transpiration or evaporation of water from aerial
surface causing absorption and ascent of sap

The region of supply of food is called source while the area of utilisation is called sink The direction of translocation can be downward, upward or both. The food manufactured by leaves passes into the storage region and other sinks in the downward direction as well as towards growing points and developing fruits in the upward direction. In spring season, the stored food present in root and stem is translocated upwardly to buds for their growth.
The translocating nutrients consist of soluble carbohydrates (mostly sucrose), amino acids, organic acids, hormones and other organic solutes.
Translocation occurs through phloem. The channels of transport are sieve tubes (sieve cells in non-flowering plants). Sieve tubes are specialised for this purpose. They are devoid of nuclei and internal membranes. The cytoplasm of one tube cell is continuous with that of adjacent sieve tube cells through sieve plates. The translocation activity of sieve tubes is controlled by companion cells which lie adjacent to sieve tube cells.

#### Mechanism of Pholem Transport

Fig. 19 Translocation of organic solutes as per mass flow hypostesis

The transport of organic solutes or nutrients occurs through a physical process but entry and exit of nutrients from the phloem can occur only through an active process which utilises energy from ATP. With the help of energy, food materials pass into the phloem from the region of manufacture or srorage (source end) . After entering the sieve tubes the nutrients being in high concentration, exert an osmotic pressure which causes entry of water into this region. A high turgor pressure develops. It forces the nutrients to pass towards the regions which have low turgor pressure. The movement is like a mass flow (Munch 1930). Low turgor pressure is maintained in the area where being withdrawn for consumption (growing points) or storage (root, stem, fruits) by an active process.

## EXCRETION

The biological process of removal of harmful The biological process of removal of harmful nitrogenous wastes from the body is called exretion.

### Introduction

During cellular respiration, various metabolic reactions occur in the body leading to formation of various waste products such as carbon dioxide, urea, etc. These waste products are harmful if they are allowed to accumulate in the body. Therefore removal of these waste products is must. The process of removal of these metabolic wastes from the body is known as excretion. The process of maintaining the right amount of water and ionic balance is called osmoregulation.

Singnificance of excretion
(i) The unwanted by-products of the metabolic of the metabolic activities are removed.
(ii) Many toxic chemicals, which damage the cells and affect metabolic activities, are removed.
(iii) The ionic concentration of body fluids is maintained by excretion and osmoregulation.
(iii) The water content and pH of body fluids is regulated by it.

EXCRETION IN ANIMALS

In animals principal wastes produced by various metabolic activities are nitrogenous substances like ammonia, urea and uric acid along with respiratory wastes (CO2) and others.

#### EXCRETION IN HUMAN (Human Excretory System)

In human beings excretion mainly occurs through a urinary system.  Urinary or excretory system consists of  (1) The kidneys
(2) The ureters
(4) The urethra

(1) Kidneys
External Structure
Colour  – Dark red
Shape  – Bean shaped
Weight  – 125 – 170 gms.
Size  – 10 cm length, 5 cm breadth, 3 cm thickness.
Position  – Located laterally either sides of
vertebral column.

Kidneys are the main organs of urinary system. Each kidney is bean shaped, lateral border is convex and its medial border is concave in the middle and convex at each. In the centre of the medial concave border there is present a notch known as the hilium, which contains the renal blood vessels and nerves and the renal pelvis, which is the funnel-shaped upper end of the ureter. Urine produced by the kidneys is temporarily stored in the urinary bladder and passed out through urethra.

• Functions of the Kidney
1. It maintains water equilibrium, pH equilibrium, ionic equilibrium of the blood and osmotic equilibrium.
2. It helps to excrete out waste product urea in the dissolved form from the blood.
3. It excretes poisonous substances like drugs, toxins etc., from the body.
4. It regulates blood pressure by controlling the fluid balance in the body.
5. Many ions derived from food are excreted in the urine.They include sodium, potassiun magnesium,. calcium, chloride, phosphate, sulphate and oxalate ions. (These movements of ion are important in helping to maintain the acid-base balance of the body and keeping the pH of arterial blood at 7.40.)

Internal Structure
The internal structure of kidneys can be divided into two parts. Its outer part is called cortex and inner part is called medulla.

Fig -2 Internal Structure of kidney

NEPHRON

The nephron is the structural and functional unit of the kidney. Each kidney of man is formed of about one million nephrons. Each nephron has a length of about 3cm. It is differentiated into 4 regions.

(a) Bowman’s capsule
(b) Proximal convoluted tubules (PCT)
(c) Loop of henle
(d) Distal convolulated tubule (DCT)

(a) Bowman’s capsule
It is a large double walled cup. It lies in the renal cortex. It contains a tuft of capillaties called glomerulus and the outer wall is continuous with the rest of the nephron. The space between the two walls of the Bowman’s capsule is continuous with the lumen of the next part of the nephron. The bowman’s capsule and the glomerulus together constitutes the renal corpuscle or malpighian body.

(b) PCT
It starts from the back of the Bowman’s capsule and it is bighly convoluted. It lies in the renal cortex. The wall consists of a single layer of columnar cells bearing a lot of microvilli on the surface.

(c) Loop of Henle
It is a V shaped segment of the nephron located in the renal medulla. It consists of two straight parallel limbs : a descending limb which is a continuation of the PCT and enters into the renal medulla and an ascending limb which re-enters the renal cortex and joins the DCT.

(d) DCT
It is greatly twisted like the pct and lies in the renal cortex. The terminal relatively short part of the DCT is called the collecting tubule. It
open into the collecting duct. The collecting ducts receive the collecting tubules of several nephrons.

Fig – 3 Structure of Nephron

(2) Ureter
They are a pair of whitish narrow distensible muscular tubes of about 30 cm length. Each ureter arises from hilus part of the kidney. It moves downwardly and opens obliquely into urinary bladder. Ureters carry urine from kidneys to the urinary bladder.

(3) Urinary
Bladder  It is a median pear shaped distensible sac that occurs in the pelvic part of abdomen. It stores urine brought by the two ureters. The storage capacity is 300-800 ml.

(4) Urethra
It is a tube that takes urine from urinary bladder to outside. The opening of urinary bladder into ‘urethra is guarded by a ring of muscles or sphincter. Urethra is 4 cm long in females and about 20 cm long in males. Its opening is separate in females but is common with reproductive tract in males.

#### PHYSIOLOGY OF URINE FORMATION (EXCRETION)

Main function of nephron is to form urine. There are three main processes involved in the urine formation :

1. Glomerular ultrafiltration

• It is the filteration of body fluids and solutes from the blood, out of the glomerular capillaries  into the Bowman’s capsule due to the pressure in the glomerulus.
• All substances from the blood are filtered out except the large protein molecules. This fluid in the glomerular capsule is called glomerular filtrate.
• It consists of water, urea, salts, glucose and other plasma solutes.
• Blood coming out of the efferent arteriole is therefore thick.
• About 180 litres of glomerular filterate is ormed by both kidneys in a day but urine excreted is, about 1-2 litres a day. This shows that most of glomerular filterate is reabsorbed.

2. Tubular Reabsorption

• Glomerular filterate contains a lot of useful materials like glucose, salts such as that of sodium and water.
• These substances are reabsorbed from the renal tubule at various levels and in varied proportions.
• Glucose is reabsorbed completely from the proximal convoluted tubules.
• More than 85% of water is reabsorbed from the proximal, distal and even in collecting tubules.
• Sodium chloride is reabsorbed in the proximal and distal tubules.
• Potassium is completely reabsorbed from the proximal tubule.
• Phosphate is reabsorbed in the proximal tubule, etc, Other substances reabsorbed are uric acid, sulphates, vitamin C,amino acids etc.

3. Tubular Secretion

• This occurs mainly in the distal convoluted tubule and the collecting duct of the nephron.
• It is an active, vital process performed by the cells of the cuboidal epithelium lining the tubules which excrete additional wastes from the blood stream into the filtrate by active transport.
• In this process substances like potassium, hydrogen, creatinine and certain drugs like phenol,  penicillin etc., are directly excreted by the tubular cells from the blood.
• The fluid which now flows through the last parts of the tubule is urine which consists of water, urea, uric acid, mineral ions like sodium, potassium, chloride, phosphates etc.

Composition of urine

It is a transparent fluid produced by the excretory system. Normal urine is a yellow fluid and slightly (pH = 6) Urine contains –
(i) Water – 96%
(ii) organic substanace – 25%  (urea, uric acid, creatine, creatinine, vitamines)
(iii) Inorganic substances – 1.5%  (Na, Ca, Phasphate, Sulphate)

#### Artificial Kidney or Haemodialys

is Kidney is a very important organ which is essential for maintaining internal homeostasis as it is engaged in elimination of the nitrogenous and other metabolic by-products. Even if one kidney is damaged, the second kidney can carry on the function of excretion completely. However, if both the kidneys are damaged, a new compatible kidney has to be grafted. Till that period, waste products are removed with the help of haemodialysis (blood dialysis), injury or infection or artificial kidney.  Artificial kidney is a physico-chemical device to remove excretory products from blood in case of temporary disfunction (due to toxins, injury or infection) or near failure of kidneys. It is based on the principle of dialysis or separation of smaller solutes or ions from larger particles with the help of an ultrafilter. The artificial kidney or dialysis machine consists of a number of cellophane tubes embedded in a dialysate or dialysing fluid. The dialysing fluid has the same osmotic concentration as that of blood. However, it contains more of glucose. Nitrogenous waste products, phosphates and sulphates are excluded.

Fig – 4 Aritificial kidney/Haemodialysis

Blood from an artery, or a vein fitted to a pumping mechanism, is mixed with heparin, cooled at 0° C and passed into cellophane tubes of artificial kidney. Nitrogenous waste products, sulphate and phosphate of blood pass into dialysing fluid. Purified blood is warmed and mixed with antiheparin. It is passed back into vein. The whole process takes 3-4 hours.

· Uses of Aritificial kidney/Haemodialysis

1. Toxins
Haemodialysis helps in removing toxins from the body before they are able to damage the body permanently.

2. Uraemia
Patients suffering from kidney infections and uraemia (excess of urea in blood) are provided relief for some time.

3. Renal Failure
In case of near permanent damage to kidney, haemodialysis provides time to the patient to find a kidney donor.

4. Normal Life
In between two dialysis, a patient can lead a near normal life.

5. Clean Procedure
Haemodialysis is a clean procedure where chances of infection are minimum.

Excretion in plants
Plants produce a number of waste products during their life processes.

• The main waste products produced by plants are carbon dioxide, water vapour and oxygen.
• Plants get rid of excess water by transpiration.
• The gaseous wastes of respiration and photosynthesis in plants (carbon dioxide, water vapour and oxygen) are removed through the ‘stomata’ in leaves and ‘lenticels’ in stems and released to the air.
• Many plant waste products are stored in cellular vacuoles. Wastes products may be stored in leaves that fall off, other waste products are stored as resins and gums.
• Plants excrete some waste substances into the soil around them.
• Some of the plant wastes which are useful to humans are – Natural rubber, gum, resins and essential oils like sandalwood oil, eucalyptus oil, clove oil and lavender oil.

### CONTROL AND COORDINATION

‘The nervous system, in coordination with the endocrine system communicates, integrates and coordinate the various organs and organ system in the body’

#### INTRODUCTION

There are various organ systems in all living organisms carrying out various physiological processes. These organ systems cannot work independently. They are linked in one way or the other. Working together of all these systems is called coordination. Coordination is mainly of two types :

1. Chemical coordination in both plants and animals,
2. Nervous coordination in animals.

#### COORDINATION IN ANIMALS

Life itself is a dynamic state where every organism must continually spend energy and obtain it from environment. So, the life of an organism is dependent upon its surrounding environment. All organisms are capable of sensing environmental changes and respond according to them. This character of living organisms is known as irritability, reactivity, behaviour or responsiveness. This character is less developed in plants due to their static nature. Irritability helps organisms to interact with day-to-day changing environmental circumstances. Organisms give responses to these changing conditions and remain adjustable in their habitat. This capacity of adjustment in of organisms is called adaptability. In higher animals, along with nervous system an additional control system is present which is called endocrine (or hormonal) system.

The evolution of complexity in multicellular animals required the development of a system for the control and coordination of the activities of various cells of the body. The control and coordination in a cell requires—
(i) information of changes in the external environment
(ii) transmission of changes in the external environment
(iii) exchange of information between concerned cells

(A) Nervous system
We know that nervous system is composed of some specialised cells called neurons or nerve cells. These cells produce electrical signals called nerve impulses and chemical substances called neurotransmitters. The control of nervous system is speedy and flexible but is localised and occurs for a short period of time.

(B) Endocrine system (Hormonal system)
This system is made up of endocrine glands which coordinate other system by sending chemical messengers termed as hormones (primary messengers). The hormonal control is generally slow but is effect is diffused.

NERVOUS SYSTEM IN ANIMALS
Nervous system in animals is the system which coordinates all the other system within the organisms as well as external environment of the organisms. All the multicellular organisms (except sponges) posses simple or complex nervous system. The structural and functional unit of nervous system is specialised cell called neuron or nerve cell.

#### Neurons

Neurons or nerve cells are specialised cells of body capable to receive, conduct and transmit excitations or impulses throughout the body. Nerve cells are specialised for receiving stimuli (as sensory or receptor cells) and transferring excitations from one to the other. The neurons are the largest cells present in the human body, sometimes reaching 90-100 cm in length. A neuron is typically divided into three parts—
(i) Cell body (cyton)
(ii) Dendrites
(iii) Axon

Fig – 1 A Nerve cell

(i) Cyton or cell body

It is the main part of neuron. It is a nucleated body, also called soma or perikaryon. Cell body is of various shapes (rounded, pyriform or stellate) consisting of abundant granular cytoplasm called neuroplasm and large spherical nucleus. The cytoplasm contains mitochondria, Golgi apparatus, neurofibrils, neurotubules and special ribosome containing granules called Nissl’s granules. The Nissl’s granules are characteristic feature of nerve cell. Centrioles are absent in cell body.
Function: It accepts nerve impulses from dendrites and transfer them to axon (nerve fibres).

(ii) Dendrites (dendrons)
A cyton produces five to seven short, slender (tapering) and branched structures known as dendrites. Dendrites also contain Nissl’s granules and neurofibrils. Function: These cytoplasmic processes receive impulses and transmit them towards the cell body.

(iii) Axon
It is a single, relatively thicker, long, unbraIiched cytoplasmic extension arising from the cell body. The cell membrane of axon is called axolemma and cytoplasm is called axoplasm. Nissl’s granules are not found in axon but neurofibrils are present.Axon is branched at terminal ends called telodendria Each telodendria bears a terminal knob. Telodendria of an axon make contact with other neurons at synapse.  Knobs of one neuron lie upon dendrites of adjacent and protective sheath around it, called myelin sheath. Myelin sheath itself is made up of individual cells (Schwann cells) with abundant fatty materials. The sheathed axon is called nerve fibre and a number of nerve fibres are joined to form a nerve. The nerve fibres having myelin sheath are called myelinated nerve fibres while without myelin sheath are called non-myelinated nerve fibres. At certain places in myelinated nerve fibre, sheath is not present. These areas are called nodes of Ranvier. Function : Axon transmits impulses away from the cell body to another neuron or target cell.

#### Transmission of Nerve Impulses (ELECTROCHEMICAL MECHANISM)

Neurons are situated end to end in bodies of animals and transmit nerve impulses throughout the body. Nerve impulse is a self-propagated electric current which travels from one end (dendrites) to another end (axon end) of a neuron for the conduction of a message. Each neuron receives an impulse through dendrites and passes it to the next neuron in a channel and the information finally reaches to the effector organ. The neurons are not connected. There is a small gap between the terminal portion of axon of a neuron and the dendron of the other neuron. This is called synapse. These occurs a presynaptic knob formed by the axon terminal. The dendrite terminal is slightly bordered and depressed to form postsynaptic depression. The narrow space between the presynaptic knob and postsynaptic depression is called synaptic cleft and is filled with a fluid containing neurotransmitter. We know that any two neurons are not in direct contact with each other. When an electrical impulse reaches the end of axon, it stimulates the release of neurotransmitter (for example, acetylcholine within the gap (or synapse). The neurotransmitter molecules come in contact with the membrane of postsynaptic depression. It acts as a stimulus and produce an impulse to be carried on further. In this way, nerve impulses are transmitted.

Fig – 2 Neuromusular junction

#### REFLEX ACTION AND REFLEX ARC

These are nerve-mediated, automatic, involuntary and spontaneous actions that occur without the will of an animal. These responses are natural and automatic and occur suddenly on receiving a stimulus. A reflex action is an immediate involuntary response which do not require any thinking by the brain. A reflex action may be defined as a spontaneous, automatic and mechanical response towards stimulus without the will of an animal. Reflex actions (reactions) are the simplest responses neurologically. Functionally, these are the basic units of nervous coordination.  Examples of reflex actions are watering of mouth at the sight of delicious food, blinking of eyes due to sudden appearance of some objects in front of the eyes, coughing, yawning, sneezing and sudden withdrawal of hands or feet with a jerk on sudden contact with hot, cold or sharp objects.

Fig. 3 T.S. of spinal cord and arrows are showing reflex arc

Reflex responses occur immediately and very fast. These fast reflex reactions protect the body against injurious effects of sudden stimuli. A number of reflex responses occur in the daily life of animals. The reason of fastness of the reflex action is that these actions occur without the sensory impulse being carried to the brain for analyses. It is an automatic response and is controlled. by the spinal cord.

On receiving a stimulus, the dendrites of sensory neurons, i.e., receptor, pass the message in the form of electric impulse to the spinal cord. The relay neurons in the spinal cord pass the message to motor neurons. The spinal cord in turn sends information via motor neurons through electrical impulse to the effectors, i.e., muscles or glands which show responses. For quick response, reflex action involves the spinal cord but the information goes to the brain also where the thinking process takes place.

•  Reflex Arc
A reflex action involves coordination between receptor organ, sensory neurons, a part of CNS, motor neurons and effector organ. The path taken by nerve impulse in a reflex action is called reflex arc. The entire impulse circuit of a reflex response is as follows :Stimulus → Receptor → Sensory neurons → CNS → Motor neurons → Effector

This route or sequence by which a nerve impulse acts to be effective is known as reflex arc. The nerve fibres carry the impulses to their cell bodies (cyton) located in the dorsal root ganglion of the nerve. Axons of these neurons then carry the impulses into the grey matter of the spinal cord.

Fig. 4 Reflex arc

Reflex arc involves five parts

(i) Receptor organ (sensory organ)
It is the organ which receives the stimulus and initiates a sensory nerve impulse.

(ii) Sensory nerve (afferent nerve)
it conducts sensory nerve impulse from the receptor organ to the part of CNS (brain or spinal cord).

(iii) Part of CNS (spinal cord or brain)
The neurons in spinal cords or brain analyse and interprets the sensory impulse and sets upon appropriate motor impulse. The reflex formed from the spinal cord are called spinal reflexes and the reflexes formed by the brain are called cerebral reflexes.

(iv) Motor nerve (efferent nerve)
It conducts motor nerve impulse from the CNS to the specific effector organ (muscle or gland).

(v) Effector organ
Impulse terminates and response occurs as per the instructions given by the CNS to the effector organs, i.e., muscles or glands.

#### Parts of nervous System

Nervous system can be divided into two main parts-
Central Nervous System (CNS) (consisting of brain and spinal cord)  and Peripheral Nervous System (PNS) (consisting of all the nerves arising from brain and spinal cord).
PNS is further divided into two parts, Voluntary Nervous System (VNS) (It is under the control of our will.) and Involuntary Nervous System (INS) or Autonomic Nervous System (ANS) (It is not under our control and controls the activity of internal body organs.) Involuntary nervous system is again of two types— Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PNS).  These two systems control the functioning of various body parts. The classification of nervous system is outline below :

Fig. 5 Main parts of human nervous system

[I]Central Nervous System (CNS)

Central Nervous System (CNS) is considered as the supreme power of controlling all the body responses. It consists of a brain and spinal cord. Both of them are protected by hard skeletal structures. Brain is protected by skull and spinal cord is protected by vertebral column.

#### (1) Brain

Fig. 6 External view of human brain

It is the widest and uppermost part of CNS. It is present in the cranial cavity of cranium (brain box) of skull (head). Brain box protects brain from mechanical injury. Brain is a soft organ which weighs 1.2-1.4 kg. Brain constitutes approximately 98% of the whole nervous system. Brain contains about 100 billion neurons.  Human brain is the most advanced and developed among all the animals found on the earth. It is the centre of thinking and main coordinating centre of the body.

Brain is covered by three meninges or membranes, i.e.,
(i) Piamater
(ii) Arachnoid membrane
(iii) Duramater

The spaces between the meninges and the brain cavities are filled with a clear, slightly-alkaline fluid called cerebrospinal fluid. This fluid supplies useful materials to the brain cells and collects metabolic wastes from these cells. The meninges and the cerebrospinal fluid give support to the brain and protect it from external pressure, shocks and other hazards. The blood vessels of pia-arachnoid mater supply oxygen and nutrients to the brain by cerebrospinal fluid of brain cavity which acts as the tissue fluid of brain. Venous drainage of CO2 and other metabolic wastes is done by veins of epidural space.

Fig. 7 Different parts of the human brain

Functions of brain Functions of brain

(i) It receives information from the sensory receptors, process the information, generate the appropriate responses and send the instructions to effectors.
(ii) It controls, regulates and coordinates the overall functions of the body.
(iii) It is the site of intelligence, memory, reasoning, learning, and emotions.

#### Parts of brain

Fig. 8 Lateral view of human brain

The brain is divided into three main regions—
(a) Fore brain
(b) Mid brain
(c) Hind brain

Fig. 9 Location of various sensory areas of cerebral hemisphere

(a) Fore brain
It is made up of cerebrum, hypothalamus and thalamus.

• Cerebrum
It is the largest·and main thinking part of the brain and is made up of two hemispheres-called the cerebral hemispheres. The cerebrum has sensory areas, association areas and motor areas.
(i) The sensory areas receive the messages.
(ii) The association areas associate this information with the previous.
(iii) Other sensory informations.
(iv) The motor areas are responsible of the action of the voluntary muscles.
Cerebrum is responsible for the intelligence, memory, consciousness and will power.
• Thalamus
It is an area which coordinates the sensory impulses from the various sense organs -eyes, ears and skin and then relays it to the cerebrum.
• Hypothalamus
Hypothalamus, though a small region situated below the thalamus, is an important region of the brain. It receives the taste and smell impulses, coordinates message from the autonomous nervous system, controls the heart rate, blood pressure, body temperature and peristalsis. It also forms an axis with the pituitary which is the main link between the nervous and the endocrine systems. It also has centres that control mood and emotions.

(b) Mid brain
It is a small portion of the brain that serves as a relay centre for sensory information from the ears to the cerebrum. It also controls the reflex movements of the head,neck and eye muscles. It provides a passage for the different neurons going in and coming out of the cerebrum.

Fig. 10 Sagital (median) section of human brain

(c) Hind brain
It consists of cerebellum, pons and medulla oblongata.

• Cerebellum
Cerebellum is like cerebrum. It consists of outer grey cortex and inner white medulla. It is responsible for maintaining the balance while walking, swimming, riding, etc. It is also responsible for precision and the fine control of the voluntary movements.  For example, we can do actions like eating while talking or listening. One has to concentrate for talking sensibly. However the action of eating , while talking is done automatically. This is controlled by the cerebellum.
• Pons
Pons literally means bridge. It is hidden as it is well protected because of its importance. It has the cardiovascular centre and the breathing centre.
• Medulla
It is a somewhat triangular part between pons varolii and spinal cord. It is the posterior part of brain which lies below the cerebellum. It froms most of the ventral part of the hindbrain. Medulla oblongata contains vital reflex centres which control the rate of heartbeat, breathing movements, blood pressure (B.P.) by expansion and contration of blood vessels, peristaltic movement of alimentary canal, swallowing, coughing, sneezing, vomiting and salivation.

#### (2) Spinal cord

It is a collection of nervous tissue running along the back bone. It is, in fact, protected by the vertebral column. It is a continuation of the brain.
The functions of the spinal cord are :
1. Coordinating simple spinal reflexes
2. Coordinating autonomic reflexes like the contraction of the bladder
3. Conducting messages from muscles and skin to the brain,
4. Conducting messages from brain to the trunk and limbs.

Fig. 11 cross section of spinal cord

Fig. 12 Connection of spinal cord with brain

#### [II] Peripheral Nervous System (PNS)

All the nerves connecting the CNS (brain +spinal cord) with receptors and effectors (muscles and glands constitute the pheripheral nervous system.  Peripheral nervous system connects CNS with different parts of the body with the help of nerves arising from the brain and the spinal cord.  In humans, there are 12 pairs of nerves which arise from the brain (cranial nerves) and 31 pairs of nerves which arises from the spinal cord (spinal nerves).  In addition to these nerves, there are some special kinds of nerves, mostly arising from the spinal cord which connect internal organs such as heart, kidney, lungs, blood vessels, glands, etc. These nerves are called visceral nerves.

Difference between cranial nerves and spinal nerves

Thus, PNS consists of all three type of nerves.
(i) cranial nerves
(ii) spinal nerves
(iii) visceral nerves

(i) Cranial nerves
Cranial nerves arise from the brain and extend to various parts of the head. They are 12 pairs in number, of which 3(I, II, VIII) are sensory, 5 (III, IV, VI, XI, XII) are motor and 4(V, VII, IX and X) are mixed nerves.

(ii) Spinal nerves
Spinal nerves arise from the spinal cord and extends throughout the body except head. They are 31 pairs in number. They are mixed type of nerves.

(iii) Visceral nerves
Visceral nerves are a particular set of nerves that control many activities of the internal organs of the body like kidneys, lungs, heart, blood vessels and urinary bladder inspite of regulating normal functions of the body. Most of these nerves arise from the spinal cord and a few from the brain. The visceral nerves constitute the autonomic nervous system.

#### Endrocrine system

A group of endocrine gland which produce various hormones is called an endocrine system. In addition to nervous system, the endocrine system also helps coordinating the acitivites of our body.

Endocrine glands – The glands which pour their secretions directly in the blood are called endocrine glands.

Hormones – are secretions of the endocrine glands and one of the most important substance that controls the body chemistry. Also known as “Chemical messengers.”

Fig. 13 Endocrine glands in human beings

Physical and chemical properties hormones

• These are secreted by endocrine glands.
• Hormones are secreted only when required.
• Their secretion is regulated by feedback mechanisms.
• These are generally released in the blood stream.
• The molecules of most of the hormones are small.
• The secretion of hormone is always in very small quantity.
• Hormones are destroyed after use i.e. hormones can not be stored in the body.
• hyroxine is an exception.

### Endocrine glands in human body

#### FEEDBACK MECHANISM TO CONTROL THE SECRETION OF HORMONE

Usually glands secrete hormones continuously or at intervals. The quantity of secretion of hormone depends on many factors like age, health state of individual, biological cycle and the body requirement  in particular circumstances. Therefore, regulation of hormones in the body is a well-defined and regulatory process. Living organisms maintain homoestasis, i.e., maintenance of favourable internal environment. Hormones play a significant role in maintaining homeostasis. To maintain homeostasis, it is necessary to keep the level ofhormones at an optimum level. This is achieved through the feedback mechanism.  Feedback mechanism refers to a regulatory mechanism where presence of a substance at certain level promotes or inhibits its further formation. The feedback control mechanism is mostly negative but in rare cases, it is positive.

(A) Negative Feedback Control
In this type of control, when the level of a certain hormone rises in the blood above normal its synthesis slows or stops. Let us see following example

• Blood glucose homeostasis When you eat a meal which is rich in carbohydrate the sugar (glucose) level in the blood increases. This increased glucose level stimulates the b cells of islet of Langerhans of pancreas to secrete insulin. Insulin directs the target cells to utilise glucose in respiration or to store as glycogen and thereby bring blood glucose level to normal. On decreasing of blood glucose level, the serection of insulin by pancreas decreases. In this way, through direct negative feedback the blood glucose homeostasis is maintained by insulin.

Fig. 14 Blood glucose homeostasis by direct negative feedback

• Blood thyroxine homeostasis
On receiving an external stimulus, the hypothalamus in brain produces T-RH which stimulates the anterior pituitary to secrete TSH. TSH stimulates thyroid gland to produce thyroxine. If thyroxine concentration increases in the blood, it causes negative feedback on hypothalamus to secrete less T-SHRH and subsequently TSH secretion from anterior pituitary also lessens. When TSH level increases in blood, it causes hypothalamus to secrete lesser T-RH.

Fig. 15 Blood thyroxine homeostasis by indirect negative feedback

If thyroxine hormone level decreases below normal, it generates negative feedback on hypothalamus and anterior pituitary. These glands then secrete more T-RH and TSH respectively for increased secretion of thyroxine. Thus, by an indirect negative feedback mechanism the blood thyroxine homeostasis is maintained.

(B) Positive Feedback Control
In this type of control, a hormone increases its own production. This could be understood by the example of oxytocin. Oxytocin is relased from posterior lobe of pituitary on receiving stimulus by uterine contractions during the onset of labour pain in females before the child birth. Oxytocin increases the intensity of uterine contractions. The increased contractions stimulate the production of oxytocin. This cycle stops on the birth of the child.

COORDINATION IN PLANTS

Plants are less complex organisms as compared to animals. They lack nervous system, so, they do not respond guickly to stimulus unlike animals. When we touch (stimulus is provided) Chhui-mui plant (Mimosa pudica), then it frequently folds its leaves. A question comes to our mind, “If plants lack nervous system, how can Mimosa respond so quickly?” “How do plants respond and react to various environmental stimuli like light, gravity, water, touch and chemicals?” The answer of these questions lies in the fact that although nature has not provided plants with brain and nervous system, but they have hormones which help them to respond. These plant hormones are called phytohormones. Phytohormones affect the plant growth as well as the movement of plant parts like leaves, stem and roots. Plants control various movements only through chemical coordination. Generally, responses of plants cannot be observed immediately, as they take considerable time to respond.

Fig. 16 Mimosa pudica (Chhui-mui plant)

Mimosa is a sensitive plant. it shows quick response but other plants may take considerable time for responding in most cases

Phytohormones act differently as compared to animal hormones. They coordinate in two ways-
(i) They control movements by affecting the growth.
(ii) They affect the shape of cells by bringing changes in the amount of water (turgor changes) and plasmolysis.

#### Chemical coordination in plant

It takes place by the plant hormones or phyto hormones. They help to coordinate growth, developement and response to the environment. They synthesis in minute quantity in one part of the plant body and simply diffuse to another part. Where they influence specific physiological processes.

1. Auxin
(i) Promote cell enlargement and differentiation in plants.
(ii) Cause initiation of root of formation on stem cuttings or callus.
(iii) Promote growth of fruits.
(iv) Show promotive effect on growth of stem and slows down the growth of roots.
(v) Cause growth of apical buds (apical dominance) and prevent growth of lateral buds.
(vi) Prevent premature leaf and fruit fall (reduction in abscission).
(vii) Regulate tropic (geotropic and phototropic) movements in plants.
(viii) Use as weedicides [chemicals that kills the unwanted plants (weeds)].
(ix) Control of lodging.
(x) Synthetic auxins are used in agriculture and horticulture as weedicides.
(xi) Induce formation of seedless fruits without involving fertilisation, i.e., parthenocarpy.

(2) Gibberellins
(i) Promote stem elongation (dwarf varieties grow to normal height because the hormone promote internodal growth) and cell differentiation in the presence of auxin.
(ii) Break dormancy of buds and seeds.
(iii) Stimulate growth of leaf, stem and increase size and number of fruits.
(iv) Induce parthenocarpy (formation of fruits without seeds) in many plants.
(v) Can replace requirements of photoperiodic length for flowering in certain plants.
(vi) Neutralise the effects of growth inhibitor (ABA)

(3) Cytokinins
(i) Promote cell division and are also required for differentiation of cells and tissues.
(ii) Delay ageing (senescence) in plant organs like cut flowers, vegetables and fruits.
(iii) Promote the opening of stomata in leaves.
(iv) Break dormancy in buds and seeds.
(v) Promote growth of fruits.
(vi) Play vital role in morphogenesis in plants.
(vii) Inhibit apical dominance and allow growth of lateral buds.
(viii) Regulate transport of nutrients.
(ix) Increase resistance to diseases and temperature stress.

(4) Abscisic Acid (ABA)
(i) Controls plant growth by inhibiting the activity of growth promoters.
(ii) Induces dormancy of buds and seeds.
(iii) Controls the closing of stomata during stress conditions in order to prevent water loss through transpiration.
(iv) Causes abscission (falling) of flowers, fruits and leaves.
(v) Promotes wilting and senescence of leaves.
(vi) Affects synthesis of a-amylase enzyme.
(vii) Causes tuberisation in potato.
(viii) Promotes flowering in short day plants.

(5) Ethylene (Volatile/gaseous plant hormone)
(i) Promotes ripening of fruits and dehiscence of dry fruits
(ii) Promotes senescence of leaves
(iii) Stimulates abscission of flowers, fruits and leaves
(iv) Causes breaking of dormancy in buds and seeds
(v) ‘Triple response’ is an important character of ethylene. This includes swelling of nodes, stimulation of lateral growth and inhibition of elongation.
(vi) Sex modification

#### Plant movement

The plants respond to various stimuli very slowly by growing. E.g. when a seed germinates the root goes down and the stem comes up into the air. But the leaves of sensitive plant move very quickly in response to touch by folding and drooping without growing. So plant show two different types of movement

Classification of plant movements : These are of two types

(A) Tropic movement

Tropic movement is the directional movement of the part of a plant caused by its growth. The growth of a plant part in response to the stimulus can be towards the stimulus (positive tropism) or away from the stimulus (negative tropism).

Types of tropic movements
(1) Phototropism
(2) Geotropism
(3) Chemotropism
(4) Hydrotropism
(5) Thigmotroprism

(1) Phototropism
The movement of a part of the plant in response to light is called phototropism. The plant part moves towards light is called positive phototropism and the plant part moves away from light then it is called negative phototropism.

(2) Geotropism
The movement of a part of the plant in response to gravity is called geotropism. Roots of a plant move downwards in the direction of gravity it is called positive geotropism and stem of a plant moves upwards against the direction of gravity it is called negative geotropism.

Fig. 18 Plant showing geotropism

(3) Chemotropism
The movement of a part of plant in response to a chemical stimulus is called chemotropism. E.g. Growth of pollen tube towards the ovule during the process of fertilisation in a flower.

(4) Hydrotropism
The movement of a part of plant in response to water is called Hydrotropism. Roots of seedling show positive hydrotropism.

(5) Thigmotropism
The movement of a part of plant in response to contact or support is called thigmotropism.  E.g. Pea plant climb up other plants or fences by mean of tendrils. Tendrils of are sensitive to touch. When tendrils come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of tendril away from the object. This causes the tendril to circle around the object and thus cling to it.

Fig. 20 Tendrils wrap around a support

(B) Nastic movement
Movement which is neither towards nor away from the stimuli. It is growth independent movement.

Seismonasty
Such movements occur in response to touch (shock). These movements are very quick and are best seen in ‘touch-me-not’ plant (Mimosa pudica), also called ‘Chhui-mui’ or ‘Lajwanti’ or ‘sensitive plant’. If we touch the leaves of the chhui-mui plant with our finger, we find that all its leaves immediately fold up ane droop by using electrical chemical means to convey this information from cell to cell. After sometime, the leaves regain their original status. Here, no grmvth is involved. Instead, plant ceil change shape by changing the amount of water in them (turgor changes), resulting in folding up and drooping of leaves.

Fig. 21 Mimosa pudica leaves exhibit nastic movement

Difference between tropic and nastic movement