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Chapter 9FOOD AND NUTRITION

To remain alive and to maintain the body processes all organisms take in nutrients. Nutrients are chemical substances needed by the body. They provide energy, the fuel of life. They repair the older body cells and form new ones.

Learning objectives:

Introduction of nutrition and nutrients. Importance of food to obtain nutrients. Synthesis of macro molecules from micro molecules. Autotrophic nutrition in plants. Mineral requirements in plants for photosynthesis. Special modes of nutrition in plants.

Heterotrophic nutrition in animals. Nutrition in human beings and components of their food. Concept of balanced diet and its importance.

Disorders of the gut.

All living organisms require energy to carry on their life processes. To meet these demands they intake two main categories of molecules from environment: already synthesized high-energy compounds (food) or the raw materials from which new protoplasm can be synthesized. The intake and processing of these materials is called nutrition. Materials required for the synthesis of new protoplasm as well as for the production of energy are called nutrients.

9.1 NEED FOR FOODAll living organisms need food. They need it as a source of raw material to build new cells and tissues as they grow. They also need food as a source of energy. Food is a kind of fuel of living organisms like automobiles require petrol or diesel. In living organisms food drives essential living processes and brings about chemical changes. It provides essential materials to make proteins and enzymes. It also provides materials to maintain various processes of life such as reproduction, respiration etc.

Living organisms can be divided into two groups on the basis of their mode ofnutrition.(i) Autotrophic organisms (ii) Heterotrophic organisms

(i) Autotrophic organisms: Organisms, which can synthesize their own organic compounds (food) from inorganic raw material taken from inorganic surroundings. The molecules of raw material are small enough and soluble to pass through the cell-membrane. Most of the autotrophs are photo synthetic e.g plants, algae some bacteria etc.

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(ii) Heterotrophic organisms: Organisms, which are unable to synthesize their own organic compounds (food) from simple inorganic nutrients. They obtain synthesized food from their environment. Many of the organic molecules found in nature arc too large to be absorbed unaltered through cell membranes and they must first be digested i.e broken down into smaller, more easily absorbable molecular units.

The food of heterotrophic organisms consists of following components.1. Carbohydrates 2. Proteins 3. Fats4. Vitamins 5. Minerals 6. Water

9.2 SYNTHESIS OF LARGE MOLECULES FROM SMALLER BASIC UNITSOrganic molecules in the living bodies are found in the form of either small or large, complex molecules. Most of them are large and complex. There are two ways to manufacture a large complex molecule: One could synthesize the molecule atom by atom or one could take pre-assembled smaller molecules and hook them together. Small molecules (e.g. Glucose) arc used as sub-units to synthesize longer molecules e.g. starch. The individual sub- units are often called monomers (Greek words meaning one part), long chains of monomers arc called polymers (many part). All polymers are synthesized by a process called condensation. In this process two monomers are joined together by the removal of a water molecule, as a result a bond is formed between two sub-units, this process is called dehydration synthesis.

Monomers PolymerMonosaccharides e.g. glucose Polysaccharide e.g. starch andAmino acids glycogenFatty acid and Glycerol Proteins

Fats and oils

Simple Sugar to Starch and Glycogen:Starch, glycogen and simple sugar (glucose, fructose etc), belong to a group of organic compounds called carbohydrates. Carbohydrates contain carbon, hydrogen and oxygen. The most common simple sugar is grape sugar called glucose (C6 H12 O6). It is the most ready source of energy in cells.

Fig: 9.1 Diagram showing how complex carbohydrates arise from simple sugar

When molecules of simple sugar combine, they from complicated carbohydrate e.g. molecules of glucose and fructose combine to form a complex disaccharide sugar called sucrose (table sugar), found in sugar cane and beet root. When many simple sugar molecules join in long chain, they form the most complex polysaccharide carbohydrates such as cellulose, glycogen and starch.

Plant cells store extra carbohydrate as starch while animal cells store extra carbohydrate as glycogen which is some times called animal-starch.

9.2.2 Amino acid to proteins:Amino acids are the monomers that condense to form proteins, which are very large molecules. We can say that the building blocks of proteins are amino acids. There are 20 kinds of amino acids which combine in different kinds of proteins.

Fig: 9.2 Formation of a simple Protein molecule by the combination of amino acids

As you know that the English language has 26 letters of the alphabet and they form millions of different words. In the same way, the 20 amino acids form a



great variety of proteins. The number of amino acids combined in most proteins molecules ranges between 300 to 3000.

Main role of protein is to provide building material in the body. They help in growth and repair of body parts (healing). They make structures like muscles, nails and hairs.

9.2.3 Fatty acids and Glycerol to Fats and Oils:Fatty acids and glycerol are the monomers that condense to form fat or oil, which are insoluble in water due to absence of any polar group. A fat or oil is a molecule which is formed by the condensation of 3 molecules of fatty acid with a glycerol by removing 3 molecules of water. Oils are liquid at room temperature while fats are solid. Examples of oils are cotton seed oil corn oil coconut oil, soyabean oil. Fats generally come from animal source like butter, cream, etc.

Organisms use fat molecules as long term energy storage compounds.

Fig: 9.3 Diagram showing how fats are formed from glycerol and fatty acids

9.3 NUTRITION IN PLANTS From the view point of nutrition, the most important difference between animals and plants is that animals take in prepared organic food, digest it and use the digested products to build their tissues or to produce energy. Plants, on the other hand, first make the food they need and then use it for energy and growth. Majority of the plants are autotrophic in their mode of nutrition. Some are heterotrophic and live as parasites or saprophytes. Parasites obtain their food from other living organisms while saprophytes depend on dead organic matter.

In dealing with life processes in plants in this chapter, we shall first discuss photosynthesis and its processes.

9.3.1 Autotrophic nutrition in plants: Photosynthesis:

The process by which plants make their food is called photosynthesis. In this process a plant can build sugar by taking carbon dioxide from air and water from the soil. For the synthesis of sugar like glucose, carbon dioxide provides carbon and oxygen whereas water molecules provide hydrogen. The plant builds sugar molecules from these simple compounds. Enzymes needed for this purpose are present in the cells and energy is trapped by chlorophyll from sunlight. The process if completed in the mesophyll cells of the leaves as shown in Fig: 9.4.

The reaction is expressed by the following chemical equations:

Light Energy6CO2 + 6H2O C6H12O6 + 6O2

Chlorophyll

Carbon dioxide + Water Glucose + Oxygen

(Raw material) (Product)

This equation shows only the starting materials and end products of the process but gives no information about the intermediate reaction steps involved. It is also obvious that oxygen is produced as a by-product of photosynthesis. During day light, green plants take in carbon dioxide and give out oxygen. Thus, oxygen would appear here to be a waste product.



Fig: 9.4 Photosynthesis in plants

9.3.2 Morphology and Anatomy of leaf related with Photosynthesis:In plants, leaves are the most appropriate structures which are adapted fog photosynthesis. There are wide variations in leaf shape and structure. The following characters explain their adaptability towards photosynthesis.

1. Their broad flat shape offers a large surface area for absorption of sunlight and carbon dioxide.

2. Most leaves are thin and the CO2 has to diffuse across only short distances to reach the inner cells.

3. The large spaces between cells inside the leaf provide an easy passage through which C02 can diffuse.

4. There are many stomata (pores) mostly in the lower surface of the leaf which allow the exchange of CO2 and O2 with the air outside.

5. There are more chloroplasts in the upper cells than in the lower cell because the cells of upper surface receive more sunlight.

6. The branching network of veins and veinlets provide a good water supply to the photosynthesizing cells and no cell is very far from a water conducting vessel.

Fig: 9.5 (a) The external appearance of leaf shows the transport tissues. Fig: 9.5 (b) Transverse section through part of a leaf.

The leaves of most land plants are only a few cells thick. The upper and lower surfaces of a leaf consist of a layer of transparent cells, the epidermis. The outer surface of both epidermal layers are covered by a waxy, water proof covering, the cuticle that reduces the evaporation of water from the leaf A leaf obtains CO2 for photosynthesis from the air through adjustable pores in the epidermis called stomata which open and close at appropriate times to admit CO2. Inside the leaf, there are a few layers of cells collectively called mesophyll (which means simply middle of leaf) where photosynthesis occurs predominantly.

9.3.3 Factors necessary for photosynthesis:Many factors, both external and internal are necessary for food synthesis in plants. The external factors are sunlight, water, carbon dioxide and temperature. The internal factor is chlorophyll. It is present in special structure within a cell called chloroplast.The following conditions are necessary for the process of photosynthesis in plants.

1. Light: Carbon dioxide and water are the basic constituents required for formation of glucose. However, they will not combine in the absence of sunlight because various reaction steps necessary for synthesis of glucose require energy input. This energy is supplied by light. As light is composed of seven colours; rays of two colours chiefly red and blue, are used in the process. Photosynthesis is also affected by the intensity of light. Very intense light is harmful, while light of moderate intensity accelerates and weak light slows down the rate of photosynthesis. In the total absence of light even the chlorophyll does not develop. Photosynthesis can also take place in artificial light.

2. Chlorophyll: Chlorophyll imparts green colour to the leaves. It traps the energy of sunlight and makes it available for use by the plant. Photosynthesis will not proceed without chlorophyll and that is why it occurs only in the parts of the leaf or stem that contain chlorophyll.



3. Carbon dioxide: Plants get the carbon dioxide to be used during photosynthesis from the air. It enters the leaf through the stomata. It is used as a source of carbon for glucose. Photosynthesis will not take place without carbon dioxide. Although it comprises only 0.03 to 0.04% of the air, its supply does not exhaust as it is continuously recycled into the air. The process of photosynthesis accelerates if its proportion is increased up to 1.0%. However, greater amounts of carbon dioxide, adversely affect the process.

4. Water: This constituent is as basic as is carbon dioxide. Water is important in photosynthesis in two ways; firstly, it provides hydrogen for the building up of glucose and secondly, opening and closing of stomata is regulated by increase or decrease in the amount of water. It is important that stomata should remain open so that carbon dioxide may enter leaves. Water together with salt (e.g. nitrates), absorbed by the roots ultimately reaches leaves where it is used in photosynthesis.

5. Temperature: Suitable temperature is also necessary for photosynthesis. Normally a temperature range of 15°C to 30°C is most suitable for this process. At higher temperature the rate of photosynthesis starts declining and at 45°C it completely stops. However, depending on regions, the temperature requirements of the plants may change. For example, this process occurs at a temperature range from 0°C to 10°C in plants of cold and mountainous regions.

9.3.4 Conversion of light energy into chemical energy:Photosynthesis is the metabolic process by which plants trap light energy, convert it into chemical energy and store it in the bonds of organic nutrient molecules such as glucose and release O2 as by-product.

Light Energy6CO2 + 6H20 C6H12O6 + 6O2

Chlorophyll (Glucose)

The simple looking chemical reaction of photosynthesis actually involves dozens of reactions. These reactions occur at different sites in the chloroplast. Whole photosynthesis process is mainly divided in two stages.

1. Light reaction 2. Dark reaction

1. Light reaction: Light reaction is also called light-dependent reaction because chlorophyll and other molecules capture light energy and convert some of it into the chemical energy.

Some of the light is utilized to split water into oxygen and hydrogen. This splitting of water is called photolysis (photo= light, lysis= to break). Oxygen which is produced during photolysis is released in the environment whereas hydrogen together which CO2 is used in building glucose.

Within the chlorplast, chlorophyll and the other pigment molecules form highly-organized assemblies called photosystems. The conversion of light energy into chemical energy in these photosystems produces two energy rich compounds. These are:

(i) NADPH2 (Nicotinamide Adenine Dinucleotide Phosphate) (ii) ATP (Adenosine Tri-Phosphate)



NADP, which already exists in the chloroplast reduces into NADPH2 by acceptinghydrogen ion released from splitting of water. NADP + H++e -

(In cell) (From water)

Another compound already present in the cell is ADP (Adenosine diphosphate) which combines with phosphate group by using light energy to form ATP (Adenosine tri-phosphate).

Light energyADP + P ATP

Enzyme

Reduction and oxidation are two important chemical concepts which help us to understand the terminology of the electron transfer chain.Reduction is the addition of electrons to a substance. In biological systems this addition of electrons is usually brought about by the addition of hydrogen or the removal of O2. Oxidation is the removal of electrons from substance.

ATP and NADPH2, both are energy rich compounds. They provide energy for the conversion of CO2 into carbohydrates during dark phase of photosynthesis.

Fig: 9.6 Photosynthesis consists of light-dependent and light- independent reactions

2. Dark reaction: Dark reaction is also called light independent reaction because light energy is not captured during this phase. Only ATP and NADPH2, which are synthesized during light reaction, provide energy to synthesize glucose by fixing CO2 and H2O. Fixation of CO2 and its conversion into glucose occurs in the chloroplast by means of a series of reactions known as Calvin cycle or dark reactions.

Glucose molecules thus formed at this stage are stored as starch in the chloroplast.

Melvin Calvin a scientist received a Nobel prize in 1961 on determining the dark reaction.

Experiment No. 1

Is chlorophyll necessary for Photosynthesis ?Since it is not possible to remove chlorophyll from a leaf without killing it, so it becomes necessary to use a leaf where chlorophyll is present only in patches. Such a leaf is known as variegated leaf and a plant with such leaves is used in this experiment.

For destarching the leaves, the potted plant is kept in a dark place for a couple of days and then exposed to daylight for a few hour. The leaf is then removed from plant. Its out line is carefully drawn to note the position of presence or absence of chlorophyll on it. Now iodine is applied to the leaf to test for the presence of starch. (Startch whenever come in contact with iodine turns blue).

This test shows that only those parts which were previously green turned blue with iodine while the white parts turned brown. This result indicates that starch is formed only in those parts of the leaf where chlorophyll exists (i.e. green parts). In other words, photosynthesis is not possible without chlorophyll. If this were possible the white parts of the leaf should have also given a blue colour with iodine.


NADPH2 (Reduced form)


Fig: 9.7 To show that chlorophyll is necessary for photosynthesis

Experiment No. 2

Is light necessary for Photosynthesis?A potted plant is destarched by keeping it in the dark room for two days. It is then transferred to light. Two of its leaves are selected for the examination. One leaf is wrapped completely in black paper. The other leaf is also wrapped in black paper but an L-shaped part of the paper is cut out so that light can reach this part of the leaf through it. The plant is placed in the sunlight for 4 to 6 hours. The two leaves are now detached from the plant and tested for presence of starch. It would be observed that the leaf which does not receive any light is free of starch (remains brown with iodine). However, in the second leaf, light could pass through the L-shaped opening in the black paper. Only this 'L' shaped area turns dark blue while the other parts of the leaf remains brown. This shows that light plays a vital role in the manufacture of starch. Since starch is manufactured due to photosynthesis, light is essential for this process.

Fig: 9.8 To show that light is necessary for photosynthesis

Experiment No. 3

Is carbon dioxide needed for Photosynthesis?Two potted plants are destarched by keeping them in a dark room. They are watered properly during this period. Each pot is enclosed in a transparent polythene bag as shown in figure 9.9.

A petri dish containing soda lime (potassium hydroxide) is placed in one of the pots to absorb any carbon dioxide present in the polythene bag. In the other pot a petri dish is placed containing sodium bi-carbonate solution which would produced carbon dioxide. The plants are then left in light for several hours. A leaf from each pot is detached and tested for starch. The leaf from the pot containing soda lime does not turn blue. Soda lime had absorbed any carbon dioxide present in the bag. The leaf from the other pot where carbon dioxide was being released by the sodium bicarbonates solution turns blue indicating the presence of starch. These results show that carbon-di-oxide is essential for photosynthesis.

Fig: 9.9 To show that CO2 is necessary for photosynthesis

Experiment No. 4

Is oxygen produced during Photosynthesis?A short stemmed funnel is placed over the shoot of an aquatic plant (Hydrilla) in a beaker of water as shown in fig. 9.10. A water filled test tube is inverted over the stem of the funnel. The funnel is placed in the beaker on supports, to allow free circulation of water. The apparatus is kept in sunlight for some time. Bubbles of gas soon appear from the plant, rise and collect in the test tube. When sufficient gas has accumulated the test tube is removed. A glowing match stick is inserted in the tube. The match stick burns with a flame showing that the gas is rich in oxygen. It is clear from this experiment that oxygen is evolved during photosynthesis.

Fig: 9.10 To show that Oxygen is set free during photosynthesis

9.3.5 Factors affecting the rate of photosynthesis:The rate of photosynthesis is affected by a number of factors. Such as light intensity, CO2 concentration, temperature and inorganic ions.



Light intensity:The rate of light reaction will depend on the light intensity. The brighter the light, the faster will water molecules split in the chloroplast. Fig.9.11 shows that an increase in light intensity does indeed speed up photosynthesis, but only up to a point. Beyond that point, any further increase in light intensity has only a small effect. This limit on the rate of increase could be because all available chloroplast are fully occupied in light absorption. So, no matter how much the light intensity increases, no more light can be absorbed and used.

Fig: 9.11 Light intensity and rate of photosynthesis

Temperature:The dark reaction will be affected by temperature. A rise in temperature will increase the rate at which CO2 combines with hydrogen to make carbohydrate. Thus rate of photosynthesis increases with the increase in temperature within optimum limits.

Carbon dioxide concentration:There is only 0.03% of CO2 in the air. Shortage of CO2 is an important limiting factor and slows down the rate of photosynthesis. Experiments show that an increase in CO2 concentration enhances the rate of photosynthesis. The stomata in a leaf may affect the rate of photosynthesis according to whether they are open or close. At low concentration of CO2 inside the leaf, the stomata will open.

9.3.6 Most of life forms are dependent on photosynthesis:The process of photosynthesis is of prime importance because all the living organisms on this earth are dependent on plants for food and O2 , they produced. The photosynthesis is the only process which can fix atmospheric CO2 into organic compounds to produce bio-molecules. Therefore, plants are also called producers of ecosystem. Thus, they are the direct or indirect source of food for all the non-photosynthetic life on earth.

Plants through photosynthesis keep carbon and oxygen cycle going on and thus maintain them in balance. During photosynthesis they fix CO2 and release oxygen in environment. Animals use O2 in respiration and release CO2 back into atmosphere.

One of the property of CO2 is that it absorbs heat of sun. If CO2 accumulates in the atmosphere, the environmental temperature would rise and our earth will warm up. Photosynthesis keep on using CO2 has an indirect cooling effect.

9.3.7 Mineral requirement in plants:CO2 and H2O are not the only nutrient material needed by a green plant. These two compounds provide only three elements, C, H, and O, but plants require more elements for the composition of their molecules, e.g. Nitrogen (N) is always present in amino acids, the building- block units of proteins which are essential components of protoplasm, some amino acid also contain sulphur (S). Phosphorous is present in ATP, nucleic acid and many other important compounds. Chlorophyll, essential pigment of photosynthesis contains magnesium while cytochrome important compound in electron, transport, contain iron. Plants absorb these elements in the form of different compounds from soil through their roots.

Table 9.1: Important minerals required by plantsElement Function

Nitrogen (N) Structural components of amino acids,many hormones and co-enzymes etc.



Magnesium (Mg) Structural component of chlorophyll,co-factor for many enzyme involved incarbohydrate metabolism, nucleic acidsynthesis and the coupling of ATP withreactions.

9.3.8 Importance of chemical fertilizers in Agriculture:Inorganic fertilizers help to replace the mineral ions consumed from the soil by successive production of crop. Usually three elements are added to the soil, by fertilizer in the inorganic form, are nitrogen, phosphorous and potassium, since these are the ones, which are mostly depleted by-the growing crop continuously.

Modern commercial inorganic fertilizers are often designated by their N-P-K percentages e.g. the widely used garden fertilizer called 5-10-5 contains 5% N, 10% P and 5% soluble K by weight.

Nitrogen is also added to the soil in the form of ammonium nitrate or ammonium sulphate. Phosphorous and potassium are added in the form of super phosphate and potassium chloride, respectively.

9.4 SPECIAL MODES OF NUTRITION Plants, usually being autotrophic, are directly or indirectly the source of food for all organisms on this earth. There are some special plants which cannot manufacture their own food and are wholly or partially dependent upon other plants or animals. Such plants are known as heterotrophic plants. Depending upon their special mode of nutrition, they can be divided into the following four types.1. Parasites 2. Saprophytes 3. Insectivores 4. Symbionts.1. Parasites: These are entirely or partially dependent upon autotrophic plants for their food supply. They grow on the stem or branches of the host rather than in soil. An important feature of these plants is that they have special roots known as haustoria which absorb ready made food from the host plant. These roots come in contact with the xylem and the phloem tissues after penetrating the stem and continuously absorb water and salts from their hosts.

A well known parasitic plants is cuscuta. It is a total parasite; its weak and yellowish stem twines around shrubs and the branches of host trees.

Fig: 9.12 Cuscuta—A parasite plant

2. Saprophytes: These plants have no chlorophyll and derive their food from dead organic matter. Some flowering plants like monotropa and neottia are also saprophytic in nature. These plants are found in thick jungles where sunlight cannot reach the ground and the soil is rich in decomposing organic matter. As there are no root hairs in these plants they cannot draw their nourishment from the soil. The roots of these plants develop in association with a special type of fungus. A part of the hyphae of this fungus enters the roots of these plants. These hyphae thus serve as 'root hairs' and help in the absorption of the food from the dead organic matter.

Fig: 9.13 Monotropa.—A saprophyte

3. Insectivores: These plants are found in marshy areas of many countries. These marsh lands are deficient in nitrogen compounds and nitrates. To make up for this deficiency



of nitrogenous compounds in their bodies, such plants feed on insects. They attract insects with their peculiar shape, colour and nectar and then trap them inside their modified leaves. The prey is killed, digested by enzymes and finally absorbed.

The insectivorous plants can make their food by photosynthesis because of chlorophyll in their leaves and can survive without eating insects. However the insect-fed plants are stronger and healthier. They bear more flowers, fruits and seeds.

Pitcher-plant is a common insectivore. It is found along Eastern Himalayas. In this plant the lamina of leaves is modified into an elongated pitcher with a lid at the top. It is here that insects are trapped. The leaf base becomes flat and behaves like leaf lamina. It is green due to the presence of chlorophyll. The petiole is twisted and curved to keep pitcher in straight position.

Fig: 9.14 A leaf of a pitcher plant with pitcher

4. Symbionts: An association of two organisms in which both the partners get benefits is called symbiosis. For example, the association between nitrogen-fixing bacteria and roots of leguminous plants is symbiosis. Lichens are another example of symbiosis. Lichens are formed by association of a fungus and an alga so, they are modified organisms. The fungus provides shelter and water to the alga. The alga makes food by photosynthesis.

Fig: 9.15 Symbionts: A lichen is an association of an alga and a fungus. The alga produces food; the fungus may provide protection and moisture.

9.5 NUTRITION IN ANIMALS Animals cannot manufacture their food from simple inorganic substances so they have to obtain' organic molecules from then-environment in the form of food. Such a way of nutrition is called animal like nutrition or holozoic nutrition. As animals obtain their food from other organisms, this type of nutrition is also called heterotrophic nutrition. According to their type of nutrition animals are of many types:

(1)Carnivores (2) Herbivores (3)Omnivores (4) Frugivores(5)Insectivores (6) Parasites (7) Saprobes

1. Carnivores: This type of nutrition in which animals feed upon other animals is called carnivorous nutrition. Such animals are called carnivores. For example cat, dog, etc. Canine teeth of carnivore mammals are strong, long, sharp and pointed for tearing flesh of other animals.

2. Herbivores: In this type, animals use plants as their food. For example, horse, cattle, deer, etc feed upon leaves and grass. Such animals are called herbivores. They do not have canines. Many birds such as sparrow, parrot, etc. are also herbivores.

3. Omnivores: It is the mode of nutrition in which animals feed upon flesh as well as plants. Man, cockroach etc. fall into this category .These organisms are called omnivores.

4. Frugivorea: Animals like parrot, etc which feed on fruits like guava, figs etc. are frugivores and this type of nutrition is called frugivorous.



5. Insectivores: In this type nutrition, animals feed upon insects. For example wall lizard and frog feed upon-a-variety of insects. Such animals are called insectivores.

6. Parasitic: A parasite lives in close association with the other living organism called host for obtaining its food. Organisms with this type of nutrition are called parasites. The relationship is advantageous to the parasite but harmful to the host. Some parasites live on the external surface of their hosts. They are called ectoparasites e.g. mosquito, lice, etc. They obtain their food from the surface of the host. Others live inside the bodies of their hosts. They are called endoparasites e.g. tape worms and round worms in the intestine of vertebrates. They obtain nourishment from inside the body.

7. Saprozoic: The organisms who obtain food from dead organisms are called saprobes and this type of nutrition is called saprozoic. Saprobes secrete the enzymes out side their bodies, on the food to digest it and then absorb it in the fluid form. Fungi and many bacteria fall in this category.

9.6 NUTRITION IN MAN 9.6.1 Constituent of food:Food is a set of chemicals that is basically required for growth and for obtaining energy. Moreover, food is needed to make enzymes for various metabolic processes.

The food which animals, including humans, take in consists of the following components or nutrients.

(1)Carbohydrates (2) Fats (3) Proteins(4)Vitamins (5) Minerals (6) Water

1. Carbohydrates: These are the fuel of the body because they are the most direct source of energy. Common examples are starch, sugars, etc. The most common simple sugar is grape sugar called glucose. It is the most readily available source of energy.

2. Fats: Fats belong to a group of organic compounds called lipids. Fats are high energy food. They provide double amount of energy upon oxidation, in contrast to the same quantity of carbohydrates.

We obtain fats from animal sources e.g. ghee, butter, cream, fish oil etc, as well as from plant sources e.g. mustard oil, soyabean oil, peanuts etc.

Animals store fats beneath the skin and around some visceral organs. Besides serving as source of energy they insulate the body and protect internal organs. They also serve as building material of protoplasm and membrane systems.

3. Proteins: Proteins are the building materials of protoplasm. They are obtained from meat, pulses, milk, cheese, dry fruits, etc. They consist of smaller units called amino acids. Proteins are required for growth, repair, defence of body, clotting of blood, etc., the deficiency of proteins in diet especially that of essential amino acids containing proteins, severely affects such functions. They are structure building compounds which make many body structures like hair, nails, muscles, etc.



4. Minerals: Minerals are ionic substances which are required in metabolic activities of the body. They do not provide us energy but ensure proper growth and functioning of the body. Some important minerals are described below:

Calcium: It is obtained from milk, eggs, fruits, and cereals. It strengthens the bones and teeth. It also helps in muscular contraction, blood clotting and conduction of nerve impulse.

Iron: It is found in meat, liver, eggs, apple, spinach and other vegetables. It is used in synthesis of haemoglobin and myoglobin in blood and muscles, respectively.

Phosphorus: It is found in milk, eggs, meat, vegetables etc. It is required for bones, teeth, formation of plasma membrane, nucleic acids, and ATP.

5. Vitamins: Vitamins are organic compounds which are needed in minute quantities for proper growth and development of the body. Plants can synthesize all vitamins from simple substances but animals have to obtain them through their diet. There are different vitamins which are denoted by letters of the alphabets such as A, B, C, D, E, K. They are classified as fat soluble vitamins e.g. A, D, E, K and water soluble vitamins e.g. B, C. Fat soluble vitamins can be stored along with, fat but water soluble vitamins cannot be stored so we require continuous intake of them. Table 9.2 shows different vitamins alongwith their sources, their deficiency disorders and characterization of disorders.

Table: 9.2 Vitamins and their functionsSolubility Name of Sources of Characters Disorders

Vitamin vitamins of disorder caused bylack /

deficiencyVitamin A Fish-liver oil, Essential for Dry cornea,

animal liver, vision, growth dry skin poormilk, cheese, and night vision.fresh green functioning ofvegetables. skin, etc.

Vitamin D Fish-liver oil, Bones remain Ricketsbutter, egg soft and (decrease inyolk, milk. ultimately absorption ofAlso made by become calcium andaction of deformed. In phosphorus in

soube

sunlight on adults bones intestine).skin. become

painful and

vitamins

can befracturedeasily.

Vitamin E Plant oils, Few deficiency Anemiagreen leafy effects aresalad etc. noticed in

adults. Severedeficiency ininfants maycause highrate ofdestruction of


RBC.Vitamin K Dark green Prolong Blood does

leafy clotting time not clotvegetables. excessiveMade by bleedingbacteria inintestine.

Vitamin B Husk of wheat Wasting of Beri BeriComplex grains and muscles;Vitamin B1 brown rice. circulatory

failure andparalysis

Vitamin B2 Leafy Sore mouth, Sorevegetables, eyes and skinfish, eggs.

Nicotinamide Meat, fish, Diarrhea, Pellagra

vitamins

milk, eggs. dermatitis andmentaldisorder

Vitamin C Citrus fruits Bleeding from Scurvyand green gums, woundsvegetables. fail to heal

6. Water: Water makes up nearly 70 percent of the total body mass. It is required as solvent in most of the metabolic activities of the body. It also helps in the absorption and transportation of the digested food. It helps plants in photosynthesis for intake of minerals from the soil and in movement of food.

9.7 DIETARY FIBRES (Roughage) Dietary fibre or roughage is made up of the indigestible cell walls of plant cells that we take in our food such as fruits, vegetables. It provides bulk to the food in the intestine by retaining water. It also stimulates the gut for peristaltic movement which makes the passage of food easier through the gut for defecation. Absence or shortage of dietary fibre in food may cause constipation or intestinal disorders.

9.7.1 Nutrition and food technology:We eat food in order to obtain energy for the maintenance of life and also to provide raw materials to build and repair the body. Thus there is a continuous need of food. Unfortunately, the production of food is seasonal and not uniform throughout the world. In order to ensure a continuous supply of food, some of it must be preserved and stored for later use.

Food is destroyed either by the growth of micro-organisms such as bacteria, fungi or due to the enzymes of the cells of food. Man knows since the ancient times, the methods to preserve the food but these methods were not effective in preserving food for longer time. The nutritional value and taste were considerably lost in food preserved through such traditional methods.

With the help of modern science, various methods have been developed to preserve the food for longer period of time without affecting its nutritional value and taste. Some of the important methods are as follows:

1. Pasteurization: It was discovered by Louis Pasteur to prevent milk from turning sour. You all know very well that milk is boiled after purchasing it from milk- man. Increase in



temperature of milk up to the boiling point, kills most of the germs (bacteria) present in it thus milk can be kept longer. In the absence of boiling, it turns sour very quickly. The modern way of milk pasteurization comprises of heating to 71 °C and then immediate cooling. As a result most of its bacteria are either killed or if survive, their growth is retarded so the milk can be preserved for few days.

2. Refrigeration: Refrigeration is another way of preserving food. In this method food is kept at very low temperature at -30°C to -40°C. Due to very low temperature the bacteria are either killed or their growth is retarded. Now-a-days, food quickly freezes (-18°C) in about 30 minutes. It renders taste and texture of the food.

3. Dehydration: It is the oldest method of preserving food by dehydration. Although drying of food does not kill micro-organisms, it preserves the food as it makes water unavailable to micro-organisms which requires it to grow and multiply. Dried food is easily stored and transported due to its light weight. However, it often brings about a change in texture and taste of the preserved food.

4. Canning: In this method, food is adequately cooked and then sealed while hot in a sterile, metallic and air tight container. Heating kills the microorganisms as well as inactivates the enzymes.

HEALTH PROBLEMS RELATED TO NUTRITIONThe problems related to nutrition are as follows.1. Under-nutrition 2. Mal-nutrition 3. Over-nutrition

1. Under-nutrition: It is a problem of poor countries of the world where there is insufficient food for the people. Famine stricken countries such as Ethiopia are facing this problem. Under-nutrition especially affects the children. Due to insufficient food, their physical as well as mental growth are severely affected. Such children or persons This condition is called marasmus.

Fig: 9.16 A child is suffering reduce to a skeleton only.

2. Mal-nutrition: It refers to a diet missing in one or more basic nutrients. It can affect person of any age or group. It can badly affect the pregnant women and infants. It has been noticed that mal-nutrition is the major cause of death among the children upto the age of five in the world especially in developing countries.

Fig : 9.17 Effects of malnutrition (Girls of the same age)

In Africa and Asia, due to poverty and famine, the diet is usually deficient in proteins and carbohydrates. Deficiency of protein in dite increases susceptibility to diseases besides retardation in growth.

3. Over- nutrition: It is observed in developed countries where people take excess nutrients. Obesity is the most common disorders due to over-nutrition. Obesity is caused by excessive consumption of refined carbohydrates and fats.



Balanced diet:A balanced diet contains adequate amount of nutrients. It helps in proper growth, metabolism, and maintenance of good health. Unfortunately despite extensive research, it is not yet possible to say exactly how much of each type of food a person must take in order to satisfy all of its requirements. The problem of doing this is complicated by the fact that the body's food requirements vary according to age, body size, sex, occupation, and health. For example children need more food for their proper growth. Youth on the other hand need more food than elderly people because of their active physical work. It has been recommended that an average adult healthy person requires the necessary energy 50 percent from carbohydrate, 40 percent from fats and 10 percent from proteins. Fats are necessary in diet as they contain fat soluble vitamins as well as fatty acids. It is also recommended that adults should eat at least 1gm of protein per kg of body weight per day. How ever infants should be given 2gm per kg from birth to six months. It is further suggested that 60 percent of daily intake should consist of animal proteins since this contains more essential amino acids.

Raw food (100g) Energy (K.cal)Rice 360Eggs 163

Butter 716Milk (Mother) 60

Milk (Cow) 65Sugar 387Beef 183Fish 176

Mutton 153Beans 35

Orange 45Apple 58

9.9 DIGESTION IN MANMan, like other animals takes food that consists of complex and larger molecules. For example, imagine your food when you take a chicken sandwich. The bread of the sandwich contains starch which is insoluble and chemically different from glycogen or glucose. Similarly fat/oil in the butter of the sandwich are also insoluble. Also the proteins of sandwich are useless to you in the form they are eaten. Thus such large indiffusible food molecules must be broken into smaller diffusible molecules so that they can be absorbed by the cells either to provide energy or to serve other purposes.- This process is called digestion. This entire process takes place inside a long, coiled, muscular tube of varying diameter. This tube called alimentary canal, opens at the anterior end of the body through an opening called mouth and at the posterior end through another opening called anus. Ingestion takes place at mouth and egestion at anus. Alimentary canal is associated with a number of glands like salivary glands, liver and pancreas which secrete digestive juices containing special chemicals called enzymes to bring about the chemical digestion of food. The alimentary canal together with its glands are called the digestive organs.

The alimentary canal is differentiated into buccal cavity, oesophagus, stomach, small intestine and large intestine. The process of digestion involves following different stages;

1.Ingestion 2. Digestion 3. Absorption4.Assimilation 5. Egestion



9.9.1 Ingestion:The process of taking in of food into the mouth or body of animal is called ingestion. In the mouth cavity also called buccal cavity or oral cavity, this food is cut down into smaller pieces with our teeth. This crushing of food make its swallowing easy, helps in mixing the saliva in it and makes the work of digestive juices (emzymes) easier and quicker. The process of breaking the food mechanically into smaller pieces is called mechanical digestion while the chemical break down of food into smaller chemical molecules is called chemical digestion which is brought about by enzymes.

1. Teeth: As stated above, teeth in our oral (mouth) cavity perform mechanical digestion. In both of our jaws, teeth are embedded in jaw sockets. We have two sets of teeth during life time. The first set of teeth, milk teeth appears at about 6 months of age. Later, about at the age of 7 years, the milk teeth gradually fell and are replaced one by one by permanent teeth. The maximum number of permanent teeth is 32. (i.e, 16 in upper, while 16 in lower jaw).

Structure of tooth:Each tooth consists of three parts i.e. crown, neck and root.Crown is the part of tooth projected above the gum level. It is the biting or chewing surface of tooth. Neck is the part surrounded by gum while root is the part embedded in bone.

The outer surface of crown is covered by a very hard white substance, the enamel. It is non-living and protects teeth besides giving lustrous appearance to teeth. The root as well as the portion inside the enamel is dentine. It is less harder than enamel. Inside the dentine, there is a cavity, the pulp cavity. It is filled by soft connective tissue called pulp . It also contains nerves and blood vessels that supply the growing tooth with food and oxygen. The root of each tooth is covered with another hard material called cement.

The tough fibers of periodontal membrane attach the cement to the jaw bone so that each tooth is fixed firmly in socket.

Fig: 9.18 Structure of a tooth

Types of teeth:According to the shape and function following types of teeth are present in our oral cavity.

i) Incisors ii) Canines iii) Premolars and iv) Molars.

Molar: The molars are large strong teeth efficient at grinding food.Premolar: Also known as bicuspids, because of other two distinct edges grind the food.Incisors: These teeth have a chisel shaped, sharp cutting edge ideal for biting. Canines: The canines are sharp pointed teeth, Ideal for tearing food.

Fig: 9.19 Types of teeth

i) Incisors: The flat chisel-shaped teeth resent in front of oral cavity are incisors. They are eight in number, four in upper while four in the lower jaws. They are used in cutting.

ii) Canines: Beside incisors lie canines on each side in both jaws. They are four in number and are pointed. They are used for tearing and pulling flesh. That's



why they are very long and prominent in carnivores such as lion. Herbivore animals usually do not have canines.

iii) Premolars: In both jaws each canine is followed by two premolars. They are 8 in number and each with two distinct edges. They are involved in grinding the food.

iv) Molars: Premolars of each side of both jaws are followed by three molars. They are 12 in number. They also grind food. The last molar is called wisdom tooth.

The arrangement of teeth can be represented by the following formula called dental formula. I2/2, C 1/1, Pm 2/2, M 3/3

It represents each type of tooth in half of the upper jaw and half of the lower jaw.

2. The causes of tooth decay and its prevention: Tooth decay refers to erosion of enamel and dentine. Its major reason is dental plaque which is a sticky substance consisting of food remains, mucus and bacteria. The plaque develops as a hard layer over teeth due to not brushing or improper brushing of teeth after each meal. It develops due to eating too much sweets such as candies, chocolates etc. The bacteria feed on left over sweet which is broken down to produce an acid that gradually destroys enamel forming a cavity in it.

Particles of sugary food get trapped in cracks in the teeth. Bacteria feeding on the sugar form acids, which dissolve the enamel and dentine and hole starts forming. There are nerves in the pulp cavity, so the tooth becomes very painful when hole reaches the pulp. The infection can spread rapidly through the pulp cavity and may form an abscess at the root of the tooth.

Fig: 9.20 Tooth decay

If this decay is ignored, the erosion penetrates deep to destroy dentine. This enables bacteria to infect pulp. This results in tooth ache and tooth is gradually destroyed. Tooth decay can be reduced by cutting down sugary diet and proper brushing with a fluoride tooth paste.

Visit a dentist regularly for check up for healthier teeth.

9.9.2 Digestion:

1. Digestion of food in mouth: The process of mechanical and chemical digestion begins in mouth. The teeth grind the food while three pairs of salivary glands of oral cavity secrete saliva. It contains an enzyme called ptyalin which acts upon starch to break them partly into maltose (sugar).This masticated and partially digested food takes the form of a ball called bolus is then pushed into the oesophagus.

Fig: 9.21 The human alimentary canal

2. Digestion of food in stomach: Stomach is a large bag-like, thick walled structure which stores food as it passes down the oesophagus. Here food is digested chemically as well as mechanically. Internally, its walls contain gastric glands which secrete gastric juice which contains HCl and enzymes called renin and pepsin. HCl kills the germs present



in food. It also softens the food. Renin helps to curdle milk in infants. Pepsin acts on proteins to break them into peptones. The thick walls of stomach churn up the food. After staying here for few hours, the food becomes a thick fluid-like chyme which is released bit by bit into the small intestine.

Peristalsis: The movement of food from oesophagus and onward up to the anus takes place by means of an automatic movement or peristalsis (Fig: 9.22) of alimentary canal.

Fig 9.22 Peristalsis

3. Digestion and absorption of food in small Intestine: Stomach is followed by a long, narrow tube called small intestine where the remaining process of digestion is completed as well as the absorption of nutrients from the digested food takes place. Its first part lying immediately after the stomach is duodenum which receives a common duct formed by the fusion of a duct coming from the gall bladder of the liver and another duct coming from the pancreas. Through these two ducts, the secretion of liver called bile and the secretion of pancreas known as pancreatic juice are poured simultaneously in the duodenum upon the acidic chyme which is coming from the stomach. Both of these secretions contain bicarbonate ions which first neutralizes chyme and then turns it alkaline.

4. Enzymes: Enzymes are chemical substance that work as catalyst in chemical reactions of a cell. These proteins are useful as they speed up chemical reactions without being used up by themselves. Enzymes performing the process of digestion are called hydrolytic enzymes. They are secreted by digestive glands.

a) Liver: The liver is the largest gland in the body. It is reddish brown in colour. It is located in the abdomen underneath the diaphragm. For the process of digestion, it secretes an alkaline, greenish yellow juice called bile which is stored in a sac-like gall-bladder attached with it. There are no enzymes in bile. It contains some salts. Its most important salt is sodium bicarbonate. It also contains bile pigments. However, they are not involved in digestion. Bile helps in breaking down of larger molecules of fats into small droplets. This process is called emulsification. It makes the digestion of fats easier in the small intestine.

b) Pancreas: It is a long, leaf-like organ situated between the duodenum and the stomach. Its secretion is called pancreatic juice. It is colourless and poured through the pancreatic duct into the duodenum. It contains sodium bicarbonate and many enzymes. Three important pancreatic enzymes are discussed below:i) Amylase: It breaks down starch into maltose. ii) Trypsin: It acts upon the proteins to convert at into smaller peptides. iii) Lipase: It breaks fat droplets into fatty acids and glycerol.

9.9.3 Absorption of food in small intestine:Duodenum is followed by ileum, the next portion of small intestine where the rest of the digestion is completed by the enzymes present in intestinal juices secreted by the glands present in the walls of small intestine itself. Its enzymes aminopeptidases and disaccharidases convert peptides into amino acids' and maltose/lactose/ sucrose into glucose, respectively.

After the process of digestion of food is completed here, the digested food in the form of soluble molecules glucose, fructose, amino acids, fatty acids, glycerol, etc. is absorbed into the body through very fine, finger like projections called villi present on the internal walls of ileum.



Each villus is about 1mm long. There are about 5 million villi in the ileum. Due to villi, the internal surface area of ileum has estimated to be 30 square meters for absorption of food.

The villi greatly increase the internal surface area of the ileum. Inside each villus, there is a dense network of blood capillaries and a single lymph vessel or lacteal. Both blood capillaries and lacteal absorb the digested food. Nutrients other than fatty acids diffuse through the surface cells of villi and are taken into the blood flowing in capillaries of villi. These capillaries join together to form a larger blood vessel called the hepatic portal vein which carries the absorbed food to the liver. Some fatty acids, after they are absorbed by surface cells of rilli, recombine to form fats which are passed onto the other side into lacteal rather than blood capillaries. Lacteals of villi join together to form lymph vessels which finally deliver the fats into blood stream through lymphatic system.

Fig: 9.23 Structure of Villus

Table: 9.4 Digestive juices, their sources. secretion / enzymes and the action.

Name of Source Secretion/ Actiondigestive juice Enzyme

Saliva Salivary glands in Ptyalin Breaks downoral cavity starch into

maltose.

Gastric juice Gastric glands in HCl Pepsin Renin Germicidal,stomach activates pepsin,

breaks downproteins intopeptones. Curdlesmilk.

Bile Liver Nil Turns acidicchyme alkalineand emulsifies fat.

Pancreatic juice Pancreas Trypsin Breaks downproteins intopeptides.

Amylase Breaks downstarch intomaltose.

Lipase Breaks down fatdroplets into fattyacids and glycerol.

Intestinal juice Intestinal glands Amino peptidase Breaks downin small intestine peptides into

amino acids.

Disacch-aridase Breaks downmaltose and otherdisaccharides intoglucose.



9.9.4 Assimilation of digested food:

The soluble nutrients after being absorbed are transported through the blood to each and every cell of the body. Depending upon the requirement of the cell, this food can be used either to build new protoplasm or to obtain energy to perform various activities. The incorporation of food by a cell in its components is called assimilation.

Our food consists of different components. Some of its components | such as roughage remain undigested. This undigested food along with considerable quantity of water is passed from the ileum into the large intestine. It is a wider tube but shorter in length than small intestine. It consists of caecum, appendix, colon and rectum. In the large intestine reabsorption of water occurs so the undigested food first becomes paste-like and then slightly harder. Meanwhile, the intestinal bacteria cause fermentation of the undigested matter which is now termed as faeces.

9.9.5 Egestion:

The faeces are stored in the rectum, the last portion of alimentary canal where it is stored for the time being and then egested outside the body through a terminal opening called anus.

9.10 DISORDERS OF GUT

Proper functioning of the digestive system or gut needs regular intake of balanced and germ free diet. However, some times due to the intake of contaminated food, some disorders of gut may develop. Some disorders of gut are discussed below:

1. Vomiting: Whenever we take food containing harmful or poisonous substances, the contents of stomach are expelled out through the mouth by antiperistaltic movements. This process is called vomiting. It may occur when we over eat and helps to expel out the food from the stomach giving us some relief. The sensation, just before vomiting, that the food in the stomach wants to come out is called nausea. There are a number of other reasons for vomiting such as peptic ulcer, appendicitis, many other diseases, psychological or emotional problems, travel sickness, bad smells, pregnancy etc.

2. Diarrhoea: Diarrhoea refers to the condition of large number of watery motions. It is usually caused by infection of colon or food poisoning. Due to continuous diarrhoea, the body can lose large quantity of water which could be fatal if not rehydrated. Infants and young children are easily dehydrated due to diarrhoea. In case of diarrhea, they must be given continuously solution of ORS (Oral Rehydrated Salt). The physician must be consulted immediately to diagnose and treat the patient.

3. Constipation: This is just reverse of diarrhoea. It is the condition in which there is infrequent or difficult passing of dry, hard faeces occurs. It is said to be the mother of all diseases. It is a disorder of large intestine which absorbs excessive amount of water from undigested food. It can be avoided by drinking lot of water and eating more fibre containing food.



4. Appendicitis: It is the inflammation (burning, painful sensation) of the appendix associated with vomiting and abdominal pain. It could be due to obstruction of the appendix either by faeces or worms which cause localized swelling Pain in right side of lower abdomen. In such a case, physician must be consulted irnmediately for diagnosis and treatment . If the condition remained ignored for some time, the appendix may burst cavity that could be extremely fatal for the patient.

5. Enterobiasis: Thread worms cause a disease called enterobiasis. These are minute, thread like worms which live in the large intestine of man. At night time, the female worms come down and lay eggs at the preanal region. It produces severe itching around the anus. Upon scratching the anus, the microscopic eggs are transferred on fingers and nails. Such contaminated hands can cause reinfection of the same person or others who take food or drink contaminated with the eggs. Proper treatment and development of hygienic habits can over come the thread worm infection.



SUMMARYThe intake of nutrient by living organisms is called nutrition.

Living organisms can be divided into two groups on the basis of their modes of nutrition i.e. Autotrophs and heterotrophs. The heterotrophs eat food which contain bio-molecules like carbohydrates, proteins, fats, vitamins, minerals and water. Simple sugar, starch and glycogen belong to a group of compounds called carbohydrates. Proteins are the polymers of nitrogenous monomers called amino acid. Proteins are building as well as biocatalyst molecules of the body. Most of the plants prepare their food by the process of photosynthesis. In this process a plant can build sugar by taking CO2, H2O in the presence of chlorophyll and light.

During light reaction photolysis of water and photophosphorylation occur as a result of it O2, ATP and NADPH2 molecules are formed.Solar energy is converted into chemical energy in the form of ATP and NADPH2 which is utilized during dark reaction for the fixation of CO2. The Dark reaction is light-independent phase where glucose and finally starch is synthesized. Natural and artificial fertilizers are the source of mineral nutrients for plant. Although majority of plants are autotrophs, some plants like, parasites, saprophytes, insectivores and symbionts are partially or totally heterotrophs. Animals can not prepare their food from simple inorganic substances and hence are all heterotrophs. Fats provide double amount of energy than carbohydrates. Minerals ensure proper growth and functioning of the body. Water is biological solvent. Malnutrition develops due to intake of inappropriate quantities of food. Vomiting occurs due to antiperistalsis.



EXERCISE

1. Fill in the blanks with appropriate terms: i) Ready source of energy in the cell is________ . ii) Chemical name of cane sugar is_______ . iii) The process of conversion of light energy into chemical

energy is called___________. iv) _________and__________light is absorbed by reaction centre

during photosynthesis. v) Another name of dark reaction is____________. vi) Deficiency of Vitamin B causes___________. vii) Indigestible cell walls of plant cells is called_________. viii) Adults should take_______gm protein per kg of their body

weight per day. ix) The part of teeth projected above the gum level is called________ x) Starch breaks into maltose through the action of enzyme_______

2. Write whether the statement are true or false: i) Glycogen and starch are the polymers of glucose. ii) Fats and oils are the consendation products of amino acid. iii) ATP formation is called phosphorylation, This process takes

place during dark reaction,iv) ATP and NADPH2 provide energy for the fixation of CO2

during dark reaction. v) Widely used garden inorganic fertilizer is called 6-12-6. vi) Vitamin K deficiency is related to abnormality in the proccess

of blood clotting. vii) Calcium is required for the formation of blood. viii) Condition in which a person is reduced to the skeleton due

to insufficient diet is marasmus. ix) Carbohydrates are digested in stomach. x) Herbivore animals do not have incisors.

3. Encircle the appropriate answer:

i) Organisms which use inorganic material from environment as nutrient are:(a) Saprophytes (b) Parasites(c) Autotrophes (d) None of them

ii) Food of heterotrophs consists of (a) Proteins (b) Fats(c) Carbohydrates (d) All of them

iii) Glycogen is a molecule that belongs to (a) Carbohydrate (b) Fats(c) Protein (d) Vitamins

iv) CO2 from air is taken by leaf through (a) Stomata (b) Epidermis(c) Mesophyll (d) Lenticle

v) Cuscuta is a leafless plant, it is (a) Total parasite (b) Partial parasite(c) Saprophyte (d) Symbiotic

vi) Animals who feed upon dead organic matter are (a) Parasites (b) Saprozoic(c) Herbivores (d) Omnivores

vii) It is considered as building material of protoplasm. (a) Lipids (b) Carbohydrates-(c) Vitamins (d) Proteins,

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viii) Following are not fat soluble vitamins (a) A and D (b) E and K (c) B and C (d) D and E

ix) Rickets develops due to the deficiency of vitamin (a) A (b) B (c) C (d) D

x) Which of the following secretion lacks enzyme (a) Saliva (b) Gastric juice(c) Bile (d) Pancreatic juice.

4. Write detailed answers of the following questions: i) Why life on earth is completely dependent on plants and how? ii) Why leaves are the major sites of photosynthesis? iii) Describe some special modes of nutrition found in plants. iv) Write a note on chemical fertilizers of plants? v) What is roughage and how it is related to our health? vi) What is mal-nutrition? Why is it a health problem? vii) Write a detailed note on balanced diet. viii) State and explain the process of mechanical and chemical

digestion in man. ix) What is tooth decay? x) Explain the role of liver in the digestion. xi) What are villi? Explain their role in increasing the absorptive

surface of intestine.

5. Define the following terms: i) Nutrition ii) Limiting factor iii) Photosynthesisiv) Autotrophs v) Heterotrophs vi) Saprophytevii) Balanced diet viii) Dietary Fibre ix) Pasteurizationx) Enzyme xi) Peristalsis xii) Appendicitis

6. Distinguish between the following: i) Autotrophs and heterotrophs ii) Light and Dark reaction iii) Protein and carbohydrate iv) Carnivore and Herbivore v) Digestion in stomach and digestion in intestine

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