Nutrition in Plants Notes Class 10 Science

The word nutrition is derived from the term nutrient. Nutrients can be defined as the substances, which an organism obtains from its surrounding and uses them either as an energy sources or for biosynthesis of body constituents. Thus nutrition is a process of intake as well as utilization of nutrients by an organism. Food is a kind of fuel which provides energy to all the living organisms.

Types of nutrients

Nutrients can be organic or inorganic in nature. The organic constituents of nutrients are carbohydrates, lipids, proteins and vitamins. The inorganic constituents of nutrients are minerals and water. Depending upon the quantity and functions, nutrients may be of the following types :

1. Macronutrients

These nutrients mainly provide energy e.g. carbohydrates, lipids and proteins.

2. Micronutrients

Although they do not provide energy yet their deficiencies cause specific diseases and abnormalities in animals including humans e.g. minerals, vitamins and water.

Modes of Nutrition :

There are large number of organisms and they live in different environmental conditions. Similarly, they have various methods of deriving nutrients from the environment. Methods of procuring food or obtaining food by the organisms is called modes of nutrition. Depending on the modes of obtaining nutrients, all the organisms can be classified in two major groups : 1. Autotrophic and 2. Heterotrophic

Table

Autotrophic Mode of Nutrition :

The term autotrophic has a Greek origin and made up of two words : ‘auto’ = self and ‘troph’ = nutrition

(1) Autotrophic nutrition is a kind of nutrition in which the organisms synthesize their own organic food utilizing only the inorganic raw materials present in the surroundings.

(2) Such organisms which can prepare their own organic food from inorganic raw materials and remain independent of external sources of organic carbon (compounds) for provision of their own organic constituents are called autotrophs.

(3) The autotrophic nutrition may be photoautotrophic or chemoautotrophic.

(a) Photoautotrophs

Green plants synthesize food through the process of photosynthesis, using simple raw materials like water, CO₂ in the presence of sunlight. Chlorophyll present in the chloroplast of green plants are the sites of photosynthesis.

\mathop {{\text{6C}}{{\text{O}}_{\text{2}}}}\limits_{{\text{(Carbondioxide)}}} {\text{  +  }}\mathop {{\text{12}}{{\text{H}}_{\text{2}}}{\text{O}}}\limits_{{\text{(Water)}}} {\text{  +  Light energy }}\xrightarrow[{{\text{Chlorophyll}}}]{{{\text{Photosynthesis}}}}{\text{ }}{{\text{C}}_{\text{6}}}{{\text{H}}_{{\text{12}}}}{{\text{O}}_{\text{6}}}{\text{  +  6}}{{\text{O}}_{\text{2}}}{\text{  +  6}}{{\text{H}}_{\text{2}}}{\text{O}}

Since autotrophic plants are able to produce food for others also therefore they are also known as producers. Because the autotrophic nutrition is the characteristic of plants therefore it is also called holophytic nutrition.

(b) Chemoautotrophs

Some non-green bacteria like sulphur bacteria use chemical energy to manufacture their food. This energy is derived from chemical reactions occurring in the bacteria. This process is called chemo synthesis. Chemosynthetic bacteria do not require light as the source of energy.

2H₂S + O₂ → 2H₂O + S + 126 K.Cal

2S + 2H₂ + O₂ → 2H₂SO₄ + 141.8 K.Cal

Heterotrophic Mode of Nutrition :

(Heterotrophic : ‘hetero’ = different and ‘troph’ = nutrition)

(1) Heterotrophic nutrition is a kind of nutrition in which the organisms derive energy from the intake and digestion of the organic substances prepared by autotrophs (photoautotrophs and chemoautotrophs) and other organic sources.

(2) The heterotrophs get organic molecules by the intake of plants or animals (living or dead) or their products.

(3) In this type of nutrition, the complex organic substances are broken down into simple soluble molecules which are absorbed and digested. Finally these digested molecules are metabolised by the heterotrophs to build new organic molecules or to obtain energy. Examples of heterotrophs are all animals, bacteria, fungi and non-green plants.

(4) Types of heterotrophic nutrition :

Heterotrophic mode of nutrition is divided into following four types :

Saprotrophic nutrition
Parasitic nutrition
Holotrophic nutrition
Mixotrophic nutrition

1. Saprotrophic nutrition :

(i) The term ‘Sapro’ means rotten. Thus, saprotrophic nutrition refers to such kind of nutrition in which the organisms derive their nutrients from dead and decaying (rotten) organic matter (such as rotten leaves, rotten bread, dead animals, household wastes, non-living organic matter present in the soil etc)

(ii) The organisms having saprotrophic mode of nutrition are called saprotroph.

(iii) Examples of saprophytes are many fungi (yeasts, mucor, mushroom etc) and bacteria. The saprophytic organisms usually secrete extracellular digestive enzymes onto the dead organic matter which hydrolyse them into simple soluble products. Then the soluble food, in the form of fluid, is absorbed through the body surface by the saprophytes. In fact, the term saprophytes refers to all those plants which get their nutrition from dead organic matter (e.g. fungi, bacteria etc.)

(iv) A few animals also absorb soluble nutrients from non-living organic matter. Such a nutrition in animals is called saprozoic nutrition.

(v) Both saprophytic and saprozoic nutritions together are called saprotrophic nutrition.

2. Parasitic nutrition (Para = other)

(i) A parasite is an organism or virus that lives in an intimate association with another living organism from which it derives an essential part of the materials for its existence.

(ii) Parasitic nutrition is a type of nutrition in which the organism (or parasites) derive their nutrients or food from other living organisms.

(iii) The organism that supports or provides substances to a parasite is called a host. In other words, the organism from which food is absorbed is called ‘host’.

(iv) In return, the host is not benefited by the parasite. A host may be either a plant or an animal. Examples of parasites are : Several fungi (Albugo, Phytophthora, Puccinia etc.), bacteria, some flowering plants like , Cuscuta (amarbel) and some animals like, ‘Plasmodium’ (which causes malaria in man), Ascaris (round worm), Enterobius (pin worm), Taenia (tape worm), Fasciola (liver fluke) etc.

3. Holotrophic nutrition

Majority of invertebrates and all vertebrates take plants, animals or their products through the mouth and break up the large organic molecules into smaller ones in their own body with the help of digestive enzymes. The simple molecules are then absorbed into the cells while undigested food is expelled out by the body. Since it is characteristic of animals, it is also called holozoic nutrition. Depending upon food habits, holozoic animals are classified into three categories.

(i) Herbivores

They eat only plant materials. e.g. Cow, horse, rabbit, deer etc.

(ii) Carnivores

They are flesh eating animals. e.g. Lion, tiger etc.

(iii) Omnivores

They eat on both plant and other animals. e.g. Crow, bear, man etc.

4. Mixotrophic Nutrition

Organism like Euglena carries on autotrophic as well as saprotrophic nutrition as the same time. This is called mixotrophic nutrition.

Symbiotic Nutrition :

When two organisms live in association and derive food from each other they are called symbionts and their nutrition is known as symbiotic nutrition. e.g. E.coli (a bacteria) live in the human intestine and synthesizes Vit. B₁₂, which is used by man and E.coli receives, in return food and shelter from human intestine.

Exercise 1

1. The word ‘sapro’ means :

(A) Cell sap

(B) Dead

(D) Rotten

Answer

(B)

2. Animals ingest solid food through their mouth. This type of nutrition is called:

(A) Saprotrophic

(B) Parasitic

(D) Autotrophic

Answer

(C)

3. Which type of nutrition is observed in Cuscuta :

(A) Saprophytic

(B) Parasitic

(D) Autotrophic

Answer

(B)

4. Autotrophic nutrition occurs in :

(A) Fungi

(B) Plants

(D) Both (B) and (C)

Answer

(D)

5. Which of the following statements about the autotrophs is incorrect :

(A) They synthesis carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll

(B) They store carbohydrates in the form of starch

(D) They constitute the first trophic level in food chains.

Answer

(C)

6. The autotrophic mode of nutrition requires :

(A) CO₂ and water

(B) Chlorophyll

(D) All of the above

Answer

(D)

Photosynthesis

(1) (Photo : light, Synthesis : to make) is an endergonic, anabolic process by which green plants (producers) make their own food (like glucose) from simple inorganic substances (like CO₂ and H₂O) by using sunlight in the presence of chlorophyll.

Green Plants Make their Own Food by Photosynthesis

(2) By the middle of 19^th century, the key features of plant photosynthesis were known, namely, that plants could use light energy to make carbohydrates from CO₂ and water. The empirical equation representing the total process of photosynthesis for oxygen evolving organisms was then understood as

CO₂ + H₂O $\xrightarrow{{{\text{Light}}}}$ [CH2O]_n + O₂

where [CH2O] represented a carbohydrate (e.g. glucose, a six-carbon sugar)

Site of Photosynthesis :

(1) The chemical reactions of photosynthesis takes place in chloroplast.

(2) Chloroplasts are plastids, which are plant cell organelles having 3μ to 6μ diameter. In a cross section of leaf, plastid can be seen just below the upper epidermis in a tissue, called the Palisade.

(3) Chloroplast is bounded by an envelope of double membrane outer and inner. Envelope surround the stroma or matrix which is gel-like. Within stroma, thylakoids (grana), ribosomes, DNA and RNA molecules are present.

(4) Thylakoids are membranous network stacked like a heap of coins, forming grana (singular : granum). In one granum number of the thylakoids may be one to 50 or more. Thylakoids of grana are connected with each other with the help of stroma lamella. CO₂ fixation occurs in stroma.

(5) Synthesis of carbohydrates also occur in stroma.

The raw materials for photosynthesis are carbon dioxide and water.

Diagrammatic representation of an electron micrograph of section of chloroplast

Essential Conditions for photosynthesis : Raw materials for photosynthesis

Sunlight :

Chlorophyll is mainly present in green plants which traps sunlight and converts into chemical energy during photosynthesis. Plant utilizes only visible light which consists of seven colors, out of them green color light has minimum absorption. But this gets reflected which makes plants look green in color.

Chlorophyll

It is a green pigment and mainly present in the green leaves of the plants. There are many different types of chlorophylls, namely a, b, c, d, e and bacteriochlorophyll. Out of these, chlorophyll ‘a‘ and chlorophyll ‘b‘ are the most abundant and most common forms of chlorophyll.

Conversion of light into electrical energy. Accessory pigment molecules absorb
light and funnel it to the reaction centre for conversion to electrical energy.

Carbon Dioxide

(1) Carbon dioxide is a gas which is present in the air (0.03%). Carbon dioxide comes into the air through various processes like the burning of fuels and respiration by plants and animals.

(2) The green plants take carbon dioxide gas from the air for carrying out photosynthesis.

Stomata are present on the surface of a leaf

(3) The carbon dioxide gas enters the leaves of the plant through the stomata (singular stoma) present on their under surface. The aquatic plants (or water plants) use the carbon dioxide gas dissolved in water for carrying out photosynthesis.

(4) During the daytime, when the intensity of sunlight is high, the rate of photosynthesis increases due to which the rate of consumption of carbon dioxide by the plants during daytime is large.

(5) But during the morning time and the evening time (when the intensity of sunlight is low), the rate of photosynthesis decreases due to which the rate of consumption of carbon dioxide by the plants during morning and evening is much less.

(6) We know that when the plants are using up carbon dioxide in photosynthesis, at the same time they are producing carbon dioxide during respiration.

(7) Photosynthesis and respiration are two exactly opposite processes. Photosynthesis makes food (like glucose) by using carbon dioxide and water and releasing oxygen; whereas respiration breaks food (like glucose) by using oxygen, and releasing carbon dioxide and water.

(8) In the morning and evening hours, the rates of photosynthesis and respiration become equal.

(9) The point at which photosynthesis and respiration in a plant are exactly balanced, and one process uses up the products of the other process is called compensation point. Compensation point can be reached in the morning or evening hours when the intensity of sunlight is low and photosynthesis takes place at a slow rate.

Water

It is required by plants for photosynthesis and is absorbed by the roots of plants from the soil through the process of osmosis. Water gets transported upward through the xylem to the leaves.

Factors Affecting the Rate of Photosynthesis

The factors which affect the rate of photosynthesis are light, CO₂, H₂O and temperature.

(a) Effect of light

In the dark photosynthesis does not take place, if light intensity is slowly increased, the rate of photosynthesis increases to optimum point after which it becomes constant. Very high light intensity slows down the photosynthesis. Chlorophyll absorbs blue and red light mostly. Usually plants show high rate of photosynthesis in red light than in blue light. the green light has minimum effect.

Part of Electromagnetic Spectrum Showing Visible Range.

(b) Effect of CO₂

The amount of CO₂ available to a plant if increased causes increase in rate of photosynthesis, but after a point it becomes constant. This point is called as saturation point.

(c) Effect of H₂O

If the amount of water available to plant decreases, the rate of photosynthesis decreases because deficiency of water causes closing of stomata which stops the gaseous exchange.

(d) Effect of temperature

As the temperature increase, the rate of photosynthesis increases upto a certain temperature. At high temperature, the rate of photosynthesis decreases because enzymatic functions get adversely affected at very high temperature.

Exercise 2

1. The site of photosynthesis in plants is :

(A) Mitochondria

(B) Chloroplasts

(D) Dictyosomes

Answer

(B)

2. Light waves where photosynthesis is maximum are :

(A) Orange

(B) Green

(D) Violet-Blue and Red

Answer

(D)

3. In photosynthesis :

(A) Carbon dioxide is oxidised

(B) Carbon dioxide is reduced

(D) Both (B) and (C)

Answer

(D)

4. Which of the following is most important for photosynthesis :

(A) Chlorophyll

(B) Carotenes

(D) Proteins

Answer

(A)

5. The maximum suitable temperature at which photosynthesis occurs

(A) 25°C

(B) 45°C

(D) 40°C

Answer

(C)

Mechanism of Photosynthesis

The process of photosynthesis occurs in two sets of chemical reactions light reaction and dark reaction.

Light reaction

(a) During light reaction the photosynthetic pigments absorb light energy in the form of photons.

(b) Chlorophyll molecule is excited and emits electrons.

(c) The emitted electrons travel through the electron transport chain present in the chloroplast. This process is mediated by a number of electron acceptors.

(d) ATP is synthesized from ADP and inorganic phosphate, which is used as a source of energy during dark reaction.

(e) In light reactions, photolysis (breakdown of water in the presence of light) of water also takes place:

H₂O →2H^– + O₂ + 2e^–

(f) The released hydrogen ions reduce the NADP molecule into NADPH, which is also used up during dark reaction.

Dark reaction

(a) The NADPH molecules, as well as the ATP produced during the light reaction, are utilized in the stroma of the chloroplast for synthesis of carbohydrate from carbon dioxide. This process is called dark reaction.

(b) In this process, carbon dioxide enters into a cycle of reactions, starting from ribulose bisphosphate.

Figure : A highly simplified outline of the mechanism of photosynthesis

Table 1 : Differences between Light and Dark Reaction

S.No.		Light Reaction	Dark Reaction
1	Light	It is required for the reaction	It is light independent.
2	Conversion	The reaction converts light energy into chemical energy.	The reaction uses chemical energy in building organic substances.
3	Chlorophyll	It is essential for the reaction	Chlorophyll is not required directly.
4	Occurrence	It occurs in thylakoids of chloroplasts	It occurs in stroma part of chlorplasts.
5	Products	Its products are ATP and NADPH2	Its main product is starch
6	Oxygen	Oxygen is liberated as a by-product	It does not produce oxygen.
7	Electron Transport	Light Reaction involves movement of electrons along a transport chain	There is no involvement of an electron transport chain.

Some Experiments Related to photosynthesis

Experiment-1 : To show that chlorophyll is essential for photosynthesis

♦ Take a potted plant with variegated leaves.

♦ Place the plant in a dark place for about three days to destarch its leaves.

♦ Now keep this plant in pright sunlight for 3-4 hours.

♦ Pluck one of the variegated leaves from the plant, boil it first in water for few minutes and then in alcohol using a water bath so as to remove chlorophyll from the leaf.

♦ Wash the decolourized leaf with water. Place the leaf in a petridish and pour iodine solution over the leaf.

♦ After few minutes rinse off the excess iodine and observe the leaf.

You will observe that only those parts of the leaf have turned blue-black which were green. The parts which were not green do not turn blue-black This shows that starch is formed only in those parts of the leaf which contains chlorophyll. It proves that chlorophyll is necessary for photosynthesis.

Figure : (a) Variegated leaf (b) Leaf after treatment with iodine solution

Experiment 2 : To show that sunlight is essential for photosynthesis

♦ Take a potted plant having green leaves and place it in a dark place for about three days to destarch its leaves.

♦ Cover a part of a leaf the Ganong’s light screen

♦ Keep the plant in sunlight for a day.

♦ Remove the Ganong’s light screen from the leaf.

♦ Detatch the leaf, boil it in alcohol to remove chlorophyll from it and test for the presence of starch in the leaf.

Figure : To show that sunlight is necessary for photosynthesis

You will observe that the uncovered part of the leaf has turned blue-black (figure). This shows that starch is formed only in those parts of leaf which was exposed to sunlight and starch is not formed in the part of the leaf which was covered with the Ganong’s light screen.

Experiment 3 : To show that carbon dioxide is essential for photosynthesis

♦ Take a potted plant with long leaves and place it in a dark place for about three days to destarch its leaves.

♦ Take a wide mouth bottle with some potassium hydroxide (KOH) solution (it absorbs carbon dioxide gas from the air present in the bottle) and insert the upper half of a leaf of the plant with the help of split cork in the bottle (as shown in figure ).

♦ Make the bottle airtight and place the apparatus in pright sunlight for few hours.

♦ Now detach the leaf and test for the presence of starch in it.

Figure : To show that CO₂ is essential for photosynthesis

Nutrition in Animals

Holozoic Nutrition

Based on their food habits, holozoic animals are broadly classified into three categories : herbivores, carnivores and omnivores.

(1) Those consuming only algae or plant materials are called herbivores (e.g. Cow, Horse and Rabbit).

(2) Flesh-eating animals (e.g. Lion, Tiger and wolf) are called carnivores,

(3) Animals that eat both plants and other animals (e.g. Cockroach, Rat, Bear, Crow, Man etc.) are considered as omnivores.

Some other terms related to nutrition.

Insectivores – Feed on insects e.g. toads, lizards, spiny anteater etc.

Piscivores – Feed on fishes e.g. birds like pelicans etc.

Larvaevores – Feed on larvae e.g. fish like Gambusia etc.

Frugivores – Feed on fruits e.g. monkeys, bats etc.

Folivores – Feed on leaves e.g. sheep, goat etc.

Grainivores – Feed on grains e.g. pigeion etc.

Sanguivores – Feed on blood e.g. leeches, female mosquitoes, bed bugs etc.

Detritivores – Feed on decaying organic matter e.g. earthworm etc.

Cannibals – Feed on their own fellows e.g. cockroach, snake, scorpion etc.

Scavanger – Feed on dead and rotten flesh e.g. vulture etc.

Process of nutrition

The process of nutrition involves following steps :

Ingestion. Intaking of food.
Digestion. Breaking of complex food components into simple soluble components. Digestion is of two types :

(i) Intracellular digestion : When digestion of the food material occurs within the cells, it is called intracellular digestion. This type of digestion occurs in protozoans (Amoeba) and sponges.

(ii) Extracellular digestion : When digestion of food material occurs outside of the cells in a cavity, it is called extracellular digestion. This type of digestion occurs in higher animals like fish, frog, snake, man etc.

III. Absorption. Passing of digested food through the wall of small intestine into the blood or lymph.

Assimilation. Use of simple food components for the synthesis of complex components in different body cells.
Egestion. Elimination of undigested food as faeces.

Nutrition in Amoeba

Figure : AmoebaNutrition in Amoeba

(a) Ingestion : Amoeba ingests food by pseudopodia when food particle comes near to amoeba, it gets engulfed with a little water to form a food vacuole. This vacuole is also termed as temporary stomach.

(b) Digestion : Many lysosomes which contain digestive enzymes fuse with this food vacuole. Food is digested in food vacuole by the action of these enzymes. Enzymes break down the food into small and simple molecules by chemical reactions.

(c) Absorption : The digested food present in vacuole is absorbed directly into cytoplasm by diffusion.

(d) Assimilation : The part of food absorbed in amoeba is used to produce energy through respiration. The remaining part leads to the growth of amoeba. After this growth amoeba can reproduce into two daughter cells.

(e) Egestion : Amoeba has no fixed site for removing undigested food. Vacuole with undigested food material moves near the cell membrane and ruptures at any place and undigested food is thrown out of the body.

Figure : Nutrition in Amoeba

Nutrition in complex multicellular animals

♦ In complex animals all the processes involved in nutrition are performed by a combination of digestive organs.

♦ This combination of digestive organs is called digestive system.

♦ In higher animals a tube running from mouth to anus of an animal in which digestion and absorption of food takes place is called alimentary canal or gut.

♦ Area at the back of the mouth immediately above wind pipe and food pipe is called pharynx.

Human Digestive System and Digestion

The various parts of human digestive system in sequence are buccal cavity, oesophagus (or food pipe) stomach, duodenum, jejunum, ileum (parts of small intestine), caecum, colon and rectum (parts of large intestine).

The glands which are associated with the human digestive system are salivary glands, gastric glands, intestinal glands, liver and pancreas.

The various steps of nutrition are as:

Ingestion

In human being mouth is a special organ for ingestion or intake of food. Food contains carbohydrates, fats, proteins, water, vitamins, mineral salts and roughage. Roughage provides bulk of the food and stimulates peristalsis to eliminate faces.

Digestion

The process of digestion in the different parts of human alimentary canal is as follows:

(a) In buccal or oral cavity : The oral cavity is a space where the food is chewed and mixed with saliva. The opening of this cavity is called mouth. Digestion of food begins in this cavity itself. The mouth cavity contains teeth, tongue and salivary glands. The tongue is a muscular sensory organ, with taste buds on it. It helps in tasting and in the movement of food in the oral cavity during chewing. The teeth have a very special role because they cut and break the food into smaller bits. The small sized bits have relatively larger surface area for the enzymes to act on for better digestion. An adults human normally has 32 teeth. These teeth are different in shape and perform different functions as follows:

	Type	Shape	Function	No. in each jaw
1	Incisors	Chisel–shaped	Biting	4
2	Canines	Dagger–shaped	Tearing	2
3	Premolars	Cusped broad edge	Grinding	4
4	Molars	Cusped broad edge	Grinding	6

Human beings have two sets of teeth

(I) Deciduous or milk teeth : These occur in infants. They start appearing at the age of 6–11 months and are completed by the age of two years. Milk teeth are 20 in number.

(II) Permanent teeth : From 6–12 years, milk teeth are lost and replaced by 32 permanent teeth.

The salivary glands produce saliva. The human saliva contains an enzyme called ptyalin which digests the starch into maltose sugar.

Figure : Digesive System in Human Beings

(b) In oesophagus : Mouth opens into pharynx which leads to a long tube called oesophagus (commonly called as food pipe). The wall of oesophagus is highly muscular which participate in contraction and expansion movements which are called as peristaltic movement. This movement pushes the food into stomach. No digestion of food takes place in oesophagus.

Figure : Peristalsis in oesophagus

Stomach

The stomach is an elastic bag like muscular structure located below the diaphragm. It serves as the store house of food where partial digestion also takes place. The stomach is broadly divisible anterior cardiac, middle body and posterior pyloric part. Cardiac sphincter lies in the opening between oesophagus and stomach which prevent back flow of food into the oesophagus. Another, pyloric sphincter guards the opening between the stomach and the duodenum which periodically permits partially digested food to leave the stomach and enters into the duodenum. Because the stomach i a muscular structure therefore food is churned and breaks down into smaller pieces and forms a semisolid paste called as chyme. The inner lining of a stomach also has gastric glands which has three types of secretions.

(i) Mucus which helps to protect the stomach wall from its own secretion of hydrochloric acid and from the action of digestive enzymes.

(ii) HCl which kills harmful bacteria, soften the hard parts of food and provide acidic medium in the stomach for digestion.

(iii) Enzymes like pepsinogen and prorennin. These are inactive forms of enzymes which are activated into pepsin and rennin by the action of HCl.

Proteins Proteoses and peptones [Peptides]

Calcium paracaseinate Peptones

About 2-3 litres of gastric juice is secreted per day.

Small Intestine

It is a tube about 6.25 meters long in human. It is coiled and folded in the abdomen. The length of the small intestine differs in various animals depending on the food they eat. Herbivores eating grass need a longer small intestine which gives enough time to the cellulose for the digestion. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine. It comprises of following three parts:

(i) Duodenum : It is 25 cm long and is the shortest and widest part of small intestine. It is some what ‘C’ shaped. It receives both bile duct from the liver and main pancreatic duct from the pancreas.

(ii) Jejunum : It follows the duodenum. It is about 2.5 meters long.

(iii) Ileum : It is the longest part of small intestine. It is about 3.5 meters long.

Figure : Structure of Villi

The small intestine serves both for digestion and absorption. It receives digestive juice like pancreatic juice, intestinal juice and bile. Bile is an alkaline yellowish green watery fluid produced in the largest gland of human body i.e. liver. Bile is stored in gall bladder. It consists of pigments, bile salts, cholesterol and ions like sodium and bicarbonate. Sodium bicarbonate neutralizes the acid content of food received from the stomach and makes it alkaline to enable the pancreatic and intestinal juices to act. Bile salts reduce the surface tension of fats and break them down into tiny droplets. This is called emulsification. They droplets provide larger surface area for the action of enzymes.

Pancreas

Pancreas is second largest gland of the body, yellowish in colour which lies in the fold of duodenum. It secretes pancreatic juice which is a colourless watery fluid, slightly alkaline, due to the presence of sodium bicarbonate. Pancreatic juice contains three proenzymes – trypsinogen, chymotrypsinogen, procarboxypeptidase and one enzyme – elastase. All these are concerned with protein digestion.

Proteins Large peptides

Fat Emulsified at

Emulsified at Fatty acid + glycerol

Pancreatic juice also contains starch digesting enzyme called pancreatic amylase which converts a starch into maltose.

Intestinal juice contains carbohydrate digesting enzymes like maltase, sucrase and lactase which act as follows:

Maltose glucose + glucose

Sucrose glucose + fructose

Lactose glucose + galactose

Absorption

Absorption : Absorption of digested food takes place mainly in ileum and jejunum parts of small intestine. The wall of these has finger like projections called villi. The villi enormously increase the inner surface area of intestine (nearly 8 times) which facilitate the absorption of digested food.

Assimilation

Assimilation : These absorbed end products of food are used by the body cells for obtaining energy as well as for growth and repair of the body.

Egestion

A part of food which we eat cannot be digested and absorbed further by our body enters in the large intestine which has three parts viz. caecum, colon and rectum. Large intestine secretes no enzymes but absorbs much water leaving behind a semi solid faces which passes into the rectum and expelled out at intervals. The expulsion of undigested remains of food from the alimentary canal through anus is called defecation or egestion, which is regulated by the anal sphincter.

Digestive Glands

Salivary gland

Three pairs of salivary glands open into buccal cavity, Salivary glands secrete saliva, which perform the following functions.

♦ It lubricates food and helps in swallowing.

♦ It contains enzyme salivary amylase which converts starch into maltose.

Liver

It is the largest gland of human body. It secretes bile juice which contains bile salts and bile pigments. Bile juice is stored in gall bladder and is carried to the duodenum by common bile duct. Bile juice.

♦ Helps in emulsification of fats.

♦ Provides alkaline medium.

♦ Activates pancreatic and intestinal enzymes

Pancreas

It is the second largest gland of human body. It secretes pancreatic juice. This juice contains trypsin for digesting proteins, pancreatic amylase for breakdown of starch and pancreatic lipase for digestion of fats.

Dental Caries

Dental caries or tooth decay causes gradual softening of enamel and dentine. It begins when bacteria acting on sugars produce acids that softens or demineralises the enamel. Masses of bacterial cells together with food particles stick to the teeth to form dental plaque. Saliva cannot reach the tooth surface to neutralise the acid as plaque covers the teeth. Brushing the teeth after eating removes the plaque before the bacteria produce acids. If untreated, microorganisms may invade the pulp, causing inflammation and infection.

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Photosynthesis

Essential Conditions for photosynthesis : Raw materials for photosynthesis

Factors Affecting the Rate of Photosynthesis

Mechanism of Photosynthesis

Nutrition in Animals

Nutrition in Amoeba

Nutrition in complex multicellular animals

Human Digestive System and Digestion

Stomach

Small Intestine

Pancreas

Absorption

Assimilation

Egestion

Digestive Glands

Liver

Dental Caries

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Nutrition

Photosynthesis

Essential Conditions for photosynthesis : Raw materials for photosynthesis

Factors Affecting the Rate of Photosynthesis

Mechanism of Photosynthesis

Nutrition in Animals

Nutrition in Amoeba

Nutrition in complex multicellular animals

Human Digestive System and Digestion

Stomach

Small Intestine

Pancreas

Absorption

Assimilation

Egestion

Digestive Glands

Liver

Dental Caries

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