Nutrition

"Nutrition is the process of procuring and utilization of food."

1.0Introduction

All living organisms require energy and other raw materials for performing all the vital activities and for body building, repair, growth, development and regulation. Both energy and raw materials are obtained from the food. The food taken in by an organism contains a large number of nutrients like carbohydrates, fats, proteins, minerals, vitamins and water. Carbohydrates and fats provide energy. Proteins are required for body building, growth and healing. Vitamins and minerals are the regulating nutrients.

Nutrition is the process of intake of nutrients (like carbohydrates, fats, proteins, minerals, vitamins and water) by an organism as well as the utilization of these nutrients by the organism.

2.0Modes of nutrition

Way of obtaining food by the organisms are called modes of nutrition.

3.0Autotrophic nutrition

It is the process by which organism take in simple inorganic substances from outside and use them to synthesize organic molecules and then convert into stored forms of energy. For example, green plants prepare their food by using carbon dioxide and water in the presence of chlorophyll and sunlight. The organisms having autotrophic mode of nutrition or can make their own food are called autotrophs or autotrophic organisms.

Examples: Green plants and some bacteria.

Photosynthesis

Photosynthesis is the process of preparing organic food (carbohydrate) by combining carbon dioxide and water, using solar energy by help of chlorophyll pigments. The sugar produced in photosynthesis is stored in the form of starch in plants and it is the source of reserved internal energy.

The overall equation of photosynthesis is -

$$\begin{gathered} 6{\mathrm{CO}}_2+12{\mathrm{H}}_2\mathrm{O}\underset{\text{ Chlorophyll }}{\mathrm{Sunlight}}\underset{\text{ (Glucose) }}{\text{ (from air) (from soil) }}{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{H}}_2\mathrm{O}+6{\mathrm{O}}_2 \\ \text{ (Glater } \end{gathered}$$

Requirements for photosynthesis - (1) Sunlight (2) Photosynthetic pigment (3) Carbon dioxide (4) Water

Sunlight

Sun is a natural source of light for photosynthesis.

Photosynthetic pigments:

These are chlorophylls which are responsible for absorbing light energy. Photosynthetic pigments are present in all the green parts of the plant.

Carbon Dioxide:

All the plants need carbon dioxide to form carbohydrates. The carbon dioxide is obtained by the plants from the atmospheric air. In the terrestrial plants, the ${\mathrm{CO}}_2$ enters into the cells of leaves through tiny pores called stomata which always remain present on the surface of leaves. In aquatic plants, ${\mathrm{CO}}_2$ is obtained from the water where it remains present in dissolved form. Such plants absorb ${\mathrm{CO}}_2$ in dissolved form through diffusion, all over their surface from the surrounding water.

Water:

Water is always needed by the plants for its use during photosynthesis. It is absorbed by the roots of the plant from the soil through the process of osmosis. Inside the chloroplasts of the leaves, the water molecules split into hydrogen and oxygen with the help of light energy of the sun.

Stomata

These are tiny pores or microscopic aperture guarded by two kidneys shaped or bean shaped guard cells. Stomata are present on the surface of the leaves.

• Functions of stomata (i) Massive amount of gaseous exchange takes place in the leaves through stomata. Exchange of gases also occurs across the surface of stem and roots. (ii) Transpiration takes place through the stomata. Large amount of water is lost in the form of water vapour through stomata is known as transpiration.
  

Guard cells

These are kidney shaped cells which cover a single stoma. They contain chloroplast also.

• Function of guard cells They regulate the opening and closing of the stoma and also perform photosynthesis. Opening and closing of stomata When the guard cells swell (turgid) due to the entry of water, the stomata get opened. But when the guard cells shrink (flaccid) due to the loss of water, the stomata get closed.

Generally, stomata open during daytime and close during night time but in desert plants stomata open in the night time to check excessive loss of water.

Some nutrients like nitrogen, phosphorus, iron, magnesium required by the plants are also transported to different parts of the plant along with the water. Nitrogen is an essential element used in the synthesis of proteins and other compounds (chlorophyll, DNA and RNA). Nitrogen is taken up in the form of inorganic nitrates or nitrites from the soil or it is taken up as organic compounds which have been prepared by bacteria from atmospheric nitrogen.

• The leaves of a plant prepare food $A$ by photosynthesis. Food $A$ then gets converted into food B which is stored in the leaves. What are A and B?
• Why do we boil the leaf in alcohol when we are testing it for starch?
• What element does a plant need to be able synthesize into proteins?
• What type of the plants do we use in the experiment to prove that chlorophyll is necessary for photosynthesis?

Site of Photosynthesis

Photosynthesis takes place in the green plastid (Chloroplast or Kitchen of the cell) present in tissues inside leaves and young stem.

When we observe the cross section of a leaf under microscope, we can see the mesophyll cells full of green dots. These green dots are chloroplasts containing chlorophyll pigments.

Mechanism of photosynthesis

During photosynthesis following events occur (i) Absorption of light energy by chlorophylls. (ii) Conversion of light energy into chemical energy and splitting of water molecule into hydrogen and ${\mathrm{O}}_2$. (iii) Hydrogen reduces ${\mathrm{CO}}_2$ and synthesis of glucose (reduction of ${\mathrm{CO}}_2$ into carbohydrates) occurs.

The events of photosynthesis can be categorized into two main events light reaction and dark reaction.

Importance of photosynthesis

(i) Photosynthesis is an anabolic process in nature for providing food supply to the living organisms. (ii) It purifies the atmospheric air, by consuming ${\mathrm{CO}}_2$ and evolving oxygen. (iii) It converts light energy into chemical energy.

4.0Heterotrophic nutrition

Mode of nutrition in which the organisms derive their nutrition by taking readymade food, from other dead or living plants and animals e.g., Animals, fungi and most of bacteria. The survival of heterotrophs depends directly or indirectly on autotrophs. Heterotrophic mode of nutrition is classified into three types on the basis of methods of obtaining food.

(i) Holozoic nutrition - Ingestive nutrition

Mode of nutrition in which, the animals take complex solid food or whole material and break down (digest) it inside the body. They may be herbivores (Cow), carnivores (Lion) and omnivores (Rat).

(ii) Saprotrophic nutrition

In this type of nutrition, the organisms obtain their food from decaying organic substances. They are also called saprotrophs. They breakdown the food material outside the body and then absorb it. e.g., Bacteria, Fungi (bread moulds, yeasts and mushrooms).

(iii) Parasitic nutrition

Mode of nutrition in which organisms (parasite) derive nutrition from other plants and animals (host) without killing them. e.g., Cuscuta (Amarbel), ticks, lice, leeches and tapeworms.

• Organism which lives in/on the body of host and derive their nutrition from them is called parasite and organisms which provide food and shelter to the parasite are called host.

5.0Nutrition in Amoeba

The digestive system is different in various organisms since the food and the way it is obtained differs in these organisms. The mode of nutrition in amoeba is holozoic and it is omnivorous.

(i) When Amoeba comes in contact with food particles, it forms pseudopodia which engulf the prey by forming a food cup. This process is ingestion or phagocytosis.

(ii) When the tips of encircling pseudopodia touch each other, the food is encaptured into a bag called food vacuole. The food vacuole serves as a temporary stomach secreting digestive juices.

(iii) The digested food gets absorbed and diffuses into the cytoplasm and then assimilated.

(iv) Assimilation is the utilization of digested food in various anabolic and catabolic reactions and conversion (resynthesis) of absorbed food into complex molecules for various purposes such as production of energy growth, repair and storage.

(v) The egestion of undigested food takes place at any point on the surface of the body.

6.0Digestive system of human

Human digestive system consists of the alimentary canal and digestive glands and it involves mastication, swallowing, digestion of food and elimination of undigested matter.

Alimentary canal

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

• Mouth It is a transverse slit bounded by two soft movable lips. The lips serve to close and open mouth, holding the food in between and also help in speaking.
• Buccal cavity/mouth cavity/oral cavity Mouth leads into a large space known as mouth cavity or oral or buccal cavity. It accommodates muscular tongue, teeth and salivary glands.

(i) Tongue The floor of the mouth cavity is occupied by large, muscular, mobile tongue. It is the organ of taste with taste buds on its upper surface.

• Functions of tongue
• It moves food in buccal cavity for mixing with saliva.
• It helps in swallowing food.
• It plays a role in speech.
• It helps to clean the teeth.

(ii) Teeth Four different types of teeth are present in our buccal cavity. Four types of teeth found in humans are Incisors (biting the food), Canines (tearing of food), Premolars and molars (crushing and grinding of food).

(iii) Salivary glands These secrete saliva which contains a digestive enzyme called ptyalin or salivary amylase that breaks down starch. Starch $\stackrel{\text{ Salivary Amylase }}{\to }$ Maltose + Dextrin

• Pharynx The buccal cavity opens into a short narrow chamber called pharynx. It is a common passage for both food and air.
• Oesophagus (food pipe) The oesophagus is a collapsible muscular tube leading the food by peristalsis from pharynx to stomach. There are no digestive glands, but mucus glands are present.

Stomach

It is a thick, muscular and J shaped sac present on the left side of upper part of abdomen just below the diaphragm. Gastric glands are present in the wall of stomach. These release gastric juice which contains mucus, hydrochloric acid and two inactive protein digesting enzyme called pepsinogen and prorennin. The muscular walls of the stomach help in mixing the food thoroughly with digestive juices.

HCl activates pepsinogen to pepsin and prorennin to rennin.

$$\begin{gathered} \text{ Pepsinogen }\stackrel{\mathrm{HCl}}{\to }\text{ Pepsin } \\ \text{ Prorennin }\stackrel{\mathrm{HCl}}{\to }\text{ Rennin } \end{gathered}$$

It produces an appropriate acidic medium ( $\mathrm{pH}=2$ ). It facilitates the action of enzyme pepsin and kills the bacteria present in food. Pepsin breaks down proteins into peptides.

Proteins $\stackrel{\text{ Pepsin }}{\to }$ Peptides Rennin is a milk protein digesting enzyme. Mucus lubricates the food and protects the inner lining of the stomach from the action of HCl . Sphincter muscles regulate the exit of food from stomach into intestine due to peristaltic waves of stomach.

Intestine

It is the largest part of alimentary canal which is fitted into a compact space because of extensive coiling. It is distinguished into small intestine and large intestine.

(i) Small intestine The small intestine is the site of the complete digestion of carbohydrates, proteins and fats. It receives the secretions of the liver and pancreas for digestion. Digestion of proteins in man starts from stomach. In buccal cavity there is no digestion of proteins because saliva does not contain proteolytic (protein digesting) enzyme. Liver is lobed and reddish brown coloured largest gland of body present in the right side of upper part of the abdomen. It synthesizes bile juice. Gall bladder is present below the right lobe of liver. It stores bile. Emulsification is the phenomenon of physically breaking of large sized fat globules into large number of fat droplets by the bile-salts of the bile juice. This increases the surface area for digestion of fats by the lipase enzyme. Pancreas is a yellow- coloured gland present just behind the stomach. It secretes pancreatic juice. Pancreatic duct carries pancreatic juice to small intestine.

Food is mixed with three digestive juices (bile juice, pancreatic juice and intestinal juice). Bile juice (from the liver) provides alkaline medium and emulsifies fats (conversion of Gall bladderlarger fat globules into smaller fat droplets) but it is a non-enzymatic digestive juice so has no chemical action on food. Pancreatic juice (from the pancreas) contains trypsin, pancreatic amylase and pancreatic lipase enzyme which digest the proteins, starch and emulsified fats into peptides, maltose, fatty acids and glycerol respectively.

$\begin{array}{c}\text{ Proteins }\stackrel{\text{ Trypsin }}{\to }\text{ Peptides }\\ \text{ Fats }\stackrel{\text{ Pancreatic lipase }}{\to }\text{ Glycerol + fatty acid }\\ \text{ Starch }\stackrel{\text{ Pancreatic amylase }}{\to }\text{ Maltose(sugar) + Dextrin }\end{array}$

The wall of the intestine secretes intestinal juice which contains enzymes for complete digestion of peptides into amino acids, maltose into glucose and fats into fatty acids and glycerol.

$\begin{array}{c}\text{ Proteins }\stackrel{\text{ Intestinalenzyme }}{\to }\text{ Amino acid }\\ \text{ Maltose }\stackrel{\text{ Intestinal enzyme }}{\to }\text{ Glucose }+\text{ Glucose }\\ \text{ Fats }\stackrel{\text{ Intestinal enzyme }}{\to }\text{ Fatty acid + Glycerol }\end{array}$

The inner lining of the small intestine has numerous fingers like projections called villi which increase the surface area for absorption of digested food. These are richly supplied with blood vessels which take the absorbed food to each and every cell of the body where it is assimilated for various purposes. The length of small intestine differs in various animals depending on the food they eat. Herbivores eating grass need a longer small intestine to allow the cellulose to be digested. Meat is easier to digest hence carnivores like tiger have a shorter small intestine.

(ii) Large intestine It is the site of absorption of water from indigestible food. It helps in formation and temporary storage of faeces.

Anus

The digestive wastes solidify into faeces and are removed/egested (defecation) from the body via anus. The exit of waste material is regulated by an anal sphincter.

7.0Biology Diagrams made Easy

8.0Chapter At a Glance

• What would happen if green plants disappear from earth? Green plants are the source of energy for all organisms. They trap the solar energy and convert it into chemical energy in the form of food (starch) and they give off oxygen. If all green plants disappear from the earth, then all the herbivores will die due to starvation so carnivores will also die. Without plants, animals would have no oxygen to breathe and would die.
• Why does less availability of water reduce the rate of photosynthesis? Under water deficient conditions the stomatal aperture closes to reduce the loss of water by transpiration. As a consequence, the entry of ${\mathrm{CO}}_2$ is also stopped into the leaves. That's why rate of photosynthesis will be reduced due to less availability of both water and carbon dioxide which are required for photosynthesis.
• What is dental caries and how are they caused? It is the tooth decay which starts with the destruction of the enamel layer of the tooth. Masses of bacterial cells together with food particles stick to the teeth to form dental plaque. These bacteria act on sugars and produce acids that softens or demineralizes the enamel. If the dental caries is not treated, it can spread to the dentine and pulp of the tooth, causing pain and inflammation of the tooth.
• It is said that 'small intestine is the site of the complete digestion', Why is it so? In the small intestine food is acted upon by the secretions of liver, pancreas and small intestine which helps in the complete digestion of various food components carbohydrates, proteins and fats.
• Why are villi richly supplied with blood vessels? Villi increases the surface area of absorption. The absorbed food from villi enters into the blood supply of villi and takes the absorbed food to each and every cell of the body, where it is utilized for obtaining energy, building up new tissues and the repair of old tissues.
  

9.0SOME BASIC TERMS

• Destarching of leaves: Removal of all stored starch from the leaves.
• Unicellular: Made up of single cell.
• Multicellular: Made up of many cells.
• Osmosis: Osmosis is the net diffusion of water across a selectively permeable membrane towards a higher solute concentration.
• Vital: Absolutely necessary.
• Organic substances: Substances which consist of carbon, hydrogen.
• Synthesized: Prepared.
• Omnivore: An omnivore is an organism that eats plants and animals.
• Variegated: Having different colour especially in irregular patches.
• Pale: Light in colour.
• Petridish: A covered dish that is not very deep, used for growing bacteria.
• Symbiotic: Involving two types of animals or plant in which each provides the conditions necessary for the other to continue to exist.
• Regulate: Control.
• Splitting: The action of dividing.
• Anabolic: Building up.
• Appendix: is a vestigial structure attached to the large intestine in the human body.
• Mastication: Chewing.
• Herbivore: Animals who eat only plants and plant products.
• Carnivore: Animals who eat other animals.
• Defecation: The removal of faeces from the body.