CBSE Class 7 Science Advanced Biology Nutrition in Plants and Animals Notes Set 01

Nutrition in Plants and Animals

Introduction

Food gives living things the energy they need to grow, develop, fight harmful substances and stay healthy. The useful part of food is the nutrient, a substance that supports and maintains life and growth. Nutrition is the whole process by which an organism gets its nutrients: taking in food, digesting it, absorbing it, using it in body activities and finally getting rid of the waste. What an organism eats is its diet, and it mostly depends on what is available. A poor diet disturbs the working of the body.

Nutrients

Nutrients are grouped by the quantity needed. Macronutrients are needed in large amounts: carbohydrates, fats and proteins. Micronutrients are needed in small amounts: vitamins and minerals.

Carbohydrates are of two kinds. Simple carbohydrates are sugars (glucose, fructose, sucrose); they are sweet and give energy quickly. Complex carbohydrates (starch, cellulose) must first be broken down into simple sugars in the body before they give energy. Cellulose gives no energy to humans, but as fibre it helps to clear waste from the body.

Proteins are the most plentiful substance in the body after water. Haemoglobin of blood is a protein, and so is keratin, which forms hair and nails. Fats are the main energy store of the body.

A food that is eaten regularly and forms the main part of the diet of a group of people is called a staple food.

Vitamins

Vitamins are chemicals needed in very small quantities for the proper working of the body. Vitamin B and C dissolve in water (water-soluble), while A, D, E and K dissolve in fat (fat-soluble). Fat-soluble vitamins can become harmful if taken in more than the required amount. A lack of a vitamin causes a deficiency disease.

Vitamin D is called the sunshine vitamin because the skin makes it when exposed to sunlight. Vitamins B and C are easily spoiled by heat, so too much cooking can destroy them.

Balanced Diet

The body needs carbohydrates in the largest amount, then proteins and fats, and only tiny amounts of vitamins and minerals. Both too much and too little of any of them is harmful. A balanced diet contains all the essential nutrients in the right proportions and keeps the body and mind healthy. No single food has every nutrient, so foods are put into five groups: cereals; fruits and vegetables; milk and cheese; meat; and fats and oils. The balanced diet pyramid shows how much of each group to eat: the most from the grain group at the base and the least from the fats and sweets group at the top.

Modes of Nutrition

Depending on how they obtain food, organisms follow one of two modes: autotrophic nutrition or heterotrophic nutrition. Heterotrophic nutrition has three types: saprophytic, parasitic and holozoic.

Autotrophic Nutrition

1. An autotroph makes its own food.
2. The main method is photosynthesis: green plants use water, carbon dioxide and chlorophyll, in the presence of sunlight, to make carbohydrate food. Chlorophyll is the green pigment that traps light and also colours the leaves green.
3. Green plants, some bacteria and algae are autotrophs.
4. Autotrophs are the main producers of energy in the world; every other organism depends on them directly or indirectly.

Photosynthesis

The word means making (synthesis) with light (photo). It takes place in the leaves. Air enters the leaf through tiny pores called stomata, carrying carbon dioxide to the chlorophyll. The overall reaction is:

\[ 6CO_2 + 6H_2O \xrightarrow{\text{sunlight, chlorophyll}} C_6H_{12}O_6 + 6O_2 \]

Steps of the process:
1. Chlorophyll in the leaf absorbs sunlight.
2. Through a series of reactions, water molecules are split into H and OH.
3. Oxygen from the OH part is released into the air.
4. The hydrogen combines with carbon dioxide to form glucose.
So the two end products are glucose and oxygen.

Heterotrophic Nutrition

A heterotroph cannot make its own food and depends on other organisms. All animals and non-green plants are heterotrophs.

Bread mould growing on spoiled bread is an example of a saprophyte.

Nutrition in Plants

Plants can be grouped by the way they get food.
1. Photosynthetic plants: green plants with chlorophyll that make carbohydrates from carbon dioxide and water using sunlight.
2. Insectivorous plants: trap and consume small animals and insects to get nutrients, especially nitrogen. Examples: pitcher plant and Venus flytrap.
3. Parasitic plants: take part or all of their food from another living plant. Example: Cuscuta.

Nutrition in Animals

Animals show four main types of nutrition: holozoic, parasitic, saprophytic and symbiosis.

Holozoic Nutrition

Animals take in ready-made food in liquid or solid form. On the basis of food, they are divided into three groups.

Herbivores have teeth and a digestive system suited to plant material. Carnivores have sharp teeth and a digestive system suited to flesh; they are also called predators and the animals they eat are prey (tiger is the predator, deer is the prey). Omnivores have teeth and a digestive system suited to both.

Symbiosis

Symbionts are partners (animal and animal, animal and plant, or plant and plant) that live together and both gain. Example 1: protozoans live in the gut of termites, digest the wood for the termite and in return get a safe home. Example 2: aphids give a sugary liquid to ants, and the ants protect the aphids from parasites and predators.

Steps in Nutrition

There are five steps in human nutrition, in this order:
1. Ingestion: taking food into the body.
2. Digestion: breaking complex food into simpler substances.
3. Absorption: taking the digested food into the body (blood).
4. Assimilation: using the absorbed food and energy for the activities of the body.
5. Egestion: removing the undigested waste.

Human Digestive System

The digestive system breaks complex food into simple substances the body can absorb. Its parts are the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.

Mouth

Digestion begins in the mouth. The teeth chew the food and the tongue mixes it with saliva. Saliva is made by the salivary glands and contains water, salts, mucus and the enzyme amylase, which acts on carbohydrates (starch). The tongue also carries taste buds. Mumps is an infection of the salivary glands. Tooth enamel is the hardest substance in the human body.

Humans have four kinds of teeth.

Pharynx

The pharynx is a tube that joins the mouth to the oesophagus. It opens into the oesophagus through an opening called the gullet.

Oesophagus

The oesophagus is a long muscular tube that carries food to the stomach. Its muscles keep squeezing (contracting) and loosening (relaxing) in a wave. This movement is peristalsis, and it pushes the food smoothly down to the stomach.

Stomach

The stomach holds gastric juice and hydrochloric acid (HCl). Digestion of proteins starts here. A coat of mucus protects the stomach wall from the acid.

Small Intestine

The small intestine is the main place of absorption. It is a long tube lined with finger-like villi that absorb nutrients and energy into the blood. Digestion is completed in its first part, where intestinal juice and secretions of the liver, pancreas and gall bladder are poured in. The liver makes bile, which helps in fat digestion; the pancreatic juice helps in digesting carbohydrates, proteins and so on. Bile is made in the liver and stored in the gall bladder.

Large Intestine, Rectum and Anus

The large intestine is a long tube in which reabsorption takes place, that is, water is taken back into the body from the undigested waste. The waste then passes into the rectum, a small sac-like part where it is stored for a short time. The anus is the opening at the end of the digestive system through which the waste goes out.

What Happens at Each Stage of Human Nutrition

In the mouth: teeth cut the food into small pieces and the tongue mixes it with saliva to make a soft ball called a bolus, which is pushed into the pharynx and swallowed. Taking the food in is ingestion. Amylase of saliva starts changing starch into sugar, which is why a well-chewed piece of bread begins to taste sweet (starch changes to maltose).

In the oesophagus: no digestion; peristalsis moves the food.

In the stomach: gastric glands make gastric juice containing water, hydrochloric acid and the enzyme pepsin. The acid activates pepsin, which turns proteins into simpler substances called peptones. Food stays 3 to 4 hours and is churned into a pulp called chyme.

In the small intestine: the three parts are duodenum (the upper part), jejunum and ileum. The duodenum receives bile and pancreatic juice. Bile breaks fat into tiny droplets, a process called emulsification. Pancreatic juice has three enzymes: amylase (carbohydrates), trypsin (proteins) and lipase (fats). Digested food is absorbed through the wall of the small intestine; the ileum does both digestion and absorption.

In the large intestine: three regions (caecum, colon, rectum); no enzyme is made; it mainly absorbs water, and the faecal matter leaves through the anus.

Mechanical digestion means breaking up food by physical action such as chewing with the teeth. Chemical digestion means breaking down proteins, fats and carbohydrates with enzymes.

Points to Remember

1. Food keeps us alive and healthy and contains carbohydrates, fats, proteins, vitamins and minerals.
2. Carbohydrates give energy, fats store energy and proteins build the body.
3. Vitamins are needed in specific small amounts for the proper working of the body.
4. Green plants make food by photosynthesis, which takes place in the leaves.
5. Human nutrition has five steps: ingestion, digestion, absorption, assimilation and egestion.
6. Digestion starts in the mouth and continues up to the ileum of the small intestine.
7. Blood carries the digested food to the liver.
8. Undigested food leaves the body through the anus.