Life Processes such as Nutrition, Respiration, Circulation and Excretion are necessary for the survival of living beings. Energy is needed for running life processes.

Food is an essential requirement for obtaining energy needed for performing vital activities. Food also helps in growth, maintenance, repair and protection from various diseases.

Types of Food

Type of food 

Food items

1. Energy yielding foods

Nutrients: carbohydrates, oils and fats

Food items: sugar, starch, rice, potato, sweets, oils, butter, ghee, gur, nuts

2. Growth and tissue forming food

Nutrients: proteins

Food items: milk, egg, beans, pulses, meat, fish, chicken, mutton

3. Protective and regulatory food

Nutrients: vitamins and minerals

Food items: fruits, green vegetables, lemon, orange, apple, tomato, carrot

Plant Nutrition

Plants prepare their own food in the presence of sunlight hence they are autotrophs. Solar energy is trapped by green plants to produce organic food such as sugar (glucose) with the help of atmospheric carbon dioxide (CO2) and water (H2O) from soil. This process is called Photosynthesis in which water is absorbed by roots and CO2 diffuses into leaves through stomata.

$$  \ce{6CO2 + 6H2O ->[chlorophyll][Sunlight] C6H12O6 + O2 ^ + energy} $$

Leaves of plants are the organs which undertake photosynthesis as they have chloroplasts.

Animal Nutrition

Most animals feed on green plants and other small animals to get energy because animals are incapable of preparing their own food. Animals are thus called Heterotrophs and such mode of nutrition is heterotrophic nutrition.

Ingestion (Intake of food): Mouth, tongue, teeth

Digestion (Breakdown of food): Mouth, stomach, duodenum, small intestine

Absorption: Small intestine - blood absorbs products of digestion and carries them to different parts of the body

Assimilation: Tissues of different organs use them to build parts and get energy

Egestion: Rectum stores, anus and removes undigested food