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
- Energy yielding foods: carbohydrates, oils and fats; For example, sugar, starch, rice, potato, sweets, oils, butter, ghee, gur, nuts
- Growth and tissue forming food: proteins; For example, milk, egg, beans, pulses, meat, fish, chicken, mutton
- Protective and regulatory food: vitamins and minerals; For example, fruits, green vegetables, lemon, orange, apple, tomato, carrot
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 carbondioxide (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.
Leaves of plants are the organs which undertake photosynthesis as they have chloroplasts.
Most animals feed on green plants and other small animals to get energy because animals are incapable of preparing their own food. Animals are 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