Page 5 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key
P. 5
1. Food and Its Sources
Chapter in a Nutshell
v All living organisms require food to live.
v Various components in food such as carbohydrate, fats, proteins, vitamins and minerals are
known as nutrients.
v Besides nutrients, water and roughage are also present in the food.
v The process of taking in food and its utilisation by the body using simple organic substances
is called nutrition.
v There are two modes of nutrition—autotrophic nutrition and heterotrophic nutrition.
v The mode of nutrition in which organisms make their own food is known as autotrophic
nutrition.
v Organisms using autotrophic mode of nutrition are known as autotrophs. For example:
green plants and algae.
v The mode of nutrition in which organisms are dependent on plants or other organisms for
food is known as heterotrophic nutrition.
v Organisms using heterotrophic mode of nutrition are known as heterotrophs. For example,
humans.
v Plants prepare their food in the leaves, so leaves are also known as the kitchen or food
factories of plants.
v Leaves contain a green pigment called chlorophyll that gives green colour to them.
v The function of chlorophyll is to absorb light energy from the Sun and help the leaves to
prepare food.
v The process of preparing food by the leaves of the plant by using carbon dioxide, from the
air and water, in the presence of sunlight and chlorophyll is known as photosynthesis.
v Leaves take in carbon dioxide through tiny pores on their surfaces called stomata. Stomata
give out oxygen, which is produced after photosynthesis.
v Excess water is released by the leaves through stomata by a process called transpiration.
v Excess glucose produced after photosynthesis is stored in the leaves in the form of a complex
carbohydrate called starch.
v Essential requirements for photosynthesis are—sunlight, carbon dioxide, chlorophyll and
water.
v The opening and closing of stomata is controlled by the turgidity of guard cells that surround
the stomata.
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