Page 6 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

v The stomata are open when the guard cells are turgid whereas on losing the turgidity, they

are closed.
v Water is absorbed from the soil by the roots of plants and carried to the leaves with the help

of a vascular tissue called xylem.
v Leaves of plants, such as cactus, that grow in hot and dry environment with scarcity of

water, are modified as spines to prevent loss of water though respiration.
v Chlorophyll is also present in those plants whose leaves are not green in colour (e.g., Coleus).

v The other colour pigments are in greater amount hence mask the green colour of chlorophyll.
v Apart from carbohydrates plants also synthesize proteins, fats and vitamins.

v For the synthesis of proteins, plants need nitrogen which is provided by a bacterium
rhizobium. This bacterium converts atmospheric nitrogen into nitrates which is easily

utilised by the plants.
v The factors that affect the rate of photosynthesis are – intensity of sunlight, concentration

of carbon dioxide, temperature and water.
v Photosynthesis is very important as it provides oxygen to all the living things directly or

indirectly and hence maintains the balance of oxygen and carbon dioxide in the environment.
v Some plants which are deficit of chlorophyll derive their nutrients from other plants. Such

plants are called parasitic plants. For example, cuscuta, mistletoe, etc.
v The plants that derive their nutrients by trapping and digesting insects and small animals

are called insectivorous plants. For example, pitcher plant, Venus flytrap, etc.
v In saprotrophic mode of nutrition, organisms obtain their food from dead and decaying

organic matter. Organisms obtaining nutrition from saprotrophic mode of nutrition are
called saprotrophs. For example, fungi and certain bacteria.

v A relationship between organisms of two different types in which they share shelter and
nutrition is known as symbiotic relationship.

v This relationship is mutual and none of the partner is harmed. For example, symbiotic
relationship between fungi and algae.

v After growing crops in a field, the soil becomes deficit of some nutrients. To maintain the
fertility of the soil, fertilisers and manures are spread in the field.

v Two types of fertilisers are NPK and urea.
v NPK is an inorganic fertiliser that provide nitrogen, phosphorus and potassium to the soil.

v Urea is an organic fertiliser that provides only nitrogen to the soil.
v Replenishment of nitrogen can be accomplished by growing leguminous crops.

v Rhizobium bacteria is present in the root nodules of leguminous plants. It helps converting
atmospheric nitrogen into nitrogenous compounds (nitrates) that can be used by leguminous

plants for their own growth. This is known as nitrogen fixation.

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