Question

Which of the following is not an extrinsic factor affecting plant growth ?
A. Light
B. Temperature
C. Water
D. Phytohormones

Answer 1

Hint: The green plants make or rather synthesise their own food they need through photosynthesis and therefore called autotrophs.

Complete Answer:
- Photosynthesis physicochemical process by which plants use light energy to drive the synthesis of organic compounds. ultimately all living forms on earth dependent on Sunlight for energy. Photosynthesis is important due to two reasons: it is a primary source of all food on earth and It is also responsible for the release of oxygen into the atmosphere by green plants. Factors affecting photosynthesis are both intrinsic and extrinsic.
- The rate of photosynthesis is very important in determining the yield of plants including crop plants. Photosynthesis is under the influence of several factors, which include both internal (plant) and external (environment).
- The internal factors or the factors of plants include the number, size, orientation of leaves, mesophyll cells and chloroplasts, internal $CO_2$ concentration and the amount of chlorophyll. Phyto hormones are also an internal factor.
- The external factors would include the availability of sunlight, optimum temperature, $CO_2$ concentration and water.
- As a plant photosynthesis all these factors will simultaneously affect its rate. Hence, though several factors interact and simultaneously affect photosynthesis or $CO_2$ fixation one factor is the major cause or it is the one that limits the rate. Hence at any point the rate will be determined by the factor available at sub optimum levels.

So the correct answer is (D).

Note: When several factors affect any biochemical processes, Blackman’s law of limiting factors comes into effect.