Tag: growth and development

Answer is option A i.e. "a and b only"
Light between 400-700 nm wavelength constitute the photosynthetically active radiation (PAR). Maximum absorption of light by chlorophyll a occurs in red and blue regions of the absorption spectrum. So that, the rate of photosynthesis is maximum in red and blue light of the visible spectrum.

Plant growth regulators also called as phytohormones are the plant hormones that help in the various processes of plant-like flowering, ripening of fruit etc. They are secreted in the root, shoot and include all part of the plant body and any tissue is able to release and any tissue is able to accept them and work accordingly. These are auxin, gibberellin, cytokinesis etc.

Answer is option C i.e. "Critical concentration"
The concentration of the essential element below which plant growth is retarded is termed as critical concentration. Below this minimum level, plants start to show nutrient deficiency.
While, optimum concentration is the most desirable or satisfactory level of a nutrient. Maximum concentration is the highest concentration of nutrient and nutrient toxicity occurs when excess consumption of a nutrient does harm to an organism.

Growth in plants is affected by a number of environmental factors. The most important ones are light and temperature. This is because plants are autotrophic organisms and use light energy to produce their food. Since plants are living organisms, their metabolism requires ambient temperature and pH. This is because all the metabolic reactions are catalyzed by enzymes.

The living differentiated cells that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation. Example: formation of meristems - interfascicular cambium and cork cambium from fully differentiated parenchyma cells.

The first sign of geotropic response occurs at a short distance away from the apex except in monocots in which case it occurs at the nodes where meristems are formed. The bending of a plant organ in response to gravity is called as gravitropism or geotropism.  Geostimulation results in rapid and marked changes in the node-puvinus, internode and sheath. These changes involves water content, dry matter accumulation, endogenous gibberellic acids and GA4 metabolism.

Chlorophyll molecules are light trapping green pigments in plants. They are made up of a cyclic tetrapyrrole head and a long phytol tail attached to the head. One atom of magnesium is directly coordinated to the four pyrrole rings in the cyclic tetrapyrrole head. Thus, magnesium is an important structural component of chlorophyll molecules. The iron is an essential micronutrient for plants. It is required for synthesis of chlorophyll and has several other functions also. Plants also require an exposure to light in order to synthesize chlorophyll.  Apparently because in the absence of light chlorophylls are not required at all; trapping of light being there chief function. In absence of light plants will be thin and pale. Such plants are called etiolated plants.