Tag: growth and development

Differentiation is the developmental process by which cells undergo structural changes to acquire specialized functions. Growth, cell division, and cell elongation are related processes but do not specifically define the acquisition of specialized form and function.

Seed germination requires sufficient amount of P$ _pr$fr. P$ _r$ is synthesized by germinating seeds and is converted to P$ _pr$ when exposed to red light. However, when  seeds are exposed to far-red light, they will not germinate as P$ _r$ is converted to P$ _r$.

Rate of plant growth and development depend upon various factors including temperature surrounding the plant. Each plant has a specific temperature range for optimum growth. The temperature affects plant growth processes such as photosynthesis, respiration, transpiration, protein synthesis, etc. In general, temperature range for plant growth is 0$^o$C to 35$^o$C. However, optimal day and night temperature range varies for plant growth.

In chloroplasts, the main pigment present is chlorophyll which is green in color. Growth of plant is affected by the different wavelengths of light as pigments in chloroplasts absorb different wavelengths of light for photosynthesis. White light is a mixture of many wavelengths of colors. Chlorophyll will absorb energies from all visible light except green. Hence exposing white light to a green plants will result in the fastest rate of photosynthesis which in turn result in fastest growth. Hence, optimum growth occurs in white light followed by blue or red.

A carbon-to-nitrogen ratio is a ratio of carbon to the nitrogen in a plant. In general, a high C/N ratio produces a high acid content and low methane production. In plants young tissues have less C/N ratio. Plants with high C/N ratio have more mechanical tissues and larger root system.

Photosynthesis requires light between 400 and 700 nm. Blue light promotes vegetative growth. Red and far-red promotes stem elongation. Red and blue light promotes flowering. Photoperiodism is best seen in red light as chlorophyll strongly absorbs red light and carries out photosynthesis. Hence, red light stimulates plant growth.

Short day plants require the long duration of the dark period. If the dark period is interrupted with a brief exposure to red light (660 nm), the flowering will not take place. The inhibitory effect of red light on flowering during the critical dark period in short day plants can be overcome by a subsequent exposure to far-red rays. This is due to the fact that when exposed to far-red light, P$ _fr$ is converted to P$ _r$.

Differentiation is the process by which cells move from a less specialized (such as stem cells) form to a more specialized form having a specific function. Dedifferentiation is the process whereby completely differentiated cells regress to a simpler state (such as stem cells) and gain the capacity to divide again. The process by which a group of once specialized cells (de-differentiated) return to their original specialized state is known as redifferentiation. Regeneration is the process of renewal or restoration of growth to recreate damaged tissues, limbs etc. So, the correct answer is 'dedifferentiation'.

Pollenkitt is a sticky, oily coating found on the surface of insect-pollinated pollen grains. Besides lipids, it consists mainly of carotenoids, which give it its characteristic yellow or orange color and help protect against UV radiation.