Question

Respond To All Questions From Part A To C
Respond To All Questions From Part A To C A. What are the roles of active transport and osmosis in the opening and closing of stomata? B. What factors control the opening and closing of stomata? C. Why are annual rings of a mature woody dicot stem composed of light and dark sub-rings?

Answer 1

Answer (a)

Guard cells control the opening and closing of stomata. In the presence of light, guard cells take up the water through osmosis and become turgid. As inner walls are rigid, due to the water uptake, walls are pulled apart this leads to the opening of the stomata. In the absence of light or darkness, water is lost and inner walls come closer this causes the closing of stomata.

Stomatal opening also correlates with the transport of H⁺ ions out of the guard cells.

Answer (b)

Factors that controls the opening and closing of stomata are:

a) Light : It plays an important and predominant role in opening of stomata. Blue and red light are essential for the stomata opening.

b) Water content : Water content of epidermal cells plays a role in stomatal opening, as opening of stomata is a turgor phenomena.

c) Temperature: Rise in temperature results in stomatal opening.

d) Mineral elements : Deficiency of certain minerals like nitrogen, phosphorus and potassium affects the opening and closing of stomata.

Answer (c)

One layer of spring and summer woods, when taken together are considered as single annual ring. Annual rings reveal the alterations or events like drought, excessive rain, fire, insect and plagues that occurs in the environment.

In summer, new woods formed are darker in colour because xylem vessels are smaller. Whereas, spring season woods are lighter in colour because xylem vessels are larger so that it can conduct large amount of water which is necessary for the growth in spring season.