Question

which of the following is a net sugar source for a deciduous angiosperm tree?

A. new leaves in early spring

B. fruits in summer

C. roots in early spring

D. roots in early autumn

Which type of mutant would be most likely to produce a bushier phenotype?

A. strigolactone underproducer
B. auxin overproducer
C. cytokinin underproducer
D. strigolactone overproducer
E. gibberellin overproducer

Which of the following observations provides the strongest evidence against root pressure being the principal mechanism of water transport in the xylem?

A) Not all soils have high concentrations of ions.
B) Root pressure requires movement of water into the xylem from surrounding cells in the roots.
C) Over long distances, the force of root pressure is not enough to overcome the force of gravity.
D) There is no water potential gradient between roots and shoots.

During the night time, due to lack of transpiration, the water potential within the vascular cylinder ____________.

A. lowers due to accumulation of minerals

B. increases due to accumulation of minerals

C. lowers due to loss of minerals

D. increases due to loss of minerals

Mammalian eyes sense light because the photoreceptor cells have molecules called opsins, which change structure when exposed to light. Which of the following plant molecules would be analogous to mammalian opsins in their light-sensing ability?

A. auxin and phytochrome

B. auxin and Pfr

C. Pfr and phytochrome

D. cytokinins and phototropins

I need to know the reasons for the answers to these questions. Thank you in advance!

Answer 1

1.) As we know deciduous angiosperm trees are those trees which shed off their leaves in autumn and regrow in spring season. In the summer, they show high photosynthetic activity with large production of glucose. On the onset of autumn, the light intensity starts decreasing causing reduction in photosynthetic activity and glucose produced in leaves starts moving toward roots. Later in the mid and late autumn, the roots become net source of the starch in deciduous trees. These storage organs provide food to plant in adverse conditions such as cold, drought.

So, option(A) is incorrect, because in the early spring leaves just started to grow, they are still not mature to gain complete photosynthetic activity so as to act as net sugar source.

option(B) is incorrect, because the sugar source would be a storge organ which help plant to overcome adverse conditions. Fruits grow in summer and fall off in summer end, so they cannot act as net sugar source because storage organs should help plant survive in adverse conditions such as winter in this case (with zero photosynthetic activity) and fruit cannot help this way because they falls prior to onset of adverse conditions.

Option (C) is CORRECT, as the food stored in roots during autumn act as net sugar source until the favourable conditions return back. So, in the early springs, leaves regrow at the expense of energy derived from sugar stored in roots.

Option(D) is incorrect, because in the early autumn, the sugar had not translocated into roots. It is the early autumn with less sunlight and low photosynthentic activity in leaves giving signals to roots to store food. The roots act as source of sugar in late autumn when all the sugar from leaves translocate to them.

2.) The auxin and gibberellin, both plant hormone helps in cell elongation, thus help the plant to grow taller. So, mutant with the overproduction of both these hormones would produce a taller plant not a bushier type. So, option (A) and (E) is incorrect.

The cytokinin is responsible for cell division and cell differentiation and help in lateral growth of shoot, overcome apical dominance, leaves and fruit formation. As it do not have significant role in determining the height of plant, so its underproduction will affect lateral shoot growth and it will also not able to overcome apical dominance, thus plant will be taller. Option(b) is incorrect.

The strigolactone is responsible to determine the height of the plant. The mutants with strigolactone overproduction will achieve more height and will be taller. So, option(d) is incorrect. But on the other hand mutant with underproduction of strigolactone become dwarf and have bushier phenotypr. Option(C) is CORRECT.

3.) According to root pressure theory, accumulation of more ions in the xylem causes its water potential to fall down. The soil have greater water potential and lower solutes than root xylem due to which water from soil start entering into xylem which creates a root pressure. This pressure pushes the water upward toward the stem agaimst the gravity. But this pressure cannot push water to greater heights because the force of gravity overpower the root pressure thus restricting the flow. It is the strongest evidence against root pressure theory. So, option (C) is correct.

The soil have high concentration of water and it is the xylem vessels that maintain high concentration of ions to move water into roots. So, option(A) is incorrect.

The root pressure require movement of water in the xylem from the surrounding soil of root not from surrounding cells of root. So, option (B) is incorrect.

There is always a water potential gradient between roots and shoots because the water continuously lose from leaves by transpiration thus lowering their water potential and roots always absorbing water from roots thus have higher water potential. So, option (D) is also incorrect.

4.) The transpiration is low at night but xylem vessels of roots continuously pump mineral ions to them, this causes an increase in the accumulation of minerals and as we know the water potential lowers on addition of minerals.

So, option (A) is correct, that accumulation of minerals lowers the water potential at night.

Option (B) is incorrect because increase in the number of minerals do not increase water potential.

Same way, option(C) and (D) is incorrect because in the night there is no loss of minerals or ions.

Note: Due to time constraints, all the parts couldn't be completed, so, try posting the left questions again.