The ability of a population of fibroblasts to migrate along the surface of a tissue culture dish depends on adhesion between the cell surface and the extracellular matrix molecules coating the dish. The dish is coated with laminin, and the only cell-surface protein capable of binding laminin is a cell-adhesion protein called an integrin. Integrins are integral plasma-membrane proteins that function as heterodimers. Under these conditions the rate at which a fibroblast can migrate along the laminin coated culture dish is proportional to the strength of adhesion between the cell and the laminin substrate. The table below lists the rate of cell migration observed for fibroblasts genetically engineered to generate the indicated phenotypes.

 Which of the following is the most likely explanation for failure of overexpression of the integrin alpha subunit to alter the rate of fibroblast migration?

#Question id: 10464

#Unit 6. System Physiology – Plant

As with cryptochrome and phytochrome, the N-terminal photosensory region of the phototropins controls the activity of the C-terminal half of the protein, which contains a serine/threonine kinase domain. Following are some statements about photosensory region of the phototropins.

a) The activation of the C-terminal kinase domain then leads to receptor autophosphorylation on multiple serine residues that is required for all phototropin-mediated responses

b) In the dark, the N-terminal region, including the LOV domains, “cages” and inhibits the activity of the kinase domain

c) In the light, the N-terminal region, including the LOV domains, “cages” and inhibits the activity of the kinase domain

d) Absorption of blue photons by the LOV domains results in primary photochemical changes that lead to the uncaging of the kinase domain and its activation by the unfolding of the Jα-helix

Which one of the following combination of above statements is correct?

#Question id: 10465

#Unit 6. System Physiology – Plant

This feature is an adaptive, as the redistribution of chloroplasts within the cells modulates light absorption and prevents photodamage, diagram shows of chloroplast distribution patterns in Arabidopsis palisade cells in response to different light intensities;

m) A-low light, B-high light, C-darkness

n) A-high light, B-darkness, C-low light

Based on the above light intensities, each shows different chloroplasts position such as,

i) chloroplasts avoid sunlight by migrating to the side walls of palisade cells

ii) chloroplasts move to the bottom of the cell, although the physiological function of this position is unclear

iii) chloroplasts optimize light absorption by accumulating at the upper and lower sides of palisade cells

Which of the following correct combinations shows light intensities and chloroplast movements?

#Question id: 10466

#Unit 6. System Physiology – Plant

In Arabidopsis, phot1 mutants have a normal avoidance response and a poor accumulation response, phot2 mutants lack the avoidance response but retain a fairly normal accumulation response, while phot1/phot2 double mutant lack both the avoidance and accumulation responses. These results indicate that,

#Question id: 10467

#Unit 6. System Physiology – Plant

The COP1-SPA complex acts as a positive regulator as well as acts as negative regulator  by shown in statements;

a) Act as negative regulator−that targets transcription factors for degradation during phytochrome and cryptochrome responses

b) Acts as a positive regulator−that targets transcription factors for degradation during phytochrome and cryptochrome responses

c) Acts as a negative regulator− during UV-B signaling by interacting with the C-terminal region of UVR8 in the nucleus UVR8- COP1-SPA complex then activates the major transcription factor HY5, which controls the expression of many of the genes induced by UV-B

d) Acts as a positive regulator during UV-B signaling by interacting with the C-terminal region of UVR8 in the nucleus UVR8- COP1-SPA complex then activates the major transcription factor HY5, which controls the expression of many of the genes induced by UV-B

Whichof the following combination from avbove statements of UVR8 is true?

#Question id: 10468

#Unit 6. System Physiology – Plant

Why are stomata required in leaf surface?

#Question id: 10469

#Unit 6. System Physiology – Plant

When aquatic plants are kept in terrestrial habitat; what adaptations do these plants develop themselves?