Following statements are regarding to the mechanism of migration of pollen tube.

A. The embryo sac is the product of three mitotic divisions of the diploid megaspore; it comprises seven cells and eight haploid nuclei.

B. The two polar nuclei in the central cell will fuse with the second sperm nucleus and produce the endosperm that will nourish the egg. The other six cells, including the egg, contain one haploid nucleus each.

C. After compatible pollen germinates, the pollen tube grows toward the micropyle.

D. The three cells from the pollen are connected to one another at the tip of the tube, and waves of sodium ions play a key role in the growth of the tube.

Which of the following combinations are correct?

#Question id: 2422

#Unit 2. Cellular Organization

 What actin-binding protein mediates gel-sol transitions?

#Question id: 2423

#Unit 2. Cellular Organization

What is the function of thymosin beta-4?

#Question id: 2424

#Unit 2. Cellular Organization

Which of the following statements correctly describe(s) actin?

a. Actin is a highly conserved protein.

b. Multiple actin genes may be found in higher eukaryotes.

c. Actin is the most abundant protein in a eukaryotic cell.

d. Individual actin filaments can be observed by electron microscopy.

e. One end of an actin filament is different from the other. 

#Question id: 2425

#Unit 2. Cellular Organization

Which of the following is (are) actin-based structures?

a. adherins belt                        b. contractile ring        c. mitotic spindle

d. nuclear lamina         e. stress fibers

#Question id: 2426

#Unit 2. Cellular Organization

Actin assembly in vitro

a. consists of three phases.     

b. requires addition of actin oligomers termed nuclei.

c. requires ATP hydrolysis.

d. is reversible.

e. requires actin-binding proteins.

#Question id: 2427

#Unit 2. Cellular Organization

Known functions of actin-binding proteins include

a. severing of long filaments to generate shorter filaments.

b. inhibition of filament polymerization.                   

c. bundling of filaments.

d. acceleration of filament polymerization rates.

e. capping of the (+) end.