Mechanical barriers provide a first line of defence against insect pests and pathogens, these mechanical barriers developed by plants;

COLUMN A	COLUMN B
A. Thorns	i) It can be found on the stem and petioles of roses and are formed by the epidermis
B. Spines	ii) Found on a lemon tree (Citrus sp.) are modified branches, as can be seen by their position in the axil of a leaf
C. Prickles	iii) Found on shoot and leaves of tomato (Solanum lycopersicum) are derived from epidermal cells
D. Trichomes	iv) which are characteristic of cacti (Opuntia spp.) in the New World, are modified leaves

Match correctly following combination of barrier developed by plants ;

#Question id: 2437

#Unit 2. Cellular Organization

Membrane extension involves

a. bending actin filaments.                   

b. myosin II.

c. the Arp2/3 nucleation of new filaments.

d. actin depolymerization.     

e. actin polymerization.

#Question id: 2438

#Unit 2. Cellular Organization

Rac, a GTPase superfamily protein,

a. is related to Ras.                             

b. may be activated by growth factors.

c. stimulates lamellipodia formation. 

d. stimulates filopodia formation.

e. stimulates stress fiber assembly.

#Question id: 2439

#Unit 2. Cellular Organization

α- and β-tubulin

a. are highly conserved.                                 

b. bind GTP.

c. hydrolyze GTP to GDP.                 

d. are found in all eukaryotes.

e. are related to the bacterial protein FtsZ.

#Question id: 2440

#Unit 2. Cellular Organization

Microtubule assembly in vitro requires

a. ATP.                                                           

b. a threshold (critical) concentration of tubulin.

c. warming the solution to 37°C.                   

d. microtubule-associated proteins.         

e. GTP.

#Question id: 2441

#Unit 2. Cellular Organization

Which of the following statement(s) is (are) true of microtubule assembly?

a. GDP-tubulin normally assembles into microtubules.

b. Microtubule (-) ends grow faster than microtubule (+) ends.

c. Tubulin subunits assemble to form a protofilament.

d. Microtubules consist of multiple protofilaments.

e. Microtubules with a GTP cap will shorten.

#Question id: 2442

#Unit 2. Cellular Organization

The drug colchicine acts to

a. promote microtubule assembly.     

b. inhibit microtubule assembly.

c. sever microtubules.                        

d. block cell division.

e. cap microtubule ends.