Page 05 7. In multicellular organisms, only target cells respond to a specific signal because A signalling molecules only come into contact with target cells B only target cells have receptor molecules for the signalling molecule C non-target cells do not respond when the signalling molecule binds to its receptor D receptor molecules in non-target cells do not change conformation when the signalling molecule binds. 8. The hormone thyroxine is A hydrophobic and unable to pass through the cell membrane B hydrophilic and unable to pass through the cell membrane C hydrophobic and able to pass through the cell membrane D hydrophilic and able to pass through the cell membrane. 9. Biological molecules move over short distances by diffusion. The time taken for diffusion can be calculated using the equation below. t = time taken (seconds) x = distance travelled by the diffusing molecule (cm) D = diffusion co-efficient (cm2 per second) = x 2 D t 2 Acetylcholine is a neurotransmitter with a diffusion co-efficient of 4 × 10–6 cm2 per second. The gap across the synapse is 5 × 10–6 cm wide. How many seconds would it take acetylcholine to cross the synapse? A 1·250 B 6·250 × 10–6 C 3·125 × 10–6 D 1·600 × 10–6 10. Type 1 diabetes is caused by A excessive production of insulin B loss of insulin receptor function C failure of GLUT4 to respond to insulin binding D insufficient production of insulin. [Turn over