Describe the genetic and hormonal control of male sexual characteristics in a human.

Outline how the hormone auxin controls phototropism in plant shoots.

Compare and contrast hormonal and nervous communication.

a. male if (X and) Y chromosomes present ✔

b. gene on Y chromosome/SRY promotes development of testes (from embryonic gonads) ✔

c. testes secrete testosterone ✔

d. testosterone stimulates sperm production/spermatogenesis ✔

e. testosterone stimulates development (in fetus) of male genitals/primary sexual characteristics ✔

f. testosterone stimulates development of male secondary sexual characteristics
OR
testosterone causes changes to become adult male during puberty ✔

Allow first alternative for mpf if two secondary sexual characteristics are named instead of the general term ‘secondary sexual characteristics’.

a. grows/bends towards (brightest) light/sun ✔

b. auxin moved from lighter to shadier side (of shoot/stem tip/apex) ✔

c. moved by auxin efflux pumps ✔

d. auxin promotes cell elongation/cell growth / auxin causes cell wall acidification/loosening ✔

e. more growth on shady side of stem (due to auxin concentration gradient) ✔

f. binds to auxin receptors (in target cells) ✔

g. auxin/auxin receptors promote expression of genes (for growth)/for H⁺ secretion into wall ✔

Similarities

a. both used for communication between cells/tissues/organs/parts of the body / WTTE ✔

b. both cause a response/change in specific/target cells
OR
both use chemicals that bind to receptors / hormones and neurotransmitters are both chemicals ✔

c. both can stimulate or inhibit (processes in target cells) / WTTE ✔

d. both can work over long distances/between widely separated parts of the body / WTTE ✔

e. both under (overall) control of the brain/CNS / brain (has role in) sending hormones and nerve impulses ✔

f. both use feedback mechanisms/negative feedback / both used in homeostasis ✔

Differences

m. example of use of hormonal and use of nervous communication ✔

There were some excellent answers that easily scored the three marks, but also many poorer ones, sometimes with no mention of genetic control or testosterone.

Candidates tended either to know the mechanism of phototropism very well, or not at all. It wasn't always clear that the terms shoot, stem and leaf were correctly distinguished in some candidates' minds.  

Weaker candidates found this a real challenge as it was necessary to understand the nature of the nervous and endocrine systems well enough to be able to point out similarities and differences. Often there was no obvious comparing or contrasting in the answers.