▶️ Answer/Explanation
Detailed Solution
(a)
- The SRY gene on the Y chromosome promotes development of testes from embryonic gonads.
- Testes secrete testosterone, which:
- Stimulates sperm production (spermatogenesis).
- Causes development of primary male sexual characteristics (male genitalia) in the fetus.
- Triggers development of male secondary sexual characteristics during puberty (e.g., facial hair, deeper voice).
(b)
- Shoots grow or bend toward the light (phototropism).
- Auxin is redistributed from the lighter side to the shadier side of the shoot tip.
- Auxin moves via auxin efflux pumps down the shoot.
- Higher auxin concentration on the shaded side promotes cell elongation by acidifying the cell wall and loosening it, enabling cells to stretch.
- This uneven growth causes the shoot to bend toward the light.
- Auxin binds to receptors in target cells, triggering expression of genes involved in growth or stimulating secretion of H⁺ ions into the cell wall.
(c)
apest g
| Feature | Hormonal Communication | Nervous Communication |
|---|---|---|
| Type of signal | Chemical messengers (hormones) in bloodstream | Electrical impulses + neurotransmitters |
| Speed of response | Slow | Fast |
| Duration of effect | Long-lasting | Short-lived |
| Mode of transport | Through blood | Along neurons and across synapses |
| Target cells | Cells with specific hormone receptors anywhere in the body | Specific cells at synapses (muscle, gland, neuron) |
| Control | Controlled by endocrine glands and regulated by feedback mechanisms | Controlled by CNS and PNS, rapid feedback |
| Example of function | Testosterone controls male sexual development | Reflex actions, muscle contraction |
| Distance of signaling | Can act over long distances | Usually acts over very short distances |
Markscheme
a. Genetic and Hormonal Control of Male Sexual Characteristics: [3]
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’ ✔
b. Auxin Control of Phototropism in Plant Shoots: [5]
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) auxin/auxin receptors promote expression of genes (for growth)/for H+ secretion into wall ✔
c. Comparison and Contrast of Hormonal and Nervous Communication: [7]
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 ✔