(a) Explain briefly sexual reproduction in Rhizopus. (b) A student suddenly stepped on a big snake, he cried for help and ran away. (i) Name the hormone pro...
Question 1 Report
(a) Explain briefly sexual reproduction in Rhizopus.
(b) A student suddenly stepped on a big snake, he cried for help and ran away.
(i) Name the hormone produced in the body for the reaction.
(ii) In which part of the human body is the hormone named in (b) (i) produced?
(iii) State five changes that must have taken place as a result of the hormone named in (a) (i).
(c) (i) In tabular form, state three differences between excretion in flowering plants and excretion in humans,
(ii) List two organelles found in plant cell that are responsible for the excretion of metabolic wastes.
Answer Details
(a) Sexual reproduction in Rhizopus: when two hyphae from opposite mating strains (+ and -) grow close together, each puts out a short side branch called a progametangium. The tips swell and are cut off by cross-walls to form two gametangia, each containing many nuclei (gametes). The walls between the touching gametangia dissolve and their contents fuse (plasmogamy then karyogamy). This produces a thick-walled, resistant zygospore. The zygospore undergoes a resting period, then germinates by meiosis to produce a sporangium that releases haploid spores which grow into new mycelia.
(b)(i) Hormone produced: adrenaline (epinephrine).
(ii) Site of production: the adrenal (suprarenal) glands, specifically the adrenal medulla, located above each kidney.
(iii) Five changes caused by adrenaline
- Increased heart rate and force of heartbeat.
- Increased rate and depth of breathing.
- Raised blood sugar level (conversion of glycogen to glucose in the liver).
- Widening (dilation) of the pupils of the eyes.
- Diversion of blood from the gut and skin to the muscles (and erection of body hair; increased sweating).
(c)(i) Three differences between excretion in flowering plants and in humans
| Excretion in flowering plants | Excretion in humans |
|---|---|
| No specialised excretory organs | Has specialised organs (kidneys, lungs, skin) |
| Wastes produced slowly and in small amounts | Wastes produced rapidly and in larger amounts |
| Some wastes are reused (e.g. oxygen, carbon dioxide) or stored in tissues | Wastes are mostly removed from the body, not reused |
| Nitrogenous waste is little; main products are oxygen, carbon dioxide and water | Produces much nitrogenous waste (urea) |
(ii) Two organelles in plant cells responsible for excreting metabolic wastes: the vacuole (stores waste in the cell sap) and the plastids/chloroplasts (release oxygen and other products). (Golgi bodies are also acceptable.)
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