(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.
Explanation
(a) Sexual reproduction in Rhizopus - By conjugation;
- It is usually between two strains of hyphae
- Known as + and - plus and minus/ opposite mating types
- The hyphae come in contact
- And produce small projections of their walls
- Which develop into progametangia with several nuclei
- The two progametangia enlarge
- Each progametangium develops a cross wall to divide into two parts; the gametangium and suspensor
- Subsequently the wall dissolves/breaks; and their contents/nuclei fuse to form a zygote
- The zygote develops a thick wall to form a resistant zygospore
- The zygospore germinates during favourable / damp / wet condition
- Into hyphae which bear sporangia.
(b) (i) Name of hormone Adrenalin /Adrenaline
(ii) Part where hormone is produced Adrenal gland/Medulla.
(iii) Changes that must have taken place as a result of the hormone
- Increase in heart beat
- Increase in rate of respiration
- Arterioles of skin and alimentary canal constrict
- Dilation of blood vessels that cause more blood to flow to the muscles/heart/lungs
- Increase in muscular tone/voluntary muscles become tensed
- Glycogen is converted to glucose/increase in blood sugar level
- To produce more energy
- Dilation of pupils of the eye
- Momentary freight/fear/anxiety/heavy breathing
- Spleen releases more Red Blood Cells from its reserve
- Increase in blood pressure
(c) (i) Differences between excretion in flowering plants and excretion in humans.
| Flowering plants | Humans |
| No definite excretory organs | Definite excretory organs /presence of kidney/liver/skin |
| waste products include tannins/resins/alkaloids/gums etc | waste products include urine/urea/sweat/salts etc |
| Excretory products produced in small quantity | Excretory products produced in large quantities |
| Excretory products released at a slower rate | Excretory products released at a faster rate |
| most excretory products tannins/resins/alkaloids/gums are stored | most excretory products are completely removed |
| some excretory products/carbondioxide/oxygen/water vapour can be reused | some excretory products/urea/uric acid cannot be reused |
| Excretory products are derived from simple organic molecules | excretory products are derived from complex organic molecules. |
(ii) Organelles in plant cells responsible for excretion of metabolic wastes.
Mitochondrion/ mitochondria; chloroplast/ chloroplasts.