(a) (i) List five excretory organs found in living organisms. (ii) Give one example of an organism in which each type is found. (b) (i) state two ways in wh...
Question 1 Report
(a) (i) List five excretory organs found in living organisms.
(ii) Give one example of an organism in which each type is found.
(b) (i) state two ways in which the excretory organs of earthworm is similar to that of mammals.
(ii) Give three differences between them.
(c) Describe the mechanisms of opening and closing of the stomata.
Answer Details
(a)(i) Five excretory organs found in living organisms, with (ii) an example organism for each
| Excretory organ/structure | Organism |
|---|---|
| Kidney | Mammal (for example man) |
| Contractile vacuole | Amoeba (or Paramecium) |
| Flame cell (protonephridia) | Planarian / tapeworm (Platyhelminthes) |
| Nephridium | Earthworm |
| Malpighian tubule | Insect (for example cockroach) |
(The leaf/stoma of green plants and the general body surface are also acceptable examples.)
(b)(i) Two ways the excretory organ of the earthworm is similar to that of mammals
- Both use tubular structures (nephridia in earthworm, nephrons in the mammalian kidney) that filter body fluids/blood.
- Both remove nitrogenous waste and excess water and reabsorb useful substances, producing urine.
(b)(ii) Three differences between them
| Earthworm (nephridia) | Mammal (kidney) |
|---|---|
| Many pairs of nephridia, one pair per segment | A single pair of kidneys |
| Excretes mainly ammonia/urea | Excretes mainly urea |
| Each nephridium opens separately to the exterior by a nephridiopore | Kidneys drain through ureters to a common bladder and urethra |
(c) Mechanism of opening and closing of the stomata
- Opening (in light/day): In the presence of light the guard cells photosynthesise and actively pump in potassium ions; sugar/solute concentration in the guard cells rises, lowering their water potential. Water then moves into the guard cells by osmosis, making them turgid. Because the inner wall of each guard cell is thicker and less elastic than the outer wall, the turgid guard cells curve apart, opening the stoma.
- Closing (at night/water shortage): Potassium ions and sugars leave the guard cells, raising their water potential; water passes out of the guard cells by osmosis and they become flaccid. The guard cells straighten and come together, closing the stoma. This also happens when the plant is short of water, to reduce transpiration.
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