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Biology Paper 2, Nov/Dec 2010  
Questions:   1 2 3 4 5 6 7 8   Main
General Comments

Question 7

(a) Defme the term osmosis. [3 marks]
(b)            State two ways each in which osmosis is of importance to:

               (i)         plants;
              (ii)         animals. [4marks]

(c) A normal terrestrial plant was watered daily with a hypertonic solution for about seven (7) days.                                   
         It was discovered that the plant was not doing well. Explain why.                                     [5 marks]

(d) (i)Explain briefly how marine organisms overcome the problem of high salinity in their environment?
     (ii) List four examples of organisms found in the benthic zone of a marine habitat. [ 4 marks]



This was the more popular question in this section and the performance of candidates was fair. Most candidates could properly defme the term osmosis and state ways in which osmosis is of importance to plants but could not properly state the importance of osmosis to animals.

Expected answers were:
- Re-absorption of water from glomerular filtrate;
- Absorption of water by the colon;
- Movement of water from one living cell to another.

Most of the candidates who attempted this question could state why a plant watered with hypertonic solution was not growing properly, but could not state how marine organisms overcome the problem of high salinity in their environment and seemed unfamiliar with organisms in the benthic zone of a marine habitat; some candidates rather gave examples of organisms found in fresh water habitats e.g. Tilapia, toad, etc.

Expected answers include:

How Marine organisms overcome high salinity
- they drink excess sea water to overcome high salinity restore/replenish water loss by osmosis;
- excrete excess salts out of their body through their gills;
- pass out large amounts of hypotonic urine;
- cartilaginous fishes maintain equal/similar osmotic pressure with sea pressure;
- they possess scales on the skin to prevent permeability of water by osmosis.

Organism found in Benthic zone of marine habitat
- Squids;
- Octopus;
- Latchet fish;
- Angler fish;
- Shark;
- Corals;
- Sea urchin;
- Whales;
- Mackerel;
- Dolphin;
- Crab.                            


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