Question 2
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(a)State three features of the small intestine that increase the rate of absorption of digested food. [3 marks]
(b)Explain briefly what happens to the glucose formed in a plant during photosynthesis. [3 marks]
(c) Explain briefly the mode of feeding in each of the following organisms: (i) Euglena; [4 marks] (ii) Spirogyra. [4 marks]
(d)State three characteristics of an Estuarine habitat. [3 marks]
(e)State three differences between an aquatic habitat and a terrestrial habitat. [3 marks]
Observation
Just a few candidates could state the features of the small intestine that increases the rate of absorption of digested food.
Many candidates could not answer (b).
Candidates could not give proper answers to the mode of feeding in Euglena and Spirogyra
Only a few candidates knew how to answer the question on Estuarine habitat
The candidates that answered (e) could not correspond their answers properly
The expected answers are:
(a) Features of the small intestine that increase the rate of absorption of digested food
- Ridges/furrows on inner linings;
- Small finger-like projections/villi;
- Minute projections/microvilli on the villi;
- Thin epithelial lining of the villi;
- Highly vascularised/well supplied with blood;
- Intestine is long/it has a large surface area.
(b) Fate of glucose formed in a plant during photosynthesis
- Glucose combines with Nitrogen/Sulphur/Phosphorus to form proteins for growth;
- Glucose is stored as starch;
- Glucose is oxidised to form carbon dioxide/water/energy in respiration;
- Glucose is also converted into lipids/cellulose which is stored.
(c) Mode of feeding of
(i) Euglena
- Exhibits both autotrophic and heterotrophic modes of nutrition;
- In autotrophic mode of feeding, the chlorophyll in its stellate chloroplast absorbs sunlight energy;
- And the dissolved carbon dioxide in the pond water diffuses into the cell of Euglena;
- Inside the chloroplast, the absorbed solar energy/sunlight is used in the synthesis of glucose from water and carbon dioxide;
- Glucose is converted into starch and stored in the paramylum granules;
- In heterotrophic mode of feeding, it takes in organic matter/diatoms e.t.c.;
- Through the gullet;
- And digests it in the reservoir.
(i) Spirogyra
- Manufactures its own food through photosynthesis;
- Its spiral chloroplast/chlorophyll absorbs the sunlight energy;
- It absorbs carbon dioxide from water/its environment to manufacture food;
- The manufactured food is used;
- while the rest/excess is stored in its pyrenoid in the form of starch;
(d) Characteristics of an Estuarine Habitat
- It is shallow;
- It has a high level of nutrients;
- Salinity/pH/O2 level fluctuates;
- Turbidity is high during rainy season;
- It is affected by tides;
- Species diversity is low;
- Muddy/soft soil/substratum
(d) Differences between an aquatic and terrestrial habitat
| Aquatic habitat | Terrestrial habitat |
|---|---|
| - Temperature is lower | temperature is higher; |
| - Water is the medium for growth/reproduction | soil is a medium for growth; |
| - Presence of dissolved oxygen | presence of atmospheric oxygen; |
| - Organisms are not affected by humidity | organisms are affected by humidity; |
| -Organisms are affected by tide/waves/ water current | organisms are not affected by tide/waves/ water current |
| - Organisms are not affected by wind action | organisms are affected by wind action; |
| - Light affects the distribution of organisms more | light affects the distribution of organisms less; |
| - Water is abundant | water is not abundant. |