Question 2
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(a)Describe briefly the process involved in the conversion of food to chyme in the stomach of a mammal. [4 marks]
(b)Complete the table below by stating one enzyme, digestive juice, food acted upon and
end-product in the corresponding spaces.
One EnzymeOne juice
One food acted upon
One end-product
Pepsin
(i) -----------
Lipase
(ii)---------------
(iii)---------------
(iv)---------------
(v) --------------------
(vi) -------------------
(vii) -------------------
(viii)-------------------
Maltose
(ix)-----------------------
[9 marks]
(c) Describe an experiment to show that carbon dioxide is necessary for photosynthesis.[7 marks]
Observation
Some students scored better in this question while others performed poorly may be due to their poor knowledge of digestion. Some candidates failed to describe the process of conversion of solid food to chyme.
Some candidates were able to complete the table but spelling errors make them score low marks.
Many candidates also avoided the description of the experiment to show that carbon dioxide is necessary for photosynthesis.
The expected answers are:
(a) Process of conversion of food to chyme in the stomach of a mammal
The stomach is a large thick-walled muscular sac; made of three layers of muscles; that contracts in different directions when food enters into it; bringing about a twisting/squeezing/churning effect; enabling food to mix with digestive juice; and HCL; this movement then converts food to the semi-liquid called chyme.
(b) Table
Enzyme |
Juice |
Food acted upon |
end product |
Pepsin |
ii. Gastric |
v. Protein |
viii. Peptone/ polypeptide |
|
iii. Saliva/pancreatic juice |
vi. Cooked starch/carbohydrate |
Maltose |
Lipase |
iv. Intestinal/Pancreatic juice |
vii. Fats and Oil |
ix. Fatty acid and glycerol |
(c) Experiment to show that carbon dioxide is necessary for photosynthesis
Two potted plants are de-starched by placing them in a dark cupboard for 24hours;
a leaf each from both plants are then tested for starch to ensure they have no starch/have been de-starched; the potted plants are placed on a board each; a beaker containing caustic soda is placed beside plant A; to absorb carbon dioxide; while a beaker containing water is placed beside plant B as control; they are both covered with bell jars labelled A and B respectively; the rim/edge is smeared with vaseline/petroleum jelly to make it air tight; the setup is exposed to sunlight/light for 4-6 hours; a leaf each from both plants are plucked and tested for starch.
Observation: It is observed that leaf from plant A is negative/does not contain starch/remains brown in colour while leaf from plant B is positive/contains starch/turns blue - black.
Conclusion: Carbon dioxide is necessary for photosynthesis.
OR
De-starch a well-watered potted plant by putting it in darkness for 48 hours; insert a leaf into a flask containing water which serves as a control experiment; and another leaf into another flask containing KOH/ potassium hydroxide/ caustic potash; ensure both flasks are air tight by smearing the split corks with Vaseline; leave the potted plant in a well-lit place for 6 to 9 hours; detach the leaves and test them for starch.
Observation: It is observed that the leaf in the flask containing caustic potash contains no starch while the leaf in the controlled experiment contained starch.
Conclusion: Carbon dioxide is necessary for photosynthesis.