Question 1:
Green plants synthesize their food through the process of photosynthesis. The chemical process of photosynthesis can be summarized as in the schematic diagram below.


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(a) State the meaning of photosynthesis based on the schematic diagram. [2 marks]

(b) Starting with water and carbon dioxide as the raw materials, describe how a green plant produces starch molecules. [8 marks]

(c) It is found that the process of photosynthesis contributes to the balance of nature.
Explain how air pollution may have an effect on photosynthesis and the balance of nature. [10 marks]

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Answer:
(a)
A process whereby a green plant produces glucose from carbon dioxide and water in the presence of chlorophyll and sunlight.

(b)

• Chlorophyll absorbs light energy to produce ATP/ electrons.
• Photolysis of water produces hydrogen ions and hydroxyl ions.
• The H⁺ ions combine with electrons to form hydrogen
• The hydrogen/ ATP will be used in the dark reaction
• It occurs in the grana
• Takes place in the absence of light
• Carbon dioxide combines with hydrogen to form glucose and water
• Glucose undergoes condensation and is converted to starch for storage
• It occurs in a series of chemical reactions which require ATP
• The reaction occurs in the stroma

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(c)   

1. The importance of photosynthesis for the balance of nature:

• Absorbs carbon dioxide from the atmosphere
• Replaces oxygen in the atmosphere
• Maintains the percentage of oxygen in the atmosphere

2. The sources of pollution are motor vehicles and urbanization which will liberate heavy smoke and increase the amount of particles in the air.
3. The particles accumulate on the leaf surfaces. They cover the stomata and reduce the intensity of the light that reaches the leaves.
4. As a result, the rate of photosynthesis decreases. Less carbon dioxide is reabsorbed from the atmosphere and less oxygen is released. It also promote the greenhouse effect and global warming.

 

 

Question 1:
(a) Diagram 1.1 shows human digestive system.
Structure S in Diagram I is involved in the digestion of fat.


(i) Name structure S.
(ii) Name the enzyme which digests fat in S.
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(iii) Diagram 1.2 shows a mechanism of an enzyme reaction.
Draw the diagram in the spaces III and IV provided in Diagram 1.2 to complete the mechanism of the enzyme reaction.


(b)(i) Explain how starch is digested in the duodenum.

(ii) A student eats too many oranges.
Explain the effect of eating too many oranges on the digestion of starch in the duodenum.
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(c) In a food preparation process, a housewife carries out the following steps:
Step 1: Marinate pieces of meat with strips of unripe papaya in a basin.
Step 2: Immerse the basin in a container filled with water at 40^oC for 30 minutes as in Diagram 1.3.


Explain why the housewife carries out Step 1 and Step 2.



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Answer:
(a)(i)
Structure S: Ileum

(a)(ii)
Enzyme which digests fat in S is Lipase

(a)(iii)


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(b)(i)
The pancreas secretes an amylase into the duodenum which hydrolyses starch to maltose.

(b)(ii)
- The duodenum medium becomes acidic
- Which is not suitable for the action of the amylase on starch
- Slows down the digestion of starch

(c)
- Papaya contains papain/ protease
- The pieces of meat and papaya strips increase the total surface area
- To increase enzyme action
- Protease will tenderize the meat
- Takes place in water at 40^oC, which is the optimum temperature for enzyme reaction

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Question 1:
(a)(i) After absorption of nutrients in the small intestine, the undigested substances in the colon result in the formation of faeces.
Explain the formation of faeces in a human. [4 marks]

(ii) Malnutrition is a condition due to taking an unbalanced diet in which certain nutrients are lacking, in excess or in the wrong proportions.
Explain the effect on a child who is given insufficient amounts of any two nutrients of food for a long period of time. [6 marks]
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(b) Table below shows the food intake by a boy aged 15 years in his daily menu. The daily energy requirement for him is 12500 kJ.


(i) Based on the Table, state the value of energy contained in this daily food intake.
Does the food intake satisfy his daily energy requirement? [2 marks]

(ii) This boy takes this menu continuously for a long time. [8 marks]

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Answer:

(a)(i)

• The contents in the small intestine that are not absorbed enter the colon.
• The intestinal content consists of a mixture of water, indigestible food, bacteria, dead cells and pigments.
• The contents move slowly along the colon by peristalsis.
• Water is reabsorbed and faeces are formed.

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 (ii)

• A child who is deficient in protein may suffer from kwashiorkor.
• Protein is needed for normal growth. Lack of protein causes growth of the child to be stunted.
• A child who is deficient in vitamin C may suffer from scurvy.
• Vitamin C is needed for healthy gums and skin. Lack of vitamin C causes swollen and bleeding gums.
• A child who is deficient in roughage may suffer from constipation.
• Roughage is needed to stimulate peristalsis.
• Lack of roughage causes difficulty in defaecation.

 (b)(i)
Total energy = 8230 kJ
The energy produced from the food taken daily is insufficient.
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(b)(ii)