SPM Biology 2018

Question

3. Diagram 3 shows a human digestive system.

Rajah 3 menunjukkan system pencernaan manusia.

(i) Name gland X.

Namakan kelenjar X.

(ii) Bread contains starch. Explain the role of gland X in the digestion of bread in P.

Roti mengandungi kanji. Terangkan peranan kelenjar X dalam pencernaan roti di P.

(iii) Explain why the process of digestion of bread does not occur in Q.

Terangkan mengapa pencernaan roti tidak berlaku di Q.

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(b) (i) Name organ R.

Namakan organ R.

(b) (ii) A person has a gallstone as in Diagram 3. Explain the effect of this condition to the digestion of lipid in S.

Seorang individu mempunyai batu hempedu seperti dalam Rajah 3. Terangkan kesan keadaan ini kepada pencernaan lipid dalam S.

(c) Explain one difference in the digestion of protein that occurs in Q and S.

Terangkan satu perbezaan dalam pencernaan protein yang berlaku dalam Q dan S.

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Answer ( 1 )

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    2020-12-28T20:04:43+08:00

    3. a) i) Salivary gland

    ii) Gland X (salivary gland) produces saliva which contains salivary amylase. Since bread contains starch, at P the salivary amylase enzyme can hydrolyse the starch with the presence of water into maltose.

    starch + water → maltose (write salivary amylase on top of the arrow) 

    iii) Q, the stomach secrets gastric juices which contain hydrochloric acid. This hydrochloric acid stops the action of salivary amylase as it creates a low pH environment which is unsuitable for the action of salivary amylase. Thus, digestion of the bread which contains starch doesn’t occur.

     

    b) i) Gall bladder

    ii) S is the duodenum. The gall bladder produces bile salts which emulsifies lipids into tiny fat droplets. This provides a greater surface area for enzymes to act on. If the bile duct is blocked with the formation of bile stones then bile cannot enter the duodenum and the emulsification of lipids cannot occur, it then becomes very difficult to digest lipids.

    Or

    If the bile duct is blocked then bile cannot enter the duodenum and an alkaline environment cannot be created which is needed for the activity of lipase. Digestion of lipids becomes very difficult.

     

    c) In Q (stomach) proteins are hydrolysed into smaller polypeptide chains with the presence of water and pepsin enzyme.  Whereas in S (duodenum) the polypeptides get hydrolysed into shorter chains of peptides with the help of the enzyme trypsin and the addition of water.

     
    write down the equation to be clearer.
    proteins + water →  polypeptides (write pepsin on top of the arrow) 

    polypeptides + water → peptides (write trypsin on top of the arrow) 

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