Form 4 BiologyChapter 4 Chemical Composition of the Cell

Objective Questions

1 Which of the following substances contains magnesium and nitrogen?Magnesium Nitrogen

A Amino acid ProteinB Amino acid StarchC Chlorophyll ProteinD Chlorophyll Starch

2 In the human alimentary canal, carbohydrate is digested as shown below:

enzyme 1 enzyme 2Starch Maltose Glucose

Which of the following accurately describes the enzymes involved in this process?Enzyme 1 Enzyme 2

A Amylase LipaseB Amylase MaltaseC Lipase PepsinD Amylase Ptyalin

3 Among the elements that are found in mineral salts, which of the following element’s importance to humans is true?

Element ImportanceA Iodine Synthesis of hormonesB Iron Blood clottingC Sodium Synthesis of antibodiesD Calcium Formation of bones and teeth

4 An enzyme is a protein that is different from inorganic catalysts. The specific action of the enzyme is related withA protein molecules not having metal ionsB protein molecules having metal ionsC protein molecules do not dissolve in body fluidsD the outer surface of protein molecules having difference shapes

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5 Which of the following is represented by Figure 1?

Figure 1A DNAB GeneC NucleotidesD Nucleic acid

6 Which of the following substances will be used up first when a mammal is suffering from hunger?A Protein in the musclesB Glycogen in the liverC Protein in the bloodD Fat below the skin

7 The photosynthetic process will stop at temperatures above 60°C becauseA the hormones in the plants are destroyedB ATP cannot be formedC cell respiration occurs too quicklyD the enzyme structure is denatured

8 Which chemical element combines to form starch and cellulose molecules?I CarbonII HydrogenIII NitrogenIV OxygenA I and II onlyB I, II and IV onlyC I, III and IV onlyD I, II, III and IV

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9 Enzymes are required by living things forI food digestionII DNA formationIII the entry of water into the cell through osmosisIV the entry of salt into the cell through diffusionA I and II onlyB I, II and III onlyC I, III and IV onlyD I and III only

10 Which of the following statements is true?I A gene consists of a chain of DNA segmentsII A DNA molecule consists of a pair of polynucleotide chainsIII Each gene is located on a certain locus in a chromosomeIV The base sequence in the DNA molecule can determine the type of protein

that will be produced by the cellA I and II onlyB II, III and IV onlyC I, II and III onlyD I, II, III and IV

11 Figure 2 shows a part of the DNA molecular structure. J, K, L and M are the basic units in the DNA molecule.

Figure 2Which of the following is represented by J, K, L and M?

J K L MA Sugar Base Phosphate PhosphateB Phosphate Base Sugar PhosphateC Base Sugar Base PhosphateD Phosphate Sugar Base Base

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Structured Question

The DNA molecule contains genes, which are the basic hereditary unit and can be passed on from the parent to the child. Figure 1 shows a part of a deoxyribose nucleic acid double helix molecule (DNA).

(a) (i) Where is the DNA molecule found in a cell?(ii) Based on the figure of the DNA molecule, explain why the DNA molecular

structure is termed as Double Helix?

(b) The DNA molecule is built from basic molecules such as those shown in the figures below.

Key: P = phosphate S = sugar N = nitrogenous base

(i) What is the name of the basic molecule that forms the DNA?

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Watson-Crick DNA model

Figure 1

(ii) Based on the basic DNA molecule diagram, what it’s the structure that differentiates between the different types of molecules?

(iii) In the DNA molecule, the basic molecules are paired. Draw a pair of basic DNA molecule.

(c) A sequence of basic molecules is identified to carry information for a certain characteristic in an animal. What is represented by the sequence of the basic molecules?

(d) Mutation occurs when the DNA structure changes.(i) Mutation on which human cell can be passed on to the child?(ii) State one factor that can cause mutation in humans.

Essay Question

(a) Explain the characteristics of enzymes that influence the action of the enzyme.(b) Describe one experiment to investigate the effect of temperature on the action

of a named enzyme.

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Answers

Objective Questions

1 C2 B3 D4 D5 C6 B

7 D8 B9 A10 D11 D

Structured Question(a) (i) Nucleus

(ii) DNA consists of 2 polynucleotide chains that are coiled together

(b) (i) Nucleotide (ii) Type of nitrogenous base(iii)

(c) Gene

(d) (i) Reproductive cell (ii) Chemical substance such as the mustard gas

Essay Question(a) Enzymes accelerate biochemical reactions but are not changed at the end of the

experiment. As such, enzymes are required only in small quantities in the body.

The action of the enzymes is specific, that is each enzyme only catalyses the reaction that involves certain substrates.

Enzymes exhibit protein characteristics such as being sensitive towards changes in temperature. Enzymes are destroyed at a temperature of 60°C and the enzymatic action is stopped. At a low temperature of 10°C, the enzymatic action is slow. Enzymes react at the maximum level at the optimum temperature.

The enzymatic action is influenced by the medium pH. Each enzyme reacts at the maximum level at its optimum pH.

The same enzyme catalyses the reverse reaction.

Example: Starch + water maltose

Maltose starch + water(b) Purpose: To study the effect of temperature on the enzyme activity

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amylase

amylase

Apparatus/Material: -

Procedure:1 5 ml of saliva is collected and diluted by adding 5 ml of distilled water into

a small beaker.2 Test tubes labelled P, Q, R, S and T are prepared. 5 ml of starch suspension

is poured into each test tube.3 Each test tube is placed in the water bath at temperatures of 5°C, 28°C,

37°C, 45°C and 60°C.4 After that, 1 ml of saliva solution is added into each test tube and the

stopwatch is started immediately. The content of each tube is stirred and a drop of the contents is removed at 1 minute intervals to be tested with iodine solution. This step is repeated until the iodine solution does not change colour.

Result:

Test tube

1 2 3 4 5 6 7 8 9 10

P 5Q 28R 37S 45T 60

Conclusion:The action of the enzyme is influenced by temperature. Enzymatic action is slow at low temperatures, and increases with the increase in temperature until 37°C. The enzymatic action is at the maximum at 37°C. After 37°C, the enzymatic action decreases and stops at 60°C.

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Time (minute)

Temperature (°C)