BioBooster DB024

Semester II 2021/2022

BIO BOOSTER
BIOLOGY UNIT
KOLEJ MATRIKULASI MELAKA
BIOLOGY 2 DB024
SEMESTER 2 SESSION 2021/2022

ANSWER SCHEME

1. (a) FIGURE 1 shows the tropical rain forest ecosystem.

FIGURE 1
(i) Identify the tropical rain forest ecosystem Q, R and S. [3 marks]
Q: Canopy layer
R: Understory layer
S: Shrub layer

(ii) Which layer have bryophyte and centipede in FIGURE 1. [1 mark]

Ground layer

(iii) Give one example of plants in layer P. [1 mark]

Meranti/Tualang/Jati/Cengal
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Semester II 2021/2022

(b) A food chain of paddy field consists of paddy, grasshopper, bird, rat, snake
and eagle.
Construct a complete food web using all given biotic components in the box
and explain energy transfer occur between first trophic level and second
trophic level. [6 marks]

Primary consumer feed on producer. 1 mark

Energy is transferred from 1st trophic level to 2nd trophic level. 1 mark
Only 10% of energy is transferred to the next trophic level / 90% of
energy is lost to environment. 1 mark
Energy is lost from herbivores through respiration/ excretion /and
egestion. 1 mark Any 4
Energy lost in respiration can’t be transferred to other living organisms
but // energy lost in feces and urine can be transferred to detritivores or
decomposers. 1 mark
Secondary consumer feed on primary consumer. 1 mark

2. (a) Differentiate between continuous and discontinuous variation.

[2 marks]

Continuous variation Discontinuous variation

Has intermediate group/phenotypes Has no intermediate
group/phenotypes
Quantitative inheritance/ Qualitative inheritance/
characteristics can be measured characteristics cannot be
measured
Caused by environmental and Caused by genetic factors only//
genetic factors// phenotypic phenotypic expression is not
expression is influenced by influenced by environmental
environmental factor factor
Characteristic is controlled by two Characteristic is controlled by
or more genes/ polygenes one gene/ different allele at a
single locus
Shows a normal distribution curve Shows a discrete distribution
curve
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Semester II 2021/2022

Individual cannot be grouped into Individual can be grouped into

distinct and discrete phenotype distinct and discrete phenotype
Any 2 answers

(b) State the factors that cause genetic variation.

[2 marks]
- Genetic recombination / crossing over / independent assortment /
random fusion of gamete
- mutation / gene mutation / chromosomal mutation

(c) FIGURE 2 shows the normal distribution curves of the early population of an
Organism. The arrows show the direction of natural selection.

FIGURE 2

(i) Sketch the curves on the diagrams below to show the effect of natural
selection.
[2 marks]

Curve = 1
Label axis + curve = 1

(ii) Identify the type of natural selection based on answer mention in

2(c)(i).
[1 mark]
Stabilizing selection

(iii) Describe briefly the results of natural selection mention in 2(c)(i).

[2 marks]
• Natural selection that favours intermediate phenotypes
• Acts against / eliminates both extreme phenotypes
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Semester II 2021/2022

3. FIGURE 3 shows the mechanism of enzyme action.

I I

Enzyme Enzyme Enzyme

Stage X

FIGURE 3

(a) Name the action mechanism shown in FIGURE 3.

[1 mark]

Induced-fit mechanism

(b) What is formed at stage X? How does this step help to increase rate of reaction?
[2 marks]

Enzyme-substrate complex is formed at stage X. -1m

Enzymes (speed up the reaction) by lowering the activation energy. -1m

(c) Describe the events that occur when molecules I binds to the enzyme.
[4 marks]

▪ Molecules I bind to active site of enzyme.

▪ The binding of molecules I / substrate induces changes in the
conformation of active site of enzyme.
▪ Active site of enzyme becomes fully complementary/compatible with the
substrate // Allowing the molecule I/substrate fit to enzyme precisely.
▪ Enzyme - substrate complex formed.
▪ Enable the enzyme to carry out catalytic function.
▪ Product is formed and released, enzyme changes back to original
conformation.
(Any 4 marks)
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Semester II 2021/2022

(d) Why this mechanism cannot occur when someone having a high fever? Give your
reason.
[2 marks]

▪ High temperature cause denaturation of enzymes.

▪ Break down hydrogen/ionic bond/disulfide bridge/van der Waals
interaction and change the conformation in active site of enzyme //
active site undergoes conformational change// enzymes loses its globular
shape.

4. FIGURE 4 represents two main stages in cellular respiration.

FIGURE 4

(a) Name the

(i) reaction that occurs at steps 2, 3 and 4 and [1 mark]

Oxidative decarboxylation // oxidation and decarboxylation

(ii) the two by-products of the reaction in (a)(i). [2 marks]

NADH (+ H+) and CO2 / carbon dioxide

(b) (i) Explain briefly substrate level phosphorylation. [1 mark]

(An enzyme facilitates direct) transfer of a phosphate group from a
substrate to ADP forming ATP

(ii) At which step does the substrate level phosphorylation occur and how many
ATP(s) are produced at this step from one molecule of glucose? [2 marks]
Step 1 : 2 ATP
Step 5 : 2 ATP
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Semester II 2021/2022

(c) State what happens to the hydrogen atom produced at step 6. [1 mark]
Hydrogen atom is accepted by FAD and reduced to FADH2

(d) (i) What happen to NADH + H+ produced from glycolysis and Krebs cycle?
[1 mark]
It will enter electron transport chain // transfer/donate electron to
electron transport chain

(ii) How many productions of NADH + H+ from one molecule of glucose?

[1 mark]
10

5. FIGURE 5 shows a diagram of the Calvin cycle in photosynthesis.

FIGURE 5

(a) Name phases P, and R. [2 marks]

P : Carbon fixation
R : Regeneration of RuBP / Ribulose bisphosphate / CO2 acceptor

(b) Describe what happen during phase Q. [3 marks]

- Each 3-phosphoglycerate receives one phosphate group (Pi) from ATP

forming 6 molecules of 1,3-bisphosphoglycerate.
- 6 molecules NADPH + H+ donate electrons to reduce 6 molecules of 1,3-
bisphosphoglycerate.
- Each 1,3-bisphosphoglycerate loses one Pi, becoming 6 molecules of
glyceraldehyde 3-phosphate (G3P).

(c) State the numbers of ATPs used in FIGURE 5. [1 mark]

9 ATP
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Semester II 2021/2022

6. FIGURE 6 shows the cross section of a pair of guard cells.

A C

D
B

FIGURE 6

(a) Based on FIGURE 6,

(i) what is the labelling of stoma? Give ONE function of stoma.
[2 marks]

C; -1m

Allow water evaporation/water loss via transpiration // -1m

Allow gaseous exchange

(ii) describe the structure labelled B?

[1 mark]
Has uneven thickness / the thinner outer walls and the thicker inner
wall

(b) Explain the stomatal opening by using the role of potassium ions.
[3 marks]

▪ ATP produced in the guard cells during light dependent reaction

is used to pump the proton/hydrogen ions/H+ out of the guard
cells.
▪ Potassium ions/K+ diffuse from the adjacent cells into the guard
cells.
Any 3
▪ Guard cells become hypertonic // water potential becomes more
negative / decreases (due to accumulation of K+).
▪ Water diffuses into the guard cells by osmosis.
▪ Thus, the guard cells become turgid, widening the stomatal
opening.
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7. (a) FIGURE 7 shows the transport system in human body.

FIGURE 7
(i) Identify labelled X, Y and Z. [2 marks]
X: Sinoatrial node / SA node
Y: Bundle of His

(ii) Name the chamber of the heart which has thickest wall. Explain its
importance. [3 marks]
Chamber: Left ventricle
Importance:
-Left ventricle needs to pump blood to all parts of the body
- Higher pressure / contraction to pump blood throughout the
body
- to produce stronger contraction
(iii) Why there is a delay (0.1s) during the conduction of electrical impulse
from AV node to the walls of ventricles? [1 mark]
To allow both atria finish contracting / empty completely (before
the ventricles contract)
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Semester II 2021/2022

8. FIGURE 8 shows the structure of a nephron in the human kidney.

FIGURE 8

a) Name the structures labelled Q and R. [2 marks]

Q: Proximal convoluted tubule
R: Collecting duct

b) (i) State the main process which occur in structures P. [1 mark]

Ultrafiltration

(ii) Explain how blood pressure affects the formation of glomerular filtrate in P.
[2 marks]
- Provide high hydrostatic pressure of blood in glomerulus
- Forcing small substances/water/glucose/amino acid/NaCl to pass
through the pores of blood capillary/glomerulus

c) Why is glucose not found in the urine? [1 mark]

All glucose is reabsorbed at proximal convoluted tubule
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Semester II 2021/2022

9. a) FIGURE 9 shows a diagram of the motor neuron.

B
C

FIGURE 9

Label A, B and C. [3 marks]

A : Dendrite
B : Myelin sheath
C : Nodes of Ranvier

b) Explain the mechanism of hormone action by gene activation [6 marks]

● Steroid/ lipid soluble hormones diffuse into cytoplasm through
plasma membrane of targeted cell
● and binds with specific receptor protein forming hormone-receptor
complex
● The hormone-receptor complex formed enters the nucleus
● and binds to specific gene on the DNA and leads to transcription
forming mRNA.
● The mRNA enters cytoplasm through nuclear pore // mRNA binds with
ribosomes to be translated into new protein through translation
process
● and translated into new protein such as enzyme that produce specific
response / effect
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Semester II 2021/2022

10. (a) FIGURE 10(a) shows the basic structure of an antibody produced during the
humoral immune response to a specific pathogen.

FIGURE 10(a)
(i) Name the type of protein that make up antibody.
[1 mark]
Globular protein

(ii) What is the part A? State its function.

[2 marks]
A: Antigen binding site
Function: Bind with specific antigen

(iii) Explain why the conformation of V on the antibody molecule is

different from one antibody to another.
[1 mark]

Amino acid sequences in variable region varies extensively from

one antibody to another / conformation of antigen-binding site of
antibody is specific to particular antigen
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Semester II 2021/2022

b) FIGURE 10(b) show mechanism of humoral immune response.

FIGURE 10b
FIGURE 10(b)
(i) Identify cells X and Y.
[2 marks]
X: Helper T cell / TH cell
Y: B lymphocyte / B cell
(ii) Describe development of cell Y.
[ 2 marks]
- Cell Y is produced / originate in (stem cell of) bone marrow
- and undergo maturation / become mature in bone marrow

(iii) What happen if cell X is not activated?

[1 mark]
- No secretion of interleukin-2 / IL-2 // Cell Y is not activated