4551/2

4551/2 AnswersSection A

Question 1Marks

(a)A : rough endoplasmic reticulum

B : nucleus

C : mitochondrion

D : Golgi apparatus

4 = 3 marks

Reject: Wrong spelling 2-3 = 2 marks

1 = 03

(b)P1 Chromosomes/DNA in organelle B (nucleus) determine the type of protein synthesized.

P2 - Synthesis of polypeptide/protein occurs at ribosomes on the surface of organelle A (RER).

P3 - Transport vesicles carrying the polypeptide from organelle A fused with organelle D (Golgi Apparatus).

P4 - These proteins are modified, sorted and packaged in organelle D.

P5 - Organelle E (Secretory vesicles) then bud off from organelle D and travel to the plasma membrane to be secreted.

Any 31

1

1

1

1

Max 3

(c)

(i)P Carrier protein

Q Channel protein / Pore protein

S Phospholipids

Reject: wrong spelling11

1

(ii)2

(iii)Amino acid Facilitated diffusion

Oxygen Diffusion / simple diffusion

1

1

13 marks

Question 2Marks

(a)Mitosis1

(b)L ( N ( K ( M 1

(c)(i)K AnaphaseN Metaphase Reject: wrong spelling11

(ii)K Chromosome//sister chromatids separates and moves towards opposite poles of the cells/spindleN Chromosomes line at the metaphase plate// equator of the cell1

1

(d)

(i)X centromereY chromatids //non-sister chromatids Reject: wrong spelling11

(ii)Synapsis of the homologous chromosomes

Formation of chiasma and crossing over1

1

(iii)Variations to the species/organism

Ensure survival/continuation of species1

1

12

Question 3Marks

(a) (i)Vascular bundle1

(ii)Xylem and Phloem Reject: wrong spelling1

(b)Able to explain the adaptation of P based on the following criteriaF1 Palisade (mesophyll) cells are cylindrical and are closely packed together

F2 contain many chloroplastsE - to absorb maximum amount of light for photosynthesis.F1/F2 + E

2

(c)

P1 Increased evaporation of water from the surface of mesophyll cells

P2 increased osmotic pressure of mesophyll cells

P3 causes water to diffuse from xylem to mesophyll cells

1

1

1

(d)

(i)Guard cells1

(ii)F1 Guard cells (Z) has chloroplast to absorb light for photosynthesis and produce glucoseE1 OP of guard cells increases causing water to move in from neighbouring cells by osmosis // turgidity of cells increase

F2 Outer wall of guard cells is thinner than inner wallE2 causes the cells to bend outwards and the stoma (Y) to openF1+ E1 = 2

F2 + E2

= 2

12

Question 4Marks

(a)(i)P cerebrumQ Medulla oblongataR cerebellum Reject wrong spelling.11

1

(ii)Able to state the function and give an exampleInvoluntary response // breathing rate//heart beat1

(iii)Able to state the consequence of an injury in RCannot coordinate body movement1

(b)(i)Able to name structure P and QP mitochondrion

Q synaptic/neurotransmitter vesicle

Reject: wrong spelling1

1

(ii)Able to state one important function of the synapse

Control and integrate the transmission of nerve impulse //allow nerve impulse to be transmitted in one direction only1

(iii)Able to explain the transmission of nerve impulse across a synapseP1 - When the nerve impulse arrives at the synaptic knob,

P2 -a neurotransmitter/ synaptic vesicle is triggered to move towards the presynaptic membrane.

P3 -Neurotransmitter is released from the synaptic vesicle into the synaptic cleft

P4 - Neurotransmitter diffuses across the cleft to the post-synaptic membrane of the second neurone

P5 -where it stimulates the generation of another impulse.

P6 - Energy is needed for this process.

Any four consecutive Ps.1

1

1

1

1

1

Max 4

12

Question 5Marks

(a)(i)Able to name any two phases of the growth curve of humansF1 Infant phase F2 Childhood phase

F3 - Adolescent phase

F4 - Adult phase

F5 - Senescence and death phase

Any two F

E1 The growth rate is rapid (for both boys and girls)

E2 The growth rate becomes slower. Boys grow slightly faster than girls

E3 Growth rate is faster. In the early stage, girls grow more rapidly than boys.

E4 Growth rate is zero.

E5 Growth rate is negative.

E must be corresponding to F1

1

1

1

1

Max 2

1

1

1

1

1

Max 2

(ii)Able to indicate correctly the phase based on answer in a(i)

2

(b)Maximum physical growth has been achieved in adult phase/ before 40 years old.

Muscles and cartilage of the body start to degenerate when people are about 40 years old.

11

c. Axes labels with units

Staircase graph

Arrows to show ecdysis (max 5 arrows)1

1

1

11

Section B

Question 6Score

(a)(i)Adaptive features of structure M and N:

F1: Moist surface.1

E1: Dissolve oxygen or carbon dioxide easily.1

F2: Thin// one-cell thick.1

E2: Rapid diffusion of gases// direct contact with respiratory surfaces.1

F3: Large number of tracheoles in insect// alveolar wall in human being.1

E3: Large surface area that increases surface area for efficient gaseous exchange.1

Total:[6 marks]

Score

(a)(ii)F1: Gaseous exchange happens is due to differences in partial pressure of a particular respiratory gas//

Diffusion of gas molecules happens down its partial pressure gradient.1

F2: Partial pressure of oxygen at the alveolus is higher than the blood capillary.1

E2: Oxygen diffuses from alveolus into blood capillary.1

F3: Partial pressure of carbon dioxide in the blood capillary is higher than the alveolus.1

E3: Carbon dioxide diffuses from blood capillary into alveolus.1

Note: F1 is optional.

Total:[4 marks]

Score

(b)F1: During inhalation:

E1: Floor of buccal cavity is lowered.1

E2: Operculum closes.1

E3: Buccal cavity enlarges.1

E4: Pressure in buccal cavity is lower than the outer environment.1

E5: Water is drawn into the mouth.1

F2: Exhalation:

E6: Mouth closes, floor of buccal cavity is raised.1

E7: Volumn of buccal cavity decreases.1

E8: Pressure in buccal cavity is raised.1

E9: This forces water flows through the lamella and gaseous exchange takes place.1

E10: Operculum opens for water to flow out.1

Note: F1 and F2 together is one mark.1

Total:max

[10 marks]

Question 7Score

(a)(i)Diagram 7.1:

F1: This relationship is known as mutualism.1

E1: Example: Nitrogen-fixing bacteria, Rhizobium sp. live inside the root nodules of a leguminous plant such as peas & beans.1

F2: Both organisms benefit.1

E2: Rhizobium sp. converts atmospheric nitrogen into ammonium compounds that are absorbed by leguminous root//

The plant provides the bacteria with living space, shelter, protection & energy-rich organic compounds.1

Diagram 7.2:

F1: This relationship is known as parasitism.1

E1: Example: tapeworm in the human intestine.1

F2: Parasite benefits but harm the host/ human.1

E2: Host loses nutrients to the parasite// parasite gains the nutrients.1

Total:[8 marks]

Score

(a)(ii)P1: Reduction in their nervous systems & sense organs.1

P2: Reduced digestive tracts & absorb nutrients through the whole body surface.1

P3: Protective cuticles// produce mucus// anti-enzymes to prevent being digested by their hosts enzymes, acids or alkalis.1

Any two

Total:[2 marks]

Score

(b)F1: Atmospheric fixation.1

E1: Convert nitrite ions to nitrate ions.1

F2: Fixation by nitrogen-fixing bacteria.1

E2: Example: Rhizobium sp. Lives in the nodules of leguminous plant// Nostoc sp. Lives freely in the soil.1

E3: Fix atmospheric nitrogen and convert it into ammonium compounds.1

F3: Nitrates are taken up by the roots of plants and converted into proteins.1

E4: When animals eat the plants, the organic nitrogen is transferred into the body of animals. 1

E5: Death and decomposition of organisms/ plants/ animals.1

E6: Decomposition of animal waste produces ammonia/ ammonium.1

Roles of nitrifying bacteria.

E7: Nitrosomonas sp. converts ammonia into nitrites.1

E8: Nitrobacter sp. converts nitrites to nitrates.1

F4: Denitrification/ denitrifying bacteria converts nitrates back into atmospheric nitrogen to complete the nitrogen cycle.1

Total:max

[10 marks]

Question 8Score

(a)(i)Able to name the phenomenon and explain the causes of the phenomenon based on the following criteria:

C1: name the phenomenon (1M);

C2: state the cause of the phenomenon (1M);

C3: explanation (3M)

C1: Landslide.1

C2: Forests are cleared for housing// road construction// agriculture// mining// industries.1

C3:

P1: Absence of plant roots systems.1

P2: Make the soil structure unstable// top layer of the soil disintegrates easily.1

P3: When it rains heavily for a long period of time, the rain water is not absorbed by the plant anymore.1

Or any other possible explanation.

Total:[5 marks]

Score

(a)(ii)Able to explain the effect of phenomenon in (a)(i) to the environment based on the following criteria:

E: Effect of phenomenon.

P: Explanation of the effect.

E1: Flash flood.1

P1: The eroded soil is carried by moving water and deposited at the bottom of rivers, which in turn contributes to the sedimentation of the rivers.1

P2: Rivers become shallow.1

E2: Water pollution.1

P3: Eroded soil will make the water muddy.1

E3: Leads to the death of aquatic organisms.1

P4: Lack of (dissolved) oxygen.1

Note: Any 2 E with corresponding 3 P.

Total:[5 marks]

Score

(b)Able to explain measures that we can take to reduce the increment of greenhouse gases.

F1: Implementation of law.1

E1: Control the emission of carbon dioxide from factories/ vehicles.1

F2: Use of technology.1

E2: The use of biomass fuel to reduce the burning of fossil fuels.//

E3: Liquefy the carbon dioxide and store it underground.1

F3: Education.1

E4: Educate the public the concept of 3Rs (recycle, reuse and reduce).1

F4: Efficient use of energy1

E5: Use energy saving electrical goods such as energy saving light bulbs.1

E6: Use special home design to reduce the need of heating, cooling and lighting.1

F5: Use renewable energy.1

E7: Solar energy/ wind/ water energy.1

F6: Reforestation.1

E8: Replanting programmes.1

Note: Any 5F and corresponding 5E explanation.

Total:[10 marks]

Question 9Score

(a)Able to name and explain the type of variation due to different height among people.

F1: Continuous variation.1

F2: The characters are quantitative/ measurable.1

E1: Its graph shows a normal distribution/ bell-shaped.1

E2: Diagram

1

E3: Exhibits a spectrum of phenotypes with intermediate characters//

Individuals display a range of small differences in height.1

E4: Individuals range from shortest to tallest, with average heights much more common than either extreme.1

E5: Difference in this phenotype is not distinctive.1

F3: Influenced by both genetic and environmental factors.1

E1: Genetic factor: genes from both parents.1

E2: Example of environmental factor: food intake// degree of physical activity/ exercise1

F4: Controlled by polygene/ great number of genes.1

E1: Genes show additive effect.1

Note: F1 + any other F or E.

Total:[10 marks]

Score

(b)(i)Able to explain gene mutation.

F1: Random/ spontaneous/ permanent// irreversible change in the nucleotide sequence of DNA// amount of DNA.1

E1: Gene/ point mutation occurs at a single locus or gene position on a chromosome1

E2: May occur on a recessive or a dominant gene.1

E3: Involves deletion, insertion or substitution of a nucleotide base.1

E4: A change in the sequence of nitrogenous bases.1

E5: May result in a defective protein or no protein being produced.1

Note: 1F and any 3E.

Total: [4 marks]

(b)(ii)Able to explain two types of gene mutation that change DNA.

Normal gene sequence

F1: Base substitution1

1

E1: Replacement of one or more nitrogenous bases.1

F2: Base insertion1

1

E2: Insertion of an extra nitrogenous base.1

F3: Base deletion1

1

E3: Removal of a nitrogenous base.1

Note:

Any 2 F with diagrams and respective E.

E can be written separately in paragraph or incorporated in the diagram drawn.

Reject any other letters used for nitrogenous bases.

Any 2F with corresponding E.

Total:[6 marks]

Amino acid

oxygen

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