2004 SPM Sample answers

a) An athlete has just completed a 400 metre track event. His leg muscles are painful due to muscle fatigue. The athlete then carries out the following actions.

· Wears a track suit

· Takes a few long deep breaths

· Walks freely as a ‘cooling down’ activity.

Explain why the athlete carries out these actions.

b) Human and fish respiratory systems are adapted to function in their respective habitats. Compare and explain the adaptations.

Answer

a) The athlete wears a track suit so that there is no sudden decrease in temperature in his muscles.

A sudden decrease in temperature will cause the accumulation of lactic acid and muscles pain/cramp.

He draws a deep breath several times to oxidize lactic acid that has been accumulated and pays back the oxygen debt.

He walks freely so that his muscles take time to oxidize 1/6 of lactic acid to carbon dioxide, water and energy and 5/6 of the lactic acid is converted back to glucose.

b)

	Human	Fish
Organ	Human’s respiratory structure is the lungs	Fish’s respiratory structure is the gills
Habitat	Human lives on land	Fish lives in the water
Function	Lungs do not need a medium to function	Gills need flow of water through the gills for gaseous exchange
Adaptation	Human lungs have a lot of alveoli and covered with a large network of blood capillaries. Gaseous exchange occur by diffusion through the alveoli	Water is drank in and flows through the gills for absorption of oxygen to blood capillaries which are cross linked with the filaments of gills. Then water flows out through the operculum and absorbs carbon dioxide from the blood capillaries to the water to be released
Characteristics	Total surface area is big with 700 million alveoli/ many alveoli to increase total surface area for diffusion Thin alveolar wall which helps in the diffusion of gases, The wall of the alveolus is moist whereby respiratory gases can dissolve in it, The alveolus is well supplied by blood capillaries to facilitate diffusion and transportation of the gases.	Has thin epithelial wall of gill filaments to facilitate diffusion of gases. Many plate like projections (lamella) at gill filaments to increase the total surface area for diffusion A network of blood capillaries in the gill filaments to facilitate diffusion and transportation of the gases.

Answers to Hands on Pg 72

Section B

3a)

(a) Waxed cuticle

• Reduces loss of water through transpiration.

Upper epidermis

• Transparent thin layer of cells which allows sunlight to reach the mesophyll layer.

Palisade mesophyll cells

• Elongated cells perpendicular to the surface.
• They are densely packed and rich in chloroplasts to allow maximum absorption of sunlight.

Spongy mesophyll cells

• Irregular in shape, loosely arranged and contain chloroplasts.
• Large air spaces between cells allow gaseous exchange between the cells and the surrounding air.

Stoma

• Regulate the passage of oxygen, carbon dioxide and water vapour across the surface of the leaf.

Guard cells

• Contain chloroplasts.
• Control the closing and opening of the stoma.

Vascular bundle

• Xylem is used for the transport of water and mineral salt.
• Phloem is used for the transport of soluble food materials from the leaf to other parts of the plant.

b) Photosynthesis involves light reaction and dark reaction.

Light reaction

• Chlorophyll absorbs light energy.
• Light energy causes the chloropyhll to emit electrons.
• Light energy also splits the water molecules, into H⁺ ions and OH^- ions.
• OH^- ions combine to produce water and oxygen.

24OH^- - 24e --->12H₂O + 6O₂

• H⁺ ions accepts an electron to form a hydrogen atom which is used in the dark reaction.

Dark reaction

• Hydrogen atom reduces CO₂ to form CH₂O
• 6 units of CH₂O combine to form 1 unit of glucose, C₆H₁₂O_6.

4. a)

Bread is a carbohydrate which consists of starch.

Starch is digested into glucose.

Half-boiled egg contains proteins which are digested into amino acids.

Glucose and amino acids are absorbed into the villi of the ileum.

Glucose and amino acids enter the blood capillaries of the villi and are transported by the

hepatic portal vein to the liver.

From liver, glucose and amino acids are transported to body cells.

Glucose is oxidised to release energy.

Excess glucose is converted to glycogen and stored in the liver.

Amino acids are used for synthesis of new protoplasm in the body cells.

Amino acids are used for synthesis of hormones, enzymes and plasma proteins.

Excess amino acids are converted to urea and excreted through the kidneys.

Margarine contains lipids.

Lipids are digested into fatty acids and glycerol.

Fatty acids and glycerol are absorbed into lacteals in the villi.

Glycerol and fatty acids are transported in the lymphatic system before entering the blood circulatory system.

Glycerol and fatty acids recombine to form lipids.

Lipids are used as components of the plasma membranes.

Excess lipids are stored as fat in the adipose tissue.

b)

Rice is starch.

Starch is a complex molecule which consists of polysaccharide chains.

The size of starch molecule is too big to move across the intestinal wall.

Starch needs to be broken down into smaller and simpler units.

These smaller units (monosaccharides) are able to move across the intestinal wall into the blood stream.

Salt, which is also known as sodium chloride, dissolves in water to form sodium ions and chloride ions.

Sodium ions and chloride ions are small enough to pass through the intestinal wall to be absorbed into the blood stream.

Therefore, salt does not need to be digested.

Answers to Hands on Pg 71-72

Section A

1. a) i) Daily protein need = 20/7.5 = 2.67 gkg^-1 body mass

ii) Daily protein need = 70/55 = 1.27 gkg^-1 body mass

b) A child needs more protein to build new cells and tissues for growth. A teenage boy at the age of 17 has almost reached puberty. Hence, less protein is needed because his growth rate is slower.

c) Meat and soya beans contain all the essential amino acids needed by our body. However, vegetables do not contain all the essential amino acids.

d) Vitamin D is needed for the absorption of calcium and phosphorus. A growing child needs more calcium and phosphorus for the formation of strong bones and teeth. Hence, a child needs more vitamin D. As for the teenage girl, she needs less vit D because her bones and teeth are almost completely formed.

e) A teenager needs more iron for the production of haemoglobin to transport oxygen because he/she is more active and bigger in size as compared to a child. A teenage girl will need more iron than a teenage boy because she loses blood through menstruation.

2. a) i) To study the need of light for photosynthesis

ii) To study the need of carbon dioxide for photosynthesis.

b)i) To prevent the covered part of the leaf from receiving sunlight.

ii) Solution X is potassium hydroxide solution and is used to absorb carbon dioxide from the air around the leaf.

c) i) Dark blue on the part of the leaf which is not covered with black paper.

ii) The whole leaf gives a yellowish brown colour.

d) No photosynthesis takes place on the covered part of leaf P as it does not receive any light. Leaf Q shows the absence of starch because there is no carbon dioxide for photosynthesis to take place.

e) The plant needs to be put in a dark room for 24 hours to ensure the leaves of the plant do not contain starch at the start of the experiment.

Sample question on photosynthesis

Question :
Green plants synthesize their food through the process of photosynthesis. The chemical process of photosynthesis can be summarized as in the schematic diagram below.
a) State the meaning of photosynthesis based on the schematic diagram above.
b) Starting with water and carbon dioxide as the raw materials, describe how a green plant produces starch molecules.
ANSWER
a) A process where a green plant produces glucose which will undergo condensation to form starch from carbon dioxide and water in the presence of chlorophyll and sunlight.

b)During light reaction, chlorophyll captures light energy which excites the electrons of chlorophyll molecules to higher energy levels.
In the excited state, the electrons can leave the chlorophyll molecules.
Light energy is also used to split water molecules into hydrogen ion (H⁺) and hydroxyl ions (OH^-) (Photolysis of water).
The hydrogen ions (OH^-) then combine with the electrons released by chlorophyll to form hydrogen atom.
The energy from the excited electrons is used to form energy-rich molecules of ATP.
Hydroxyl ion loses an electron to form a hydroxyl group.
This electron is then received by chlorophyll.
The hydroxyl groups then combine to form water and oxygen gas.
During the dark reaction, the hydrogen atoms are used to fix carbon dioxide in a series of reactions catalysed by photosynthetic enzymes and caused the reduction of carbon dioxide into glucose.
The glucose monomers then undergo condensation to form starch which is temporarily stored as starch grains in the chloroplasts.