9.4.1 Human Activities that Endangered an Ecosystem (Structured Question 1 & 2)

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Question 1:
(a) Diagram I shows the effects of farming activities near a pond.

Explain how the farming activities cause the death of the aquatic plants and the fishes in the pond.
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Diagram II shows a new industrial area situated near a residential area.

Discuss the good and the bad effects caused by the industrial activities on human and environment in years to come.

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- Farmers use fertilisers that usually contain nitrates and phosphates.
- Fertilisers which contain nitrates/ phosphates may leach into the pond when it rains.
- Algae in the lake grow faster.
- They may grow so much that they completely cover the water.
- Black out the light for plants growing beneath them.
- Photosynthesis rate is reduced.
- Dissolved oxygen also reduced.
- Plants on the top of the water and beneath the water eventually die.
- Their remains are a good source of food for bacteria.
- Bacteria decomposed the dead plant rapidly.
- The large population of bacteria respires, using up oxygen, so there is very little oxygen left for other living organisms.
- BOD increased.
- Water population increases.
- Those aquatic plants and fish which need oxygen die.

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- More job opportunities
- More economic activities and development projects
- Attract tourists
- Improve infrastructure

- Can cause respiratory problems/ asthma/ bronchitis/ irritates the eye
- Crime rate increases

- Industries emit poisonous gases such as sulphur dioxide/ oxides of nitrogen/ smoke/ fine solid particles
- Contribute to air pollution
- Oxides of nitrogen and Sulphur dioxide dissolve in rain water to form acid rain.
- Makes the soil acidic and unsuitable for the cultivation of crops
- Smoke and haze reduce light intensity reaching stomata and cause the rate of photosynthesis to decrease
- Which subsequently reduces crop yield
- Carbon dioxide leads to the greenhouse effect, resulting in an increase in the atmospheric temperature
- Cause the extinction of organisms

6.4.3 The Need for Proper Handling of Radioactive Substances (Structured Questions)

Question 1:
(a) Diagram 1.1 and 1.2 shows activities which involved the radioactive substances.

(i) State the radioactive radiation used in medical field in Diagram 1.1. [1 mark]

(ii) State the uses of Carbon-14 in Diagram 1.2. [1 mark]

(iii) State one effect of nuclear explosion to human being. [1 mark]

(iv) What substance is used to make a container to keep radioactive substance safe? [1 mark]

(b) Diagram 1.3 shows the nuclear power station.

(i) Name the radioactive substances used in Diagram 1.3. [1 mark]

(ii) State the energy generated from the power station in Diagram 1.3. [1 mark]

Gamma radiation

To estimate the age of ancient objects

Can cause serious health problems or even death

Thick concrete/ Thick lead


Electrical energy

6.4.2 Production of Nuclear Energy and Its Uses (Structured Questions)

Question 1:
Diagram 1 shows a nuclear fission process of radioactive substance.

(a) Name energy S and ray T in the boxes provided in Diagram 1. [2 marks]

(b) State one use of:
(i) Energy [1 mark]
(ii) Ray T in medical field.[1 mark]

(c) State one method to detect the presence of ray T. [1 mark]

(d) What is the effect on human beings if exposed to ray T. [1 mark]

Energy S: Nuclear energy
Ray T: Radioactive radiation


- To generate electrical energy
- To generate large amounts of heat and light in nuclear explosions
(any one)


- Used as radioactive tracers
- Used for sterilising medical supplies
- Used in radiotherapy treatment to kill certain cells such as cancer cells
(any one)

Use a detector such as the Geiger-Muller counter.

Causes radiation sickness, internal bleeding, infertility, cancer and mutations. 

6.4.1 Radioactive Substances (Structured Questions)

Question 1:
Diagram 1 shows three radioactive radiations, P, Q and R.

(a) Name radioactive radiations P and R. [2 marks]

(b) State the charges of radioactive radiation P and Q.[2 marks]

(c) Name the substance that can stop the penetration of radioactive radiation R. [1 mark]

(d) Name the radioactive radiation which is used to kill cancer cells. [1 mark]

P: Alpha radiation
R: Gamma radiation

P: Positively charged
Q: Negatively charged

(c) Thick block of lead or concrete.

(d) Gamma radiation

Question 2:
Diagram 2 shows the use of a radioactive substance in food preservation.

(a) State the function of gamma radiation in this process. [1 mark]

(b) State two uses of gamma radiation other than food preservation.[2 marks]

(c) Name one material which can stop gamma radiation. [1 mark]

(d) State two dangerous effects of gamma radiation to human beings. [2 marks]

To kill microorganisms in the potatoes without changing their taste and appearance.

- To kill cancerous cells
- To control the thickness of paper, plastic or metal
- To kill or sterilize pests
(any two)

Lead which is a few centimetres thick

- Kills body cells
- Causes cancer
- Causes mutation
(any two)

6.3 Proper Handling of Radioactive Substances

6.3 Proper Handling of Radioactive Substances

6.3.1 Effects of Radioactive Radiation on Living Things
1. Radioactive substances are highly hazardous.
2. The energy in radiation can destroy molecules in living tissues and kill cells.
3. The effects of radioactive radiation on living things depend on the total amount of radiation received.
4. Diagram below shows effects of exposure to radioactive radiation over different period of time:

6.2.3 Process of Generating Electricity from Nuclear Energy

6.2.3 Uses of Nuclear Fusion
1. Nuclear energy is used to
(a) Generate electrical energy
(b) Operate satellites
(c) Propel cruises, aircraft carriers and submarines

Nuclear power station

6.2.4 Process of Generating Electricity from Nuclear Energy
1. In a nuclear power station, nuclear energy is produced in a nuclear reactor to generate electricity.
2. Figure below shows the main components in a nuclear power station.

 Nuclear power station

Graphite moderator
Fast moving neutrons are slowed down by collisions with nuclei in the moderator so that they can cause further fission. In some nuclear power plant, the moderator is water.
b.  Uranium rod (Fuel)
Produces nuclear energy from chain reactions of nuclear fission.
c.  Control rod
Control the rate of chain reaction.
d.  Coolant
To take away the heat from the nuclear reactor.
e.  Thick concrete wall
To prevent the escape of harmful radiations.
f.   Steam generator
Water in the generator is heated and changed into steam. The steam then drives the turbines.
g.  Turbine
To turn the dynamo in the electrical generator to produce electricity.

3. Figure below shows the summary of the process taking place and transformation of energy in a nuclear power station.

Energy transformation during generation of electricity

8.7.1 The Abiotic and Biotic Components of the Environment (Structured Question 1 & 2)

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Question 1:
R, S and T in Figure below show three types of interactions between organisms.

Name the type of interaction represented by R and S.

Describe the interaction represented by R.
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In the interactions represented by S and T, what terms are used to describe organisms X and Y?

State one characteristics of organism X that adapts it for the interaction.

The rubber tree in the interaction represented by S dies.
Explain what will happen to organism X.

Saw dust can be used in the interaction represented by T for the commercial cultivation of mushrooms.
Explain how mushrooms can grow on saw dust.

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Organism R: Mutualism/ symbiosis
Organism S: Commensalism

Nitrogen-fixing bacteria in the root nodules fix nitrogen to form ammonia which is used by the plant while Rhizobium bacteria get shelter from the plant.
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X: Epiphyte
Y: Saprophyte

The presence of aerial roots which absorb moisture from the air

X continues to grow because it photosynthesises.

Mushrooms grow on dead organic matter.
Mushrooms secrete enzymes which digest the complex organic matter to simple substances.

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6.2.2 Nuclear Fusion

6.2.2 Nuclear Fusion
1. Nuclear fusion is a process that two light nuclei combine to form a heavier and more stable nucleus together with the release of a huge amount of nuclear energy.

Nuclear fusion

The energy produced by nuclear fusion is safe to use as no radioactive radiation is produced during the process.
3. A hydrogen bomb uses the principle of nuclear fusion for its design. A hydrogen bomb releases more nuclear energy than an atomic bomb.
4. Fusion is much more difficult to achieve than fission because the hydrogen nuclei repel each other.
5. Fusion reactor is not commercially produced because nuclear fusion occurs at a very high temperature and pressure.
6. Nuclear fusion only occurs naturally in the sun to release heat energy and light energy.

6.2.1 Production of Nuclear Energy and Its Uses

6.2.1 Production of Nuclear Energy and Its Uses
Nuclear energy can be produced in nuclear reactors through the following two methods:
(a)  Nuclear fission
(b)  Nuclear fusion

6.2.1 Nuclear Fission
1. Nuclear fission is a process involving the splitting of a heavy nucleus into two nuclei of roughly equal mass and shooting out several neutrons at the same time.

Nuclear fission of uranium to produce nuclear energy

Nuclear fission occurs when a high energy neutron bombards a uranium nucleus. The nucleus becomes unstable and splits into two (or more) lighter nuclei with the release of two or three neutrons and a large amount of nuclear energy.
3. The nuclear fission can only occur in some types of heavy and unstable nuclei such as uranium-235 and plutonium-239.
4. A chain reaction occurs as the process of nuclear fission keeps on repeating. The neutrons produced will bombard more uranium-235. The chain reaction produces more neutrons and releases more nuclear energy.
5. Uncontrolled chain reaction occurred when atomic bombs exploded in Hiroshima and Nagasaki in Japan during Second World War. Thousands of lives were lost and properties destroyed.

6.1 (C) Radioisotopes

(C) Radioisotopes
Radioisotopes are isotopes of a radioactive substance.

Examples of Radioisotopes
Carbon-14 (Carbon dating)
Cobalt-60 (Radiotherapy)
Uranium-235 (Nuclear fuel)
Plutomium-239 (Nuclear fuel)

Uses of Radioisotopes
1.   There are two types of isotopes, namely
a.   the stable isotopes (non-radioactive)
b.   the non-stable isotopes (radioactive).
2.  Unstable isotopes go through radioactive decay and emit radiation and they are known as radioisotopes.
3.  Radioisotopes have many applications in industry.

Uses of Radioisotope in Medical
Gamma rays of cobalt-60 can be used to destroy cancer cells in patients. This treatment is known as radiotherapy.

Tracer to Detect Blood Clots or Tumour
1.   A small amount of sodium-24 is injected into the patient's body.
2.  Radioactive imaging is then used to detect accumulation of sodium-24 and therefore detect tumours and blood clots before they become dangerous.

Sterilising Medical Instrument
1.   Gamma ray emitted from radioactive cobalt-60 can kill germs such as bacteria and fungus.
2.  Medical instruments such as surgical equipment, syringes and bandages can be sterilised by using gamma rays.

Uses of Radioisotope in Agriculture
Pest Control

Male insect is sterilised by exposing to radioactive radiation and then released back to the ecosystem. This can ensure that their reproducing effort do not generate new generation and hence reduces the population of the insect.

1.   The metabolism of phosphorus by plants can be studied using phosphate fertilisers that contain phosphorus-32.
2.  A small amount of phosphorus-32 is used in fertilisers.
3.  The radiation produced by phosphorus-32 decay is detected by a Geiger-Muller counter. This method can trace the passage of phosphate ions in plants.
4.  Carbon-14 is used to study the passage of carbon during photosynthesis in plants.

Develop New Species of Plant
1.   Radioactive radiation is targeted to the seeds of plants and hence causes mutation to the genes.
2.  By chance, this may develop some superior agricultural products.


Radioisotope carbon-14 is used to study and estimate the age of ancient artifacts. This method is named as the radiocarbon dating.

Preserve Food

1. The gamma rays from cobalt-60 are used to kill bacteria in food to make fresh vegetables and fruits last longer without any change in quality, flavour and texture of food.
2.  Gamma rays are used to inhibit budding in potatoes and germinating in onions.

Monitoring Thickness of Steel/paper Sheet

 1. In a factory, the thickness of paper can be controlled by measuring the quantity of radiation penetrating the paper with the Geiger-Muller counter.
2. Apart from paper, the thickness of plastic, aluminium or iron can also be controlled by using beta rays.

Detecting Underground Leakage

1. A small quantity of radioactive substance is put into water, gas or oil in an underground pipe.
2. The movement of the radioactive substance can be traced by using the Geiger-Muller counter.

Monitoring Content of Food


1.   Radiation is used for checking whether a food container has the right amount of food stuff.

Measuring the Wearing Rate of Engine