AnswerKey

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AnswersChapter 1 Our Genes

1.1 Traits and Heredity Unit 1. (a) traits

(b) heredity(c) genetics(d) genes(e) fertilization(f) zygote

2. (a) The study of heredity(b) (i) Gregor Mendel

(ii) The father of genetics(iii) Garden peas(iv) Each parent donates a heredity

factor to the offspring.

1.2 Chromosomes 1. (a) Chromosomes are the thread-like

structures in the nucleus cells that carry the genes.

(b) During cell division(c) Chromatin(d)

(e) 46 2. (a) Diploid number

(b) The pair of chromosomes that is similar in size and shape

(c) 39(d) (i) 39

(ii) Haploid number 3. (a) The fusion of the female gamete and

the male gamete(b) Gamete: 19 chromosomes Zygote: 38 chromosomes

1.3 DNA and Genes

1. (a) Deoxyribonucleic acid(b) Chromosomes are made up of DNA.(c) Gene(d) Gene is a length of DNA that

determines a certain characteristic. 2. (a) DNA resembles a twisted ladder.

Each side of the ladder are made up of sugar-phosphate molecules. The rungs of the ladder are made of paired molecules called nitrogen bases.

(b)

Sugar - phosphatebackbone

Nitrogen bases

(c) (i) 4

(ii) Adenine, guanine, cytosine, thymine

3. It helps to understand how genes play the roles in hereditary diseases, and find ways to improve them.

1.4 Inheritance of Traits 1. (a) Alleles are the forms of a gene that

controls a trait.(b) (i) Dominant allele and recessive allele

(ii) The dominant allele will show its effect when it is present. A recessive allele will show its effect in the absence of the dominant allele.

2. (a) An organism that has two same alleles for a trait.

(b) An organism that has two different alleles for a trait.

(c) (i) Homozygote(ii) Heterozygote(iii) Homozygote

3. (a) Genotype refers to the alleles that an individual receives during fertilization for a trait.

(b) Phenotype refers to the physical appearance of an individual resulting from the expression of its genotype.

(c) (i) Homozygous dominant(ii) Black hair(iii) Heterozygous (iv) Black hair(v) Homozygous recessive(vi) Brown hair

1.5 Genetic Disorders 1. (a) A genetic disorder is caused by abnormal

genes or chromosomes.(b) Color-blindness, hemophilia, sickle-cell

disease, Down syndrome 2. (a) His body cannot produce blood clotting

materials to stop bleeding.(b) He bleeds easily from small cut which

may lead to death. 3. (a) A Down syndrome patient has an extra

chromosome in his body.(b) Flatter face, slanting eyes, slow learner

Map It Out

1. Gene therapy 2. Cloning 3. DNA fingerprinting 4. Genetic engineering 5. Genetic medicine

Enrichment Exercises

Objective Questions 1. A 2. D 3. B 4. C 5. B 6. D 7. C 8. A 9. B 10. A 11. D 12. C 13. D 14. D 15. B 16. A 17. D 18. B 19. C 20. A

Subjective Questions

1. (a) (i) Fertilization

(ii) Genes(b) (i) 46

(ii) 23(c) Down syndrome

2. (a) Hereditary information(b) A dominant gene is a gene which

shows its effect whenever it is present. A recessive gene will only show its effect in the absence of dominant gene.

(c) (i) Presence of dimples(ii) Presence of dimples(iii) Absence of dimples

3. (a) Abnormal gene or abnormal chromosomes

(b) Green and red(c) It is a genetic disorder where the blood

is unable to clot at a wound. Excessive bleeding may occur and may result in death.

(d) Sickle-cell disease(e) This is a genetic disorder caused by an

additional chromosome in the cells.

Chapter 2 Interdependence among Living Organisms and the Environment

2.1 Interdependence among Living Organisms

1. (a) Population (b) Ecosystem (c) Community(d) Habitat(e) Ecology

2. (a) Seaweed, prawns, fish(b) Plants make food using non-living

materials such as carbon dioxide from animals. Prawns depend on seaweed for food, oxygen and shelter. Fish feed on prawns and depend on seaweed for oxygen.

2.2 Interactions between Living Organisms

1. (a) Mutualism (b) Parasitism (c) Commensalism(d) Prey-predator(e) Competition

2. (a) (i) Competition (ii) The cats are competing for food.(b) (i) Mutualism (ii) Nodules provide a place for the

bacteria to live in. The bacteria produce nitrate for the plant.

(c) (i) Prey-predator (ii) The eagle which is the predator

catches the chick which is the prey for food.

(d) (i) Parasitism (ii) Rafflesia gets its food from the

root of the forest plant (host). The plant slowly dies.

(e) (i) Mutualism

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(ii) The hermit crab provides a place for the sea anemone to be attached to and to make its home. It also carries the sea anemone wherever it goes. The hermit crab catches its food from among the animals that move in between the sea anemone.

(f) (i) Commensalism (ii) The bird nest fern gets to live

higher up in the tree where it can get sunlight. It makes its own food and gets water from its surroundings. The growth of the bird nest fern does not affect the tree.

(g) (i) Prey-predator (ii) The tiger is the predator. It is

eating the deer which is its prey.(h) (i) Commensalism (ii) Remoras attach themselves to

the shark. They get to go where the shark goes. The shark is not affected by the presence of the remoras.

3. (a) The use of natural interaction between organisms to destroy an organism without upsetting the ecosystem.

(b) • Pesticidesarechemicalswhichcankill all organisms, including those that do not harm us.

• Pesticidescanpollutetheairandwater.

• Usingbiologicalcontrolismuchcheaper than using pesticides.

(c) • Snakesandowlsareintroducedintooil palm plantations to control the rat population (prey-predator).

• Ichneumonwaspsareintroducedinto oil palm plantations. The ich-neumon wasps lay their eggs in the caterpillars that feed on the leaves of oil plams. When the eggs hatch, the larvae will eat the caterpillars (parasitism).

2.3 Food Web

1. (a) Plants which can produce food by using energy from the Sun.

(b) Animals that eat plants and other animals.

(c) Organisms that break down dead plant and animal materials by converting them into minerals in the soil.

(d) The food relationship between organisms in an ecosystem.

2. (a) Producer – Rice plants Herbivores – Rats and grasshoppers

(b) Four(c) The Sun(d) Rice plants. They supply food directly

or indirectly to all the organisms in the community.

(e) This is because energy is used for life processes like growing, breathing, reproducing, excreting and moving.

Therefore, the more organisms involved in a food chain, the more energy will be used up and very little energy will be left for the organism at the end of the food chain.

3. (a) Grass → grasshopper → toad → snake.

(b)

Snake

Toad

Grasshopper

Grass

(c) The animals will have no food to eat and they will all die or migrate somewhere else.

2.4 Nutrient Cycles 1. (a) (i) Carbon in the soil

(ii) Fossil fuels(iii) Combustion

(b) (i) Photosynthesis(ii) The plants reduce the amount of

carbon in the air as carbon dioxide by changing it to other form, sugar.

(c) Respiration(d) Decomposers break down the organic

remains and return the carbon back into nature when they respire.

2. (a) mineral salts, water(b) the air, photosynthesis(c) fats, carbohydrates, proteins(d) transpiration, respiration(e) condenses, clouds

3. (a) (ii) (b) (i) (c) (iv) (d) (iii)

2.5 Limiting Factors of Population Size

1. The size of a population that occupies an area.

2. A factor that limits or restricts the number of individuals in a population.

3. • Limitedresourcessuchasfood,waterandliving space

• Theincreaseoftheirpredators. • Spreadofdiseases • Environmentaldisasterssuchasfloods,

wildfires, volcano eruptions and tidal waves

• Humaninterventionandpollution

2.6 Biodiversity

1. Biodiversity refers to the diverse species of plants and animals in different ecosystems on Earth.

2. • Itprovidesvariousbiologicalproductsthathave economical value such as timber, food, medicines, rubber and organic oils.

• Itprovidesmanyenvironmentalservicessuch as pollination, nutrient cycling, regulation of the atmospheric composition and weather.

• Itprovidesfood,shelterandotherbasicneeds to all living things.

Map It Out

1. Prey-predator 3. Commensalism 2. Symbiosis 4. Mutualism

Enrichment Exercises

Objective Questions 1. A 2. A 3. A 4. A 5. B 6. C 7. A 8. D 9. C 10. B

11. C 12. B 13. B 14. C 15. B 16. B 17. D 18. D 19. A 20. D

Subjective Questions

1. (a) Prey-predator(b) • Controlsthesizeofthepopulation

of rabbits • Createabalancedandstable

environment(c) • Itisbiggerinsizethantherabbit. • Ithaspowerfuljaws/sharpteeth/

sharpclaws/goodvision(d) Itcanrunfast./Itsscopeofvisionis

wide(e) Itdoesnotcausepollution./Itisnot

costly./Itdoesnotaffectthehealthofhumans.

2. (a) • Grass→ Snail → Chicken → Snake → Eagle

• Grass→ Grasshopper → Frog → Snake → Eagle

• Grass→ Grasshopper → Chicken → Snake → Eagle

• Grass→ Caterpillar → Frog → Snake → Eagle

(b) Chicken and frog(c) The population of frogs will increase.(d) The grass is able to produce its

own food through the process of photosynthesis.

(e) They break down dead animal and plant materials into simpler substances which can be used again by green plants.

3. (a) (i) Respiration(ii) Decomposition/Decaying(iii) Combustion(iv) Photosynthesis

(b) Carbondioxideisusedtomakefood./Oxygen is produced.

(c) Presence of water, sunlight and chlorophyll

Chapter 3 Natural Resources and the Environment

3.1 Environmental Issues 1. (a) Air pollution happens when the air

contains pollutants such as smoke, dirt, dust and poisonous gases in harmful amounts.

(b) (i) Acid rain is formed when gaseous pollutants from vehicles and factories dissolve in rainwater.

(ii) It corrodes metals, marble and stonework. It increases the acidity of rivers and ponds, killing small living things in them.

(c) (i) Usingscrubbers(ii) Installing catalytic converters in

vehicles 2. (a) Greenhouse effect

(b) Carbon dioxide(c) It traps heat that should be radiated

back to space, thus causing the temperature of the atmosphere to rise.

(d) Deforestation/Burningoffossilfuels(e) Trees absorb carbon dioxide during

photosynthesis and this helps to reduce the amount of carbon dioxide in the atmosphere.

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3. (a) Cause:Untreatedchemicalandradioactive waste from factories are released into rivers.

Effects: Poisons aquatic life, causes cancer and other diseases

(b) Cause: Excessive pesticides and fertilizers from farms are washed away into the rivers.

Effects: Causes rapid growth of algae and lowers the oxygen level in the water.

(c) Cause: Mud and sand from deforestation and construction sites are washed into the rivers.

Effects: Water becomes brown and muddy. Rivers become shallow.

(d) Cause: Oil spills from tankers into the seas.

Effects: Kills seabirds and marine life. 4. • Implementlawstodiscouragepeoplefrom

discharging waste materials into drains, rivers and seas.

• Conductpublicawarenesscampaignson the importance of conserving and preserving water.

• Treatsewagebeforereleasingitintoriversand seas.

3.2 Natural Resources 1. (a) Natural resources are useful materials

that are found in nature.(b) Renewable natural resources and non-

renewable natural resources

2. (a) Forest, animal, air, water(b) Coal, petroleum, metal, mineral

3. (a) Fossil fuels are the remains of plants and animals that are turned into fuels by the great heat and pressure in the Earth. Examples: Coal and petroleum.

(b) Fossil fuels are non-renewable resources that are limited and cannot be replaced quickly by the natural processes.

(c) By using other renewable resources such as solar energy, wind energy and wave energy.

4. (a) Reduce, reuse and recycle(b) • Reuseunwantedthingstomake

other useful things such as unwanted pail into a flower pot

• Reducetheuseofplasticbagsbyusing cloth bags that can be used over a time

• Recyclealuminumcans,bottlesandnewspaper

5. (a) Moderation, reasonableness and self-immunity

(b) Knowledge and virtues(c) We can plant our own forest. We can

use these trees to build our houses. The trees should be chosen wisely to avoid wastage. Replanting the trees should be done to sustain our forest.

3.3 Ecosystem and Balance 1. (a) The equilibrium that exists when the

needs of all living things are being met and the conditions remain the same for a long period of time.

(b) Changestothelivingthings/Changestoclimate/Changestothephysicalfeatures

(c) Manyspeciesmaymoveout/Somespecies may die.

(d) • Implementationoflaws • Useoftechnologytoimprovethe

ecosystem • Educatethepeopleofthe

importance of a balanced ecosystem • Usebiologicalcontrolinsteadof

pesticides and herbicides to control pests

2. New technology helps us to reduce waste by recycling aluminum cans, glass and newspaper. Besides reducing wastes, it also reduces the demand for raw materials, thus reducing mining and deforestation.

With new technology, cars using solar energy instead of fossil fuels are invented. This reduces the demands for fossil fuel, thus reducing mining and air pollution.

3. The public will understand the importance of the ecosystem and the ways to maintain a balanced ecosystem. They know the consequences of unbalanced ecosystem. Therefore they will work toward maintaining one.

Map It Out

A 1. Air pollution 2. Landpollution 3. Water pollutionB 1. Renewable natural resources 2. Water 3. Air 4. Plants 5. Animals 6. Non-renewable natural resources 7. Minerals

Enrichment Exercises

Objective Questions

1. D 2. C 3. A 4. D 5. A 6. D 7. B 8. B 9. C 10. C 11. A 12. B 13. D 14. C 15. C 16. D 17. A 18. D 19. A

Subjective Questions

1. (a) (i) Carbon monoxide prevents blood from carrying oxygen and it can cause death.

(ii) Carbon dioxide(iii) It causes global warming.

(b) (i) Chlorofluorocarbons(ii) It depletes the ozone layer.

2. (a) (i) Renewable resources are natural resources that are replaceable by ongoing natural processes.

(ii) Forest/Air/Animals/Water(b) (i) Non-renewable resources are

natural resources that are available in limited amount and are not quickly replaced by natural processes.

(ii) Coal/Petroleum/Metal/Minerals(c) Uselessnon-renewableresources/

Userenewableresources/Recycle(d) Wind turns the windmills to generate

electricity.

3. (a) The equilibrium state that exists when the needs of all living things are being

met and the conditions remain for a long period of time.

(b) Soilerosion/Landslides/Extinctionofflora and fauna

(c) (i) Catalytic converters convert harmful gases into harmless gases

(ii) Bacteria are used to break up the oil.

(d) • Therenewableresourcesareinexhaustible.

• Theyarepollutionfree.

Chapter 4 Forces and Motion

4.1 Acceleration 1. (a) Acceleration is the rate of change of

velocity.

(b) Acceleration = Change in velocity

Time

2. (a) (i) Acceleration = 24 – 66

= 3 m s–2

(ii) The velocity of the bus increases by 3 m s–1 every second.

(b) (i) Acceleration = 8 – 185

= –2 m s–2

(ii) The velocity of the motorcycle decreases by 2 m s–1 every second.

3. (a) Newton’sSecondLawofMotionsaysthat when a resultant force acts on an object,theaccelerationoftheobjectis directly proportional to the resultant force and has a magnitude that is inversely proportional to its mass.

(b) Resultantforce=Massoftheobject× Accelerationoftheobject

4. (a) 6 N(b) To the left(c) F = ma a =

Fm

= 660

= 0.1 m s–2

5. (a) F = ma = 10 × 2 = 20 N

(b) Resultant force = F1 – frictional force F1 = 20 + 8 = 28 N

(c) a = v – u

t v = at + u = (2 × 8) + 0 = 16 m s–1

6. (a) Theweightofanobjectistheforceofgravitywhichactsontheobject.

(b) Weight = mass × force of gravity = 990 × 9.8 = 9702 N

4.2 Action and Reaction Forces

1. Newton’sThirdLawofMotionstatesthatwhenanobjectexertsaforceonasecondobject,thesecondobjectexertsaforceofequal magnitude but opposite in direction on thefirstobject.

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2. (a)

Action force

Reaction force

(b)

Bullet

Reaction forceAction force

(c) Reaction forceAction force

4.3 Buoyant Forces and Liquid 1. Buoyant force is an upward force which acts

onanobjectthatisbeingcompletelyorpartially immersed in a fluid.

2. It states that the buoyant force acting on a completelyorpartiallyimmersedobjectisequal to the weight of the fluid it displaces.

3. (a) 8 N(b) 7.5 N(c) 8 N – 7.5 N = 0.5 N(d) 0.5 N

4. (a) The buoyant force that acts on the boat is equal to the weight of the boat.

(b) The weight of the anchor is more than the maximum buoyant force acting on it.

5. (a) opened(b) air(c) sea water(d) greater(e) air(f) sea water(g) less

4.4 Static Friction and Kinetic Friction 1. (a) Friction is a force that stops movement

of two contacting surfaces and acts in the direction that opposes motion.

(b) The surfaces are not smooth.

2. (a) Static friction acts on two contacting surfaces that are not moving when a force is applied.

(b) Kinetic friction acts on two contacting surfaces that are moving when a force is applied.

(c) Static friction

3. (a) a = v – u

t

= 10 – 0

10 = 1 m s–2

(b) F = ma = 1000 × 1 = 1000 N(c) Resultant force = Applied force –

friction Friction = Applied force – resultant force = 3000 N – 1000 N = 2000 N

(d) Kinetic friction

4.5 Moment of Force

1. Moment of force is the measure of the ability ofaforcetoturnorrotateanobjectthatitacts on.

2. (a) Clockwise moment: 100 N × 60 m = 6 000 Nm Anti-clockwise moment: 150 N × 40 m = 6 000 Nm The lever is balanced.

(b) Clockwise moment: (30 N × 20 cm) + [30 N × (20 + 60) cm] = (30 N × 0.2 m) + (30 × 0.8 m) = 30 Nm Anti-clockwise moment: 80 N × 30 cm = 80 N × 0.3 m = 24 Nm The lever is not balanced.

3. Clockwise moment = Anti-clockwise moment (0.8 – X) × 20 = X × 12 16 – 20X = 12X 32 X = 16 X = 0.5 m

4.6 Motions of Objects

1. (a) Linearmotion(b) Projectilemotion(c) Circular motion

Map It Out

A 1. Static friction 2. Kinetic frictionB 1. Linearmotion 2. Circular motion

Enrichment Exercises

Objective Questions 1. B 2. B 3. D 4. A 5. B 6. D 7. C 8. C 9. C 10. A 11. D 12. B 13. C 14. A 15. C 16. A 17. B 18. D 19. B 20. C

Subjective Questions

1. (a) Weight = 9.8 × 200 = 1960 N

(b) F = ma a = F

m

= 400200

= 2 m s–2

(c) a = v – ut

= 8 – 0

10

= 0.8 m s–2

F = ma = 200 × 0.8 = 160 N

2. (a) For a complete or partially immersed objectinafluid,thebuoyantforceactingontheobjectisequaltotheweight of the fluid it displaced.

(b) (i) 9 N(ii) 8.5 N(iii) 50 cm3

(iv) 0.5 N(c) The apparent loss of weight of the

objectimmersedinwaterisequaltothe weight of the water displaced.

3. (a) Moment of force is a measure of the ability of a force to turn or rotate an objectonwhichitactson.

(b) Anti-clockwise moment = 20 N × 6 m = 120 Nm Clockwise moment = (6 N × 4 m) + (8 N × 12 m) = 24 Nm + 96 Nm = 120 Nm The lever is balanced.(c) Anti-clockwise moment = Clockwise

moment 80 N × X m = 60 N × 40 m

X = 240080

= 30 m

Chapter 5 Energy Changes

5.1 Forms of Energy 1. (a) (i) work

(ii) joule(b) matter(c) different(d) potential(e) kinetic(f) heat(g) sound(h) chemical(i) nuclear

2. (a) Chemical energy(b) Sound energy(c) Heat energy(d) Potential energy(e) Electrical energy(f) Lightenergy(g) Nuclear energy(h) Kinetic energy

3. (a) Potential energy(b) Potential energy(c) Chemical energy(d) Sound energy(e) Kinetic energy(f) Electrical energy

5.2 Energy Changes

1. Energy can change from one form to another, but it cannot be destroyed or created.

2. (a) Chemical energy → Kinetic energy → Sound energy

(b) Potential energy → Kinetic energy(c) Chemical energy → Heat energy +

Lightenergy(d) Chemical energy → Electrical energy →

Lightenergy+Heatenergy(e) Electrical energy →Lightenergy+

Sound energy

3. (a) Potential energy(b) Potential energy + Kinetic energy

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(c) Potential energy(d) Sound energy + Heat energy

4. (a) Potential energy. This is because position P is the highest point.

(b) Potential energy to kinetic energy(c) Kinetic energy. This is due to its velocity

and position R is the lowest point.

5. (a) (i) Its potential energy is the greatest as it is at the highest point. It does not have any kinetic energy as it is not moving.

(ii) Its kinetic energy is the greatest as its velocity is the greatest and it is at the lowest point.

(iii) Its potential energy is the greatest as it is at the highest point. It does not have any kinetic energy as it is not moving.

(b) (i) Potential energy to kinetic energy(ii) Kinetic energy to potential energy

Map It Out

1. Kinetic energy 2. Chemical energy 3. Nuclear energy 4. Heat energy 5. Electrical energy 6. Potential energy

Enrichment Exercises

Objective Questions 1. A 2. A 3. D 4. B 5. C 6. D 7. C 8. B 9. A 10. D 11. C 12. A 13. D 14. B 15. A 16. B 17. D 18. C 19. A 20. A

Subjective Questions

1. (a) (i) Energy is the ability to do work.(ii) Joule

(b) (i) The greater the speed of a moving object,thegreaterisitskineticenergy.

(ii) The larger the mass of a moving object,thelargerisitskineticenergy.

(c) • Massoftheobject • Heightoftheobjectabovethe

ground • Strengthofthegravitationalforce

ontheobject 2. (a) Energy can be changed from one form

to another, but it cannot be destroyed or created.

(b) Chemical energy → Kinetic energy → Electrical energy → Lightenergy+heatenergy

(c) Chemical energy → Electrical energy → Lightenergy+ Heat energy

3. (a) (i) L(ii) P

(b) (i) Kinetic energy and potential energy(ii) Kinetic energy and sound energy

(c) 200 J

Chapter 6 Electricity

6.1 Electricity 1. (a) Electricity is a form of energy.

(b) Battery, solar cell

2. (a) The rate of flowing electrical charges.(b) The difference in electrical potential

energy.(c) The measure of how an electrical

component resists current flow.

3. (a) electrical energy (b) negative (c) positive(d) positive(e) negative

6.2 Measuring Electricity 1. (a) X : Voltmeter Y : Ammeter

(b) X : Voltage; volt Y : Current; ampere

2.

V

A

Battery

Ammeter

Voltmeter

Bulb

6.3 Current, Voltage and Resistance

1. (a) (i) Resistance(ii) Current(iii) Voltage

(b)

2

4

6

0 1 2 3 Current, I

Voltage, V

(c) Current is directly proportional to voltage.

2.

A

Battery

Resistor

Ammeter

3. (a) (i) current(ii) proportional(iii) voltage

(b) V = I × R

6.4 Parallel and Series Circuit

1. (a) A

(b) Dry cells (c) Bulb

(d) V

(e) Galvanometer(f) Variable resistor

2. (a)

V

A

or

V

A

(b)

V

A

6.5 Current, Voltage and Resistance in a Series Circuit

1. (a) Series circuit(b) V3 = 3 V, V4 = 3 V(c) The current of a series circuit is the

same at every point and all the bulbs are the same.

(d) The others are also not working because the circuit is broken.

2. (a) the same (b) I1 = I2

(c) R1 + R2 + R3 (d) V1 + V2 + V3

(e) adding more(f) fail too

6.6 Current, Voltage and Resistance in a Parallel Circuit

1. (a) 12 V(b) A1 = 2.4 A A2 = 1.2 A(c) 3.6 A

2. (a) (i) Parallel circuit(ii) Series circuit

(b) (i) The other bulbs are working.(ii) The other bulbs are not working.

(c) P(d) In circuit Q, the bulbs share the voltage

of 240 V. So each bulb glows dimly. In circuit P, each bulb gets the full voltage of 240 V. So each bulb glows brightly.

6.7 Electronic Circuits 1. (a) electronic circuits

(b) computers(c) amplifiers

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2. (a) (i) Variable resistor(ii) To control the voltage in the circuit.

(b) (i) Diode(ii) To control the flow of current in

one direction only in the circuit.

3. It contains many complete circuits with transistors, diodes and other components on a tiny silicon chip.

6.8 Cost of Electrical Energy 1. (a) Power (W) =

Electrical energy (J)Time (s)

(b) Power (W) = Voltage (V) × Current (A)(c) Electrical energy (J) = Power (W) × Time (s)

2. (a) Energy used = power × time

= 460 W1000 ×

50060 hour

= 3.83 kWh

(b) Cost of energy used = 3.833 kW × 2 Baht = 7.67 Baht

3. (a) Energy used by kettle

= 1 kW × 3060 hour

= 0.5 kWh

Energy used by fan

= 1501000

kW × 8

= 1.2 kWh

Energy used by 4 bulbs= 4 × 100

1000 × 6

= 2.4 kWh

Total of energy used in a day = 0.5 + 1.2 + 2.4= 4.1 kWh

Total of energy used in a month= 4.1 × 30= 123 kWh

(b) Cost of energy used = (100 × 2 Baht) + (23 × 3 Baht) = 269 Baht

6.9 Importance of Safety Precautions in the Use of Electricity

1. (a) hot and melts, rating, blows, damage.(b) Earth wires, two-pin, live, neutral.(c) leakage, 30 mA, switch off.(d) safety device, short circuit, current, cut

off.

2. (a) (i) Do not touch switches or electrical appliances with wet hands.

(ii) Do not connect too many electrical appliances to one source.

(iii) Do not try to put things other than a plug into a socket.

(b) (i) Damaged insulation.(ii) Overheating of cables.(iii) Damp conditions.

(c) The safety features help prevent fires, electrocutions and electric shocks.

Map It Out

1. Both are complete, closed circuits. 2. I = I1 =I2

3. I = I1 + I2

4. V = V1 + V2

5. V = V1 = V2

6. R = R1 + R2

7. 1R

= 1R1

+ 1R2

Enrichment Exercises

Objective Questions 1. A 2. A 3. D 4. A 5. D 6. D 7. C 8. D 9. D 10. A 11. D 12. D 13. C 14. D 15. C 16. D 17. C 18. B 19. B 20. D 21. C 22. D

Subjective Questions

1. (a) X : Ammeter to measure the current. Y : Voltmeter to measure the voltage.

(b) The bulb with the resistance of 4 Ω will not be affected but the bulb with the resistance of 3 Ω will not light up.

(c) 1R =

14 +

1(3 + 1)

= 12

R = 2 Ω V = IR I =

32 A

= 1.5 A

2. (a) Current = 660 W220 V

= 3 A(b) 4 A(c) A slightly higher rating fuse should be

used. So if there is a fault, the fuse will blow and break the circuit.

Chapter 7 Solar System, Stars and Galaxies

7.1 Planets 1. (a) Mercury

(b) Venus (c) Earth (d) Mars(e) Jupiter(f) Saturn(g) Uranus(h) Neptune

2. (a) A planatery system is a group of planets and moons which travel around a star.

(b) Jupiter(c) The further the planet from the Sun, the

longer the duration it takes to complete one orbit.

(d) Its surface is covered with iron oxide which is reddish in color.

7.2 Asteroids, Comets and Meteoroids

1. (a) Asteroids are small rocks that orbit the Sun.

(b) Most asteroids are located between the orbits of Mars and Jupiter.

(c) Meteoroid is a lump of dust, rocks and metals in the Solar System. When it enters Earth’s atmosphere, it usually burns up. The trail of glowing vapor is

called meteor. A meteorite is a meteor that has fallen on Earth.

2. (a) Asteroid belt(b) Asteroid belt is made up of lumps

of rocks orbiting between Mars and Jupiter.

3. (a) Comets are made up of dust and rocks mixed with frozen water, methane and ammonia.

(b) When a comet’s orbit takes it close to the Sun, the Sun will melt some of its ice. This creates a hazy cloud millions of kilometres long that looks like a tail.

(c) Halley’s Comet

7.3 Sun

1. (a) Photosphere (b) Chromosphere (c) Corona (d) Inner core (e) Solar flares(f) Sunspot(g) Prominence

2. (a) Solar flares (b) Sunspots (c) Prominence

3. (a) hydrogen, helium (b) heat, light (c) hydrogen (d) nuclear fusion(e) 5000 million

7.4 Stars and Galaxies

1. (a) A constellation is a group of stars with a pattern of an animal or a familiar object.

(b) (i) Orion(ii)

(c) A star map is used to locate the position of the stars and constellations in the sky.

2. (a) 6(b) 2(c) 3(d) 4(e) 1(f) 5

3. (a) A red giant is formed.(b) A white dwarf is formed.(c) A black dwarf is formed.(d) A red giant is formed.(e) A red supergiant is formed.(f) Supernova explosion.(g) A neutron star is formed.(h) A black hole is formed.

4. (a) Elliptical galaxy(b) Spiral galaxy(c) Irregular-shaped galaxy(d) M87, NGC147(e) Milky Way, Andromeda(f) LargeMagellanicCloud,Small

Magellanic Cloud

7

7.5 Existence of the Universe

1. (a) There are thousands of galaxies in the Universe.

(b) The Sun gives out light. The Sun gives out warmth. Green plants use sunlight during

photosynthesis to produce food.(c) The galaxies keep on expanding

outward from their boundaries and new galaxies are formed in space.

7.6 Sun-Earth-Moon

1. (a) Summer, autumn, winter, spring(b) The Earth rotates around the Sun. The

Earth is tilted.(c) P : Spring Q : Summer R : Autumn S : Winter(d) Q : Winter S : Summer(e) Thailand is situated near the Equator.

2. (a) Eclipse of the Sun or solar eclipse(b) The shadow of the Moon falls on the

Earth, blocking the Sun.(c) Y : Partial eclipse Z : Total eclipse(d) (i) Eclipse of the Moon or lunar

eclipse(ii) The shadow of the Earth falls

on the Moon, making the Moon disappear from our view for a few hours.

(iii) Night-time

3. (a) Tides are the alternate rising and falling of the ocean in a day.

(b) The gravitational force of the Moon pulls the water body toward it.

(c) (i) The Sun, Moon and Earth are in a line. The gravitational force of the Sun and Moon are combined to give those effects.

(ii) Spring-tides(d) The tides influence navigation, fishing

and water-related sport activities.

Map It Out

A 1. Medium-sized star 2. Red giant 3. Largestar 4. Red supergiant 5. Supernova

6. Neutron star 7. Very large star 8. Red giant 9. Red supergiant 10. SupernovaA 1. Eclipse 2. Day and night 3. Seasons 4. Lunareclipse

Enrichment Exercises

Objective Questions 1. C 2. C 3. B 4. D 5. A 6. D 7. B 8. A 9. C 10. C 11. A 12. C 13. B 14. A 15. D 16. A 17. B 18. D 19. D 20. C 21. B 22. C 23. C 24. B 25. C 26. A 27. D 28. A 29. A 30. B

Subjective Questions

1. (a) Solar flares(b) Radio and television programme

reception(c) (i) Prominence

(ii) During a solar eclipse(d) (i) About 150 million kilometres

(ii) Lightyears(e) The Earth is about 110 times smaller

than the Sun. 2. (a) When all the hydrogen in its core is

used up.(b) The nuclear reactions that release heat

and occur at the core stop.(c) A supernova explosion(d) (i) A black hole or a neutron star

(ii) A black dwarf(e) New stars and galaxies are constantly

being formed. 3. (a) The Moon reflects the light from the

Sun.(b) (i) We see different areas of the Moon

surface that are lit up when it moves around the Earth.

(ii) Phases of the Moon(c) M : Old Half Moon N : Old Cresent Moon O : New Moon P : New Cresent Moon Q : New Half Moon R : New Gibbous Moon S : Full Moon T : Old Gibbous Moon(d) 29.5 days

Chapter 8 Space Exploration

Astronomy and Space Exploration

1. (a) The scientific study of stars and planets.

(b) The area outside the Earth’s atmosphere.

2. (a) Galileo Galilei(b) HansLippershey(c) Yuri Gagarin(d) Neil Armstrong, Edwin Aldrin

3. (a) Robert Goddard(b) SovietUnion(c) Sputnik II(d) Apollo II(e) space shuttle

4. (a) To monitor the weather.(b) To spy on enemy troop movements and

manoeuvres.(c) To receive and transmit radio, television

and telephone signals.(d) To give the location of ships, aircraft or

people.

Map It Out

1. Communication 2. Weather forecasting 3. Remote sensing 4. Military purposes

Enrichment Exercises

Objective Questions 1. B 2. C 3. C 4. A 5. D 6. B 7. A 8. B

Subjective Questions

1. (a) An unmanned spacecraft usually sent to explore other planets.

(b) A probe can carry out simple tasks such as collecting soil samples and can move over a planet’s surface. A satellite is launched into space and orbits the Earth.

(c) Both can take photographs and transmit information back to Earth.

(d) Intelsat 2. (a) To send astronauts and equipments to

space.(b) A rocket can only be used once,

whereas a space shuttle can be reused.(c) Discovery(d) TheUnitedStatesofAmerica(e) RussiaandUnitedStatesofAmerica

8.1