BECE Past Questions & Answers – 2009 (SCIENCE)

SCIENCE2

SOLUTIONS

ESSAY

1. (a) (i) Temperature = 100°C or212°For 373K

(ii) Observations (Nails)

Nails 1, 2, 3 and 4 will drop off one after the other

– Nail1 drops first, nail 2 second, nail3 third andnail4fourth

(iii) Observations(Thermometers)

The readings of Thermometers A,B, C and D will increase progressively till they reach
100°C
– Thermometer A reaches 100°C first, B second,C third and D fourth

(iv) Mode of heat transfer – Conduction

(v) Effects of heat

 Causes increase in temperature(as shown by the thermometer readings)

 Causes change in state (candle wax melts– changes from solid to liquid)

(vi) Aim of experiment

 To show that metals are good conductors of heat

 To show that heat travels through metals

(b) (i) Why water inset-upBwas boiled

To remove dissolved air /oxygen from the water

(ii) The function of the oil on top of the water inset-up B

To prevent air(hence, oxygen) from entering/getting dissolved in the water

(iii) The purpose of the rubber stopper inset- up C

To prevent water particles or vapour or moisture from entering and contacting the nail

(v) Aim for the experiment

 To show that moisture/ water and oxygen/ air are necessary for rusting to occur.

(vi) Why grease is applied on metals to prevent rusting

To prevent moisture and air, which contains oxygen, from getting into contact with the metal, since metals containing iron will rust in the presence of air and moisture.

(c) (i) Why each activity was carried out

I – to kill the plant cells or stop the process of photosynthesis
II – remove the green pigment (chlorophyll)
III – to wash away the alcohol and soften the leaf
IV – to test for starch in the leaf

(ii) Colour change of leaf A

From cream /pale yellow / light brown to blue-black

(iii) The blue-black colouration indicates thepresenceof starch, which means that photosynthesis occurred inleafA to produce starch.

Leaf B did not change in colour because photosynthesis did not occur, and hence, no starch was produced.

2. (a) (i) Reasons for no green plants in the dark ocean depths

No light reaches there, hence no photosynthesis takes place.

(ii)
Reasons for no fruits on pawpaw plant,where there are no insects and birds
Since there are no agents of pollination, no pollination takes place; hence, no fertilization
takes place.As aresult, no fruits are produced.

(b) How soil is formed:

Soil is formed from the disintegration/ breakdown/ weathering of rocks.The broken down rock particles combine with water, decayed organic matter,air and micro organisms to form soil

(c) (i) Laws of reflection

 The angle of incidence is equal to the angle of reflection

 The incident ray, the reflected ray and the normal,at the point of incidence,all lie in the same plane

(ii) Labelled diagram

i = angle of incidence, r = angleof reflection

3. (a) (i) Deficiency disease: Night blindness

(ii)
Food nutrient:
Vitamin A

(iii)
Foodsources:

Milk, butter, cheese,egg yolk, liver,palmoil, tomatoes, carrots, lettuce,cod-liver oil,

(b) (i) Atom

• The smallest particle of a substance that can take part in a chemical reaction

• The smallest portion into which an element can be divided and still retain its properties

(ii) Components of atom that determine

(α) mass ofatom: protons and neutrons

(β) charge of atom: protons and electrons

(iii) Why an atom is electricallyneutral:

Thenumbers of protons and electronsare equal.Thepositivelycharged protons neutralize the negativelychargedelectrons, hence, makingthe atomelectricallyneutral.

(c) (i) Friction is

The force that opposes the relative sliding motion of two bodies in contact
Or:
The resistance encountered by an object moving relative to another object with which it is
in contact

(ii)
Bad effects of friction
 Reduces the efficiency of machines
 Causes wear and tear
 Causes loss of energy through heat generation
 Slows down sliding motion of a body

(iii)
Situations where friction is an advantage
 Enables walking, running, etc without slipping
 Enables vehicles to brake effectively
 Enables birds to perch on trees without falling
 Enable wheels to roll on a surface
 Enables our hands to hold items

4.
(a)
(i)
Heredity

The passing on of genetic factors from parents to children through genes:
Or: the transfer of genetically controlled characteristics from one generation to the next in living organisms

(ii)

Examples
Intelligence, shape of nose, height, colour of eyes,etc

(b) Explanationofwhetherchemical orphysical change:

(i) Rusting – Chemical change; because a new substance is formed and the change is irreversible
(ii) Burning – Chemical change; because a new substance is formed and the change is irreversible
(iii) Filtration – Physical change; because no new substance is formed and the change is reversible

5.

Gravitational, tensional,centripetal, centrifugal,magnetic, electrostatic, upthrust, cohesive, adhesive

(ii) Effects ofa force
• Can cause a moving body to come to rest (stop moving)
• Can cause a body at rest to move
• Can cause a moving body to accelerate
• Can cause a moving body to decelerate
• Can change the direction of a moving body
• Can change the shape of a body

(c) (i) The eye defect: short sightedness or myopia

(ii)
Explanation

Light rays from a distant object are focused infront of the retina, due to the eye lens being thicker than normal or eye ball being too long. Hence the brain does not receive the correct information for interpretation and so the child is unable to see.

(iii) Howthedefect can be corrected: Bythe use of aconcaveordiverginglens