BECE Past Questions & Answers – 2008 (SCIENCE)

SCIENCE2

SOLUTIONS

ESSAY

1. (a) (i) The height of the red liquid will increase as the height of the water reduces

The red liquid mixes with the water as its particles move into the water

(ii) Since the water is higher,it has greater pressure. Therefore it moves in the direction of the lower pressure

Diffusion occurs as the molecules of the red liquid move from a region of higher concentration to the water region, which is of lower concentration

(iii) A liquid uniform mixture, which has the same colour and concentration, will be formed

Since the mixture is essentially uniform, but the containers are of different sizes, the level of liquid in the smaller diameter container,B, will be slightly higher than the level in container A, due the principle of capillarity.

(b) (i) a – ammonia gas b – gas jar
c – round bottomed flask

(ii) d – Heat

(iii) The calcium oxide removes the moisture or water content from the gas produced (iv) c is tilted downwards so that condensed water does not get back into the hot flask (v) Upward delivery(or downward displacement of air)
(vi) Gas has pungent smell

Or: Moist red litmus paper turns blue in the presence of the gas

Or: The gas produces fumes in the presence of concentrated hydrochloric acid (HCl)

(vii) Any alkali plus ammonium chloride,

eg, NaOH andNH4Cl or KOH and NH4Cl or
Ca(OH)2and NH4Cl or Mg(OH)2and NH4Cl

(c) (i) I The leaf is boiled to stop the process of photosynthesis by killing the cells

II.
The leaf is dipped in warm alcohol to remove the chlorophyll(the green matter)

III
The leaf is washed in cold water to wash away the alcohol and soften it.

(ii) The part that was green

The blue-black colouration indicates the presence of starch, which means that photosynthesis occurred at the green part to produce starch.

(iii) It does not contain starch. This implies that photosynthesis did not occur there due to the absence of chlorophyll,which is necessary to absorb light for photosynthesis.

(iv) Chlorophyll is necessary for photosynthesis to occur.

2. (a) (i) An opaque object does not allow light to pass through, whereas

A translucent object allows some amount of light to pass through diffusely.

(ii)
Opaque -wooden or metallic materials,mirror, the earth,mammals, etc

Translucent -fabric, lightly-coloured water, oily spot on paper, frosted glass, etc

(b) (i) Importance of seed dispersal

 Enables plants to grow in other areas;

 Prevents the over-crowding of plants in one area

 Helps to reduce the rapid spread of plant diseases

 Prevents competition for soil nutrients among plants

(ii) FRUIT MODE OF DISPERSAL

Tridax, silk cotton,
– Wind

Cowpea, Crotalaria, Balsam
– Explosive Mechanism

Coconut,
– Water

Orange,Guava,Tomatoes, Maize – Animals (man and others)

(c) (i) Recycling – The process of converting waste materials into new useful products

(ii) Advantages of recycling

 Employment /income generation for people

 Pollution of the environment by waste materials is reduced

 Reduction of resources for production

 Saving of money that would have been used for controlling waste

 Generation of energy for increased production [any two] (iii) Recycled products in Ghana
Paper, biogas, polythene materials, rubber, particle boards, iron rods,etc [any three]

3. (a) (i) Bed wetting – The involuntary passage of urine usually during sleep.

(ii) Bed wetting diseases- ringworm, skin rash, eczema, etc [any two]

(b) (i) Hard water is water that does not easily lather with soap

Impure water is water that contains certain substances that make it unwholesome for drinking.

(ii) Stages for water treatment

 Letting water run through filters to remove suspended materials
 Adding alumto cause sediments to settle
 Adding chlorine to kill germs
 Exposing water to air(aeration) to remove any bad smell
(c) (i) Density = mass ÷volume

Mass of stone= 36.0g

Volume of stone
= 90.0cm3– 60.0cm3
= 30.0cm3
Therefore Density of stone = 36.0g÷30cm3
= 1.2 g/cm3

(ii) Since the density of the stone (1.2g/ cm3) is less than the density of the other liquid
(1.4g/cm3), the stone will float on the liquid

4. (a) (i) An echo is the result of the reflection of sound when it strikes a hard surface.

Or: the repetition of a sound caused by the reflection of sound waves from a surface

(ii) Uses of echo

 Determination of distances by bats
 Determination of velocity of sound
 Clinical diagnosis in ultra-sound equipment
 Mineral exploration
 Determination of sea bed depth in special equipment
 Detection of possible obstacles by ships [any two]

(b) (i) Common cold, Tuberculosis, Whooping cough, Pneumonia, Asthma,Lung cancer

(ii) Common cold: avoid over-exposure to cold air or dusty environment

Tuberculosis:
Avoid sharing cutlery, cups and glasses with infected persons

Whooping cough:
get vaccinated

Pneumonia:
wear warm clothes or avoid exposure to cold conditions

Asthma:
keep away from dust, pollen grains, smoke or other substances that one is allergic to

Lung Cancer:
avoid smoking

(c) (i) Biotechnology: The practical use of biological processes for man’s benefit

(ii) Products obtained from Biotechnology

Cheese,yoghurt, butter,bread, wine, beer, vaccines, insulin, antibiotic drugs, food supplements, biogas, etc [any three]

5. (a) (i) Pressure is the force per unit area

Or Pressure = force/area

(ii) Applications of pressure in everyday life

 Pumping a car tyre;
 opening a sealed can with a pointed knife;
 pumping liquid from a low level to a higher level;
 Drawing a drink into the mouth with a straw;
 drawing liquid using a syringe [any three] (b) Functions of the liver in digestion

 Converting glycogen to glucose for use by the body

 Producing bile, which is used to emulsify fats

 Storing excess glucose as glycogen or starch

 Removing excess glucose from blood

(c) (i) Compound: a substance formed by the chemical combination of elements in fixed proportions

Or: a substance containing two or more elements that are chemically combined

(ii) Properties of compounds

 Their properties are different from the individual constituents that form them.

 Heat changes occur when they are being formed

 Their constituents are in a fixed ratio

 Compounds cannot be broken down to obtain their reactants by any known physical means

(iii) (α) Hydrogen+ chlorine
→ hydrochloric acid (HCl)
(β) Magnesium+ oxygen
→ magnesiu