(i)

Surface tension is the property of a liquid which makes the surface behave as if it were stretched elastic skin.

(ii)

One way in which surface tension can be useful to man

Umbrellas/raincoats/tents/canopies made of canvas do not leak because the surface tension prevents the water from passing through the tiny holes in them

OR

In umbrellas/raincoats/tents/canopies made of canvas, water forms films like stretched elastic skin over each pore which prevents water from passing through.

(i)

(ii)

Reasons why a rhizome, a corm and a stem tuber are considered as stems

1. They have nodes and internodes
2. They have buds

(i)

Zinc and oxygen → Zinc oxide

(ii)

Calcium and chlorine → Calcium chloride

(iii)

Sodium and bromine → Sodium bromide

(iv)

Potassium and iodine → Potassium iodide

(i)

A fertile soil is the soil rich in nutrients (mineral salts) which are essential for the healthy growth of a specific plant.

(ii)

Most important nutrients in mineral salts which plants use to form food

1. Nitrogen
2. Phosphorus
3. Potassium
4. Calcium

(i)

Density of a substance is the mass per unit volume of the substance.

OR

Density = $\frac{\mathrm{Mass\; (M)}}{\mathrm{Volume\; (V)}}$

(ii)

Determination of the density of an irregular piece of stone

1. Measure/weigh the mass of stone by means of a beam/chemical balance as M g
2. Fill a large measuring cylinder with water to a suitable level and record the volume as V₁ cm³
3. Tie the stone with thread and gently lower it into the water in the measuring cylinder and record the new volume as V₂ cm³

The density of the stone is then calculated as follows:

Volume of stone = V₂ cm³ - V₁ cm³

Mass of stone = M g

Density = $\frac{\mathrm{Mass}}{\mathrm{Volume}}$

Density of the stone = $\frac{\mathrm{M\; g}}{({\mathrm{V}}_2-{\mathrm{V}}_1){\mathrm{cm}}^3}$

(iii)

Density = $\frac{\mathrm{Mass}}{\mathrm{Volume}}$

Volume = 1200.0 m³

Density = 1.95 kgm^-3

Mass = Density x Volume

Mass = 1200.0 m³ x 1.95 kgm^-3

Mass = 2340 kg

(i)

An atom is the smallest part of an element that can take part in a chemical reaction.

(ii)

Why atoms are electrically neutral

Electrically neutral atoms contain equal number of protons (positive charges) and electrons (negative charges), which cancel out/balance/make net charge equal to zero.

(i)

Crackling noises are heard from a metal sheet roof when the weather becomes very hot

1. The metal sheet roof expand when heated but the nails which hold it prevent its free movement
2. Bending occurs and the cracking noise is caused by this bending movement

(ii)

Railway tracks are laid with gaps in between their ends

1.Railway tracks are laid with gaps in between their ends to make room for expansion when the tracks are heated
2. This prevents them from bending

(iii)

A fitting mechanic washes his greasy hands with petrol and not with water

1. Petrol is a solvent for grease but water is not
2. Therefore the petrol will dissolve the grease on his hands

(i)

Carbohydrates → glucose

(ii)

Proteins → amino acids

(iii)

fats → fatty acid and glycerol

(i)

Pollination is the transfer of pollen grains from the anther of a flower to the stigma of the flower or another flower of the same species.

(ii)

Features of insect pollinated flowers

1. Petals are large
2. Petals are brightly coloured
3. The flower is usually scented
4. The flower has nectar
5. Stigma is inside the flower
6. Stigma is compact and sticky
7. Pollen grains produced per anther are few
8. Pollen grains are sticky, large, rough and heavy
9. Filaments are short and stout

(i)

Number of protons = 3
Number of neutrons = 3

Number of electrons = Number of protons

Number of electrons = 3

(ii)

(i)

Potential energy = Mass (m) x Acceleration due to gravity (g) x Height (h)

Mass = 12.0 kg
Acceleration due to gravity (g) = 10 ms^-2
Height = 20 m

Potential energy = 12.0 kg x 10 ms^-2 x 20 m

Potential energy = 2400 J

(ii)

Before the body just hit the ground, the potential energy is converted to kinetic energy

∴ Kinetic energy = Potential energy
Kinetic energy = 2400 J