i)

Embryo is the first stage of the development of a zygote (eight weeks after conception in mammals).

ii)

In the womb or uterus of the female mammal

iii)

How a developing embryo breathes in oxygen

Oxygen from the mother's blood diffuses through the placenta into the embryo.

i)

An electrical insulator is a substance/material which does not conduct electrcity

OR

An electrical insulator is a substance/material which does not allow electricity to pass through it

ii)

How a comb rubbed vigorously on dry hair attracts small pieces of paper

1. Comb rubbed in hair causes the comb to be charged
2. When the comb is brought near pieces of paper it induces an oppsite charge on the pieces of paper
3. The pieces of paper are attracted to the comb because of the opposite charges

i)

Chemical substances that are used in the preparation of ammonia gas

1. Ammonium chloride
2. Calcium hydoxide/Calcium oxide

ii)

2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2H₂O + 2NH₃(g)

OR

2NH₄Cl + CaO → CaCl₂ + H₂O + 2NH₃(g)

i)

Tilapia/Bony fish

ii)

I → mouth
II → operculum/gill cover
IV → scales/scale
V → lateral line

iii)

Habitat of tilapia/bony fish

1. Fresh water/river
2. Pond/fish pond
3. Brackish water/lagoon
4. Lake

iv)

Adaptation of fish

III (Pectoral Fin) → used for movement/swimming or pitching

VI (Eye) → for (wide) vision/seeing

i)

Soil profile

ii)

I → Top soil/humus
II → Subsoil
III → Weathered material/rock
IV → parent/(unweathered) rock/rock layer/bedrock

iii)

iv)

Effects of heavy rainfall on I (Top Soil/Humus)

1. Erosion
2. Leaching

i)

I → Cell
II → Key/switch
IV → (Standard) Resistor
VI → variable resistor/rheostat/resistance box

ii)

Energy transformation in parts of a circuit

iii)

S.I Units of current and voltage

iv)

Function of VI (Variable resistor/rheostat/resistance box)

1. Used to control/regulate current
2. Used to vary current

i)

Identification of solutions

ii)

Neutralization reaction

iii)

Salt/Neutral/Sodium chloride (Solution)

iv)

Both red and blue litmus papers would not change colour/there is no colour change/no effect on both red and blue litmus papers

v)

How to obtain salt (sodium chloride) from salt solution

Pour the resulting solution into a suitable container and allow to dry/heat to dryness/evaporate

i)

Air pollution is the release of toxic/poisonous substances into the atmosphere.

ii)

Humans activities that lead to air pollution

1. Discharge of gases from factories
2. Smoke from exhaust engines and other machines
3. Smoke from domestic fires
4. Discharge of chloroflourocarbons from aerosol sprays and some refrigerators
5. Bush burning
6. Dust from open cast mining
7. Dust from sand winning and stone quarrying
8. Dust from construction
9. Smoke from cigarette/smoking

i)

Modes of heat transfer

1. Conduction
2. Convection
3. Radiation

ii)

Medium for mode of heat transfer

1. Conduction → Solid
2. Convection → Liquid/gas/fluid
3. Radiation → vacuum/no material medium

i)

ii)

Factors that limit work output

1. Friction/wear and tear
2. Age of machine/period of usage
3. Weight of machine parts

i)

Chloroplast is an organelle or structure found in (plant) cell and it contains chlorophyll or green pigment.

ii)

Differences between aerobic and anaerobic respiration

i)

ii)

Product formed when hydrochloric acid reacts with sodium hydroxide

Sodium chloride and water is formed

(i)

Magnesium chloride and hydrogen/MgCl₂ and H₂

Illustration

Mg_(s) + 2HCl_(aq) → MgCl_2(aq) + H_2(g)

(ii)

Potassium hydroxide and hydrogen/KOH and H₂

Illustration

2K_(s) + 2H₂O → 2KOH_(aq) + H_2(g)

(i)

Effects of heat on a substance

1. Change of state/melts/vapourises
2. Expansion/contraction/change in shape
3. Increasing temperature/decreasing temperature
4. Increase in pressure

(ii)

Potassium permangante crystals dropped into a beaker of water and warmed:

iv)

Reasons

1. Presence of large/ single vacuole (IX)
2. Presence of cell wall (V)
3. Rectangular shape
4. Nucleus pushed to the side/periphery
5. Cytoplasm pushed to the side

v)

Differences between parts labelled I (Cell Membrane) and V (Cell Wall)

i)

(α) mass of irregular object (M) in I = 40 g
(β) Volume of water (V₁) in II = 40 cm³
(γ) Volume of water (V₂) in III = 60 cm³

ii)

Volume of the irregular object = 60 cm³ - 40 cm³ = 20 cm³

iii)

Density = $\frac{\mathrm{40\; g}}{\mathrm{20 }{\mathrm{cm}}^3}$ = 2 g/cm³ or 2 gcm^-3

iv)

Instruments for measuring mass of an irregular object

1. Beam balance
2. Top pan balance
3. Electronic balance

iv)

Precautions to be taken in performing the experiment

1. The object should be lowered gently into the water in the cylinder
2. Volume of the liquid should be read from the base of the meniscus or at the eye level
3. The measuring cylinder should be placed on a flat surface

i)

(α) chemical processes

II and III

(β) physical processes

I and IV

ii)

(α) Why chemical processes

1. The initial/original substance cannot be gotten back easily/irreversible
2. New substance formed
3. Change in mass
4. Accompanied by appreciable heat change

(β) Why physical processes

1. The initial/original substance can be gotten back easily/reversible
2. No new substance formed
3. No change in mass
4. Not accompanied by appreciable heat change

iii)

Examples of physical change

1. Expansion of metal on heating
2. dissolving sugar or salt in Water
3. Boiling of water
4. Melting of ice
5. Breaking/crushing of any Object

i)

ii)

Principles to consider when planning for rotational programme

1. Deep rooted crops should be followed by shallow rooted crops
2. Crops of the same family/class should not follow each other
3. Crops that use the same soil nutrients should not follow each other
4. Leguminous crops should be included in the cycle
5. A fallow period may be included in the crop rotation programme
6. Crops which attract the same diseases and pests should not follow each other

iii)

Reasons for selecting the crop named V (Soyabean)

1. Soyabean is a legume and therefore builds up soil fertility
2. Yam is a deep rooted crop and should be followed by soyabean which is a shallow rooted crop
3. Yam is a heavy feeder and must have taken good part of the nutrients
4. Yam and soyabean belong different classes of crops and therefore not likely to attract the same pests and diseases
5. Improves soil structure

iv)

Advantages of crop rotation

1. Increases soil fertility
2. Enhances soil structure
3. Prevents soil erosion
4. Improves soil nutrients and nutrient uptake regulation
5. Controls the spread of pests and diseases
6. Controls weed easily
7. There is effective use of the land
8. Harvest of different types of crops on the same piece of land