(1a) Advantages of multicellularity

• It allows division of labour, where different cells, tissues, and organs perform specialized functions efficiently.
• It increases the efficiency and survival of organisms by enabling them to carry out complex life processes.

(1bi) Differences between colonial and filamentous organisms

(1bii) Examples

• Colonial organism: Volvox
• Filamentous organism: Spirogyra

(1c) See diagram below.

(2ai) Good soil characteristics

• It contains adequate nutrients/mineral salts for plant growth.
• It has good water-holding capacity and good drainage.
• It contains plenty of humus (organic matter) and supports soil organisms.

(2aii) Methods of improving poor soil

• Application of manure or fertilizers.
• Crop rotation (or bush fallowing).

(2b) Methods of vegetative propagation with examples

• Cutting – e.g. cassava, sugarcane, rose.
• Layering – e.g. cocoa, bougainvillea, mango.
• Grafting/Budding – e.g. citrus (orange), mango.
• Use of underground stems (suckers/rhizomes/tubers) – e.g. banana (suckers), ginger (rhizome), yam (tuber).

(2c) Advantages of vegetative propagation

• True-to-type offspring.
• Early maturity/fruiting.
• Useful for plants with no viable seeds.

Disadvantages of vegetative propagation

• Low genetic variation.
• Easy disease transmission from parent.
• Low multiplication rate.

(3ai) Definition of pollination

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

(3aii) Features of insect-pollinated flower

• Large and brightly coloured petals.
• Presence of scent and nectar.
• Pollen grains are sticky and heavy.
• Stigma is sticky and not feathery.

(3bi) Functions of flowering plant

• Produces food through photosynthesis.
• Carries out reproduction through flowers.
• Absorbs water and mineral salts from the soil.
• Provides support and transport of materials within the plant.

(3bii) See diagram below.

(4a) Sense organs and their functions

• Eye – for vision.
• Ear – for hearing and balance.
• Nose – for smell.
• Tongue – for taste.

(4bi) Myopia (short-sightedness)

Myopia (short-sightedness) is a condition where nearby objects are seen clearly but distant objects appear blurred. It occurs when the eyeball is too long or the lens is too powerful, causing light to focus in front of the retina.

(4bii) See diagram below.

(4ci) The cerebrum controls voluntary actions, thinking, memory, and reasoning.

(4cii) The cerebellum controls balance, posture, and coordination of body movements.

(5a) See diagram below.

(5bi) Teeth are used for biting, cutting, tearing, crushing, and grinding food to increase the surface area for enzyme action and make swallowing easier.

(5bii) The tongue mixes food with saliva to form a bolus, helps in swallowing, and its taste buds detect different tastes.

(5biii) Saliva moistens and lubricates food and contains salivary amylase (ptyalin) which digests starch.

(5biv) The stomach stores and churns food with gastric juice, secretes enzymes and hydrochloric acid for protein digestion, and destroys harmful microorganisms.

(6ai) Definition of variation

Variation is the occurrence of differences among individuals of the same species in terms of physical appearance, physiological processes, behavioral patterns, and genetic constitution.

(6aii) Examples of variation

Continuous variation:

• Height in humans.
• Body weight.
• Skin colour.
• Intelligence level.

Discontinuous variation:

• Blood group (A, B, AB, O).
• Ability to roll the tongue.
• Sex (male or female).
• Fingerprint pattern.

(6aiii) Importance of variation

• It enables organisms to adapt to changes in the environment.
• It increases the chances of survival of a species.
• It provides the raw materials for evolution and natural selection.

(6bi) Sex-linked genes

Sex-linked genes are genes located on sex chromosomes (X or Y) whose inheritance is associated with sex; traits controlled are called sex-linked traits.

(6bii) Dominance

Dominance is the ability of one allele to express itself and mask the recessive allele.

(6biii) Hybrid

A hybrid is the offspring produced by crossing two genetically different individuals of the same species.