1a. Define Chemical Formula (2 marks)
A chemical formula is a symbolic way of showing the elements in a substance and the number of atoms of each element.
Example: H₂O (water), CO₂ (carbon dioxide).
1b. Mention the main subatomic particles of an atom (3 marks)
The main subatomic particles are:
- Protons (p⁺) – positively charged, found in the nucleus.
- Neutrons (n⁰) – neutral (no charge), found in the nucleus.
- Electrons (e⁻) – negatively charged, orbit around the nucleus.
1c. Explain a Chemical Reaction and a Catalyst (4 marks)
Chemical Reaction:
A chemical reaction is a process in which substances (reactants) change to form new substances (products). Bonds are broken and formed.
Example:
2H₂ + O₂ → 2H₂O
Catalyst:
A catalyst is a substance that speeds up a chemical reaction without being used up in the reaction.
Example: Enzymes in digestion, manganese dioxide (MnO₂) in the decomposition of hydrogen peroxide.
2a. State the Law of Conservation of Mass (4 marks)
The Law of Conservation of Mass states:
“Mass cannot be created or destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.”
2b. Mention the divisions of the brain (3 marks)
The brain is divided into:
- Forebrain – responsible for thinking, memory, and voluntary actions.
- Midbrain – controls vision, hearing, and motor movements.
- Hindbrain – controls balance, coordination, and vital functions like breathing.
2c. Mention any three parts of the eye (3 marks)
- Cornea – transparent layer at the front of the eye.
- Lens – focuses light onto the retina.
- Retina – contains cells that detect light and send signals to the brain.
3a. Draw a well-labelled diagram of the eye (marks vary)
Labels to include:
- Cornea
- Iris
- Pupil
- Lens
- Retina
- Optic Nerve
- Ciliary Body
- Sclera
- Aqueous Humor
(For Word/Notebook, a neat circular diagram with arrows pointing to each part is ideal.)
3b. Describe the parts of the eye (brief description)
- Cornea – protects the eye and helps focus light.
- Iris – the colored part, controls the size of the pupil.
- Pupil – black circular opening that allows light in.
- Lens – transparent structure that focuses light on the retina.
- Retina – layer at the back of the eye with light-sensitive cells (rods and cones).
- Optic Nerve – transmits visual information from the retina to the brain.
- Ciliary Body – helps the lens change shape for focusing.
- Sclera – tough outer layer that protects the eye.
- Aqueous Humor – fluid between the cornea and lens, nourishes the eye.
