List three excretory substances, two excretory organs, three benefits of grafting, two ways scientific methods are important, and explain lab rules about footwear, taps, and spills.

Here are the answers to the questions:

1. (a) (i) Three substances excreted from the human body are:

• Urea
• Carbon dioxide
• Water (as sweat and urine)

1. (a) (ii) Two organs in humans which perform excretory function are:

• Kidneys
• Lungs

1. (b) (i) Grafting is used in crop production to join parts of two plants so they grow as one, combining desirable characteristics such as disease resistance from the rootstock and high yield from the scion.

1. (b) (ii) Three benefits of grafting are:

• It allows for the propagation of plants that do not root easily.
• It can confer disease resistance or pest resistance to a susceptible plant by using a resistant rootstock.
• It can lead to earlier fruiting or improved yield compared to growing from seed.

1. (c) (i) Two ways in which scientific methods are important are:

• They provide a systematic and objective approach to understanding natural phenomena.
• They enable the development of new technologies and solutions to practical problems.

1. (c) (ii) One reason for each of the following laboratory rules:

• (α) do not wear rubber slippers to the laboratory: To protect feet from chemical spills, broken glass, or falling heavy objects.
• (β) close all taps before leaving the laboratory: To prevent flooding and wastage of water or gas.
• (γ) spilled liquids must be cleaned immediately: To prevent slips and falls, and to avoid chemical exposure or contamination.

1. (d) (i) Earthing (or grounding) in household wiring is the process of connecting the metal casing of an electrical appliance to the earth using a low-resistance wire. This provides a safe path for fault current to flow to the ground, preventing electric shock if a live wire touches the casing.

1. (d) (ii) Two sources of electric power generation are:

• Fossil fuels (e.g., coal, natural gas, oil)
• Hydroelectric power

2. (a) Four reasons why farmers should be discouraged from using chemical fertilizers are:

• They can lead to water pollution through runoff, causing eutrophication in rivers and lakes.
• They can degrade soil quality over time by reducing organic matter and harming beneficial soil microorganisms.
• Excessive use can lead to the accumulation of harmful chemicals in the soil, affecting crop health and potentially human health.
• They are often expensive, increasing production costs for farmers.

2. (b) (i) Temporary hard water is water that contains dissolved hydrogen carbonates of calcium and magnesium. It can be softened by boiling.

2. (b) (ii) Chemical equation to show how temporary hard water can be softened by heating:

$$\text{Ca(HCO}_3\text{)}_2\text{(aq)} \xrightarrow{\text{heat}} \text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}$$

2. (c) (i) A lever is a simple machine consisting of a rigid bar or beam that pivots around a fixed point called a fulcrum. It is used to multiply force or distance.

2. (c) (ii) Explanation of terms as applied to simple machines:

• (α) mechanical advantage: The ratio of the output force (load) to the input force (effort). It indicates how much a machine multiplies the applied force.
• (β) velocity ratio: The ratio of the distance moved by the effort to the distance moved by the load. It is also known as the ideal mechanical advantage.

2. (d) (i) Food processing is the transformation of raw agricultural products into food, or of one form of food into other forms, through various physical and chemical methods.

2. (d) (ii)

• (α) two advantages of food processing:
  • It increases the shelf life of food, reducing spoilage and waste.
  • It provides convenience for consumers, offering ready-to-eat or easy-to-prepare meals.
• (β) one disadvantage of food processing:
  • It can lead to the loss of essential nutrients (vitamins, minerals) during processing.