What are the main excretory products, organs, benefits of grafting, importance of scientific methods, and safety precautions in a laboratory setting?

Here are the solutions to the questions:

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

• Urea
• Carbon dioxide
• Water

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 like disease resistance from one plant with high yield from another.

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

• To combine the desirable traits of two different plants.
• To repair damaged plants.
• To propagate plants that do not readily root from cuttings.

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

• They provide a systematic and logical approach to solving problems and understanding natural phenomena.
• They ensure the reliability and validity of experimental results, leading to accurate conclusions and new discoveries.

1. (c) (ii)

• (α) Do not wear rubber slippers to the laboratory: To protect feet from chemical spills, broken glass, and electrical hazards.
• (β) Close all taps before leaving the laboratory: To prevent water wastage and potential flooding.
• (γ) Spilled liquids must be cleaned immediately: To prevent slips and falls, and to avoid contamination or unwanted chemical reactions.

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

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

• Thermal power plants (e.g., burning coal, natural gas)
• Hydroelectric power plants

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 water bodies.
• They can degrade soil quality over time by altering its pH and reducing beneficial microbial activity.
• Excessive use can lead to the accumulation of harmful chemicals in the soil, affecting crop health and potentially human health.
• They are often derived from non-renewable resources and can be expensive 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:

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

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

2. (c) (ii)

• (α) Mechanical advantage: The ratio of the load (output force) to the effort (input force). It indicates how much a machine multiplies the force applied to it.
• (β) Velocity ratio: The ratio of the distance moved by the effort to the distance moved by the load in the same amount of time. It is a theoretical value determined by the geometry of the machine.

2. (d) (i) Food processing refers to any method used to transform raw agricultural products into food, or to transform food into other forms for consumption. This can involve various physical or chemical treatments.

2. (d) (ii)

• (α) Two advantages of food processing:
  • Increases the shelf life of food, reducing spoilage and waste.
  • Enhances convenience by making food easier and quicker to prepare and consume.
• (β) One disadvantage of food processing:
  • Can lead to the loss of essential nutrients (vitamins, minerals) during processing.