Name three substances that are excreted from human body. Name two organs in humans which perform excretory function. What is grafting as used in crop production? State three benefits of grafting.

Here are the answers to the questions:

a)

i) Three substances excreted from the human body are:

1. Carbon dioxide
2. Urea
3. Excess water (sweat/urine)

ii) Two organs in humans that perform excretory function are:

1. Kidneys
2. Skin

b)

i) Grafting is a method of plant propagation where a shoot (scion) from one plant is joined to the rootstock of another plant.

ii) Three benefits of grafting are:

1. It produces improved or superior quality fruits.
2. It enables plants to withstand diseases.
3. It allows plants to grow in unsuitable soil conditions.

c)

i) Two ways in which scientific methods are important are:

1. They help in discovering new knowledge.
2. They ensure accuracy and reduce errors in experiments.

ii) Reasons for the following laboratory rules:

• α) Do not wear rubber slippers to the laboratory: They do not protect the feet from chemical spills or broken glass.
• β) Close all taps before leaving the laboratory: To prevent wastage of water and possible flooding.
• γ) Spilled liquids must be cleaned immediately: To prevent accidents such as slipping and the spread of chemicals.

d)

i) Earthing in household wiring is the connection of the metallic parts of an electrical appliance to the ground through a wire, ensuring any excess electric charge is safely discharged.

ii) Two sources of electric power generation are:

1. Hydroelectric power (water)
2. Solar power (sun)

a) Four reasons why farmers should be discouraged from using chemical fertilizers:

1. They reduce soil fertility over time.
2. They pollute water bodies.
3. They can cause health problems in humans.
4. They are expensive for small-scale farmers.

b)

i) Temporary hard water is water that contains bicarbonates of calcium and magnesium.

ii) The chemical equation to show how temporary hard water can be softened by heating is:

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

c)

i) A lever is a simple machine consisting of a rigid bar that turns on a fixed point (fulcrum) to move a load.

ii) Explanation of terms as applied to simple machines:

• α) Mechanical advantage: The ratio of the load moved by a machine to the effort applied.
• β) Velocity ratio: The ratio of the distance moved by the effort to the distance moved by the load.

d)

i) Food processing is the change of raw food into a form that is safe, edible, and more convenient for consumption.

ii)

• α) Two advantages of food processing:
  1. It prolongs the shelf life of food.
  2. It improves the taste and appearance of food.
• β) One disadvantage of food processing: It can lead to loss of some nutrients in food.