Define, with reference to plants, the term productivity. Explain how the productivity of plants in a garden is affected by temperature, mineral salts, and water.

The, let's tackle this one.

a)

(i) Productivity, with reference to plants, is the rate at which plants produce biomass (organic matter) through photosynthesis, often measured as the amount of energy stored per unit area per unit time.

(ii) The productivity of plants in a garden is affected by:

1. Temperature: Plants have an optimum temperature range for photosynthesis and enzyme activity. Temperatures too low slow down metabolic processes, while temperatures too high can denature enzymes and reduce water availability, thus decreasing productivity.
2. Mineral salts: These are essential nutrients for plant growth. For example, nitrates are needed for protein synthesis, and phosphates for ATP and DNA. A deficiency in any essential mineral salt will limit growth and reduce overall productivity.
3. Water: Water is a reactant in photosynthesis and is crucial for transporting nutrients, maintaining turgor pressure, and cooling the plant. Insufficient water leads to stomatal closure, reducing carbon dioxide uptake and thus lowering photosynthetic rates and productivity.

b)

(i) The two types of plant pests are:

• Insects: e.g., aphids, locusts, caterpillars.
• Mammals: e.g., rats, rabbits, deer.

(ii) Three cultural methods of controlling plant pests are:

• Crop rotation: Changing the type of crop grown in a particular area each season to break pest life cycles.
• Timely planting and harvesting: Planting or harvesting at times when pests are less active or vulnerable.
• Weeding: Removing weeds that can harbor pests or compete with crops for resources.

c)

(i) The function of nitrogen and phosphorus in plants:

• Nitrogen is essential for the synthesis of proteins, nucleic acids (DNA and RNA), chlorophyll, and enzymes, promoting leafy growth.
• Phosphorus is crucial for energy transfer (ATP), root development, flowering, fruiting, and is a component of nucleic acids and cell membranes.

(ii) The symptoms (yellow leaves, brown edges, weak stems) suggest nutrient deficiencies, likely nitrogen (yellow leaves) and potassium (brown edges, weak stems). The farmer can take the following steps:

• Apply nitrogen-rich fertilizer: To address the yellowing leaves and promote overall growth.
• Apply potassium-rich fertilizer: To strengthen stems and prevent brown edges.
• Conduct a soil test: To accurately identify specific nutrient deficiencies and adjust fertilizer application accordingly.