AQA A Level Biology复习笔记5.3.9 Percentage Yield

• Farmers use various strategies to increase the yield of their crops or livestock. These strategies include:
  • Reducing energy losses from crops to other organisms by removing pests
  • Reducing energy losses from livestock through respiration by restricting their movement and keeping them warm (i.e. indoors)

   

• Increasing yield refers to:
  • Increasing the net primary production of crops
  • Increasing the net production of livestock

   

Percentage Yield

• There are two types of yield:
  • Theoretical yield is the amount (of crop or livestock biomass) that is theoretically possible to produce, given the ideal conditions
  • Actual yield is the amount (of crop or livestock biomass) that is actually produced, given the actual conditions the crops or livestock are kept under

   

• The percentage yield is the actual yield achieved, given as a percentage of the theoretical yield possible
• Percentage yield can be calculated using the following equation:

% yield = (actual yield ÷ theoretical yield) × 100

Step 1: Write out the equation and substitute in the known values

% yield = (actual yield ÷ theoretical yield) × 100

% yield = (50 ÷ 200) × 100

Step 2: Calculate the % yield

% yield = 0.25 × 100

% yield = 25%

Step 3: Explain why the percentage yield is not 100%

• • The maximum theoretical yield (or maximum theoretical net primary production) can only be obtained if the conditions are perfect
    • This includes abiotic factors, such as temperature, water availability and light availability
    • This may also include biotic factors, such as a lack of pest species competing with the crop

     

  • The perfect conditions are very difficult to achieve for crops (especially those grown outdoors) and so the percentage yield is often well below 100%

   

Step 1: Rearrange the equation

% yield = (actual yield ÷ theoretical yield) × 100

Actual yield = (% yield × theoretical yield) ÷ 100

Step 2: Substitute in the known values and calculate the actual yield

Actual yield = (90 × 15,000) ÷ 100

Actual yield = 1,350,000 ÷ 100

Actual yield = 13,500

Step 3: Give the appropriate units

The actual yield of the herd of cattle is 13,500 kg