5.4 understand the reasons for pest control and the advantages and disadvantages of using pesticides and biological control with crop plants

Pesticides/pest control kills insects/microorganisms/mammals that feed on crops. they are useful as they are very effective. However, they are poisonous to humans so must be used carefully around foods etc (e.g. growing carrots) and some pesticides are harmful to other wildlife.

Biological control is an alternative to pesticides, it involves using other organisms to control pests (e.g. introducing hoverflies to an area to reduce the amount of aphids, as aphids kill hoverflies). This has a longer lasting effect on the crop/area than pesticides do and is less harmful to the ecosystem. However, it can cause problems. for example, the introduced species could become uncontrollable and their predator would have to be introduced to control them. It can also take longer (potentially).

5.3 understand the use of fertiliser to increase crop yield

If plants don't get enough nitrogen, potassium or phosphorus, their growth and other life processes could be affected.

These elements are naturally found in the soil, however, they could be lacking due to previous crops using them up. All fertilisers do is replace them in the soil, so the plants can grow very well.

5.2 understand the effects on crop yield of increased carbon dioxide and increased temperature in glasshouses

Okay so, I mainly covered this, along with other factors, in point 5.1, but here it is again...

If carbon dioxide is increased, the rate of photosynthesis will be increased. Meaning more photosynthesis will occur each day, meaning a bigger crop yield.

If temperature is increased, plants can grow throughout the winter and don't die of frost etc. This also lowers the rate of transpiration (as there is a lower concentration gradient inside vs outside the plant leaf so the rate of transpiration is lower).

5.1 describe how glasshouses and polyethene tunnels can be used to increase the yield of certain crops

Glasshouses and polyethene tunnels/polytunnels help to create the ideal conditions for plants, thus increasing the yield (how much grows) of a crop. Some ways they create the perfect conditions are...

- The plants are enclosed, meaning they are at no/a significantly lower rick of pests and diseases.

- Artificial light can be supplied which will increase the time per day a plant is photosynthesizing

- The suns heat can be trapped (particularly in glasshouses). This keeps the plant warm. In winter it can stop the plants from being damaged by frost etc

- As it is an enclosed space, farmers can increase the level of carbon dioxide in the glasshouse/polyethene tunnel. They can do this by burning a paraffin lamp etc (combustion fossil fuels gives carbon dioxide). This further increases the amount/rate of photosynthesis the plant endures.

All of the above increase the yield of a plant.