S9: Crop Yield and Eutrophication

Question 1

Why are glasshouses/ polytunnels used to grow crops?

Answer 1

To control the environment of growing crops, and to increase the yield

Question 2

How is Temperature and CO2 concentration controlled in a glasshouse/ polytunnel

Answer 2

Fossil fuels are burned here to increase the temp. so that it is the optimum temperature for enzymes, and increases the rate of photosynthesis.

Burning fossil fuels also releases CO2 increasing the CO2 conc. of the atmosphere in the glasshouse/polytunnel which will further increase the rate of photosynthesis.

Temp. is monitored using a data logger which may control vents or fans if it gets too hot.

Question 3

How is light intensity controlled in a glasshouse / polytunnel?

Answer 3

LED bulbs can be used 24hours of day, so plants get light, even in the night.

The wavelength of the light may be red or blue (or both) which can increase the rate of photosynthesis as these wavelengths are absorbed the most as they contain the least amount of green light (so less will be reflected by the chlorophyll)

Question 4

What is in the fertilizer used in glasshouses/ polytunnels?

Answer 4

magnesium - allows the plant to make more chlorophyll, to increase the rate of photosynthesis.

nitrates- will allow the plant to make more amino acids, which means more proteins, so more growth and repair of tissues.

Question 5

What is the chemical control of crops?

Answer 5

Using pesticides (chemical that kills pests) to stop pests feeding on the crop and damaging them. Which increases yield

Question 6

What are the problems with pesticides?

Answer 6

• Not specific to one insect, can kill all insects which can damage a food web due to the interdependence
• Pests may develop resistance to the pesticide, which can the produce offspring who are also resistant, reducing its effectiveness.
• Bioaccumulation - toxins may accumulate higher up the food chain and even in humans eating the crop.

Question 7

What is biological control of crops?

Answer 7

A predator of the pest is introduced to the crop to reduce the amount of pests, and so reduce damage and increase yields.

Question 8

What are the problems with biological control?

Answer 8

It only works if the predator is focused on one pest species not all insects, as it may cause problems in the food web or be ineffective

It works best in a polytunnel/ glasshouse as in open fields, the predator could move away

Introducing predators which are not native to the area can create an invasive species.

Question 9

Why does eutrophication occur?

Answer 9

Fertilizers get leeched into water bodies, or just due to surface runoff. Or sewage is released into waterways - which can cause the water to be overly enriched with nitrates.

(with sewage, the waste is decomposed by decomposers, and nitrates are released)

Question 10

Describe the process of eutrophication.

Answer 10

Waterbodies become overly enriched with nitrates through fertilizers or sewage. An algal bloom develops on the surface of the water

This stops light from getting into the water, so aquatic plants die as they can’t carry out photosynthesis.

Decomposers (bacteria and fungi) use O2 in the water to respire, and they begin breaking down the dead plant material releasing more nitrates into the water

O2 in the water decrease (due to respiring decomposers and the lack of photosynthesis) and the water become anoxic - so aquatic life can’t aerobically respire - so they die.

The dead aquatic life settles in the bottom where it is decomposed, and more nitrates are released, so the cycle continues.