B2. Farming Practices and Production

Question 1

Food chains and food webs
Food chains and food webs show how energy is transferred through an ecosystem. Food chains show simple lines of energy transfer. Each of the stages in a food chain is called a _______ ______. Food webs show lots of food chains in an _____________and how they overlap.

Decomposers (e.g. fungi) are also part of food webs. Decomposers break down dead or undigested material, allowing ___________to be ___________.

Answer 1

Food chains and food webs show how energy is transferred through an ecosystem. Food chains show simple lines of energy transfer. Each of the stages in a food chain is called a trophic level. Food webs show lots of food chains in an ecosystem and how they overlap.

Decomposers (e.g. fungi) are also part of food webs. Decomposers break down dead or undigested material, allowing nutrients to be recycled.

Question 2

Increasing efficiency
Most farming practices aim to increase the amount of energy that is available for human consumption. This means increasing the net primary production (NPP) of crops and the net production (NP) of livestock. There are different ways this can be done. You need to know about two of them:

Answer 2

• The energy lost to other organisms, e.g. pests, can be reduced through the simplification of food webs.
• The energy lost through the respiration of livestock can be reduced.

Question 3

Tip: ___is the energy in plants that’s available to the next trophic level in a food chain. __is the energy in consumers that’s available to the next trophic level.

Answer 3

Tip: NPP is the energy in plants that’s available to the next trophic level in a food chain. NP is the energy in consumers that’s available to the next trophic level.

Question 4

Increasing efficiency - Simplifying food webs
Pests are organisms that reduce the amount of energy available for crop growth and therefore the net primary production (NPP) of crops. This ultimately reduces the amount of energy available for _______. By simplifying the food web, i.e. getting rid of food chains that don’t involve humans, energy losses will be ________and the ____of the ____will __________.

Answer 4

Pests are organisms that reduce the amount of energy available for crop growth and therefore the net primary production (NPP) of crops. This ultimately reduces the amount of energy available for humans. By simplifying the food web, i.e. getting rid of food chains that don’t involve humans, energy losses will be reduced and the NPP of the crop will increase.

Question 5

Increasing efficiency - Simplifying food webs - Example
Figure 1 shows a simplified food web involving wheat—a crop plant grown for human consumption. The weed, the mouse and the aphid are _____. By eating the wheat or competing with it for energy, the pests reduce the wheat’s __________and the energy it has for further _________. This means that the wheat’s ____(and the wheat yield) is _________-so less energy is transferred to ________. Getting rid of food chains involving the weed, the mouse and the aphid will mean that less energy is transferred to _____, increasing the ___________of transfer to humans.

Answer 5

Figure 1 shows a simplified food web involving wheat—a crop plant grown for human consumption. The weed, the mouse and the aphid are pests. By eating the wheat or competing with it for energy, the pests reduce the wheat’s biomass and the energy it has for further growth. This means that the wheat’s NPP (and the wheat yield) is smaller-so less energy is transferred to humans. Getting rid of food chains involving the weed, the mouse and the aphid will mean that less energy is transferred to pests, increasing the efficiency of transfer to humans.

Question 6

Increasing efficiency - Simplifying food webs
To get rid of pests farmers need pest control. Farmers can reduce pest numbers using chemical pesticides.
Examples

• Insecticides kill insect pests that eat and damage _____. Killing insect pests means less _________is lost from ______, so they grow to be larger, which means NPP is ________.
• Herbicides kill weeds (unwanted plant species). Killing weeds can remove ________ ______________with the ____for energy from the ___. It can also remove the preferred ________or _____ _______of the _______ ____, helping to further reduce their numbers and simplify the food web.

Answer 6

• Insecticides kill insect pests that eat and damage crops. Killing insect pests means less biomass is lost from crops, so they grow to be larger, which means NPP is greater.
• Herbicides kill weeds (unwanted plant species). Killing weeds can remove direct competition with the crop for energy from the Sun. It can also remove the preferred habitat or food source of the insect pests, helping to further reduce their numbers and simplify the food web.

Question 7

Increasing efficiency - Reducing respiratory loss
One way that farmers increase the net production of their livestock is by controlling the conditions that they live in, so that more of their energy is used for growth and less is lost through respiration (and activities that increase the rate of respiration).

Examples (two examples)

This means that more ________is __________and more __________ ________can be _______, increasing ____ __________and the __________of _______ __________to __________. The benefits are that more food can be produced in a ________ _____of ____, often at ______ ____.

However, enhancing net production by keeping animals in pens raises ethical issues. For example(1 example)

Answer 7

One way that farmers increase the net production of their livestock is by controlling the conditions that they live in, so that more of their energy is used for growth and less is lost through respiration (and activities that increase the rate of respiration).

Examples

• Movement increases the rate of respiration, so animals may be kept in pens where their movement is restricted.
• The pens are often indoors and kept warm, so less energy is wasted by generating body heat.

This means that more biomass is produced and more chemical energy can be stored, increasing net production and the efficiency of energy transfer to humans. The benefits are that more food can be produced in a shorter space of time, often at lower cost.

However, enhancing net production by keeping animals in pens raises ethical issues. For example, some people think that the conditions intensively reared animals are kept in cause the animals pain, distress or restricts their natural behaviour, so it shouldn’t be done.

Question 8

Tip: Weeds also compete with the crop for _____, _______and _________

Answer 8

Tip: Weeds also compete with the crop for water, space and nutrients.

Question 9

Tip: Natural predators can also be introduced to the ecosystem to eat the ___species, eg ladybirds eat aphids- this is useful but doesn’t really __________the food web.

Answer 9

Tip: Natural predators can also be introduced to the ecosystem to eat the pest species, eg ladybirds eat aphids- this is useful but doesn’t really simplify the food web.