Unit 4 - Lesson 9: Increasing Crop Yields

Question 1

What does increasing crop yield mean?

Answer 1

Increasing crop yield means increasing the amount of crops available for sale.

Question 2

What is the nitrogen cycle in simple terms?

Answer 2

Plants absorb nitrogen for growth. When they die, the nitrogen is released to the soil (nitrogen cycle).

Question 3

Crops are used as cattle feed (fodder). Most nitrogen is used by the cow. When it’s slaughtered, the nitrogen is passed to the consumer. What is some of the nitrogen released back to the soil in?

Answer 3

Faeces (manure).

Question 4

How does manure (faeces mixed with straw/organic fertiliser) improve soil?

Answer 4

Manure improves SOIL STRUCTURE by making it LESS COMPACT.

Question 5

What is another way to provide nitrogen for soil, involving legumes?

Answer 5

Planting legumes with nitrogen fixing root nodules 1 year in 4 and leaving them to decompose can provide nitrogen for soil.

Question 6

What three artificial environments are good for growing plants artificially?

Answer 6

Glasshouses, polytunnels or water cultures.

Question 7

If the condition we are controlling is soil mineral ions, how do we control it and what is the reason for controlling it?

Answer 7

We control soil mineral ions by adding fertiliser or growing in water cultures (hydroponics).
Minerals are essential for healthy growth to make proteins and other compounds.

Question 8

If the condition we are controlling is soil structure, how do we control it and what is the reason for controlling it?

Answer 8

We control soil structure by ploughing to break up the soil or adding fertiliser.
Better aeration (gaps) means better drainage and better mineral uptake.

Question 9

If the condition we are controlling is soil pH, how do we control it and what is the reason for controlling it?

Answer 9

We control soil pH by adding lime (calcium salts), which makes the soil more alkaline.
Unsuitable pH can decrease mineral uptake, so we must control it.

Question 10

If the condition we are controlling is carbon dioxide, light & heat, how do we control it and what is the reason for controlling it?

Answer 10

We control carbon dioxide, light & heat by burning paraffin, gas or oil lamps, which gives heat, CO2 and H2O. Heaters and lamps can control light and temperature.
We control it to prevent these limiting factors from reducing the rate of photosynthesis.

Question 11

What are glasshouses made of?

Answer 11

Glass walls & a glass roof.

Question 12

What are polytunnels made of?

Answer 12

Polytunnels are large steel tube frames covered in polythene.

Question 13

How do glasshouses mimic the greenhouse effect?

Answer 13

By increasing the internal temperature. This increases the rate of photosynthesis and therefore plant growth up to a point. Increasing the temperature above this point will not increase the rate further.

Question 14

What are paraffin lamps used for? How do paraffin lamps work for their particular purpose?

Answer 14

To increase CO2 levels. Paraffin (like any fossil fuel) releases CO2 and H2O when combusted (burnt). The excess water vapour in the air prevents water loss by transpiration from the leaves. Increased CO2 increases the rates of photosynthesis.

Question 15

How do greenhouses being transparent help plants?

Answer 15

Being transparent, plants have more access to light. However, the daylight hours can even be extended with the use of lamps and heaters.

Question 16

What can water cultures provide the perfect balance of?

Answer 16

Mineral ions.

Question 17

What effect do pests have on the growth of crops?

Answer 17

Pests can reduce the growth of crops.

Question 18

Give two examples of how pests negatively effect the growth of crops.

Answer 18

For example, the brown wheat mite damages leaves so they cannot photosynthesise. Growth is reduced.
The corn earworm reduces the quality of the crop. The crop is edible but it doesn’t look nice, thus it’s harder to sell.

Question 19

What are the two main methods for controlling pests?

Answer 19

Pesticides & Biological Control

Question 20

What do each of these chemicals kill:
(a) Herbicides
(b) Insecticides
(c) Fungicides
(d) Molluscicides

Answer 20

(a) Plants
(b) Insects
(c) Fungi
(d) Snails & Slugs

Question 21

What do pesticides kill?

Answer 21

Pests (microorganisms, insect and/or mammals)

Question 22

What are the downsides of pesticides?

Answer 22

They can be poisonous to humans and harmful to wildlife and slow to decompose.
They build up in tissues (bioaccumulation) and concentrate in food chains (biomagnification).
They can kill harmless insects/wildlife and the pest can develop resistance (natural selection).

Question 23

Give an example of a banned pesticide.

Answer 23

DDT

Question 24

What is one positive of DDT?

Answer 24

DDT eradicated malaria during WW2 by killing the mosquitoes that carried Plasmodium.

Question 25

What are the negatives of DDT?

Answer 25

DDT is very slow to decompose. It takes 10 years to decompose by half and even then, the half that has decomposed is DDE, which is another insecticide. Pests also develop a resistance to DDT due to natural selection.

Question 26

How has DDE been found all over the world?

Answer 26

DDE has been found all over the world due to its ability to spread via the wind.

Question 27

What processes does DDT go through?

Answer 27

It builds up in lipid tissues (bioaccumulation) and passes through food chains, growing more concentrated as it moves through trophic levels (biomagnification).

Question 28

Describe the process in 3 steps of mosquitos with resistant alleles surviving.

Answer 28

1. A few mosquitos have DDT resistant alleles. Most mosquitos have non-resistant alleles. (DDT is sprayed) 2. Mosquitos with resistant alleles survive. Mosquitos with non-resistant alleles die. (Survivors reproduce over several generations) 3. Population now consists entirely of mosquitos with resistant alleles.

Question 29

What are the qualities of a good pesticide?

Answer 29

A good pesticide: - controls the pest - is biodegradable (not stay in crops or soil) - is specific (kills only the pest) - doesn't accumulate on crops - is easy to apply - is safe (to transport, store & apply)

Question 30

What is biological control?

Answer 30

Biological controls the population of a pest by introducing something to the ecosystem.

Question 31

Give an example of natural predators.

Answer 31

Ladybirds were used to kill aphids in orange groves.

Question 32

What are the biological controls?

Answer 32

- Natural predators - Herbivores - Parasites - Pathogenic microorganisms - Sterile males - Pheromones

Question 33

How are herbivores used to control the population of a pest?

Answer 33

If the pest is a plant, herbivores can control it. A moth species was used to kill the prickly pear weed in South America.

Question 34

How are parasites used to control the population of a pest?

Answer 34

The Encarsia wasp was used to kill Whitefly. It lays its eggs inside the fly, which grows darker in colour as the wasp develop inside. Eventually the whitefly dies.

Question 35

How are pathogenic microorganisms used to control the population of a pest?

Answer 35

Myxomatosis was released in Australia to control the rabbit population.

Question 36

How are sterile males used to control the population of a pest?

Answer 36

The Tsetse fly causes a serious disease called 'sleeping sickness'. To reduce cases, sterile males were introduced into the population.

Question 37

How are pheromones used to control the population of a pest?

Answer 37

Insects produce pheromones to attract a mate. The mates are attracted into a trap. This method was used to remove aphids from plum crops.