Increasing crop yield

A scientist investigates how nitrate fertiliser, and the number of seeds planted per square metre, affect the yield of wheat. She adds different masses of nitrate fertiliser to fields containing different numbers of wheat seeds, and measures the yield after a few months. The table shows her results.

Plot a bar graph of these results to show how the yield varies with the mass of fertiliser added and the number of seeds planted. For each mass of fertiliser, draw two separate bars.

Describe the effect that changing the mass of nitrate fertiliser has on the yield of wheat.

Explain the effect that changing the number of seeds planted has on the yield of wheat.

The photograph shows an insect called a fire ant. These insects are a pest because their bite is painful.

Scientists compared two different methods for reducing the population of fire ants in

In the first method the scientists treated an area with pesticide. In the second method they released an organism that killed fire ants by biological control. They then estimated the number of fire ants every 6 months for a period of 30 months. The table shows the results of their investigation.

Plot a line graph to show the change in population of fire ants when pesticide was used and when biological control was used. Join the points with straight lines.

Explain the changes in the number of fire ants over the 30-month period when the area they were in was treated with pestcide.

Give two advantages of using biological control rather than pesticide to reduce the number of fire ants.

Suggest a method that could be used to estimate the population of fire ants in an area.

Farmers in Asia add fertiliser to their crops to increase the yield. Fertilisers usually contain nitrate, phosphate and potassium. The table shows the farmers’ crop yield when the crops are given a fertiliser lacking one of these three minerals. A figure of 100% is the maximum yield with all three minerals given.

State the mineral that has the greatest effect on crop yield.

Explain why this mineral has the greatest effect on crop yield.

Which crop is most affected by the lack of potassium?

Suggest why the minerals had different effects on lowland rice and upland rice.

The yield is the mass of the useable part of the crop and is measured in kg per m². The yield is often measured in dry mass rather than fresh mass.

Suggest why dry mass is used.

Suggest how the dry mass of 10 kg of fresh potato tubers could be determined.

The table gives data as a percentage of the yield with all minerals present. Explain why a percentage is used rather than changes in kg per m².

A farmer grew another crop with all three minerals added. The maximum yield obtained was 12 kg per m². He grew the same crop with no nitrate and the yield was 5 kg per m². Calculate the percentage of the maximum yield when the crop was grown with no nitrate. Show your working.

Flies lay their eggs in the urine and faeces that sticks to the wool on sheep. The eggs hatch and the larvae damage the skin of the sheep leading to infection. To reduce this problem, farmers in New Zealand have been developing sheep that have no wool growth on their legs, their backside or on the underside of their abdomen.

Suggest why flies are attracted to urine and faeces.

Farmers have crossed different breeds of sheep to produce offspring with desired characteristics. The characteristics of different breeds of sheep are shown in the

Describe how farmers could use selective breeding to develop sheep with bare legs and bare backsides.

Describe two differences between selective breeding and natural selection.

Farmers sometimes use pesticides to prevent flies attacking sheep. Give two problems with the use of chemical pesticides.

The table describes four different geographical regions. It also gives the amount of energy converted into plant biomass each year in each region.

Plot a bar graph on the grid to show the amount of energy converted into plant biomass each year in each region.

The amount of energy converted into plant biomass each year depends on the effect that abiotic (non-living) factors have on the rate of photosynthesis. Carbon dioxide is one of these abiotic factors. Name three other abiotic factors likely to affect the rate of photosynthesis.

Regions C and D have the same climate. Plants grown in region D have more energy converted into plant biomass than plants grown in region C. One reason for this is the use of selective breeding to produce high yielding crops.

Suggest two other reasons for more energy being converted into plant biomass in region D.

What is meant by the term selective breeding ?

Describe how you could use a quadrat to estimate the plant biomass in one of the regions.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow. Japanese knotweed: a space invader Invasive species are one of the biggest threats to wildlife and plants worldwide. The Department for Environment, Food and Rural Affairs (DEFRA) is introducing new measures that will ban the sale of some of the most dangerous foreign species in the UK. DEFRA is attempting to prevent a problem before it happens. The majority of invader species are plants. Of the most recent count of 2 721 non-native species, 1 798 were plants. Over £1.5 billion has been spent removing a single plant species, the Japanese knotweed. Japanese knotweed was first introduced as a garden plant. Japanese knotweed causes problems as it lacks natural predators in the UK and is very difficult to remove completely. Also, the vegetation of the knotweed is so dense, that other plants cannot grow through it. The fast-growing plant can grow up to 4 metres tall and is so strong it can break through paving stones and tarmac.

Japanese knotweed has a large network of underground stems (rhizomes). These rhizomes have to be killed if the plant is to be completely removed. The rhizomes might also be described as ‘underground runners’. All above-ground portions of the plant need to be controlled repeatedly for several years in order to weaken and kill the entire patch. Digging up the rhizomes is a common solution where the land is to be developed, as this is quicker than the use of herbicides. Scientists have looked at the weed’s natural predators with the aim of finding one that feeds on Japanese knotweed and little else. After testing the predators on 90 different UK plant species, including plants closely related to Japanese knotweed, they discovered that the insect, Aphalara itadori, was the best control agent. It keeps the weed under control in its native Japan by feeding on the sap in the transport tissue in the leaves, which reduces the growth of the plants. The introduction of Aphalara itadori would be the first time that biological control has been used in Europe to fight a weed.

Suggest what is meant by the term invasive species (line 1).

Calculate the percentage of invasive species in the UK that are plants (lines 6 and 7). Show your working.

Give one reason why Japanese knotweed has spread so successfully in the UK.

Suggest why the dense growth of the Japanese knotweed reduces the growth of other plants (line 11).

The use of Aphalara itadori to feed on Japanese knotweed is an example of biological control. Describe another example of biological control.

Name the transport tissue in the leaves that contains sap (line 25).

Suggest why the plant growth is reduced when insects feed on the plant sap (lines 24 and 25).

Why is it important that the insect ‘feeds on Japanese knotweed and little else’ (line 21)?