Human impact & biodiversity

Figure 5 shows part of the nitrogen cycle.

Use words from the box to complete the following sentences about the nitrogen cycle.

The nitrogen compounds in plants include_........

The nitrates from rotting dead plants are released into the soil by_........

180 million tonnes of nitrates were used by crops growing on farms in the UK in 2020.

Figure 6 shows the different sources of nitrates used by the crops.

Calculate the mass of nitrates from human-made fertiliser that was used by crops in 2020.

Some of the nitrates spread on fields as fertiliser get into lakes.

Name the type of pollution caused by the build-up of nitrates in lakes.

A student investigated how the concentration of nitrate affected the types of algae growing in three lakes.

Figure 7 shows microscope images of the algae in 1 mm³ of water, and the concentrations of nitrate ions in each lake.

Figure 8 shows a bar chart for the algae in lakes X, Y and Z.

Complete the bar chart for algae L and algae M in lake Z.

State two conclusions about the relationship between nitrate concentration and the algae in these lakes.

A build-up of algae on the surface of the lake can affect plants growing at the bottom of the lake.

Which statement shows how this would affect the plants at the bottom of the lake?

In 2018, all the plants were removed from the soil in a 1000 m² area.

A wall was built around this area to keep people out.

In 2019, three species of plants were recorded growing in this area.

Two of these species were indigenous.

State what is meant by the term ’indigenous’.

Name one piece of equipment that could be used to sample the number of indigenous plants in this area.

The area was surveyed every year and the number of plants of each species (A to H) was estimated.

Figure 20 shows the results.

State the trend shown by the data in Figure 20 for plant species C from 2019 to 2023.

A scientist suggested that the decrease in the number of plants of species B in 2021 was caused by competition from one of the other species of plant.

Which species is most likely to have out-competed species B in 2021?

Explain one way that this species could have out‑competed species B.

Give one way that species H could have moved into the area.

*(c) Figure 21 shows some plants growing in a small area of a 1000 m² field.

Devise a plan to estimate the number of named plant species growing in this field.

In 2018, all the plants were removed from the soil in a 1000 m² area.

A wall was built around this area to keep people out.

In 2019, three species of plants were recorded growing in this area.

Two of these species were indigenous.

State what is meant by the term ’indigenous’.

Name one piece of equipment that could be used to sample the number of indigenous plants in this area.

The area was surveyed every year and the number of plants of each species (A to H) was estimated.

Figure 6 shows the results.

State the trend shown by the data in Figure 6 for plant species C from 2019 to 2023.

A scientist suggested that the decrease in the number of plants of species B in 2021 was caused by competition from one of the other species of plant.

Which species is most likely to have out-competed species B in 2021?

Explain one way that this species could have out‑competed species B.

Give one way that species H could have moved into the area.

Plants also need water to grow.

Explain how water is absorbed into the plant.

6 In 2000, a council planted indigenous trees as part of a reforestation programme.

(a) Why were indigenous trees used instead of non-indigenous trees?

(b) The animal biodiversity in this reforested area was measured from 2004 to 2017. Biodiversity is measured on a scale from 0 to 1. 0 = low biodiversity 1 = maximum biodiversity Figure 12 shows the results.

2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 2022

Figure 12

(i) Draw a straight line of best fit on Figure 12 to show the main trend in this data.

(ii) Estimate the animal biodiversity of the reforested area in 2022.

(c) (i) The data to calculate animal biodiversity was collected using the following method.

• a 100 m² area was chosen

• three 1 m² quadrats were placed randomly on the ground

• animals inside the quadrat were counted

• the number of each species of animal was recorded

State two ways that the quality of the results from this method could be improved.

(ii) State why point A on Figure 12 was ignored when considering the trend in animal biodiversity.

(iii) The data shown in Figure 12 was collected during the summer. Explain why animal biodiversity would be different if the data had been collected in the winter.

(d) A scientist observes that trees at the edge of a forest shade part of a field. Describe how a belt transect could be used to see how light intensity affects the biodiversity of plants growing in the field.

6 (a) Figure 10 shows a method of investigating the rate of photosynthesis in a water plant.

(Source: © ghrzuzudu/Shutterstock)

Figure 10

(i) What are the products of photosynthesis?

(ii) The rate of photosynthesis can be measured by counting the number of bubbles of gas produced in one minute. Figure 11 shows some results from this investigation in different light intensities. Light intensity was changed by moving the lamp towards or away from the water plant.

Figure 11

Describe the effect of light intensity on the rate of photosynthesis. Use information from Figure 11 to help you.

(iii) The bubbles are different sizes and can be difficult to count. Describe how the quality of the results from this investigation could be improved.

(iv) Describe how this investigation could be changed to find the effect of temperature on the rate of photosynthesis.

(b) Increased nitrates can cause eutrophication in lakes. Explain how eutrophication will affect the fish living in the lakes.

9 (a) Scientists use a technique called mark and recapture to estimate animal populations in a habitat. A sample of the population is captured and a harmless mark is added to each animal. These animals are released and after a period of time the population is sampled again. This second sample includes some recaptured animals that have marks on them. The population can be estimated using this equation number marked in the first sample × size of the second sampl e number marked in the first sample size of the second sample population size = number recaptured in the second sample A scientist used this technique to determine the change in the population size of snails in a pond from March to July. Figure 14 shows the results.

Figure 14

(i) Using data from Figure 14, calculate the difference in the population size from March to July.

Difference in the population size_{..............................................................}

(ii) State two factors the scientist should control when sampling the habitat in March and July.

(b) This pond is affected by eutrophication. Explain one possible cause of eutrophication.

*(c) Reforestation has a beneficial effect on air composition and biodiversity. Animal conservation projects can also have a beneficial effect on biodiversity. Explain the beneficial effects of reforestation and animal conservation projects.

There are three levels of organisation in an ecosystem.

Which order shows the levels of organisation from lowest to highest?

Figure 3 shows food webs for two gardens.

Slug pellets are put on the soil around the lettuce plants in garden A and garden B.

Slug pellets kill slugs.

A scientist predicts that the number of caterpillars will decrease in garden A.

Give one reason why the number of caterpillars will decrease in garden A.

The scientist predicts that the number of caterpillars will increase in garden B.

Give one reason why the number of caterpillars will increase in garden B.

Figure 4 shows the population of slugs in garden A for five years.

Slug pellets were used during the first year.

slug

Describe the trend in the slug population from year 1 to year 5.

Flatworms from New Zealand that eat slugs are now living in the UK.

Which term describes a species from one country that is living in another country?

Figure 5 shows tiny white animals called mites on the skin of a slug.

The mites feed on blood.

Explain why these mites are classed as parasites.

The population of native white‑clawed crayfish in English rivers is decreasing due to an increasing population of American imported signal crayfish.

Figure 1 shows a white‑clawed crayfish.

Which term is used to describe the American imported signal crayfish now that it is living in English rivers?

American imported signal crayfish may eat white‑clawed crayfish.

Explain one other reason why the increasing population of American imported signal crayfish may have caused the decrease in white‑clawed crayfish.

The Environment Agency is developing methods of increasing the population of white‑clawed crayfish in English rivers.

Which term describes these methods?

White‑clawed crayfish cannot survive in rivers with a low concentration of oxygen.

Explain how eutrophication can cause the population of white‑clawed crayfish to decrease.

Figure 18 shows the leaves and flowers of water lily plants (Nymphaea odorata) on a lake.

Water lilies have stomata on the upper surface of the leaves.

Explain why water lilies have no stomata on the lower surface of the leaves.

The white petals of the water lily flowers cannot photosynthesise.

Which structure in leaf cells is the site of photosynthesis?

Glucose is made by photosynthesis.

Glucose is converted to another sugar to be transported in the plant.

What is the name of this sugar?

Describe how this sugar is transported from the leaves to the flowers of the water lily.

Figure 19 shows water lilies growing in a lake in Europe.

One water lily plant was brought from America 10 years ago and planted in the lake shown in Figure 19.

Explain why this non‑indigenous plant now covers the whole surface of the lake.

Explain how the water lilies will affect the biodiversity of this lake.

Figure 1 shows the sources of pollution and different levels of water pollution in a river.

Which part of the river will have the largest number of bloodworms?

Give the names of the two indicator species from the box which provide evidence for clean water.

Explain why sewage pollution in the river can decrease the oxygen levels in the water.

Excess fertilisers can cause a build‑up of nitrates in the rivers and lakes.

State the name given to a build‑up of nitrates in the lake.

State why the build‑up of nitrates is less likely to affect a river than a lake.

Figure 2 shows the leaves and flowers of water lily plants (Nymphaea odorata) on a lake.

Water lilies have stomata on the upper surface of the leaves.

Explain why water lilies have no stomata on the lower surface of the leaves.

The white petals of the water lily flowers cannot photosynthesise.

Which structure in leaf cells is the site of photosynthesis?

Glucose is made by photosynthesis.

Glucose is converted to another sugar to be transported in the plant.

What is the name of this sugar?

Describe how this sugar is transported from the leaves to the flowers of the water lily.

Figure 3 shows water lilies growing in a lake in Europe.

One water lily plant was brought from America 10 years ago and planted in the lake shown in Figure 3.

Explain why this non‑indigenous plant now covers the whole surface of the lake.