The Organism in the Environment (Edexcel IGCSE Biology: Double Science)

Lichens are organisms that grow well on stone walls in unpolluted air.

Lichens grow less well in polluted air.

Car exhaust fumes contain sulfur dioxide that pollutes air.

A scientist investigates the effect of pollution by cars in a city.

This is her method.

• Measure the percentage area of a stone wall in the city centre covered by lichen
• Repeat this measurement at different distances from the city centre

The table shows her results.

Distance from city centre in km	Percentage area covered by lichen (%)
0	0
2	6
4	20
6	30
8	50
10	64
12	70

Explain the results shown in the table.

Describe a method to measure the percentage of a stone wall covered by lichen.

Adding water to a powder called sodium metabisulphite will release sulfur dioxide gas.

Devise a laboratory investigation to find out the effect of sulfur dioxide gas on the heat released by germinating seeds.

Include experimental details in your answer and write in full sentences.

Genetic modification is a process used to improve crop yield.

Describe the role of a named vector in the process of genetic modification.

Weeds are plants that grow where they are not wanted.

Removing weeds reduces competition for mineral ions and improves crop yield.

Name the mineral ion used to make chlorophyll.

(1)

Two different methods can be used to remove weeds to improve crop yield.

• Method A: pull weeds out of the ground by hand

• Method B: spray weeds with a chemical that kills them

Design an investigation to find out which method produces the highest crop yield.

Include experimental details in your answer and write in full sentences.

(6)

The table gives some examples of biological processes.

Complete the table by giving the name of each process.

The first one has been done for you.

Examples of process	Name of process
Plants with a short growing season survive drought	Natural selection
Growth of algae in rivers polluted by fertiliser
Pollen transferred from one plant to another by an insect
Absorption of nitrate ions from soil using ATP

Zinc is poisonous to many plants and can affect natural selection.

A scientist investigates the ability of one grass species to survive at different distances from a zinc mine.

The scientist uses a sampling method to measure the percentage cover of this grass species at different distances from the zinc mine.

The graph shows the scientist’s results.

The zinc concentration in soil is higher near the zinc mine than it is further from the zinc mine.

Explain how natural selection could be responsible for the results shown in the graph between 0 and 100 metres.

(4)

Describe a method the scientist could use to compare the population size of the grass species at 50 metres and 100 metres from the mine.

(4)

Weeds are plants that compete with crop plants.

A scientist investigates the use of two different ways of reducing the population of weeds.

This is her method.

• Use chemical control in one field by spraying herbicides, a type of pesticide, that kill the weeds
• Use biological control in another field by releasing insects that eat the weeds
• Measure the mean (average) number of weeds in each field once a month from February to August

The table shows the scientist’s results.

Month	Mean number of weeds per m2
	chemical control	biological control
February	2	12
March	16	8
April	3	4
May	20	3
June	3	4
July	18	3
August	2	3

Describe a method to measure the mean number of weeds per m² in each field.

The scientist concludes that biological control is a better way of controlling weeds than chemical control.

Discuss this conclusion.

Use data from the table and your own knowledge to support your answer.

A scientist uses this method to investigate the effect of water quality on the growth of fish.

• fill a pond with filtered water
• fill another pond with unfiltered water
• place the same mass of fish of the same species in each pond
• determine the increase in total mass of fish in each pond after 180 days

The graph shows the scientist’s results.

The mean rate of increase in total mass of the fish in the filtered water is 0.214kg per day.

Calculate the difference between the mean rate of increase in the total mass of the fish in filtered and unfiltered water.

Unfiltered water contains more bacteria.

Explain why unfiltered water containing more bacteria affects the growth of fish.

Give one biotic variable the scientist controlled in the investigation.

Give a method the scientist could use to control interspecific predation in the ponds.

Deforestation is the cutting down of trees.

After deforestation, many dead leaves are left on the forest floor.

A student investigates the decomposition of these leaves.

This is her method.

• Collect four samples of dead leaves each with a mass of 6.0kg
• Label the samples P, Q, R and S
• Cut sample P into small pieces and keep at 10°C
• Cut sample Q into small pieces and keep at 20°C
• Do not cut sample R and keep it at 10°C
• Do not cut sample S and keep it at 20°C
• Measure the mass of each sample after three months

The graph shows her results.

Explain the results obtained by the student.

Calculate the difference between the rate of decomposition in sample P and the rate of decomposition in sample Q.

Give your answer in kg per month.

The student needs to control biotic variables in her investigation.

Give two biotic variables she should control.