Habitat destruction — Paper 4 · IGCSE Sciences - Co-ordinated (Double) 0654

13 Fig. 13.1 is a simplified diagram of the carbon cycle. carbon dioxide in atmosphere X industry decay decay and decomposition decay and decomposition product Fig. 13.1 (a) Identify the process that takes place at X. … [1] (b) Name the type of organism that gets its energy from decaying matter. … [1] (c) Combustion of fossil fuels increases the carbon dioxide concentration in the atmosphere. Explain how an increase in atmospheric carbon dioxide leads to global warming. … … … … … [3] (d) Deforestation prevents the removal of carbon dioxide from the atmosphere. List two other effects of deforestation. 1 … 2 … [2]

7 marks

Mark scheme: 13(a) X respiration ; 1 13(b) decomposer ; 1 13(c) solar radiation enters atmosphere ; reflected from Earth’s surface / atmosphere (as infrared) / Earth absorbs shorter wavelengths and warms up and gives out longer wavelengths (IR) / radiation (absorbed) and reradiated from Earth’s surface / owtte ; carbon dioxide, absorbs radiation / prevents radiation escaping / less radiation emitted than absorbed ; ref to the (enhanced) greenhouse effect / carbon dioxide is a greenhouse gas ; max 3 13(d) soil erosion ; loss of habitat ; species extinction ; flooding ; max 2

This question in 0654/42 Oct/Nov 2017

7 Fig. 7.1 shows two plants, A and B, of the same species. A B Fig. 7.1 (a) Plant A is healthy and plant B has an ion deficiency causing stunted growth. (i) Suggest the name of the ion that is deficient in plant B. … [1] (ii) Explain why this ion deficiency causes stunted growth. … … [1] (b) Fertilisers can prevent ion deficiencies in plants. Overuse of fertilisers can cause the eutrophication of bodies of water. Describe and explain the changes that occur during eutrophication to: (i) the plants on the surface of the water … [1] (ii) the plants under the surface of the water … … … [1] (iii) the bacteria in the water … … … [1] (iv) the oxygen content of the water. … … … [1] (c) Describe how plant roots obtain sugar from the leaves. … … … [2]

8 marks

Mark scheme: 7(a)(i) nitrate ; 1 7(a)(ii) (nitrates) needed for protein synthesis ; 1 7(b)(i) (plants on surface) grow more due to increased nitrates / fertiliser ; 1 7(b)(ii) (plants on surface) block sunlight underwater plants can’t photosynthesise (so die) ; 1 7(b)(iii) (bacteria) feed on / decompose dead plants and reproduce / increase in number ; 1 7(b)(iv) oxygen content decreases due to bacteria respiring ; 1 7(c) (glucose converted to) sucrose ; (named) sugar travels through phloem / translocation ; 2

This question in 0654/41 Oct/Nov 2018

4 The pie chart in Fig. 4.1 shows the different causes of deforestation in a country. firewood, 8% slash-and-burn agriculture, 39% livestock agriculture, 13% logging, 18% arable agriculture, 22% Fig. 4.1 (a) Calculate the total percentage of deforestation caused by agriculture. … % [1] (b) Describe how slash-and-burn agriculture can increase the carbon dioxide concentration in the atmosphere. … … … … … [3] (c) Describe the undesirable effects of deforestation on soil. … … … … … [3] (d) Forests are ecosystems. Define the term ecosystem. … … … … [2] [Total: 9]

9 marks

Mark scheme: 4(a) 74 (%) ; 1 4(b) combustion releases carbon dioxide ; photosynthesis removes carbon dioxide ; less carbon dioxide removed / less photosynthesis ; 3 4(c) soil erosion / lack of roots to hold soil together / rainfall washes soil away / landslides ; loss of nutrients ; flooding ; 3 4(d) (a unit containing all of the) organisms and their environment ; interacting together (in a given area) ; 2

This question in 0654/41 May/June 2019

13 (a) Excess use of fertilisers can cause eutrophication. Eutrophication eventually causes organisms in a lake to die. (i) Explain why producers underneath the surface of the water die. … … … … … [3] (ii) Explain why the death of producers eventually leads to the death of the fish in the lake. … … … … … [3] (b) Table 13.1 shows some information about two mineral ions found in fertilisers. Table 13.1 effect a deficiency in the mineral ion function of mineral ion mineral ion has on plant magnesium yellow leaves making amino acids Complete Table 13.1. [2] [Total: 8]

8 marks

Mark scheme: 13(a)(i) any three from increase in availability of, nitrate (ions) / ions ; (increased) growth of, plants / algae, on surface ; block (sun) light ; (plants below surface) can’t photosynthesise ; max 3 13(a)(ii) any three from decomposers / bacteria, feed on the (dead) plants ; decomposers / bacteria, multiply ; ref to respiration (of bacteria) ; oxygen removed / lack of oxygen (in the water) ; max 3 13(b) one row correct ; two rows correct ; mineral ions function effect of deficiency magnesium needed for chlorophyll synthesis yellow leaves nitrate Making amino acids stunted growth 2

This question in 0654/42 May/June 2019

7 (a) A lake is an example of an ecosystem. Fig. 7.1 shows a food chain from a lake. algae freshwater minnow perch pike osprey shrimp Fig. 7.1 (i) Identify the quaternary consumer in this food chain. … [1] (ii) State the number of trophic levels in this food chain. … [1] (iii) Explain why the number of trophic levels in this food chain is unusual. … … … … … … [3] (b) Table 7.1 shows definitions for three terms related to the environment. Complete Table 7.1 by adding the term that matches each definition. Table 7.1 definition term a network of interconnected food chains an organism that makes its own organic nutrients an organism that gets its energy from dead or waste organic matter [3] (c) A forest is also an ecosystem. Deforestation has negative impacts on the environment. Landslides are one example. Fig. 7.2 is a photograph of a landslide. Fig. 7.2 (i) Explain why deforestation can increase the chance of a landslide. … … … … [2] (ii) Describe how deforestation can lead to a decrease in the concentration of oxygen in the atmosphere. … … … … [2] [Total: 12]

12 marks

Mark scheme: 7(a)(i) pike ; 1 7(a)(ii) 6 ; 1 Question Answer Marks 7(a)(iii) it has more than five trophic levels ; energy is lost between the trophic levels ; by respiration / excretion / movement / heat / not all animal is eaten ; there is not usually enough energy to sustain a sixth trophic level ; max 3 7(b) food web ; producer ; decomposer ; 3 7(c)(i) tree roots stabilise soil ; (tree removal causes) soil to be exposed to wind / rain ; causing soil erosion ; max 2 7(c)(ii) photosynthesis produces oxygen ; fewer trees means less photosynthesis ; combustion (of trees) uses oxygen ; max 2

This question in 0654/42 May/June 2020

10 Increasing the concentration of nitrate ions in freshwater can cause eutrophication. (a) State two sources of nitrate ions which cause water pollution. 1 … 2 … [2] (b) Complete the sentences to explain how an increase in nitrate ions in water causes eutrophication. The increased availability of nitrate ions increases the growth of … on the surface of the water. Underwater plants cannot receive light and so cannot photosynthesise. Underwater plants die and are broken down by … . This causes an increase in … respiration. Dissolved … concentration in the water decreases, which causes aquatic organisms to die. [4] [Total: 6]

6 marks

Mark scheme: 10(a) fertiliser ; sewage ; AVP ; 2 10(b) producers / plants / algae ; decomposers / bacteria / fungi ; aerobic ; oxygen ; 4

This question in 0654/43 Oct/Nov 2020

10 (a) Fig. 10.1 is a flowchart showing the process of eutrophication. Complete the flowchart in Fig. 10.1. increase of excess fertiliser used on increase growth of surface … ions in soil plants the water plants can no longer dead plants are light is blocked from the … … plants under the surface so they die by bacteria dissolved … bacteria aerobically animals in the water die respire concentration of the water decreases Fig. 10.1 [4] (b) Deforestation can result in increased eutrophication, especially when it rains. Suggest why deforestation causes an increase in eutrophication. … … … … [2] (c) List two undesirable effects of deforestation on animals living in the forest. 1 … 2 … [2] (d) Trees make their own organic nutrients through photosynthesis. State the term used to describe organisms that make their own nutrients. … [1] (e) List three substances plants need to make their own organic nutrients. 1 … 2 … 3 … [3] [Total: 12]

12 marks

Mark scheme: 10(a) nitrate ; photosynthesise ; decomposed ; oxygen ; 10(b) increased, soil erosion / described ; soil contains nitrate (ions) ; 2 10(c) loss of food / disruption to food chain / web; loss of habitat ; extinction ; migration ; 2 10(d) producer ; 1 Question Answer Marks 10(e) carbon dioxide ; water ; chlorophyll ; (named) mineral ions ; max 3 3

This question in 0654/41 May/June 2021

4 (a) Table 4.1 shows the forest area in two different continents, A and B, in 1990 and 2010. Table 4.1 total forest area / thousand km2 continent in 1990 in 2010 A 9460 8640 B 9890 10050 (i) Compare the total forest area for continents A and B between the years 1990 and 2010. Use comparative data from Table 4.1 in your answer. … … … … … … [3] (ii) The change to the total forest area for continent A may affect the animals living in the forest. Describe three ways the animals may be affected. 1 … … 2 … … 3 … … [3] (iii) Explain two ways that deforestation causes the carbon dioxide concentration in the atmosphere to increase. 1 … … 2 … … [2] (b) Plants in a forest will compete for light. Auxin is a hormone that is responsible for the chemical control of shoot growth. Complete the sentences to describe how auxin causes shoots to grow towards the light. Auxin is made in the shoot … and moves and spreads through the plant. It collects on the … side of the shoot. Auxin stimulates cell … so this side will grow more. This results in the shoot bending towards the light. This growth response to light is called … . [4] [Total: 12]

12 marks

Mark scheme: 4(a)(i) Any two from: forest cover decreases in continent A ; forest cover increases in continent B ; B always has more forest cover than A ; and data manipulation with correct units ; 4(a)(ii) loss of food / disruption to food chain / web ; loss of habitat ; extinction ; migration ; 2 4(a)(iii) less photosynthesis so less carbon dioxide removed ; (more) combustion (of trees) so (more) carbon dioxide produced; 2 4(b) tip(s) ; shaded ; elongation ; phototropism ; 4

This question in 0654/43 May/June 2021

7 Discarded rubbish pollutes ecosystems such as oceans and rivers. (a) A student has written a definition of an ecosystem. Their definition is not correct. Circle the two words in their definition that are not correct. ‘An ecosystem is a unit containing all of the organisms and their offspring, interacting together, in a given time.’ [2] (b) Several countries estimate the average mass of discarded rubbish per person per day. Fig. 7.1 shows the results. 2.5 2.0 average mass of 1.5 discarded rubbish per person per day 1.0 / kg 0.5 0.0 A B C D E F country Fig. 7.1 (i) State which one of the countries in Fig. 7.1 discards the most rubbish per person per day. … [1] (ii) State the average mass of discarded rubbish per person per day in country E. … kg [1] (c) Pollution from excess use of fertilisers may cause eutrophication in rivers and lakes. Part of the process of eutrophication is an increase in the number of surface producers and the death of underwater producers. (i) Describe how an increase in the number of surface producers causes underwater producers to die. … … … [2] (ii) Explain how the death of underwater producers causes the death of aquatic animals. … … … … [3] [Total: 9]

9 marks

Mark scheme: 7(a) offspring circled ; 2 time circled ; 7(b)(i) C ; 1 7(b)(ii) 0.75 (kg) ; 1 7(c)(i) surface producers block light ; 2 so no photosynthesis ; 7(c)(ii) ref to decomposition of producers / AW ; 3 ref to (aerobic) respiration of decomposers ; reduction in (dissolved) oxygen ;

This question in 0654/42 Oct/Nov 2022

7 (a) Fig. 7.1 shows a food web. eagle snake dragonfly rat frog grasshopper fruit fly corn mango Fig. 7.1 (i) Use the information in Fig. 7.1 to state the name of one: herbivore … quaternary consumer … organism that occupies the first trophic level. … [3] (ii) State three ways that energy is lost between trophic levels. 1 … 2 … 3 … [3] (iii) State the principal source of energy for all biological systems. … [1] (b) Fertilisers are sometimes used to improve the growth of crop plants. Excessive use of fertilisers pollutes rivers. (i) Explain why this pollution increases the growth of producers in rivers. … … … … … … [2] (ii) Explain how death of producers in rivers reduces the oxygen concentration in the water. … … … … … … [2] [Total: 11]

11 marks

Mark scheme: 7(a)(i) grasshopper / fruit fly ; eagle / snake ; mango / corn ; 3 7(a)(ii) any three from: respiration / heat / metabolic processes ; not all of the organism is eaten ; not all the organism is digested / excretion / faeces / urine ; movement ; synthesis of (named) biological molecules / growth ; AVP ; 3 7(a)(iii) Sun ; 1 7(b)(i) fertilisers contain nitrate ions ; (nitrate ions required) for protein synthesis / amino acid production ; 2 7(b)(ii) ref to decomposers / decomposition ; ref to aerobic respiration ; 2

This question in 0654/42 May/June 2023

10 Fig. 10.1 shows aerial photographs of the same area taken at different times. Photograph A was taken in 1985. Photograph B was taken in 2000. Areas of forest are darker in the photograph and areas that have been cleared of trees are lighter. A darker forest areas area cleared of trees B Fig. 10.1 (a) The change shown in Fig. 10.1, between 1985 and 2000, affected the environment. (i) Explain why this change affected the concentration of carbon dioxide in the atmosphere. … … … … [2] (ii) Describe the effects of this change on animal species in the area. … … … … … [3] (b) The area in Fig. 10.1 can be described as an ecosystem. Define the term ecosystem. … … … … [2] (c) State the principal source of energy input into the ecosystem. … [1] (d) Asexual reproduction can be useful to plants in the wild. State two advantages of asexual reproduction. 1 … … 2 … … [2] [Total: 10]

10 marks

Mark scheme: 10(a)(i) (fewer trees so) less photosynthesis ; 2 less carbon dioxide removed (by trees) / more carbon dioxide in atmosphere ; 10(a)(ii) any three from: 3 extinction ; migration ; habitat / shelter / breeding grounds, destroyed ; food sources removed ; food chains / food webs, disrupted / affected ; 10(b) (a unit) containing (all of the) organisms and their environment ; 2 interacting together (in a given area) ; 10(c) Sun ; 1 10(d) any two from: 2 faster / quicker ; requires less energy ; idea that favourable traits are kept ; reproduction still possible if plant is isolated ;

This question in 0654/41 Oct/Nov 2023

4 (a) A scientist compares the relative concentrations of bacteria and dissolved oxygen in a river before and after fertiliser is added. Fig. 4.1 is a graph of the results. relative concentration dissolved oxygen bacteria distance downriver fertiliser enters river Fig. 4.1 Complete the sentences to describe and explain the changes seen in Fig. 4.1. Fertilisers entering the water contain … ions. An increase in the availability of these ions enables an increase in the … of producers on the surface of the water. Producers underneath the water are unable to … due to a lack of light and they die. The population of bacteria increases as they … the dead material. The concentration of dissolved oxygen decreases because the bacteria need oxygen for the process of … … . This entire process is called … . [6] (b) Bacteria reproduce by a type of asexual reproduction. (i) State the type of cell division used in asexual reproduction. … [1] (ii) Describe two ways that asexual reproduction is different from sexual reproduction. 1 … … 2 … … [2] (iii) State the name of one type of cell adapted for sexual reproduction in humans. … [1] [Total: 10]

10 marks

Mark scheme: 4(a) nitrate ; 6 growth ; photosynthesise ; decompose ; aerobic respiration ; eutrophication ; 4(b)(i) mitosis ; 1 4(b)(ii) any two from: 2 creates genetically identical offspring / clones ; only one parent required ; does not involve, gametes / fertilisation ; 4(b)(iii) gametes / egg / sperm ; 1

This question in 0654/43 Oct/Nov 2023

10 Scientists investigate eutrophication in a lake. They measure the relative abundance of different factors. Fig. 10.1 is a graph summarising the results. nitrate ions relative abundance light intensity dissolved oxygen under the surface time Fig. 10.1 (a) The growth of surface producers in the lake increases during eutrophication. Explain why, using the information in Fig. 10.1. … … … … … [2] (b) The number of underwater producers in the lake decreases during eutrophication. Explain why, using the information in Fig. 10.1. … … … … … [2] (c) State the name of the type of organisms that cause the change in dissolved oxygen in the lake in Fig. 10.1. … [1] [Total: 5]

5 marks

Mark scheme: 10(a) increase in nitrates ; 2 (increased) production of, amino acids / proteins (for growth) ; 10(b) decrease in light (availability) ; 2 so less / no, photosynthesis (so underwater producers die) ; 10(c) bacteria / decomposers ; 1

This question in 0654/41 Oct/Nov 2024

4 Tropical forests are some of the most important ecosystems in the world. (a) Fig. 4.1 is a food chain from a tropical forest. organism: banana tree grasshopper frog python … … … position in food chain: producer … … … Fig. 4.1 Complete Fig. 4.1 to show the position of each organism in this food chain. [2] (b) Fig. 4.2 shows another food chain that includes the python. banana tree monkey python Fig. 4.2 Explain why it is more efficient for the python to eat a monkey and not a frog. Include trophic levels in your answer. … … … … … [3] (c) The Amazon rainforest is a large tropical forest. In 1970, the Amazon rainforest covered an area of 4.1 million km2. By 2022, the area covered was estimated to be 3.3 million km2. One effect of this deforestation is a loss in biodiversity. Explain other negative effects that deforestation has on the environment. … … … … … … … [4] [Total: 9]

9 marks

Mark scheme: 4(a) grasshopper frog python 2 primary secondary tertiary or apex consumer consumer consumer predator ;; 4(b) energy is lost between trophic levels / idea that less energy will be lost ; 3 example of energy loss ; monkeys are primary consumers / frogs are higher along the food chain / idea of fewer trophic levels ; 4(c) 4 Effect (max. two) Explanation soil erosion / loss of soil / soil less lack of roots which hold soil in place fertile / landslides / flooding ; ; flooding ; silting up of rivers / rain not dispersed by roots / vegetation not there to slow flow ; loss of soil quality ; disruption of nutrient cycles / lack of humus ; reduced rainfall ; decreased transpiration from leaves ; increase of CO2 in reduced photosynthesis / less trees atmosphere / global to absorb CO2 / burning of trees ; warming / climate change ; increased air pollution ; burning of trees ; extinction ; loss of habitat/foods sources / shelter / breeding grounds ; eutrophication ; soil erosion and runoff (of minerals / nutrients) ;

This question in 0654/41 May/June 2025

3 Fig. 3.1 is a diagram showing some of the organisms in the Arctic ecosystem. polar bear gull seal little auk fish squid amphipods shrimps copepods phytoplankton Fig. 3.1 (a) (i) State the name of the type of diagram shown in Fig. 3.1. … [1] (ii) Identify the producer in Fig. 3.1. … [1] (iii) Identify one organism that occupies the second trophic level in Fig. 3.1. … [1] (iv) Identify one organism that is both a secondary and a tertiary consumer in Fig. 3.1. … [1] (v) The squid is a carnivore. Describe what is meant by the term carnivore. … … [1] (vi) Explain why the energy transfer from one trophic level to another is not efficient. … … … … … [2] (b) Deforestation on land can lead to a loss of soil as shown in Fig. 3.2. Fig. 3.2 (i) Explain how deforestation can increase the concentration of carbon dioxide in the atmosphere. … … … … … [2] (ii) Explain how deforestation can lead to flooding. … … … … … [2] [Total: 11]

11 marks

Mark scheme: 3(a)(i) food web ; 1 3(a)(ii) phytoplankton ; 1 3(a)(iii) copepods ; 1 3(a)(iv) (little) auk / fish ; 1 3(a)(v) (an animal that) gets its energy by eating (other) animals ; 1 3(a)(vi) (energy ‘lost’ by) 2 any two from: • egestion / faeces / indigestible material ; • respiration / heat loss ; • movement / muscle contraction ; • excretion ; • (there are) inedible parts / (there are) bones / (there are) teeth ; • AVP ; 3(b)(i) any two from 2 • (idea that as there are no or fewer trees so) no or less absorption of carbon dioxide OR (idea that as there are no or fewer trees so) no or less taking in of carbon dioxide; • no photosynthesis / less photosynthesis ; • carbon dioxide released by, combustion / burning / decomposition (of trees) / decomposition (of wood) ; 3(b)(ii) any two from: 2 • no or less roots or trees to hold or bind soil ; • no or less water absorbed by the roots or trees or soil OR increase in runoff ; • (increase in) deposition of soil into rivers ;

This question in 0654/41 Oct/Nov 2025