Topic 5: On the Wild Side

Question 1

5.1 Explain the term ‘ecosystem’.

Answer 1

A biological community of interacting organisms and their physical environment. It includes both abiotic and biotic factors.

Question 2

5.1 Explain the term ‘habitat’.

Answer 2

Habitat is the place, with a distinct set of conditions, where an organisms lives.

Question 3

5.1 Explain the term ‘population’.

Answer 3

A population consists of all the organisms of the same species living in a particular area (habitat), with the capability of interbreeding.

Question 4

5.1 Explain the term ‘community’.

Answer 4

A community consists of all of the organisms of different species (various populations) that live in the same habitat and interact with each other.

Question 5

5.2 How is the abundance of organisms in a habitat controlled by abiotic factors?

Answer 5

The abundance of any species varies because of abiotic factors:
- the amount of light (which is in turn affected by latitude, season, cloud cover and changes in the Earth’s orbit)
- climate i.e. the rainfall, wind exposure and temperature
- topograpy, which includes altitude (and this affects the climate), slope, aspect (which direction the land is facing) and drainage
- oxygen concentration
- the soil pH, texture and mineral ion concentration
- pollution of the air, water or land
When abiotic conditions are ideal for a species, organism can grow fast and reproduce successfully, increasing their population size (and vice versa).

Question 6

5.2 How is the abundance of organisms in a habitat controlled by biotic factors?

Answer 6

1. Interspecific competition is when organisms of different species compete with each other for the same resources. This can mean that the resources available to both populations are reduced. The populations might be limited by lack of a particular resource, and have less energy for growth and reproduction: so the population size will decrease.
2. Intraspecific competition is when organisms of the same species compete with each other for the same resources. The population of a species increases when resources are plentiful. Eventually resources will become limiting, and the population will begin to decline. A smaller population results in less competition for resources, which is better for growth and reproduction: so the population starts to grow again.
3. Predation is where an organism (the predator) kills and eats another organism (the prey). The population sizes or predators and prey are interlinked. As the prey increases, the predator population increases (because more food is available). As the predator population increases, the prey are eaten and their population begins to decrease. This means there’s less food for the predators, so their population decreases.
4. Grazing is a method of feeding in which a herbivore feeds on plants such as grasses, or other multicellular organisms such as algae.
5. Parasitism is a non-mutual relationship between species, where one species, the parasite, benefits at the expense of the other, the host

Question 7

5.2 How is the distribution of organisms in a habitat controlled by abiotic and biotic factors?

Answer 7

Organisms only exist where the abiotic factors they can survive in exist.
Interspecific competition (a biotic factor) can also affect the distribution of species: if two species are in competition, but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed.

Question 8

5.3 Explain how the concept of niche accounts for distribution and abundance of organisms.

Answer 8

A niche can be defined as the way an organism exploits its environment. The niche a species occupies within an habitat includes its interactions with other living organisms, and its interactions with non-living organisms. Every species occupies its own unique niche.
The abundance of a different species can be explained by the niche concept: two species occupying similar niches will compete, so fewer individuals of both species will be able to survive in the area.
The distribution of different species can also be explained by the niche concept: organisms can only exist in habitats where all the conditions that make up their role exist.

Question 9

5.4 Outline the stages of primary succession.

Answer 9

Primary succession begins in newly formed or exposed land, where there has never been a community before. 1. Seeds and spores are blown by the wind and begin to grow - the first species to colonise the area are called pioneer species. The pioneer species are specially adapted to cope with the hostile abiotic conditions (e.g. there’s no soil to retain water or nutrients, as well as a high salt concentration).
2. The pioneer species change the abiotic conditions as they die: microorganisms decompose the dead organic matter, forming a basic soil.
3. As the conditions become less hostile, the seeds of new organisms with different adaptions move in and grow. As these organisms die and decompose, the accumulation of organic matter in the soil increases the mineral ion content and water-holding capacity.
4. Larger and more complex organisms begin to move in. New species can change the environment so that it becomes less suitable for previous species.
At each stage, different organisms that are better adapted for the improved conditions move in, and out-compete the species already there.
Succession proceeds until a stable climax community is established. The nature of the climax community depends on the environmental conditions, such as climate, soil and species availability. While the number of niches increases as succession progresses, often the climax community will have lower biodiversity than preceding stages in the succession (as dominant species outcompete others).

Question 10

5.4 Explain what the difference between primary succession and secondary succession is.

Answer 10

Succession is the process by which an ecosystem changes over time. The biotic conditions change as the abiotic conditions change.
Primary succession begins in newly formed or exposed land, where there has never been a community before.
Secondary succession takes place on bare soil, where a previously existing community has been cleared. The pioneer species tend to be larger organisms than in primary succession (as the initial abiotic conditions are less hostile).

Question 11

5.5 Explain the overall reaction of photosynthesis.

Answer 11

Photosynthesis:
6CO2 + 6H2O (+ energy) → C6H12O6 + 6O2
The overall reaction of photosynthesis requires energy from light to split apart the strong bonds in water molecules (photolysis). Hydrogen (from the breakdown of water) is then combined with carbon dioxide, reducing it, to form a carbohydrate fuel, glucose. Hydrogen is therefore effectively stored in the fuel glucose, with oxygen being released into the atmosphere as a waste product. Glucose can later be oxidised during respiration to release energy.

Question 12

5.6 Outline the phosphorylation of ADP and the hydrolysis of ATP.

Answer 12

During respiration, glucose is oxidised to release energy. This energy is then used to make ATP in a phosphorylation reaction:
ADP(aq) + Pi(aq) (+energy) → ATP(aq)
In solution, the inorganic phosphate ions are hydrated (i.e. they are bonded to water). In the formation of ATP, the inorganic phosphate ions are separated from water: a large amount of energy is required to break these bonds.
ATP synthase then catalyses the phosphorylation of ADP into ATP. ATP(aq) is higher in energy than ADP(aq) and Pi(aq). So ATP in water stores energy in the form of chemical potential energy.

When energy is required (e.g. for metabolic reactions), ATP is hydrolysed:
ATP(aq) → ADP(aq) + Pi(aq) (+energy)
While a small amount of energy is initially required to remove the phosphate group from ATP, once removed the phosphate group hydrated: a large amount of energy is released as bonds form between the inorganic phosphate ion and water. ADP is now formed.

Phosphorylation is the addition of phosphate to a molecule.
Hydrolysis is the splitting of a molecule using water.

Question 13

5.7 Outline the light-dependent reaction in photosynthesis.

Answer 13

In the thylakoid membranes, photosynthetic pigments are arranged in photosystems (PSI and PSII).
When light is absorbed by PSII, the energy raises the electrons in the chlorophyll to a higher energy level. They are now in an ‘excited’ state. These electrons move down the electron transport chain (to PSI).
The electrons in PSII now need replacing. Light energy splits water molecules into protons, electrons and oxygen: H2O → 2H+ + 2e- + 1/2O2
The electrons produced replace those in PSII.
The protons are used in chemiosmosis: as the excited electrons from PSII move down the electron transport chain, going from one electron carrier to another in a series of redox reactions, energy is released. This energy is used by the electron carriers to pump protons from the stroma into the thylakoid space. This creates a steep electrochemical gradient across the thylakoid membrane. Protons move down the electrochemical gradient, back into the stroma, via the enzyme ATP synthase: this synthesises ATP from ADP and Pi in non-cyclic photophosphorylation.
Light energy is absorbed PSI, raising the electrons to an even higher energy level. These electrons, along with the protons from the stroma, combine with NADP to form reduced NADP.

Question 14

5.7 Outline cyclic photophosphorylation.

Answer 14

Cyclic photophosphorylation only uses PSI. In cyclic electron flow, the electron begins PSI, passing from one electron carrier to another, down an electron transport chain, and then returning to the chlorophyll. This energy is used by the electron carriers to pump protons from the stroma into the thylakoid space. This creates a steep electrochemical gradient across the thylakoid membrane. Protons move down the electrochemical gradient, back into the stroma, via the enzyme ATP synthase: this synthesises ATP from ADP and Pi in non-cyclic photophosphorylation. Cyclic photophosphorylation produces neither O2 nor NADPH (unlike non-cyclic photophosphorylation, NADP+ does not accept the electrons).

Question 15

5.8 i) Outline the light-independent reaction in photosynthesis.

Answer 15

Carbon dioxide is reduced using the products of the light-dependent reaction. The CO2 enters the leaf through the stomata and diffused into the stroma of the chloroplast.

1) In a reaction catalysed by RuBISCO, CO2 [1C] combines with ribulose bisphosphate (RuBP), a [5C] compound, to form an unstable 6C compound.
2) This rapidly breaks down into two molecules of the 3C compound, glycerate-3-phosphate (GP).
3) The hydrolysis of 2ATP (from the light-dependent reaction) provides energy to turn 2GP into 2 molecules of a different 3C compound, glyceraldehyde 3-phosphate (GALP). This is a reduction reaction, requiring 2H+ ions, provided by 2 reduced NADP molecules (from the light-dependent reaction). 2ADP, 2Pi and 2NADP are also produced.
4) Two molecules of GALP can be used to make a hexose sugar (e.g. glucose).
5) Five out of every six molecules of GALP produced in the cycle are used to regenerate RuBP. This requires ATP.

Overall:
6CO2 [1C] + 6RuBP [5C] (+ RuBISCO) = 12GP [3C] (+ 12NADP + 12ATP) = 12GALP [3C]:
2GALP [3C] = Glucose [6C]
10GALP [3C] (+ 6ATP) = 6RuBP [5C]

Question 16

5.8 ii) Discuss how the products of respiration are used in biological synthesis.

Answer 16

The Calvin cycle involves carbon fixation: where the carbon dioxide is incorporated into organic molecules. The products are simple sugars used by plants, animals and other organisms in respiration and the synthesis of biological molecules (polysaccharides, amino acids, lipids and nucleic acids).

• Carbohydrates: simple sugars (e.g glucose) are made from 2 GALP molecules, and polysaccharides are made by joining hexose sugars together.
• Lipids are made using glycerol (which is synthesised from GALP) and fatty acids (which is synthesised from GP).
• Amino acids can be made from GP.
• Nucleic acids: the sugar in RNA (which is ribose) is made using GALP.

Question 17

5.9 Outline the structure of chloroplasts in relation to their role in photosynthesis.

Answer 17

The site of photosynthesis is in the chloroplast. Chloroplasts are flattened organelles found in plant cells.
1) They have a double membrane called the chloroplast membrane - this keeps the reactants for photosynthesis close to their reaction sites. While the outer membrane is freely permeable to molecules such as CO2 and H2O, the inner membrane contains transporter molecules (membrane proteins) which regulate the passage of substances in and out of the chloroplast.
2) Thylakoids (fluid-filled sacs) have a large surface area to allow as much light energy to be absorbed as possible. The thylakoid space contains enzymes for the photolysis of water. Photosystems, electron carriers and ATP synthase are all embedded in the thylakoid membrane (to produce reduced NADP and ATP in the light-dependent reaction). Thylakoids are stacked up into structures called grana (singular: granum), linked together by bits of thylakoid membrane called lamellae (singular: lamella).
3) The stroma is the fluid surrounding the thylakoid membranes. It contains all the enzymes required for the light-independent reaction to take place. The compartmentalisation of these reactions within the stroma means that enzymes and substrates can be at concentrations that allow the reactions to be catalysed quickly.
4) Chloroplasts contain genes for some of their proteins (i.e. a DNA loop/plasmid).
[Photosynthetic pigments, including chlorophyll, combine with proteins to form a photosystem]

Question 18

5. 10 i) How is net primary productivity calculated?

ii) Outline the relationship between gross primary productivity, net primary productivity, and plant respiration.

Answer 18

NPP = GPP - R
The rate at which energy is incorporated into organic molecules by an ecosystem is the gross primary productivity (GPP) i.e. the total energy absorbed by the autotroph (producer).
Some of this energy is released in respiration (where respiratory substrates, such as the carbohydrate fuel glucose, are broken down). The rest of the energy becomes new plant biomass.
The rate at which energy is transferred into the organic molecules that make up the new plant biomass is called net primary productivity (NPP) i.e. this is the amount of energy available (at one trophic level) for the next trophic level.

Question 19

5.11 Outline how energy is transferred through ecosystems, explaining the role of each group in a food chain.

Answer 19

Producers are autotrophic organisms, capable of producing complex organic compounds from simple inorganic molecules through the process of photosynthesis. When carbon dioxide is fixed (or incorporated) into organic molecules that make up biomass, the energy fixed within these molecules can be transferred to other organisms in the ecosystem - this happens when organisms eat other organisms.

• Primary consumers (which tend to be herbivores), secondary consumers, and tertiary consumers (both of which tend to be carnivores) are all heterotrophs.
• Detritivores are primary consumers that feed on dead organic matter called detritus (e.g. woodlice and earthworms).
• Decomposers are species of bacteria and fungi that feed on the dead remains of organisms and animal faeces.
• The position a species occupies in a food chain is called its trophic level.

Question 20

5.11 Explain why only 10% of the energy available at a previous trophic level is transferred to the next trophic level.

Answer 20

The position a species occupies in a food chain is called its trophic level. The energy available in one trophic level is called the net productivity (or biomass). However not all energy gets transferred to the next trophic level:
- 60% of the available energy at each trophic level is not taken in by the next trophic level:
1. Autotrophs don’t use all the light energy available e.g. some is the wrong wavelength, some is reflected off the leave or passes through the leaf, and some misses the leaf.
2. Some parts of feed (e.g. roots or bones), aren’t eaten by organisms so the energy isn’t taken in, and decomposers break down the dead or undigested material.
3. Some food indigestible and comes out as waste (e.g. faeces).
About 40% of the energy from a previous trophic level is taken in to the next trophic level, as gross productivity. However:
1. 30% of this energy is then lost to the environment when organisms use energy produced from respiration for movement or body heat (respiratory loss).
2. 10% of the energy taken becomes biomass (e.g. it’s stored or used for growth). This is called net productivity.

Question 21

5.11 Outline how to calculate the efficiency of biomass and energy transfer.

Answer 21

Net productivity (the biomass/energy available in one trophic level) = gross productivity (the energy taken in from the previous trophic level) - respiratory loss

To calculate how efficient energy transfer from one trophic level to another is:
(Net productivity or biomass / gross productivity or energy received ) x 100

To calculate the energy transfer between two trophic levels you need to calculate the difference between the amount of energy in each trophic level (the net productivity of each level): first calculate the amount of biomass in a sample of the organisms. Then multiply this by the size of the total population. The difference in energy between the trophic levels is the amount of energy being transferred. However, there are problems: consumers might have taken in energy from sources other than the producer measured.

Question 22

5.12 Outline how records of both carbon dioxide levels and temperature form evidence for climate change.

Answer 22

Temperature records show a general trend of increasing global temperature over the last century. The temperature around the globe is measured using thermometers, giving it a reliable, if short-term record of global temperature change.
The carbon dioxide levels are similarly measured around the world, and show a correlating increase. It is generally assumed that an increase in CO2 results in an increase in global temperature. However, the difference between correlations (a common relationship between two variables) and causation (when a change in one variable caused a change in another variable) should be evaluated when given such data.

Question 23

5.12 Outline how dendrochronolgy can form evidence for climate change.

Answer 23

2) Dendrochronolgy determines how old a tree is using tree rings. Most trees produce one ring within their trunks every year. The thickness of the ring depends on the climate when the ring was formed (i.e. in a warmer climate, the conditions for growth are better and so the ring is thicker). Scientists can take cores through tree trunks, and date each ring. The thickness of the rings reveals what the climate was like each year i.e. the most recent rings are usually the thickest.

Question 24

5.12 Outline how pollen from peat bogs can form evidence for climate change.

Answer 24

3) Pollen is often preserved in peat bogs (due to the anaerobic and often acidic conditions of peat bogs slowing down the rate of decay). Peat bogs accumulate in layers so the age of the preserved pollen increases with depth. Scientists can take cores from peat bogs and extract pollen grains from the different aged layers. They then identify the plant species the pollen came from. Only fully grown (mature) plants produce pollen, so the samples only show the species that were successful at the time. Because plant species vary with climate, the preserved pollen will vary as climate changes over time e.g. a gradual increase in pollen from a plant species that’s more successful in warmer climates, or a decrease in pollen from a plant that needs cold climates, would show a rise in temperature.

Question 25

5.13 Explain the causes for anthropogenic climate change.

Answer 25

The general scientific consensus is that the recent, rapid increase in global temperature has anthropogenic causes (i.e. it’s been caused by human activity).
Solar radiation passes through the atmosphere and is absorbed by the Earth’s surface. The Earth’s surface then emits long wavelength infrared radiation back into the atmosphere. Some of this infrared radiation, absorbed by gases in the atmosphere, is re-emitted back to Earth. These greenhouse gases effectively trap the infrared radiation, causing an increase in the average surface temperature of the Earth. Human activity has led to an increase in greenhouse gases:
1) CO2 concentration is increasing as more fossil fuels like coal, oil and natural gas are burnt, e.g. in power stations or petrol in cars. Burning fossil fuels released CO2.
2) CO2 concentration is also increased by the destruction of natural sinks (which keep CO2 out of the atmosphere by storing carbon) e.g. trees take in carbon dioxide through photosynthesis and store the carbon as organic compounds. CO2 is released when trees are burnt in deforestation.
3) Methane concentration is also increasing in the atmosphere e.g through the extraction and burning of fossil fuels, the increase in decaying waste (released by respiring decomposers), and the increase in cattle (which release methane as a waste gas).

Question 26

5.14 i) How can data be used to make predictions about climate change?

Answer 26

Data that’s already been collected on atmospheric greenhouse gas concentrations can be extrapolated, i.e. used to make predictions about how it will change in the future. Often, a number of emissions scenarios are produced:
- minimum emissions: the concentrations of greenhouse gases might peak, but will then reduce (this is assuming that human significantly reduce their greenhouse gas emissions).
- medium emissions: these are stabilising scenarios in which greenhouse gas concentrations continue to increase, bu eventually level off (due to steps taken to reduce emissions).
- maximum emissions: the worst case scenarios, in which the rate of production of emissions continues to increase and greenhouse gas concentrations end up very high.
These predictions are used in (computer) models of future climate change to see how different aspects of global climate (e.g. temperature), will be affected.

Question 27

5.14 ii) Explain how models for climate change have limitations.

Answer 27

• We don’t know how greenhouse gas emission will change in the future, or what attempts there will be to manage the atmospheric concentration of greenhouse gases (and how successful they’ll be).
• We don’t know to what extent future emissions will affect the climate change.
• We don’t know to what extent other factors will affect either the atmospheric concentration of greenhouse gases, or the climate directly e.g. the change in concentration of greenhouse gases due to natural cause, without human influence, isn’t known.

Question 28

5.15 Explain the effects of climate change on plants and animals.

Answer 28

Global warming can result in changing rainfall patterns and a change in seasonal cycles, which in turn affects:

• the development and the life cycles of some organisms: organisms are adapted to the timing of the seasons and the changes that take place (e.g. in temperature, day length, weather and food). This can affect things like mating, hatching, migration, which can in lead to a reduction in development and life cycles.
• the distribution of some species: all species exist in their ideal conditions for survival. When these conditions change, they’ll have to migrate to an area where the conditions are better - this can affect the ecosystems, and biotic relationships.

Question 29

5.16 Outline the effect of temperature on the rate of enzyme activity and its impact on plants, animals and microorganisms.

Answer 29

An increase in temperature means that the enzyme and substrate molecules have more kinetic energy - they therefore move faster, and have enough energy to surpass the activation energy. This results in more frequent successful collisions, increasing the rate of reaction.
An increase in temperature can increase the rate of growth and development (e.g. by increasing the rate of photosynthesis in plants, a process catalysed by enzymes). This also means that they will progress through their life cycle faster.
However, when temperatures exceed the optimum temperature, the molecules vibrate more - this breaks the bonds in the tertiary structure of the enzyme, which forms their specific 3D shape. The active site becomes denatured, and metabolic reactions can no longer be catalysed.
If the temperature becomes too high, then the metabolic reactions will slow down. The rate of growth and development will decrease, and organisms will progress through their life cycle slower.
Temperature change can also affect the distribution of some species. All species exist in their ideal conditions for survival. When these conditions change, they’ll have to migrate to an area where the conditions are better - this can affect the ecosystems, and biotic relationships.

Question 30

5.17 Explain how evolution can come about through gene mutation and natural selection.

Answer 30

A selection pressure can affect an organisms chance of survival and reproduction. Genetic variations within a species, a result of random mutations, crossing over and independent assortment (during meiosis), can result in individuals who have advantageous genes, and therefore an advantageous phenotype. These individuals have a selective advantage, and are more likely to survive, reproduce and pass on their advantageous alleles to their offspring. Over time, the number of individuals with the advantageous alleles increases. Evolution is therefore a change in allele frequency over time.

Question 31

5.18 Outline the role of the scientific community in validating new evidence.

Answer 31

Scientists within the scientific community accept the theory of evolution because they’ve shared and discussed evidence to make sure it’s valid and reliable.

1) In the peer review process, other scientists who work in that particular area read and review the work. The peer reviewer has to check that the work is valid, that it supports the conclusions and that experiments are carried out to the highest possible standard.
2) Scientific journals are used to share new ideas, theories, experiments, evidence and conclusions. They allow other scientists to repeat experiments and see if they get the same results using the same methods. If the results can be replicates, then the evidence collected is considered to be reliable.
3) Scientific conferences allow scientists to present their work. Other scientists can then ask questions and discuss their work with them. Conferences are valuable because they’re an easy way for the latest theories and evidence to be shared and discussed.

Question 32

5.18 Outline the evidence that supports the accepted theory of evolution.

Answer 32

1) Genomics is a branch of science that used DNA technology to determine the base sequence of an organism’s genome (DNA sequencing) and the functions of its genes. This allows scientists to make comparisons between organisms’ DNA . Evolution (a change in the allele frequency) is caused by gradual changes in the base sequence of organisms’ DNA. Closely related species that diverged (evolved to become different species) more recently should have more similar DNA, as less time has passed for changes in DNA sequence to occur.
2) Proteomics is the study of proteins (e.g. the size, shape and amino acid sequence of proteins). The sequence of amino acids in a protein is coded for by the DNA sequence in a gene. Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.

Question 33

5.119 Explain how allopatric speciation occurs.

Answer 33

Speciation is the development of a new species. A population can become reproductively isolated due to geographical isolation. Geographical isolation takes place when a physical barrier divides a population of a species. Environmental conditions on either side of the barrier will be slightly different, providing different selection pressures. Genetic variations within each gene pool, a result of random mutations, crossing over and independent assortment (during meiosis), can result in individuals who have advantageous genes, and therefore an advantageous phenotype. These individuals have a selective advantage, and are more likely to survive, reproduce and pass on their advantageous alleles to their offspring. Over time, the number of individuals with the advantageous alleles will increase in each population. Due to the reduced gene flow between populations, the change in allele frequency will lead to differences accumulating in the gene pools of the separated populations, so that they eventually evolve into two separate species. This is known as allopatric speciation.

Question 34

5.19 Explain how sympatric speciation can occur.

Answer 34

Sympatric speciation occurs when two populations become reproductively isolated in the same environment without any geographical barrier, due to other isolating mechanisms:

• behavioural changes: two groups do not respond to each others’ courtship rituals.
• seasonal changes: individuals from the same population develop different flowering or mating seasons, or become sexually active at different times of the year.
• physical changes: changes in genitalia prevent successful mating.
• ecological isolation: the species occupy different parts of the habitat.

Question 35

5.20 Explain why conclusions about controversial issues can be doubtful.

Answer 35

Scientific conclusions about controversial issues (such as what actions should be taken to reduce climate change or the degree to which humans are affecting climate change) can sometimes depend on who is reaching the conclusions, i.e. biased conclusions.

e. g. A scientist working for an oil company might be more likely to say humans aren’t causing climate change (to help keep oil sales high).
e. g. A scientist working for a renewable energy company may be more likely to say humans are causing climate change (this would increase sales of energy produced from renewable sources).

Question 36

5.21 Outline how knowledge of the carbon cycle can be applied to methods to reduce atmospheric levels of carbon dioxide.

Answer 36

Carbon dioxide is absorbed by plants in the process of photosynthesis. Carbon is therefore fixed into organic molecules, becoming a part of their biomass. It is then passed on to animals when they eat the plants, and to decomposers when they break down the dead organic matter of both plants and animals. The carbon is returned to the atmosphere as all living organisms carry out aerobic respiration, releasing CO2. However, if dead organic matter isn’t decomposed (e.g. in deep oceans or peat bogs), the carbon compounds undergo fossilisation (a result of heat and pressure, taking place over millions of years). The carbon in fossil fuels is released back into the atmosphere as CO2 when fossil fuels are combusted.
To reduce atmospheric CO2 concentration, either the amount of CO2 going into the atmosphere needs to be decreased, or the amount of CO2 being taken out the of atmosphere needs to be increased.

Question 37

5.22 Give and explain two examples for the effective management of the conflict between human needs and conservation.

Answer 37

Human needs require the combustion of fossil fuels and the deforestation of trees, all adding to the greenhouse effect. However, the conflict between human needs and conservation can be managed effectively:

1) Biofuels are fuels produced from biomass (material that is or was living) - they provide an alternative to fossil fuels. They’re often made from crops, which can be replanted after harvesting, making biofuels a sustainable resource. Biofuels are considered to be carbon-neutral, with no net increase in atmospheric CO2 concentration when biofuels are burnt: the CO2 produced is the same as the amount of CO2 taken in when the material was growing.
2) Reforestation is the planting of new trees in existing forests that have been depleted. CO2 is converted to carbon compounds in the process of photosynthesis, and stored as plant tissues in the trees. This means that more CO2 is removed from the atmosphere, contributing less to global warming.