Topic 4 Ecology

Question 1

Define “species”.

4.1

Answer 1

A species is a group of organisms with similar
characteristics, which can potentially interbreed and
produce fertile offspring.

Understanding: Species are groups of organisms that can potentially
interbreed to produce fertile ofspring.

Question 2

Define “population”.

4.1

Answer 2

A population is a group of organisms of the same species who live in the same area at the same time.
* If two populations live in different areas they are unlikely to interbreed with each other.
* This does not mean that they are different species.
* If they potentially could interbreed, they are still members of the same species.

Understanding: Members of a species may be reproductively isolated in
separate populations.

Question 3

Outline how two populations of a species may become seperate species.

4.1

Answer 3

1. If two populations of a species never interbreed then they may gradually develop differences in their characters.
2. Even if there are recognizable differences, they are considered to be the same species until they cannot interbreed and produce fertile offspring.
3. In practice it can be very difffcult to decide whether two populations have reached this point and biologists sometimes disagree about whether populations are the same or different species.

Understanding: Members of a species may be reproductively isolated in
separate populations.

Question 4

Define “autotroph”.

4.1

Answer 4

• Autotrophs absorb carbon dioxide, water and inorganic nutrients such as nitrates from the abiotic (non-living) environment and use them to synthesize all the carbon compounds that they need.
• An external energy source such as light is needed to do this.

Understanding: Species have either an autotrophic or heterotrophic
method of nutrition (a few species have both methods).

Question 5

Define “heterotroph”.

4.1

Answer 5

• some organisms obtain their carbon compounds from other organisms, they are heterotrophic, which means feeding on others.

Understanding: Species have either an autotrophic or heterotrophic
method of nutrition (a few species have both methods).

Question 6

Outline the two main modes of nutrition.

4.1

Answer 6

There are two main modes of nutrition: autotrophic and
heterotrophic.
* autotrophs make their own food
* heterotrophs get food from other organisms

Understanding: Species have either an autotrophic or heterotrophic
method of nutrition (a few species have both methods).

Question 7

Define “mixotroph”.

4.1

Answer 7

Some unicellular organisms use both methods of nutrition. Euglena gracilis for example has chloroplasts and carries out photosynthesis when there is suffcient light, but can also feed on detritus or smaller organisms by endocytosis.
* Organisms that are not exclusively autotrophic or heterotrophic are mixotrophic.

Understanding: Species have either an autotrophic or heterotrophic
method of nutrition (a few species have both methods).

Question 8

Outline the discrepancies in plant and algae nutrition.

4.1

Answer 8

• There are small numbers of both plants and algae that do not fit the trend, because although they are recognizably plants or algae, they do not contain chloroplasts and they do not carry out photosynthesis.
• These species grow on other plants, obtain carbon compounds from them and cause them harm. They are therefore parasitic.

NOS: Looking for patterns, trends and discrepancies: plants
and algae are mostly autotrophic but some are not.

Question 9

Define “consumer”.

4.1

Answer 9

• Consumers feed off other organisms.
• These other organisms are either still alive or have only been dead for a relatively short time.
• Consumers ingest their food. This means that they take in undigested material from other organisms. They digest it and absorb the products of digestion.

Understanding: Consumers are heterotrophs that feed on living organisms
by ingestion.

Question 10

Define “detrivores”.

4.1

Answer 10

Detritivores ingest dead organic matter and then digest it internally and absorb the products of digestion.

Understanding: Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.

Question 11

Define “saprotroph”.

4.1

Answer 11

• Saprotrophs secrete digestive enzymes into the dead organic matter and digest it externally.
• They then absorb the products of digestion.
• They are also known as decomposers because they break down carbon compounds in dead organic matter and release elements such as nitrogen into the ecosystem so that they can be used again by other organisms.

Understanding: Saprotrophs are heterotrophs that obtain organic nutrients from dead organic matter by external digestion.

Question 12

Define “commnity”.

4.1

Answer 12

A group of populations living together in an area and interacting with each other is known in ecology as a community.

Understanding: A community is formed by populations of diferent
species living together and interacting with each other.

Question 13

Define “ecosystem”.

4.1

Answer 13

• Communities of living organisms interact in many ways with the soil, water and air that surround them.
• The non-living surroundings of a community are its abiotic environment.
• A community forms an ecosystem by its interactions with the abiotic environment.
• There are many of these interactions, but particularly important are transfers of chemical elements between populations in the community and the abiotic environment because these are an essential part of nutrient recycling

Understanding: A community forms an ecosystem by its interactions
with the abiotic environment.

Question 14

Outline how Autotrophs and heterotrophs obtain inorganic nutrients from the abiotic environment.

4.1

Answer 14

• Autotrophs obtain all of the elements that they need as inorganic nutrients from the abiotic environment, including carbon and nitrogen.
• Heterotrophs on the other hand obtain these two elements and several others as part of the carbon compounds in their ood.

Understanding: Autotrophs and heterotrophs obtain inorganic nutrients from the abiotic environment.

Question 15

List the supply of chemical elements needed in living organisms.

4.1

Answer 15

• Carbon, hydrogen and oxygen
• Nitrogen and phosphorus

Understanding: Autotrophs and heterotrophs obtain inorganic nutrients from the abiotic environment.

Question 16

Outline how nutrients recycled.

4.1

Answer 16

Organisms absorb the elements that they require as inorganic nutrients from the abiotic environment, use them and then return them to the environment with the atoms unchanged.

Understanding: The supply of inorganic nutrients is maintained by
nutrient cycling.

Question 17

Define “sustainable”.

4.1

Answer 17

Something is sustainable if it can continue indefnitely.

Understanding: Ecosystems have the potential to be sustainable over
long periods of time.

Question 18

List the requiremens needed in a sustainable ecosystem.

4.1

Answer 18

There are three requirements for sustainability in ecosystems:
1. nutrient availability
2. detoxifcation of waste products
3. energy availability.

Understanding: Ecosystems have the potential to be sustainable over
long periods of time.

Question 19

Outline how energy is supplied to organisms.

4.2

Answer 19

• Plants, algae and some bacteria absorb light energy and convert it by photosynthesis into chemical energy in carbon compounds. Because these organisms make their own food they are called producers.
• Consumers, detritivores and saprotrophs obtain energy from their food. There is chemical energy in carbon compounds in the food. Carbon compounds and the energy contained in them can pass from organism to organism along food chains, but all food chains start with a producer that originally made the carbon compounds by photosynthesis.
• Light is therefore the initial energy source for the whole community.

Understanding: Most ecosystems rely on a supply of energy from
sunlight.

Question 20

Outline how light energy is converted to chemical energy.

4.2

Answer 20

• Producers absorb sunlight using chlorophyll and other photosynthetic pigments.
• This converts the light energy to chemical energy, which is used to make carbohydrates, lipids and all the other carbon compounds in producers.
• Producers can release energy from their carbon compounds by cell respiration and then use it for cell activities. Energy released in this way is eventually lost to the environment as waste heat.
• However, only some of the carbon compounds in producers are used in this way and the largest part remains in the cells and tissues of producers. The energy in these carbon compounds is available to heterotrophs.

Understanding: Light energy is converted to chemical energy in carbon
compounds by photosynthesis.

Question 21

Explain how a food chain works.

4.2

Answer 21

• A food chain is a sequence of organisms, each of which feeds on the previous one.
• Consumers obtain energy from the carbon compounds in the organisms on which they feed.
• The arrows in a food chain therefore indicate the direction of energy fow.

Understanding: Chemical energy in carbon compounds flows through food
chains by means of feeding.

Question 22

List the activities in living organisms requiring energy.

4.2

Answer 22

Living organisms need energy for cell activities such as these:
* Synthesizing large molecules like DNA, RNA and proteins.
* Pumping molecules or ions across membranes by active transport.
* Moving things around inside the cell, such as chromosomes or vesicles, or in muscle cells the protein fibres that cause muscle contraction.

Understanding: Energy released by respiration is used in living organisms and converted to heat.

Question 23

Outline what happens to energy released by respiration in living organisms.

4.2

Answer 23

Energy stored in organic molecules (e.g. sugars and lipids) can be released by cell respiration to produce ATP
* This ATP is then used to fuel metabolic reactions required for growth and homeostasis
* A by-product of these chemical reactions is heat (thermal energy), which is released from the organism

Understanding: Energy released by respiration is used in living organisms and converted to heat.

Question 24

Outline the conversions of energy that living organisms can perform.

4.2

Answer 24

• Light energy to chemical energy in photosynthesis.
• Chemical energy to kinetic energy in muscle contraction.
• Chemical energy to electrical energy in nerve cells.
• Chemical energy to heat energy in heat-generating adipose tissue.
• They cannot convert heat energy into any other form of energy.

Understanding: Living organisms cannot convert heat to other forms of energy.

Question 25

Explain how heat is lost from ecosystems.

4.2

Answer 25

All organisms release energy from carbon compounds by cell respiration and use the energy for essential processes.
* Energy used in this way is converted into heat which is lost from the organism.
* No organisms can convert the heat energy back into chemical energy, and the heat is eventually lost from the ecosystem.

Understanding: Heat is lost from ecosystems.

Question 26

Define “biomass”.

4.2

Answer 26

Biomass is the total mass of a group of organisms. It consists of the cells and tissues of those organisms, including the carbohydrates and other carbon compounds that they contain. Because carbon compounds have chemical energy, biomass has energy.

Understanding: Energy losses between trophic levels restrict the length
o ood chains and the biomass of higher trophic levels.

Question 27

Explain the reason for the trend between trophic levels.

4.2

Answer 27

Trend: the energy added to biomass by each successive trophic level is less.
* Most of the energy in food that is digested and absorbed by organisms in a trophic level is released by them in respiration for use in cell activities. It is therefore lost as heat.
* The organisms in a trophic level are not usually entirely consumed by organisms in the next trophic level. Energy in uneaten material passes to saprotrophs or detritivores rather than passing to organisms in the next trophic level.
* Not all parts of food ingested by the organisms in a trophic level are digested and absorbed. Some material is indigestible and is egested in feces. Energy in feces does not pass on along the food chain and instead passes to saprotrophs or detritivores.

Understanding: Energy losses between trophic levels restrict the length
o ood chains and the biomass of higher trophic levels.

Question 28

Explain why losses of energy throughout the food chain restrict the number of trophic levels.

4.2

Answer 28

• As the losses occur at each stage in a food chain, there is less and less energy available to each successive trophic level.
• After only a few stages in a food chain the amount of energy remaining would not be enough to support another trophic level.
• For this reason, the number of trophic levels in food chains is restricted.

Understanding: Energy losses between trophic levels restrict the length
o ood chains and the biomass of higher trophic levels.

Question 29

Explain why biomass decreased along a food chain.

4.2

Answer 29

• Biomass, measured in grams, also diminishes along food chains, due to loss of carbon dioxide and water from respiration and loss from the food chain of uneaten or undigested parts of organisms

Understanding: Energy losses between trophic levels restrict the length
o ood chains and the biomass of higher trophic levels.

Question 30

Outline the effect of autotrophs on the atomosphere.

4.3

Answer 30

• Autotrophs absorb carbon dioxide from the atmosphere and convert it into carbohydrates, lipids and all the other carbon compounds that they require.
• This has the effect of reducing the carbon dioxide concentration of the atmosphere.

Understanding: Autotrophs convert carbon dioxide into carbohydrates
and other carbon compounds.

Question 31

Outline the presence of carbon dioxide in aquatic habitats.

4.3

Answer 31

• Carbon dioxide is soluble in water.
• It can either remain in water as a dissolved gas or it can combine with water to form carbonic acid (H2CO3).
• Carbonic acid can dissociate to form hydrogen and hydrogen carbonate ions (H+ and HCO-3 ).
• This explains how carbon dioxide can reduce the pH of water.

Understanding: In aquatic habitats carbon dioxide is present as a
dissolved gas and hydrogen carbonate ions.

Question 32

Explain how aquatic ecosystems obtain carbon.

4.3

Answer 32

• Both dissolved carbon dioxide and hydrogen carbonate ions are absorbed by aquatic plants and other autotrophs that live in water.
• They use them to make carbohydrates and other carbon compounds.

Understanding: In aquatic habitats carbon dioxide is present as a
dissolved gas and hydrogen carbonate ions.

Question 33

Distinguish how land plants and aquatic plants absorb carbon dioxide.

4.3

Answer 33

Autotrophs use carbon dioxide in the production of carbon compounds by photosynthesis or other processes.
* In land plants with leaves this diffusion usually happens through stomata in the underside of the leaves.
* In aquatic plants the entire surface of the leaves and stems is usually permeable to carbon dioxide, so diffusion can be through any part of these parts of the plant.

Understanding: Carbon dioxide difuses from the atmosphere or water
into autotrophs.

Question 34

Outline how carbon dioxide is produced by living organisms.

4.3

Answer 34

• Carbon dioxide is a waste product o aerobic cell respiration.
• It is produced in all cells that carry out aerobic cell respiration.
• Carbon dioxide produced by respiration digguses out og cells and passes into the atmosphere or water that surrounds these organisms.

Understanding: Carbon dioxide is produced by respiration and difuses out
of organisms into water or the atmosphere.

Question 35

Outline how methane is produced.

4.3

Answer 35

• The gas methane is **produced naturally by a group of prokaryotes called methanogenic archaeans. **
• They break down organic matter in anaerobic conditions and release methane as a waste product.
• This process happens in swamps, bogs and othersites where there are anaerobic conditions, so dead organic matter is not fully decomposed by saprotrophic bacteria and fungi.
• The methane may accumulate in the ground or diffuse into the atmosphere.

Understanding: Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some difuses into the atmosphere.

Question 36

Explain why methan concentration in the atmosphere is not high.

4.3

Answer 36

Methane is a relatively stable substance in the atmosphere,
but is eventually oxidized to carbon dioxide and water, so concentrations of methane in the atmosphere have remained low.

Understanding: Methane is oxidized to carbon dioxide and water
in the atmosphere.

Question 37

Outline how peat is formed.

4.3

Answer 37

• In some environments water is unable to drain out of soils so they become waterlogged and anaerobic.
• Saprotrophs cannot thrive in these conditions so dead organic matter is not fully decomposed.
• Acidic conditions tend to develop, further inhibiting saprotrophs from fully decomposing down the organic matter.

Understanding: Peat forms when organic matter is not fully decomposed
because of anaerobic conditions in waterlogged soils.

Question 38

Outline how coal is formed.

4.3

Answer 38

• Coal is formed when deposits of peat are buried under other sediments.
• The peat is compressed and heated, gradually turning into coal.

Understanding: Partially decomposed organic matter from past geological
eras was converted into oil and gas in porous rocks or into coal.

Question 39

Outline how oil and natural gas is formed.

4.3

Answer 39

• Oil and natural gas are formed in the mud at the bottom of seas and lakes.
• Conditions are usually anaerobic and so decomposition is often incomplete.
• As more mud or other sediments are deposited the partially decomposed matter is compressed and heated.
• Methane forms the largest part of natural gas.
• Deposits are found where there are porous rocks that can hold them and below the porous rocks that prevent the deposit’s escape.

Understanding: Partially decomposed organic matter from past geological
eras was converted into oil and gas in porous rocks or into coal.

Question 40

Define “combustion”.

4.3

Answer 40

• If organic matter is heated to its ignition temperature in the presence of oxygen it will set light and burn.
• The oxidation reactions that occur are called combustion.
• The products of complete combustion are carbon dioxide and water.

Understanding: Carbon dioxide is produced by the combustion of biomass
and fossilized organic matter.

Question 41

Define “combustion”.

4.3

Answer 41

• If organic matter is heated to its ignition temperature in the presence of oxygen it will set light and burn.
• The oxidation reactions that occur are called combustion.
• The products of complete combustion are carbon dioxide and water.
• it occurs naturally in some ecosystems where lighting can set fire to forest or grassland.

Understanding: Carbon dioxide is produced by the combustion of biomass
and fossilized organic matter.

Question 42

Outline animals containing calcium carbonate.

4.3

Answer 42

Some animals have hard body parts composed of calcium carbonate (CaCO3):
* mollusc shells contain calcium carbonate;
* hard corals that build reels produce their exoskeletons by secreting calcium carbonate.

Understanding: Animals such as reef-building corals and molluscs have hard parts that are composed of calcium carbonate and can become fossilized in limestone.

Question 43

Outline what happens to calcium carbonate in animals after their death.

4.3

Answer 43

• When these animals die, their soft parts are usually decomposed quickly.
• In acid conditions the calcium carbonate dissolves away but in neutral or alkaline conditions it is stable and forms limestone rock.
• Huge amounts of carbon are locked up in limestone on Earth.

Understanding: Animals such as reef-building corals and molluscs have hard parts that are composed of calcium carbonate and can become fossilized in limestone.

Question 44

Define “carbon flux”.

4.3

Answer 44

A flux is the transfer of the element from one pool to another. An example of carbon flux is the absorption of carbon dioxide from the atmosphere and its conversion by photosynthesis to plant biomass.

Skill: Construct a diagram of the carbon cycle.

Question 45

Define “carbon pool”.

4.3

Answer 45

A pool is a reserve of the element. It can be organic or inorganic. For example the carbon dioxide in the atmosphere is an inorganic pool of carbon. The biomass of producers in an ecosystem is an organic pool.

Skill: Construct a diagram of the carbon cycle.

Question 46

Explain how estimation of carbon fluxes can be made.

4.3

Answer 46

• It is not possible to measure global carbon fuxes precisely
  but scientists have produced estimates.
• These are based on many measurements in natural ecosystems and in mesocosms.
• Global fuxes are very large, so estimates are in gigatonnes

Application: Estimation of carbon fluxes due to processes in the carbon cycle.

Question 47

Define “greenhouse gas”.

4.4

Answer 47

Only certain gases in the atmosphere have the ability to trap
long-wave radiation and therefore act as a greenhouse gas.

Understanding: Carbon dioxide and water vapour are the most significant
greenhouse gases.

Question 48

Outline the most significant greenhouse gases.

4.4

Answer 48

• Carbon dioxide is released into the atmosphere by cell respiration in living organisms and also by combustion of biomass and fossil fuels. It is removed from the atmosphere by photosynthesis and by dissolving in the oceans.
• Water vapour is formed by evaporation from the oceans and also transpiration in plants. It is removed from the atmosphere by rainfall and snow.

Understanding: Carbon dioxide and water vapour are the most significant
greenhouse gases.

Question 49

Explain why the temperature drops so much more quickly at night in areas with clear skies than in areas with cloud cover.

4.4

Answer 49

Water continues to retain heat after it condenses to form droplets of liquid water in clouds. The water absorbs heat energy and radiates it back to the Earth’s surface and also refects the heat energy back.

Understanding: Carbon dioxide and water vapour are the most significant
greenhouse gases.

Question 50

Outline the other less significant greenhouse gases.

4.4

Answer 50

• Methane is the third most significant greenhouse gas. It is emitted from marshes and other waterlogged habitats and from landfill sites where organic wastes have been dumped. It is released during extraction of fossil fuels and from melting ice in polar regions.
• Nitrous oxide is another significant greenhouse gas. It is released naturally by bacteria in some habitats and also by agriculture and vehicle exhausts.

Understanding: Other gases including methane and nitrogen oxides have
less impact.

Question 51

Outline the two factors determining the warming impact of a greenhouse gas.

4.4

Answer 51

1. how readily the gas absorbs long-wave radiation (concentration of the gas)
2. the concentration of the gas in the atmosphere (rate it is released and rate that it remains in atmopshere)

Understanding: The impact of a gas depends on its ability to absorb long-wave radiation as well as on its concentration in the atmosphere.

Question 52

Outline how a warmed Earth emits radiation.

4.4

Answer 52

• The warmed surface of the Earth absorbs short-wave energy from the sun and then re-emits it, but at much longer wavelengths.
• Most of the re-emitted radiation is infrared, with a peak wavelength of 10,000 nm. The peak wavelength of solar radiation is 400 nm.

Understanding: The warmed Earth emits longer-wave radiation.

Question 53

Outline the greenhouse effect.

4.4

Answer 53

The Sun emits radiation and some of this reaches the Earth. The radiation is predominantly short wavelength.
1. 25% of it is absorbed in the atmosphere, with ozone absorbing much of the ultraviolet.
2. 75% of the solar radiation therefore reaches the Earth’s surface, where most of it is absorbed and converted to heat.
3. The surface of the Earth re-emits radiation, but at much longer wavelengths, mostly infrared (heat) .
4. A far higher percentage of this longer wavelength radiation is absorbed in the atmosphere before it has passed out to space.
5. Between 70 and 85% is trapped by gases in the atmosphere.
6. The gases re-emit the radiation and some of it passes back to the surface of the Earth, causing warming.

Understanding: Longer-wave radiation is reabsorbed by greenhouse gases which retains the heat in the atmosphere.

Question 54

Outline how carbon dioxide concentrations in the past can be deduced.

4.4

Answer 54

• Columns of ice have been drilled in the Antarctic
• Ice from deeper down is older than ice near the surface.
• Bubbles of air trapped in the ice can be extracted and analysed to fnd the carbon dioxide concentration.
• Global temperatures can be deduced from ratios of hydrogen
  isotopes in the water molecules.

Understanding: Correlations between global temperatures and carbon dioxide concentrations on Earth.

Question 55

Outline the correlation between carbon dioxide concentration and global temprature on Earth.

4.4

Answer 55

• Periods of higher carbon dioxide concentration repeatedly coincide with periods when the Earth was warmer.

Understanding: Correlations between global temperatures and carbon dioxide concentrations on Earth.

Question 56

Explain how concentrations of greenhouse gases influence global temperatures.

4.4

Answer 56

• The surface of the Earth is warmer than it would be with no greenhouse gases in the atmosphere.
• if the concentration of any of the greenhouse gases rises, more heat will be retained and we should expect an increase in global average temperatures.

Understanding: Global temperatures and climate patterns are infuenced by concentrations of greenhouse gases.

Question 57

Outline the climate patterns and global temperatures influenced by the concentration of greenhouse gases.

4.4

Answer 57

• More frequent extreme weather conditions (e.g. heat waves, cyclones, more powerful tropical storms, etc.)
• Some areas to become more drought affected, while other areas become more prone to periods of heavy rainfall
• Changes to circulating ocean currents
• The consequences of any rise in global average temperature are unlikely to be evenly spread.

Understanding: Global temperatures and climate patterns are infuenced by concentrations of greenhouse gases.

Question 58

Explain how the industrial revolution contributed to rising atmospheric concentrations of carbon dioxide.

4.4

Answer 58

Since the start of the industrial revolution 200 years ago, both the burning of fossil fuels and the CO2 concentration have increased faster and faster.
* Global temperatures have also increased over this period.

Understanding: There is a correlation between rising atmospheric concentrations of carbon dioxide since the start of the industrial revolution two hundred years ago and average global temperatures.

Question 59

Explain the reason for period of steepest rises in atmospheric carbon dioxide.

4.4

Answer 59

This is largely due to combustion of fossilized organic matter (coal, oil and gas)

Understanding: Recent increases in atmospheric carbon dioxide are largely due to increases in the combustion oossilized organic matter.

Question 60

Evaluate claims that human activities are not causing climate change.

4.4

Answer 60

Humans are emitting carbon dioxide by burning fossil fuels and there is strong evidence that carbon dioxide causes warming, so the claim is not supported by the evidence.
* Claims that human activities are not causing climate change will continue and these claims need to be evaluated.

Application: Evaluating claims that human activities are not causing climate change.

Question 61

Outline the effects of increased concentrations of dissolved carbon dioxide on coral reefs.

4.4

Answer 61

• CO2 released by humans have dissolved in the oceans.
• This has caused the pH to drop (ocean acidifcation)
• Marine animals such as reef-building corals need to absorb carbonate ions from seawater.
• Dissolved carbon dioxide makes the concentration of carbonate ions even lower (from chemical reactions).
• Carbon dioxide reacts with water to form carbonic acid, which dissociates into hydrogen ions and hydrogen carbonate ions. Hydrogen ions convert carbonate into hydrogen carbonate.
• With reduced carbonate concentrations in seawater not only can new calcium carbonate not be made, but it dissolves in existing corals, threatening the existence of all reef ecosystems.

Application: Threats to coral reefs from increasing concentrations of dissolved carbon dioxide.