Topic 4: Checklist Questions

Question 1

Outline that species are groups of organisms that can potentially interbreed to produce fertile offspring.

Answer 1

A species is a group of living organisms that can interbreed and produce fertile offspring.
Fertile offspring mean that the descendants of that interbreed are capable of producing more offspring

Question 2

State that species have either an autotrophic or heterotrophic method of nutrition, mentioning that a few species have both methods and be able to give and identify examples of each.

Answer 2

1. Autotrophic:
   Making their own complex organic molecules from carbon dioxide and other simple compounds (from abiotic environment)
   Almost all plants and some other organisms, eg. cyanobacteria, dinoflagellata
2. Heterotrophic:
   Organisms that obtain their organic compounds through feeding on other organisms
   All non-plant life organisms, eg. humans..

Some organisms feed both autotrophically and heterotrophically, eg. euglena gracilis

Question 3

Distinguish between consumers, detritivores and saprotrophs.

Answer 3

Consumers: eat dead organisms by ingestion

Detritivores: heterotrophs that obtain their organic nutrients from detritus by internal digestion of living organisms

Saprotrophs: Saprotrophs are heterotrophs that obtain their organic nutrients from dead organisms by external digestion

Question 4

Outline that consumers are heterotrophs that feed on living organisms by ingestion

Answer 4

Get carbon compounds by ingesting or eating
Detritivores eat other living organisms or recently living organisms
Some consumers are small, eg. paramecium take in food by endocytosis

Question 5

Outline that detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.

Answer 5

Detritivores are heterotrophs that obtain their organic nutrients from detritus by internal digestion
Eg. earthworms and dung beetles
Organism lives, dies, leaves organic material called detritus
Detritivores digest internally the organic material used as a source of energy

Question 6

Outline that saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.

Answer 6

Saprotrophs are heterotrophs that obtain their organic nutrients from dead organisms by external digestion
Also known as decomposers, because they feed on dead organic matter
Eg. fungi and bacteria
They secrete digestive enzymes onto the body they are feeding on to cause breakdown of complex organic compounds
The digested substances are absorbed and used by the saprotrophs

Question 7

State that a community forms an ecosystem by its interactions with the abiotic environment.

Answer 7

A community is formed by populations of different species living together and interacting with each other.
Complex and enormous range
Small and less complex

Question 8

Outline how the supply of inorganic nutrients is maintained by nutrient cycling.

Answer 8

1. Plants absorb carbon dioxide and water from the abiotic environment
2. They produce carbohydrates by photosynthesis
3. Plants are eaten by consumers
4. Nutrients are transferred from one organism to the next till they are released as waste
5. The supply of inorganic nutrients is maintained by nutrient cycling

Question 9

State that ecosystems have the potential to be sustainable over long periods of time.

Answer 9

Ecosystems can exist for a very long time if the recycling of nutrients is intact

Question 10

Outline that most ecosystems rely on a supply of energy from sunlight.

Answer 10

Ecosystems require a continuous supply of energy to fuel life processes and to replace energy that is lost

Question 11

Outline that light energy is converted to chemical energy in carbon compounds by photosynthesis.

Answer 11

Photosynthesis:
Traps the energy from sun
Transforms CO2 and water into glucose and many carbon based compounds through electron transport pathways, ATP synthase and calvin cycle

Question 12

State that living organisms cannot convert heat to other forms of energy.

Answer 12

It should be noted that living organisms cannot convert heat to other forms of energy, thus they release it in their immediate surroundings

Question 13

Outline how heat is lost from ecosystems.

Answer 13

All organisms lose heat by respiring, therefore heat is lost from ecosystems.

Question 14

Describe how chemical energy in carbon compounds flows through food chains by means of feeding.

Answer 14

Food chain:
Energy is lost from one trophic level to the other
When something is eaten, it is not entirely consumed, the waste material becomes food to detritivores and saprotrophs
Energy transfer is 10-20%
Top predators in the food chain receive less energy and have to consume a greater number of organisms to meet their requirements
A decrease in biomass as it goes up food chain

Question 15

Explain how energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

Answer 15

Energy is lost as heat from respiration, incomplete digestion and egestion of waste products along the food chain. As the amount of energy decreases with each trophic level, the number of individuals decreases as well. Each step of the pyramid supports the next, so there should be enough individuals to feed the next trophic level. The less energy there is, the fewer individuals the ecosystem can support.

Question 16

Understand different models used to represent organisms in an ecosystem and their significance.

Answer 16

A model that depicts the number of individuals in each trophic level of an ecosystem is called a numbers pyramid and it is usually represented as a stepped pyramid similar to the energy pyramid

Question 17

Outline that in aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions.

Answer 17

Aquatic plants and other autotrophs living in water require carbon in the form of dissolved carbon dioxide and hydrogen carbonate ions to produce more complex carbon compounds

Question 18

Outline that carbon dioxide diffuses from the atmosphere or water into autotrophs.

Answer 18

In aquatic plants, dissolved carbon dioxide diffuses into the leaves from the environment. In both cases, in water and on land, the carbon dioxide is used in the Calvin cycle to make carbohydrates and more complex carbon compounds. This lowers the concentration of carbon dioxide in the plant, setting up a concentration gradient that helps the carbon dioxide diffuse into the autotrophs

Question 19

Outline that autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.

Answer 19

Autotrophs take up carbon dioxide and give off oxygen during photosynthesis. However, both heterotrophs and autotrophs respire and produce carbon dioxide. Cellular respiration takes place in cells to produce carbon dioxide, just like in all heterotrophs. Plant cells contain chloroplasts, used for photosynthesis, as well as mitochondria, used for respiration.

Question 20

Explain how carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere.

Answer 20

During the day, carbon dioxide from respiration can be used directly by the chloroplasts for photosynthesis. In this case, carbon dioxide is not released from the leaves, as photosynthesis mainly occurs here. Carbon dioxide produced during respiration is a waste product of metabolism and diffuses out of the plant into the atmosphere or water.

Question 21

Explain how methane is produced from organic matter in anaerobic conditions by methanogenic archaeans, and some diffuses into the atmosphere or accumulates in the ground.

Answer 21

Steps:

1. Organic matter changed to organic acids and alcohol by bacteria in process called acidogenesis
2. Other bacteria convert these acids and alcohol into carbon dioxide and hydrogen and acetate (acetogenesis)
3. Methanogenic archaea can produce methane through the reaction of carbon dioxide and hydrogen or the breakdown of acetate.

Question 22

State that methane is oxidised to carbon dioxide and water in the atmosphere.

Answer 22

Methane is oxidised in the upper layers of the atmosphere through the interaction of methane with hydroxyl radicals, which are highly reactive. The reaction produces CO2 and water. The complete oxidation of methane to carbon dioxide and water involves several steps and includes several intermediate compounds.

Question 23

Outline how peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils.

Answer 23

Peat formation:
Saprotrophs must digest dead matter aerobically
But in waterlogged areas, the stagnant water creates an anaerobic environment in which the saprotrophs cannot grow
The saprotrophs die and the organic matter is only partially digested
New layers of dead matter fall and further compresses it
This forms peat

Question 24

Outline that partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulate in porous rocks.

Answer 24

Partially decomposed organic matter from past geological eras was converted into coal, oil or gas.

Fuel- fossil fuels formed a long time ago
Coal- found in thick layers beneath the surface
Oil and gas- found in porous rocks, not in gas forms
Gas reservoirs- found deep in the earth under high-pressure conditions that will maintain the gas in liquid form

Question 25

Outline that animals, such as reef-building corals and molluscs, have hard parts that are composed of calcium carbonate and can become fossilised in limestone.

Answer 25

Calcium carbonate dissolves in acid, but not in alkaline solutions.
The ocean is alkaline, thus the calcium carbonate won’t dissolve and will remain.
The conditions for limestone to form is to be slightly acidic.

Question 26

Outline that carbon dioxide and water vapour are the most significant greenhouse gases.

Answer 26

Both carbon dioxide and water vapour absorb longwave or infrared radiation and are considered the main greenhouse gases. Both gases are very abundant in the atmosphere, both naturally and due to human activity. The more greenhouse gases that are in the atmosphere, the stronger the effect of the greenhouse effect and the warmer the Earth becomes.

Question 27

Outline that other gases, including methane and nitrogen oxides, have less impact.

Answer 27

For a gas to contribute to the greenhouse effect, it needs to be able to absorb longer wavelength radiation

Methane absorbs more wavelength radiation than carbon dioxide and water vapor, and thus causes faster warming of the planet

Question 28

Explain how the impact of a gas depends on its ability to absorb longwave radiation, as well as its concentration in the atmosphere.

Answer 28

Longwave radiation emitted by the Earth’s surface is first absorbed by greenhouse gases and then re-emitted; this leads to retention of heat in the atmosphere

Question 29

Explain that the warmed Earth emits longer wavelength radiation (heat).

Answer 29

2. The Earth absorbs some of this shortwave radiation while some is reflected. This absorbed radiation is then re-emitted, mainly as infrared (heat), which is a longwave radiation (with a peak around 10 000 nm).

Question 30

Outline how longer wavelength radiation is absorbed by greenhouse gases, which retain the heat in the atmosphere

Answer 30

3. Part of this longer wavelength radiation escapes Earth’s atmosphere into space. However, much of it is absorbed by greenhouse gases in the atmosphere.
4. The greenhouse gases re-emit the absorbed light in all directions as heat. Some of this radiation is re-emitted towards the Earth, thus contributing to global warming.

Question 31

Outline that global temperatures and climate patterns are influenced by concentrations of greenhouse gases.

Answer 31

Since greenhouse gases affect global temperatures and the latter in turn affects climate patterns, then global temperatures and climate patterns must be influenced by changing concentrations of greenhouse gases

Question 32

Evaluate claims that human activities are not causing climate change.

Answer 32

Human contribution to climate change is an emotive subject and hotly argued by all the interested parties. Scientific claims must be based on evidence and made without bias, and there should be a tendency towards caution until all the evidence is fully assessed. Opponents of a theory can offer opinions based on scant or non-existent evidence without the rigour of scientific methodology. The consequences of climate change could be extremely severe so the evidence for the role of human activity must be carefully assessed.

Question 33

Explain how coral reefs are threatened by increasing concentrations of dissolved carbon dioxide.

Answer 33

Corals are very resistant to many of the threats. But their ability to regrow grow stable structures is affected by ocean acidification.

Since increasing concentration of dissolved CO2 leads to ocean acidification, like to have a negative impact on the ability to develop and on their ability to recover from damage. Their habitats will be replaced by non-calcifying organisms such as seagrass, resulting in underwater grasslands.