Ecology

Question 1

A species

Answer 1

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

Question 2

A population

Answer 2

A group of organisms of the the same species, who live in the same area at the same time.

Question 3

Autotrophs

Answer 3

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

Question 4

Heterotrophs

Answer 4

Heterotrophs cannot make all the carbon compounds that they need and instead obtain them from other organisms.

Question 5

Modes of heterotrophic nutrition

Answer 5

• Saprotrophs (aka decomposers)* obtain organic nutrients from dead organisms by external digestion. They secrete digestive enzymes into material such as dead leaves or wood. Protein, cellulose and other carbon compounds are digested externally and the saprotrophs then absorb the substances that they need - e.g. bacteria or fungi.
• Consumers* feed on living organisms by ingestion. This means that they take other organisms into their digestive system and absorb.
• Detritivores* obtain organic nutrients from detritus by internal digestion, which is dead material from living organisms such as leaves, feces or decomposing animals.

Question 6

A community

Answer 6

A group of populations of different species living together and interacting with each other in an area. Trophic relationships and the food web is one interaction, for example.

Question 7

Ecosystem

Answer 7

An area in which a community interacts with each other and their abiotic environment.

Question 8

Mesocosm

Answer 8

An ecosystem that sustainable over a long period of time, due to recycling of nutrients and water, with the addition of an indefinitely continuing source of energy, usually in form of light. Hence, autotrophs and saprotrophs are essential due to their recycling capabilities.

Three requirements for sustainability in ecosystems:

1. nutrients availability (can by recycle indefinitely)
2. detoxification of waste products (species (e.g. decomposers) usually use it as a resource)
3. energy availability (cannot be recycled, depends on continued energy supply, usually the sun)

Question 9

Field work - how to find association between species

Answer 9

Testing for association between two species using the chi-squared test with data obtained by quadrant sampling.

Question 10

Different energy sources

Answer 10

1. Plants, algae and some bacteria absorb light energy and convert it by photosynthesis into chemical energy in carbon compounds - producers.
2. Consumers, detritivores and saprtothops obtain chemical energy from their food.

Carbon compound’s chemical energy can be passed along the food chain, but all food starts with a producer. Hence, light is the initial energy source for most communities.

Question 11

Energy losses

Answer 11

1. Some organisms die before they are eaten by the successive organisms in the food chain.
2. Some parts of organisms are not eaten, such as bones, hair and gall bladders.
3. Some parts of organisms are indigestible, such as cellulose in food eaten by humans, and egested as feces
4. Cell respiration from carbon compounds used for essential processes such as muscle contraction or active transport. Energy used this way is converted into heat which is lost from the organism. No organism can convert the heat energy back into chemical energy (inside their bodies). Therefore, an external energy source needs to replace energy lost

Question 12

Trophic levels

Answer 12

The position of an organism in the food chain, which commonly contain rarely more than five levels.

The limited length of food chains can be explained by the energy flow and energy losses, since only a small proportion of energy and biomass is passed on from one trophic level to the next; the percentage is variable but unlikely to be more than 10%. This can be seen in energy pyramids.

Question 13

Energy pyramids (+ how to draw them)

Answer 13

They show how much energy flow through one trophic level in a community. The bars should be drawn to scale and symmetrically.

Question 14

Difference between energy and inorganic nutrients in ecosystems

Answer 14

• Energy* is supplied in form of light and converted to chemical energy by producers. This chemical energy is eventually converted to heat, which cannot be recycled and lost to the ecosystem.
• Nutrients* in ecosystems are limited but can be recycled Examples are carbon, nitrogen or phosphorus.

Question 15

Carbon sources in air and water

Answer 15

Autotrophs absorb carbon dioxide either from the atmosphere or from water by diffusion and converted into carbohydrates and other carbon compounds.

Question 16

Elements of the Carbon Cycle (diagrammatically)

Answer 16

Flux - transfer of carbon
Sinks/pool - carbon storage (can be organic or inorganic)

elements:
• cell respiration of producers, consumers, saprotrophs
• photosynthesis in producers 
• combustion of fossil fuels
• forest fires

Question 17

Methane in the carbon cycle (Methanogenesis)

Answer 17

Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diffuses into the atmosphere. This breaking down of organic matter occurs in swamps and other sites.

Question 18

Atmospheric monitoring of CO2

Answer 18

CO2 concentrations show an annual fluctuation. There is a drop from May to October and then a rise through the next May. This is due to an excess of photosynthesis over cell respiration globally. These changes follow northern hemisphere reasons, as the area of land is greater and CO2 concentrations are greater on land than in the sea.

Moreover, the annual fluctuation is also rising because of the human activities.

Question 19

Limestone in the carbon cycle

Answer 19

Limestone consists mainly of calcium carbonate and includes corals and molluscs have hard parts that are composed of calcium carbonate and can become fossilised in limestone (while the soft part decomposes quickly).

Approximately 10% of all sedimentary rocks on Earth is limestone. About 12% of the mass of the calcium carbonate is carbon, so huge amounts of carbon are locked up in limestone on Earth. This carbon can be released if the limestone reacts with acid –> ocean acidification

Question 20

Formation of fossil fuels

Answer 20

peat and coal
Peat forms when organic matter is not fully decomposed because of anaerobic conditions in waterlogged soils don’t allow saprotrophs to break it down further since they need oxygen for respiration. Acidic environments develop that also avoid any methanogens to break down material. When it is crushed, it converts into peat and then coal.

oil and gas
Silt is deposited on the bed of some shallow seas, together with remains of dead marine organisms. The organic matter is only partially decomposed because of anaerobic conditions. The silt was converts into shale, which compounds from the organic matter becoming oil or gad trapped in pores in the rock.

Question 21

The Greenhouse Effect (+ atmospheric concentration of greenhouse gases)

Answer 21

The solar radiation is predominantly short wavelength, of which 25% of it is absorbed in the atmosphere, with the ozone absorbing much of the ultraviolet. 75% reaches the Earth’s surface where most is absorbed and converted to heat. The surface then re-emits radiation in much long wavelengths, most infrared (heat). A far higher percentage of this longer wavelength radiation is absorbed in the atmosphere before it has passed out to space. Between 80 and 85% is trapped by greenhouse gases and re-emited back to the Earth, causing warming.

• All of the greenhouse gases together make up less than 1% of the atmosphere.

Question 22

Carbon dioxide and water vapour: greenhouse gases

Answer 22

Carbon dioxide and water vapour are the most significant greenhouse gases, which retain heat in the atmosphere.

• 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 and transpiration in plants. It is removed from the atmosphere by rainfall/snow. 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 reflects the heat energy back (hence, a clear night sky cools a place faster).

Question 23

Methane and nitrogen oxides: greenhouse gases

Answer 23

Methane and nitrogen oxides have less impact due to their low atmospheric concentration. However, methane and nitrous oxide causes much more warming per molecule than carbon dioxide or water vapour.

• Methane is third most significant greenhouse gas and is emitted from marshes and other waterlogged habitats, landfill sites with dumping of organic wastes, extraction of fossil fuels and from melting ice in polar regions.
• Nitrous oxide is released naturally by bacteria, in agriculture and vehicle exhaust.
• The concentration of gas depends on the rate at which it is released into the atmosphere and how long on average and remains there. The rate at which water vapour enters the atmosphere is immensely rapid, but it remains the only nine days on average, whereas methane remains in the atmosphere for twelve years and carbon dioxide for even longer.

Question 24

Carbon emissions and global warming

Answer 24

Over the last 150 years atmospheric carbon dioxide concentrations have risen above the natural range (seen in arctic ice), largely due to combustion of fossilised organic matter (coal, oil and gas). The temperature and CO2 concentration correlate but are not directly proportional as there are other variable factors that affect temperatures. As a result global warming is much more uneven year on year than rises in CO2 (sometimes rapid increases, sometimes not).

Question 25

Coral reefs and carbon dioxide

Answer 25

Coral reefs are threatened from increasing concentrations of disavowed carbon dioxide.

Ocean acidification makes it harder for marine life to form calcium carbonate for the skeletons and make it dissolve, since carbon dioxide reacts with water to from carbonic acid which dissociates into hydrogen and hydrogen carbonate ions.

Question 26

Carbon Fixation

Answer 26

Autotrophs convert carbon dioxide from the atmosphere into carbohydrates and other carbon compounds that they require.

Question 27

The Biochemical Carbon Cycle

Answer 27

sinks:
• calcium carbonate in limestone
• carbon compounds in organisms partially decomposed in anaerobic conditions (swamps) 
• carbon compounds in producers, consumers, saprotrophs
• CO2 in atmosphere
• CO2 in oceans
• methane in atmosphere
• coal
• oil and gas

flux:
• breakdown by acid
• fossilisation
• partial decomposition
• combustion of fossil fuels
• photosynthesis
• ocean uptake and loss
• cell respiration
• death
• oxidation
• feeding
• methanogenesis by archaea