Ecology

Question 1

What are saprotrophs?

Answer 1

Saprotrophs: Heterotrophs that obtain organic nutrients from dead organisms by external digestion
They live on (or in) non-living organic matter, secrete digestive enzymes into it and absorbing the products
Unlike other types of heterotrophs, saprotrophs do not ingest food but use enzymatic secretion to facilitate external digestion

Question 2

What are detritivores?

Answer 2

Detritivores: Heterotrophs that obtain nutrients from detritus by internal digestion
Detritus is dead, particulate organic matter – such as decaying organic material and fecal matter
Humus is the term given specifically to the decaying leaf litter intermixed within the topsoil
Detritivores include dung beetles, earthworms, woodlice, snails and crabs

Question 3

What are autotrophs?

Answer 3

Autotrophs synthesise organic molecules from simple inorganic substances
Most autotrophs derive the energy for this process from sunlight (via photosynthesis)
Some may derive the needed energy from the oxidation of inorganic chemicals (chemosynthesis)

Question 4

What are heterotrophs?

Answer 4

Heterotrophs obtain organic molecules from other organisms via different feeding mechanisms and different food sources

Question 5

What are the three main requirements for an ecosystem to be sustainable?

Answer 5

1. Energy availability: Light form the sun provides the initial energy source for almost all communities
2. Nutrient availability: Saprotrophs decomposers ensure the constant recycling of inorganic nutrients
3. Recycling of wastes: Certain bacteria can detoxify harmful waste by-products (E.g. denitrifying bacteria such as Nitrosomnas)

Question 6

Describe the process of nutrient recycling

Answer 6

1. Autotrophs produce organic molecules as they transform inorganic molecules into organic molecules
2. Consumers will then obtain the organic molecules as they will eat the produces and obtain the organic molecules
3. When those consumers die, their cells are broken down by the digestive enzymes of decomposers and the nutrients are returned to the soil

Question 7

What are mesocosms

Answer 7

1. Mesocosms are enclosed environments that allow a small part of a natural environment to be observed under controlled conditions
2. They are usually used to test the sustainability of a nutrient cycle

Question 8

What is meant by positive and negative association?

Answer 8

If two species are typically found within the same habitat, they show a positive association.
Species that show a positive association include those that exhibit predator-prey or symbiotic relationships

If two species tend not to occur within the same habitat, they show a negative association
Species will typically show a negative association if there is competition for the same resources
One species may utilise the resources more efficiently, precluding survival of the other species (competitive exclusion)
Both species may alter their use of the environment to avoid direct competition (resource partitioning)

Question 9

What is the difference between a food chain and a food web?

Answer 9

A food chain shows the direction of energy flow from one species to another whereas a food web shows all the feeding relationships in a community with arrows which show the direction of the energy flow.

Question 10

Define trophic level

Answer 10

Feeding position of an organism in a food chain

Question 11

How is energy lost?

Answer 11

When energy transformations take place in living organisms the process is never 100% efficient. This is because:
o Energy is lost as heat
o Not all the parts of an organism are swallowed
o Not all of the parts of an organism can be digested and used
o Some organisms die before being eaten by an organism in the next trophic level
Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels

Question 12

Define biomass

Answer 12

The total mass of a group of organisms – consisting of the carbon compounds contained in the cells and tissues

Question 13

What are the four different spheres of the Earth?

Answer 13

o Hydrosphere: Water
o Biosphere: Living things
o Lithosphere: Ground
o Atmosphere: Air

Question 14

Name the different forms in which carbon is exchanged

Answer 14

o Atmospheric gases: CO2 and CH4
o Oceanic carbonates: Calcium carbonate in corals and shells, bicarbonates dissolved in water
o Organic materials: Carbohydrates, lipids, proteins
o Non-living remains: Detritus, fossil fuels

Question 15

Outline the carbon cycle in aquatic environments

Answer 15

1. In aquatic ecosystems, carbon is present as dissolved carbon dioxide and hydrogen carbonate ions
2. Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere
3. When carbon dioxide from the air diffuses into water it forms an acid, which lowers the pH
4. Acidic water can dissolve organism shells, weakening them, making them more prone to predation

Question 16

How is methane produced?

Answer 16

By methanogens (Archaean microorganisms) as a metabolic by-product in anaerobic conditions with acetic acid:
Acetic acid →Methane and Carbon Dioxide
Carbon Dioxide+Hydrogen →Methane and Water

Typical methanogens habitats include: Wetlands (swamps and marshes), Marine sediments (mud of lake beds) and the Digestive tract of ruminant animals (Cows, sheep, goats)

Methane is oxidized to carbon dioxide and water in the atmosphere which is why methane are not very rare

Question 17

What is peat?

Answer 17

A type of waterlogged soil that contains large amounts of partially decomposed organic matter due to acidic and/or anaerobic conditions in waterlogged soils:

1. Dead organisms are covered in water
2. The weight of the water forces the air out, creating an anaerobic environment
3. Microorganisms that would normally decompose the dead things die off
4. Energy-rich compounds are compressed and preserved

Peat is used as a fossil fuel through burning

Question 18

What are biofuels?

Answer 18

A fuel derived directly from living matter. Advantages include: Habitats don’t have to be disrupted to be mined in, the carbon dioxide released are absorbed faster than fossil fuels (a few days vs millions of years), making the cycle time shorter

Question 19

How is limestone produced? (5)

Answer 19

Limestone is inorganic, the majority of it is made of calcium carbonate or CaCO3

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

1. Marine organisms absorb carbon dioxide from their environment
2. Carbon dioxide is transformed into calcium carbonate, which is used to make their shells
3. The animals die and their shells accumulate on the ocean floor
4. Non-porous sedimentary rock layers form on top of the shells
5. Heat and pressure turn the shells into limestone

Question 20

What is the role of the atmosphere?

Answer 20

The role of the atmosphere is to retain heat at night and prevent fluctuations in temperatures

Question 21

Name four greenhouse gases

Answer 21

The greenhouse gases with the largest warming effect within the atmosphere are water vapour (clouds) and carbon dioxide
• Water vapour is created via evaporation of water bodies and transpiration and is removed via precipitation (rain)
• Carbon dioxide is made by cell respiration and burning fossil fuels
• It is removed via photosynthesis and absorption by oceans
Other greenhouse gases include methane and nitrogen oxides. These have less impact on the overall warming effect
• Methane is emitted from waterlogged habitats (like marshes) and landfills). It is also a gaseous waste produced by ruminants
• Nitrogen oxides are released naturally by certain bacteria and also is emitted in the exhaust by certain vehicles

Question 22

What are the factors which determine the impact of greenhouse gases? (2)

Answer 22

1. The ability to absorb long wave radiation. Gases that have a greater capacity to absorb long-wave radiation will have a greater warming impact (per molecule)
2. Concentration within the atmosphere. The greater the concentration of the gas the greater it’s warming impact will be. The concentration of a gas will be determined by both its rate of release and persistence within the atmosphere

Question 23

Outline the greenhouse effect (6)

Answer 23

1. The incoming radiation from the sun is short wave ultraviolet and visible radiation.
2. Some of this radiation is absorbed by the earths atmosphere.
   Some of the radiation is reflected back into space by t3. he earths surface.
3. The radiation which is reflected back into space is infrared radiation and has a longer wavelength.
4. The greenhouse gases in the atmosphere absorb some of this infrared radiation and re-reflect it back towards the earth.
5. This causes the green house effect and results in an increase in average mean temperatures on earth.

Question 24

Reasons for the rise in Co2 Concentrations

Answer 24

1. Deforestation: The removal of trees means that less carbon dioxide is removed form the atmosphere via photosynthesis
2. Increased farming/agriculture: This involves land clearing for cattle grazing, also ruminant cattle produce methane
3. Combustion: When fossil fuels (e.g. coal, oil, gas) are combusted to release energy, carbon dioxide gas is released as a by-product.

Question 25

Consequence of Global Warming (5)

Answer 25

1. More frequent extreme weather conditions
2. Some areas to become more drought affected, while others will be more prone to heavy rainfall
3. Melting of sea ice leads to destruction of artic habits
4. Marine species, sensitive to temperature change, may become extinct
5. As the ice melts, sea levels will rise and flood low lying areas of land.

Question 26

What is the difference between weather and climate?

Answer 26

Weather - Current conditions in a small area: can change rapidly
Climate - Patterns of temperature and precipitations over large periods of time

Question 27

Outline the process of ocean acidification (5)

Answer 27

1. Carbon dioxide combines with water to form carbonic acid
2. H+ ions will lower ocean pH
3. decrease in ocean pH is predicted to threaten the survival of marine organisms that require calcium carbonate
4. Shells and coral exoskeletons are also likely to begin to dissolve when ocean conditions are more acidic
5. This could also lead to the disappearance of coral reefs

Question 28

Describe the ocean’s role as a carbon sink

Answer 28

1. The oceans are a major carbon sink and absorb roughly a third of all human produced CO2 emissions
2. However CO2 solubility is temperature dependent (more soluble when cooler), so less CO2 will be absorbed as temperatures rise
3. When oceans absorb atmospheric CO2 some of it will remain dissolved in a gaseous state but most will be chemically modified