6.3.1 Ecosystems

Question 1

Ecosystem

Answer 1

A dynamic set of interactions between the living populations of organism and its abiotic environment..

Question 2

State biotic factors that affect can affect population size.

Answer 2

3 Ps:
Parasitism
Predation
Pathogens (communicable disease)

Competition:
Intraspecific and interspecific

Question 3

Describe the different types of competition

Answer 3

Intraspecific:
Competition in a population between species that are the same.

Interspecific:
Competition between species that are not the same.

Question 4

Describe abiotic factors that can affect an ecosystem.

Answer 4

Light (in plants):
More light allows more plants as they photosynthesise more.
Competition can occur due to differing light availability.

Water availability (affects plants more):
Lack of water leads to water stress and plants wilting
Water is needed for photosynthesis

Temperature:
This affects enzymes in metabolic conditions
Seasonal change can cause migration and hibernation in animals and seed dormancy and flowering in plants.

Question 5

What is biomass and how can the biomass of an organism be calculated.

Answer 5

Biomass:
The dry weight of all organic matter in an organism.

Calculating biomass:

1. Measure the mass of an organism.
2. Place the organism in an oven and heat very low at a low temperature to allow evaporation of water.
3. Heat organism until no mass change occurs.
4. Measure the final mass —> Biomass.

Question 6

How is the energy contained in a biomass calculated?

Answer 6

Energy can be calculated by how much heat is released from combustion.

The dry biomass of an organism is heated in the presence of saturated oxygen in a calorimeter.

The energy given off in the reaction is recorded.

Question 7

Pyramid of numbers.

Answer 7

Ecological pyramid that shows the number of individuals in a trophic level.

This is not the most representative as organism differ in mass

Question 8

Pyramid of biomass

Answer 8

Ecological pyramid that shows the weight of biological matter at each trophic level.

Question 9

Pyramid of energy

Answer 9

Ecological pyramid that shows the energy content of biological matter at each trophic level.

This is the most efficient as it accurately reflects energy available at the next trophic level.

Question 10

Niche

Answer 10

A population's role in its ecosystem. This includes:
Its feeding role in the food chain.
The type of food a population consumes.
Its microhabitat.
Its reproductive method

Question 11

Detritus

Answer 11

Dead and waste matter not eaten by consumers

Question 12

Nitrogen fixation

Answer 12

The process in which nitrogen gas, N2, is converted to ammonia.
N2–> NH3

Ammonia reacts with water to form ammonium ions.

Nitrogen fixation only occurs in aerated soil as it is an oxidation process.

There are nitrogen fixing bacteria present in the soil and some in the root nodules in plants.

Question 13

What genus of nitrogen fixing bacteria are in the soil.

Answer 13

Azotobacter:

They use nitrogenase to convert nitrogen gas to ammonia.

Question 14

The genus of nitrogen fixing bacteria are present at the root nodule of legumes.

Answer 14

Rhizobium:
They have a mutualistic relationship with leguminous plants.

Rhizobium get carbohydrates made by the plant in photosynthesis.
The leguminous plants gain amino acids from the nitrogen fixed by Rhizobium.

Question 15

Nitrification and the bacteria involved in the process.

Answer 15

The process of converting ammonia into nitrite (NO2-) and nitrates (NO3-)

This involves nitrifying bacteria free in the soil:
Nitrosomonas: converts ammonia into nitrites
Nitrobacter: converts nitrites into nitrates.

Question 16

Denitrification

Answer 16

The process of converting nitrates in the soil, back to nitrogen gas in the air.

This involves the enzyme nitrate reductase:
This is an anaerobic process that takes place in waterlogged soil.

Question 17

Ammonification

Answer 17

The process carried out by decomposers:
Converts nitrogen containing compounds in dead matter (proteins, nucleic acids), urine (urea) and faeces, into ammonium compounds.

Question 18

Processes in the nitrogen cycle remove nitrogen from the air.

Answer 18

Nitrogen fixation: Conversion of nitrogen gas into ammonia.

Lightning: Electrical current which splits nitrogen in the air to ammonia.

Question 19

Processes in the nitrogen cycle add nitrogen back into the air.

Answer 19

Denitrification: The breakdown of nitrates back into nitrogen gas back bacteria.

Question 20

Difference between decomposers and detritivores.

Answer 20

Decomposers:
An organism that feeds on and breaks down dead organic matter into inorganic ions like ammonium. They perform external digestion by secreting extracellular enzymes.
Includes fungi and bacteria.

Detritivores:
Organisms that feed on detritus. They break down detritus into smaller pieces that increases surface area for decomposers.
They perform internal digestion: using extracellular enzymes internally.
Include: earthworms, woodlice.

Question 21

Processes that remove carbon dioxide from the air. (2)

Answer 21

CO2 dissolving in oceans:
The sea is a sink. Carbon dioxide dissolves and forms inorganic ions which plants can using, such as carbonates.

Photosynthesis:
Photosynthetic organism convert CO2 into organic matter like: carbohydrates, protein and lipids.

Question 22

Processes that add carbon dioxide back into the air. (3)

Answer 22

Combustion of fossil fuels:
Fossil fuels contain organic matter which is released in the formed of carbon dioxide when undergoing complete combustion

Respiration performed by all producers, consumers and decomposers:
Organic molecules broken down to release ATP. CO2 is released as a waste product.

Decomposition:
Decomposers break down organic material to release CO2.

Question 23

Death in the carbon cycle.

Answer 23

When producers and consumers die, they are broken down by decomposers.

Organic matter is converted back into carbon dioxide and release in the air.

If there are not decomposers present then organic matter in not broken down. It can become trapped under soil over thousands of years and become fossils, oil or natural gas.

Question 24

Feeding in the carbon cycle.

Answer 24

Carbon molecules are passed down the food chain.

Producers—> 1 Consumers—> 2 Consumers—> 3 consumers etc

Question 25

Primary succession

Answer 25

Area of land newly formed or exposed.
There is no soil or organic material.

This includes:
Land formed from a volcanic eruption.
Creation of sand dunes

Question 26

Pioneer community

Answer 26

Colonisation of an inhospitable environment by pioneer species: i.e lichen, algae.

Pioneer species arrive by:
Spores/ seeds blew by the wind.
Dropping from small animals and birds.

Question 27

Characteristics of pioneer species.

Answer 27

Seeds that germinate very rapidly.

Autotrophic

Tolerant to extreme conditions.

May be nitrogen fixing- able to add mineral to the soil

Question 28

Intermediate community

Answer 28

This is when pioneer organisms die and are decomposed.

This releases organic matter to form soil that contains nitrates and retains water.

This allows secondary pioneers to survive: i.e mosses.
Eventually conditions are improved which allow tertiary colonisers to survive.

More organisms die and are decomposed which increases organic material—> supporting more complex organisms

Question 29

Climax community

Answer 29

Stable community that shows little change over time.

This includes a few dominant species that are very well adapted to the environment—> outcompete species.

BUT- the more successful a dominant species, the decrease in biodiversity

Question 30

Deflected succession.

Answer 30

When human activity stops the progression of succession.

This mainly affected by agriculture:
Grazing and trampling from farm animals keep environment as ‘grassland’.
Removing existing vegetation to plant desired species–> climax community.

Question 31

Distribution

Answer 31

The location in which individual organisms are found in an ecosystem.

Question 32

Measuring distribution. (3)

Answer 32

Belt/line transect is used: Shows change in organisms present over an area.

Belt: Two parallel lines are drawn on the ground down an area: i.e 10m.
Sample is taken in the area between the two lines.

Line: A line is drawn on the ground and a sample is taken at regular intervals, i.e every 50 cm.

Question 33

Abundance

Answer 33

The number of individuals of a species present in an area at any given time.

Question 34

Measuring plant abundance

Answer 34

Quadrats: measure percentage cover
A grid is created and a rand point is generate.

Quadrats are placed according to the point.

The number of individual plants contained in the quadrat is counted.

Their species are identified using a key.

Data is recorded on an organised sheet.

Population = No. of individual plants/ Area of sample(m2)

Question 35

Measuring plant abundance

Answer 35

Quadrats can be used if animal is small and slow moving.

Capture-mark- release-recapture is mainly used.

Question 36

Describe the Capture-mark-release-recapture process

Answer 36

1. A large sample of individuals of a species is captured in a given area.
2. Each individual is marked/ tagged.
3. The individuals are released and allowed to naturally distribute themselves.
4. Individuals a captured again in the original sample area.
5. The marked and unmarked individuals are recorded.
6. Lincoln’s index is used to calculate sample size:

(No. individuals in first sample x No. individuals in second sample) / (No. of tagged individuals)

Question 37

ACFOR scale

Answer 37

Scale used to describe species abundance within a given area.

A- Abundant
C- Common
F- Frequent
O- Occasional
R- Rare 

The scale can be subjective in some cases.

Question 38

Describe some reasons why energy is lost at tropic levels.

Answer 38

• Energy released during respiration
• Some tissue cannot be eaten/ digested such as cellulose and bone
• Excretion: CO2 and urea

Question 39

Why are some ecosystems more efficient at passing biomass between tropic levels compared to others.

Answer 39

• Ectotherms use less energy to keep warm so it can be used in growth of biomass.
• A higher proportion of the available food is eaten.
• Some tissues are easier to digest than others.