Module 6 Section 6: Ecosystems

Question 1

What is a habitat

Answer 1

The place where an organism lives, e.g. a rocky shore or a field.

Question 2

What is a population

Answer 2

All the organisms of one species in a habitat.

Question 3

What is a producer

Answer 3

An organism that produces organic molecules using sunlight energy, e.g. plants

Question 4

What is a consumer

Answer 4

An organism that eats other organisms, e.g. animals and birds.

Question 5

What is a decomposer

Answer 5

An organism that breaks down dead or undigested organic material, e.g. bacteria and fungi.

Question 6

What is a trophic level

Answer 6

A stage in a food chain occupied by a particular group of organisms, e.g. producers are the first trophic level in a food chain.

Question 7

What is an ecosystem

Answer 7

All the biotic (living factors) and abiotic factors (non living factors) in a certain area

Question 8

Examples of biotic factors

Answer 8

Food
Space (territory)
Breeding partners

Question 9

Examples of abiotic factors

Answer 9

Light
Affects plants as light is needed for photosynthesis
Greater availability of light the greater the success of plant species

Temperature
Effects enzymes controlling metabolic reactions
Plants and ectothermic animals develop rapidly in warmer temperatures
Changing temperature (from seasons) can trigger migration or hibernation

Water availability
Lack of water leads to water stress which can cause death
Water stress will cause plants to wilt and reduce photosynthesis levels

Oxygen availability
Warm, slow flowing water leads to a drop in oxygen concentration
Lack of oxygen leads to suffocation of aquatic organism
Water logging also decrease amount of oxygen in soil leading to plant suffocation

Edaphic (soil)
Different soil types with different sized particles
Clay (small fine particles which are easily waterlogged), loam (mixed of sizes of particles which retains water but doesn’t waterlog), sandy (coarse, spaced out particles which doesn’t retain water but is easily eroded)

Question 10

How can population size be affected by changes in an ecosystem

Answer 10

Cyclic changes: predator prey relationships, seasonal changes, day and night cycle, tides
Directional changes: climate change, deposition in rivers, erosion of a coastline
Unpredictable/erratic changes: natural disasters, lightning

Question 11

Pattern of how species performance and intensity of abiotic factors

Answer 11

Includes factors such as temperature and pH

Question 12

When may the pattern of abiotic factors and species performance not follow the bell curve

Answer 12

Question 13

What is biomass

Answer 13

Mass of living material in a particular place

Question 14

What is living material

Answer 14

Carbon containing material

Question 15

How does energy mainly enter an ecosystem

Answer 15

Enters by photosynthesis where plants convert sunlight energy into a form that can be used by other organisms
Plants are called producers and store energy as biomass

Question 16

Another word for energy transfer in ecosystems

Answer 16

Can also be called biomass transfer in ecosystems

Question 17

How is energy transferred in ecosystems

Answer 17

When organisms eat other organisms
Producers are eaten by primary consumers, primary consumers are then eaten by secondary consumers and secondary consumers are eaten by tertiary consumers.

Question 18

How can energy transfer be shown with diagrams

Answer 18

Food chains show simple lines of energy transfer
Food webs show lots of food chains in an ecosystem and how they overlap

Question 19

When may energy be unable to be transferred and how is energy recycled back into the ecosystem

Answer 19

Energy can be locked up in the things that can’t be eaten (e.g. bones, faeces)
Gets recycled back into the ecosystem by decomposers.

Question 20

How much energy is lost through tropic levels

Answer 20

About 90%

Question 21

Why may large amounts of energy not be taken into producers or consumers in the first place

Answer 21

Around 60% is never taken in by organisms
Plants can’t use all the light energy that reaches their leaves
e.g. some is the wrong wavelength, some is reflected, and some passes straight through the leaves.
Some sunlight can’t be used because it hits parts of the plant that can’t photosynthesise
e.g. the bark of a tree.

Some parts of food, e.g. roots or bones, aren’t eaten by organisms so the energy isn’t taken in
Some parts of tood are indigestible so pass through organisms and come out as waste, e.g. faeces
These pass to decomposers

Question 22

What is gross productivity

Answer 22

This is the rest of the available energy (40%) which is absorbed by plants

Question 23

Describe the transfer of energy between organisms of different trophic levels and explain how energy can be lost between trophic levels

Answer 23

40% passed on from plants (gross productivity)
30% of total energy available (75% of gross productivity) is lost to the environment when organisms use energy produced from respiration for movement or body heat.
This is called respiratory loss.

10% of the total energy available (25% of the gross productivity) becomes biomass (e.g. it’s stored or used for growth)
This is called the net productivity.
This 10% is then passed onto the next consumer and repeats the process of respiratory loss

Question 24

What is net productivity

Answer 24

This is the amount of energy that’s available to the next trophic level.
Also called biomass

Question 25

Net productivity equation

Answer 25

Net productivity = gross productivity-respiratory loss

Question 26

How is biomass measured

Answer 26

Mostly measured as energy kJm⁻² yr⁻¹
Or in area/volume g m⁻²/ g m⁻³

Question 27

Why is biomass transfer so inefficient

Answer 27

Biomass relates to all carbon containing material in an organism
When animals eat, only a small proportion of the food they ingest is converted into new tissue
It is only this biomass that is available to the next trophic level

Question 28

Answer 28

Question 29

How to calculate the energy transfer between trophic levels

Answer 29

Calculate difference between the amount of energy in each level
This is done by measuring the dry mass (no water) of the organisms (biomass) which indicates how much energy is stored in them
Measure biomass in sample then multiply by size of population
Find difference in energy between trophic levels

Question 30

Problems with measuring energy transfer between trophic levels

Answer 30

Consumers may have taken in energy from sources others than the producer measured
Means that difference between two figures calculated wouldn’t be accurate
Need to include all individual organisms at each trophic level

Question 31

How to calculate ecological efficiency

Answer 31

Question 32

Answer 32

Question 33

How can human activities increase transfer of energy from primary productivity

Answer 33

This is the rate at which plants convert light energy into chemical energy through photosynthesis
Herbicides kill weeds to reduce competition so crops receive more energy
Fungicides and insecticides kill fungi and insects that damage crops and allow them to use more energy for growth and not fighting an infection
Can also breed resistant crops
Natural predators introduced to the ecosystem eat the pest species so crops lose less energy and biomass
Fertilisers supply minerals needed for growth so more energy from the ecosystem can be used to grow
Increase light by planting crops early in growing season
Increase water using irrigation systems or breed drought resistant crops

Question 34

How can human activities increase transfer of energy from secondary productivity

Answer 34

This is the rate at which energy is transferred from one trophic level to the next
Animals kept in warm, indoor pens so less energy is wasted moving and keeping warm and more is used for growth
Animals given feed thats higher in energy than their natural food to increase energy input and therefore energy needed for growth
Given antibiotics so less energy is used fighting off disease
Can selectively breed animals which grow faster or have larger yields
Harvest animals just before adulthood as young animals invest more energy into growth

Question 35

Positive and negatives of humans increase secondary productivity

Answer 35

Positives:
More food can be produced in a shorter space of time with lower cost
Negatives:
Animals can be kept in pain, distress and their natural behaviour is restricted

Question 36

Process of carbon cycle

Answer 36

CO2 absorbed by plants to become carbon compounds in photosynthesis

Carbon passed from primary to secondary to tertiary consumers through food chains

Dead organisms are digested by decomposers (bacteria and fungi) this is called saprobiontic nutrition

Carbon is returned to atmosphere by respiration of living organisms

Dead organic matter than can’t be reached by decomposers (bogs or deep oceans) they can become fossil fuels over millions of years

The carbon in fossil fuels (e.g. oil and coal) is released when they’re combusted

As well as coal, other types of rock can be formed from dead organic matter deposited on the sea floor:
E.g. limestone and chalk are mainly composed of calcium carbonate (CaCO3) (from shells of crabs and mussels)

Carbon returned to environment by the rocks being taken down into Earth’s crust by tectonic movement, they then release CO2 after number chemical changes which is returned to atmosphere by volcanoes

Rocks can be weathered chemically by rainwater to release mineral ions and bicarbonate ions (HCO3-) which can then be entered into rivers and oceans to combine to form carbon containing compounds like CaCO3
Rocks can be physically weathered roots or animals

CO2 can dissolve in oceans and be transported in the oceans by underwater currents
CO2 can remain in these currents for 100s of years before returning to surface and being released back into the atmosphere

Question 37

How is nitrogen useful for plants and animals

Answer 37

Nitrogen is needed to make proteins and nucleic acids
For animals and plants

Question 38

What is the use of the nitrogen cycle for plants and animals

Answer 38

Nitrogen in the atmosphere must be converted into a useable form using bacteria to make it into nitrogen compounds which can be taken up by plants and passed onto animals

Question 39

What does the nitrogen cycle show

Answer 39

Shows how nitrogen is converted into a useable form then passed on between different living organisms and the non-living environment

Question 40

What is nitrogen fixation

Answer 40

When nitrogen gas in the atmosphere is turned into ammonia by bacteria like Rhizobium and Azotobacter
Ammonia can then be used by plants
Rhizobium is found inside root nodules of leguminous plants (peas, beans) and form a mutualistic relationship with plants by providing them with nitrogen while plant provides them with carbohydrates
Azotobacter are found living in the soil and don’t form mutualistic relationships with plants

Question 41

What is ammonification

Answer 41

When nitrogen compounds from dead organisms are turned into ammonia by decomposers which forms ammonium ions
Animal waste containing nitrogen compounds are also turned into ammonia by decomposers and go on to form ammonium ions

Question 42

What is nitrification

Answer 42

When ammonium ions in the soil are changed into nitrogen compounds that can then be used by plants (nitrates)
First nitrifying bacteria (nitrosomonas) change ammonium ions into nitrites
Then other nitrifying bacteria called nitrobacter change nitrites into nitrates

Question 43

What is denitrification

Answer 43

When nitrates in the soil are converted into nitrogen gas by denitrifying bacteria
They use nitrates in the soil to carry out respiration and produce nitrogen gas
This happens under anaerobic conditions
e.g. in water logged soils

Question 44

Draw the nitrogen cycle

Answer 44

Question 45

What is primary succession

Answer 45

Primary succession is where a species colonise a new land surface
Starts with seeds and spores being blown in by wind which begin to grow into pioneer species

Question 46

Why can only pioneer species grow on a new land surface

Answer 46

The abiotic conditions are hostile and there’s no soil to retain water
Pioneers species are specialised to cope with the harsh conditions
E.g:
Have seeds that germinate rapidly
Can photosynthesise to produce their own energy
Tolerant of extreme conditions
Can fix nitrogen from atmosphere to add to mineral content of soil

Question 47

How does the intermediate community start to grow from the pioneer community

Answer 47

Pioneer species change the abiotic conditions
They die and microorganisms decompose the dead organic material (humus)
Rock is also eroded into smaller particles
This forms a basic soil
Conditions then become less hostile (basic soil can retain some water)

Means that secondary colonisers can move in and grow (mosses)
These then die and are decomposed which add more organic material and make the soil deeper and richer in minerals

This means that larger plants can grow (shrubs) in the deeper soil which can retain more water
These are the tertiary consumers

Rock continues to be eroded and mass of organic matter increases which improves soil quality

Question 48

Where are each of the seral stages found

Answer 48

Pioneer community: first seral stage
Intermediate community: multiple seral stages
Climax community: final seral stage

Question 49

How may the species diversity in the intermediate stage change relatively fast

Answer 49

At each seral stage the different plant and animal species are better adapted to the current conditions in the ecosystem
These new organisms outcompete the species that were previously present
They become the dominant species

Question 50

What is the climax community

Answer 50

Final seral stage
Community in a stable state and shows very little change over time
Normally a few dominant plant and animal species
The species that make up the climax community depends on the climate
E.g. in a temperate climate trees will form the climax community

Question 51

What is the biodiversity of the climax community like

Answer 51

Not the most biodiverse
Biodiversity tends to reach a peak mid-succession then decreases
Due to dominant species outcompeting pioneer and other species
The more successful the dominant species, the less the biodiversity in a given ecosystem

Question 52

What is deflected succession

Answer 52

Where human activities can halt the natural flow of succession and prevent the ecosystem from reaching climax community
Agriculture can cause this the majority of the time
Forms plagioclimax

Question 53

How can agriculture form plagioclimax

Answer 53

Grazing and trampling vegetation can result in large areas becoming grassland
Planting crops means removing existing vegetation so crop becomes final community
Burning a forest to clear it results in space and nutrient rich soil for new species to grow so increases biodiversity