Ecosystems

Question 1

What is an ecosystem?

Answer 1

An ecosystem is made up of all the living organisms that interact with one another in a defined area

Question 2

Biotic factors affection ecosystems:

Answer 2

• Space
• Breeding partners
• Food
• Disease

Question 3

Abiotic factors affecting ecosystems:

Answer 3

• Light
• Temperature
• Water availability
• Oxygen availability
• Soil factors

Question 4

What are the different soil factors?

Answer 4

1. Clay - fine particles, easily waterlogged, forms clumps when wet
2. Loam - different sized particles, retains water, does not become waterlogged
3. Sandy - coarse, well separated particles that allow free draining, soil does not retain water and is easily eroded

Question 5

What is biomass?

Answer 5

Mass of living material present in a particular place or in a particular organism

Question 6

How can biomass be measured?

Answer 6

• Measure the mass of fresh material present
• Water content must be discounted, so organisms need to be killed and are place in an oven until all water is evaporated
• Then mass is taken
• Therefore, only a small sample is often taken to avoid destruction of ecosystem

Question 7

Why is energy transfer not 100% efficient at the producer level?

Answer 7

• Not all of solar energy available is used for photosynthesis
• Most of it is reflected
• Some is transmitted through the leaf
• Some is an useable wavelength
• Other factors may limit photosynthesis
• Some energy converted as it is used for photosynthetic reactions

Question 8

How can net production be calculated?

Answer 8

gross production-respiratory losses

Question 9

Why is energy transfer not 100% efficient at consumer levels?

Answer 9

• Not all of biomass of an organism is eaten, e.g. plant roots or animal bones
• Some energy transferred to environment as metabolic heat
• Some parts of an organism are eaten but indigestible
• Energy ‘lost’ from animal in excretory materials, such as urine

Question 10

How can ecological efficient be calculated?

Answer 10

Energy available after the transfer/ Energy available before transfer x100

Question 11

Nitrogen Cycle:

Answer 11

1. Nitrogen fixation from mutualistic (Rhizobium) or free-living (Azotobacter) nitrogen fixing bacteria in the soil
2. Nitrification by nitrifying bacteria (Nitrosomonas) oxidise ammonia into NO2-
3. Nitrification by nitrifying bacteria (Nitrobacter) oxidised NO2- into NO3-
4. Denitrification by denitrifying bacteria (Pseudomonas) nitrates back to nitrogen gas
5. Ammonification where decomposers convert nitrogen containing compounds in dead organisms into ammonium compounds

Question 12

Carbon cycle:

Answer 12

• Respiration
• Photosynthesis
• Combustion (fossil fuels)
• Decomposition
• Feeding

Question 13

What is a decomposer?

Answer 13

Organism that feeds on and breaks down dead plant or animal matter, usually microscopic fungi and bacteria

Question 14

Why are decomposers saprotrophs?

Answer 14

Because they obtain their energy from dead or waste organic material. They digest their food externally by secreting enzymes onto dead organisms and then absorb the simple molecules

Question 15

What are detritivores?

Answer 15

• Organisms that help speed up the decay process by feeding on dead and decaying matter
• They break it down into smaller pieces of organic matter which increases the surface area for the decomposers to work on

Question 16

What are the two types of succession?

Answer 16

1. Primary succession

2. Secondary succession

Question 17

What is primary succession?

Answer 17

Occurs on an area of land that has been newly formed or exposed as bare rock. There is no soil or organic material present to begin with

Question 18

What is secondary succession?

Answer 18

Occurs on an area of land where soil is present, but it contains no animal or plant species, e.g. the bare earth that remains after a forest fire

Question 19

What are the main seral stages of succession?

Answer 19

1. Pioneer community
2. Intermediate community
3. Climax community

Question 20

What is the rate of primary succession, compared to secondary succession?

Answer 20

Primary succession is a slow process, whereas secondary succession is a rapid process

Question 21

Pioneer community:

Answer 21

• Colonisation of inhospitable environment by pioneer species e.g. lichen/algae
• Species arrive as seeds or spores carried by wind or sometimes by the droppings of birds
• Adaptations of pioneer species are:
  1. Seeds that germinate rapidly
  2. Ability to photosynthesise
  3. Tolerant to extreme environments
  4. Ability to fix nitrogen from atmosphere, adding mineral content to the soil in intermediate community

Question 22

Intermediate community:

Answer 22

• Weathering of bare rock produces particles that form the basis of soil
• When organisms of pioneer species die, small organic products released into soil, known as humus
• Soil becomes able to support growth of new species of plant (secondary colonisers) as it contains minerals, such as nitrates from pioneer species
• New species also arrive as spores or seeds
• E.g. mosses
• Pioneer species can also provide a food source for consumers so few animal species will start to colonise the area
• As environment conditions improve, new species of plant arrive (tertiary colonisers)
• At each stage, the rock continues to be eroded and mass of organic matter increases, soil also becomes more nutrient rich
• This makes abiotic factors more favourable initially for small flowering plants, like grasses, later shrubs, then finally small trees
• At each seral stage, different plant and animal species are better adapted to current conditions in ecosystem
• These organisms outcompete many of the species that were previously present and become the dominant species

Question 23

Climax community:

Answer 23

• Community is in a stable state
• Few dominant plant and animal species, best adapted to the environment
• In temperate climate, there is plenty of water so large trees will dominate
• In a sub-arctic environment, herbs or shrubs will be favoured due to low water availability
• Climax community often not the most biodiverse

Question 24

Deflected succession:

Answer 24

• Human activities can halt the natural flow of succession
• Prevents ecosystem from reaching climax community
• Final stage formed is known as a plagioclimax

Question 25

Methods of deflected succession:

Answer 25

1. Grazing and trampling vegetation by domesticated animals results in large areas remaining as grassland 2. Removing existing vegetation to plant crops, crops become the climax community 3. Burning as a means of forest clearance, often leads to a rich biodiversity as it provides space and nutrient rich ash for other species to grow