1. Community Level Systems
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Community Level Systems
OCR Gateway 2016 Biology topic 4
W Richards
The Weald School

2. B4.1 Ecosystems
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3. Ecosystems
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Definition: An “ecosystem” is the total interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.
Many different materials can cycle through ecosystems. For example, consider carbon, nitrogen and water:

4. The Carbon Cycle CO2 in air
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2. Plants and algae release CO2 through respiration
Burning fossil fuels also releases CO2
CO2 in air
1. CO2 is taken in by plants and algae for photosynthesis and turned into carbohydrates, fats and proteins
6. These microbes also release CO2 through respiration
4. Animals release CO2 through respiration
5. Animals (and plants) die and their remains are fed on by microbes and detritus feeders
3. The carbon taken in by plants is then eaten by animals and the animals that eat them

5. The Nitrogen Cycle N2 in air
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4. Denitrifying bacteria convert nitrates and ammonium compounds into atmospheric nitrogen
N2 in air
1. Nitrogen-fixing bacteria convert N2 in the air into nitrates
Denitrifying bacteria
Lightning
Waste and dead animals
5. Nitrifying bacteria convert ammonium compounds into nitrates
6. Nitrates taken in by plants
Nitrates in the soil
3. Decomposers break down waste products and dead animals and plants to form AMMONIUM COMPOUNDS
2. Plants are then eaten by animals – the nitrogen becomes PROTEIN

6. The Water Cycle 1. Condensation 3. Precipitation
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Condensation 3.
Precipitation
Why is the water cycle important to living organisms?
Maintaining habitats
Flow of nutrients
Drinking! 4.
Flow 2.
Evaporation 6.
Excretion 5.
Transpiration

7. Can you explain why these conditions help?
Decomposition
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Waste
Eating
Death
Absorption
Broken down
Microorganisms are the key to this – they break down waste and dead bodies so that the products can be used by plants for growth. Microbes work best in conditions that are:
Warm
Moist
High in oxygen
Can you explain why these conditions help?

8. More about Decay
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Decay is the process of breaking down complex structures into ______ ones. This is done be micro organisms.
The rate of decay is affected by the _______ of these microorganisms:
Temperature – the micro organisms’ rates of growth and respiration are quickest at around 40OC. They become “_________” at temperatures higher than this.
Oxygen – more oxygen means _____ micro organisms and more aerobic ________. Some decomposers still work even in low-oxygen conditions by respiring _________.
Water – micro organisms grow quickest in ______ conditions.
Words – respiration, more, moist, simpler, growth, denatured, anaerobically

9. Compost bins
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That’s a nice compost bin. What’s the point in having one?
Compost bins provide optimum conditions for rapid decay of waste biological material. The compost produced is used for fertiliser.

10. Organisation in an Ecosystem
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Individual – a single organism
Population – all of the organisms of one species in a habitat
Community – all of the organisms of different species living in a habitat
Ecosystem – the whole community AND the non-living (abiotic) conditions

11. Abiotic Factors Scientists measure lots of abiotic factors, such as:
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Scientists measure lots of abiotic factors, such as:
Recording temperature changes
Recording oxygen levels
Measuring rainfall
Other examples:
Light intensity
Soil pH and mineral content
Wind strength and direction
Carbon dioxide levels
Oxygen levels in water

12. Effect of changing Abiotic Factors
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Here are some abiotic factors again:
Temperature
Moisture levels
Light intensity
Soil pH and mineral content
Wind strength and direction
Oxygen levels in water
Carbon dioxide levels
Q. How would an increase in any of these factors affect these organisms?

13. Biotic Factors Biotic factors affecting an ecosystem can include:
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Biotic factors affecting an ecosystem can include:
Availability of food
Arrival of new predators
New pathogens/diseases
One species being outcompeted
Yum!
Yum
Harsh

14. Using Quadrats Lay down a transect line
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That’s a nice ecosystem. I think I’ll sample it using my quadrat. How do I do it?
Lay down a transect line
Mark off regular intervals, e.g. 1m
Use the quadrat every metre to sample the population size of different organisms

15. Interdependence Consider oxpeckers and buffalo:
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Consider oxpeckers and buffalo:
What patterns would you expect to see in the distribution of these two organisms?

16. Interdependent Relationships 1
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1) Parasitic relationships
Parasites take food from another living host _______. For example, if a human eats pork infected with bladderworm the worms attach themselves to the ___ wall and a young tapeworm grows, which _______ food from the gut.
Mutualistic relationships are when two organisms benefit from each other. For example, pea plants have nitrogen-fixing ______ which convert nitrogen into nitrates for plant _____. The bacteria benefit by taking sugars from the plant for ___________.
Words – growth, respiration, organism, gut, bacteria, absorbs
2) Mutualistic Relationships

17. Interdependent Relationships 2
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Predation is another example of an interdependent relationship. Consider rabbits and foxes:
Hey! I ordered a steak
Prey
Predator
Consider the populations of these two animals over time:
Population of animal
Time
Rabbit
Fox

18. Trophic Levels Here’s a simple food chain:
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Here’s a simple food chain:
Herbivore (primary consumer)
Top carnivore (tertiary consumer)
Secondary consumer
Producer
Rabbit
Cabbage
Fox
Stoat
Level 2 – Herbivores that eat producers
Level 4 – Carnivores that eat other carnivores
Level 3 – Carnivores that eat herbivores
Level 1 - Producers

19. Level 1 - Mass of cabbages
Pyramids of biomass
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In this food chain we can see that the mass of organisms in each stage is less than in the previous stage:
Cabbage
Rabbit
Stoat
Fox
We can draw a “Pyramid of Biomass” to show this pattern:
Level 4 - Mass of foxes
Level 3 - Mass of stoats
Level 2 - Mass of rabbits
Level 1 - Mass of cabbages

20. Energy flow in a food chain
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Consider the energy flow in this food chain:
100%
10% 1%
0.1%
Cabbage
Rabbit
Stoat
Fox
Clearly, not all of the ___’s energy that becomes stored in the _______ will end up in the fox. Only around ______ is passed on to the next stage in each food chain. Producers only transfer ___ of light energy.
Energy is lost to the surroundings at each stage because of a number of reasons:
Each organism has to use glucose in respiration to ____, keep warm etc
Energy is lost through faeces (______) or through CO2 and water loss
Words – 10%, move, sun, waste, cabbage, 1%

21. An example calculation
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What is the efficiency at each stage of this food chain?
37kg
3.2kg
0.45kg
0.04kg
Cabbage
Rabbit
Stoat
Fox
Efficiency =
Biomass transferred to the next level
Biomass available at the previous level
Clearly, a fox doesn’t have a mass of 0.04kg. This number represents the amount of biomass available to it. How does this affect the numbers of organisms as you go up the levels in a food chain?