6.3.1 - Ecosystems Flashcards
What are biotic factors?
Living factors that affect an ecosystem
What are abiotic factors?
Non-living factors that affect an ecosystem
What are the key abiotic factors?
Light, water availability, oxygen availability, temperature, edaphic factors
Why is light a key factor?
Most plants are directly affected by light availability as is it is essential for photosynthesis
Why is water availability a key factor?
A lack of water can lead to plants wilting, and it is also required for photosynthesis. Plants being impacted has a knock-on effect on animals, which are affected in terms of the food chain
Why is oxygen availability a key factor?
Oxygen is required for aerobic respiration
Why is temperature a key factor?
Temperature dictates the rate of enzyme controlled reactions. Also, changes in temperature can trigger important mechanisms, such as leaf fall
How are edaphic factors split?
Type of soil and soil pH
Why is the type of soil a key factor?
It impacts the types of organisms and plants that can grow in it
Why is soil pH a key factor?
Different plants grow best at different pHs.
What are the three main soil types?
Clay, loam, and sandy
Describe clay soil
It has fine particles, and is easily waterlogged. It forms clumps when wet
Describe loam soil
Loam soil has different sized particles. It retains water but does not become waterlogged
Describe sandy soil
Sandy soil has coarse, well separated particles that allow free draining. It does not retain water and it is easily eroded
What are the three key biotic factors?
Competition, predation, and new diseases
What are trophic levels?
Stages in the food chain
What is biomass?
The mass of living material in an area/organism without water (dry mass)
Why is the water not included in the biomass?
It regularly fluctuates in organisms
How is energy content/biomass measured?
Using a calorimeter (measures amount of calories)
Describe the process of calculating biomass of an organism
Collect sample, kill organism, head in oven at 80 degrees C. Heat until constant mass
What is ecological efficiency?
The efficiency by which biomass/energy is transferred from one trophic level to the next
What is the typical value of ecological efficiency?
10%
For what reasons is the ecological efficiency not 100%?
- Sunlight is reflected
- Some energy is used up for photosynthesis to take place
- Energy is lost through respiration
- Energy is lost through excretion
- Some parts of food are not eaten (bones, hair)
- Animals can get unwell
What is useful energy?
The energy used to build biomass
How can ecological efficiency be maximised?
- Keep farm animals indoors
- Maximise rate of photosynthesis using other factors
- Ensure food for farm animals has high energy content, and giving them food that can be eaten entirely
- Vaccinate farm animals
- Carry out genetic engineering or selective breeding
What is a decomposer?
An organism that feeds on and breaks down dead plant or animal matter, and turns organic compounds into inorganic compounds
What are examples of decomposers?
Fungi and bacteria
Why are decomposers saprotrophs?
They obtain their energy from dead or waste organic material
What are detritivores?
Organisms that speed up the decay process by feeding on detritus. They break it down into smaller pieces of organic material, which increases the surface are for the decomposers to work on
What is detritus?
Dead and decaying material
What are examples of detritivores?
Woodlice and earthworms
Why is the recycling of nitrogen important?
It is essential for making amino acids and nucleic acids in both plants and animals. Animals obtain nitrogen from food, but plants must take it in from their environment
In what form does nitrogen have to be to be taken up by plants?
It must be combined with other elements such as oxygen or hydrogen
What is nitrogen fixation?
The combination of atmospheric nitrogen with other elements so it can be absorbed and used by plants
Give examples of nitrogen-fixing bacteria
Azotobacter and Rhizobium
What enzyme do nitrogen-fixing bacteria contain, and what does it do?
Nitrogenase, which combines atmospheric nitrogen with hydrogen to produce ammonia
What is the difference between Azotobacter and Rhizobium?
Azotobacter is a free-living soil bacterium, while Rhizobium lives inside root nodules. Root nodules are growths on the roots of leguminous plants.
Describe and explain the symbiotic relationship between Rhizobium and the plant
Mutualistic as the plant gains amino acids from Rhizobium, while the bacteria gain carbohydrates produced by the plant during photosynthesis.
What is nitrification?
The process by which ammonium compounds in the soil are converted into nitrogen-containing molecules that can be used by plants
What bacteria in the soil are used for nitrification?
Free-living bacteria in the soil called nitrifying bacteria. Two examples are Nitrosomonas and Nitrobacter
What type of reaction is nitrification?
An oxidation reaction, so it only occurs in well-aerated soil
Describe the first step of nitrification
Nitrosomonas oxidises ammonium compounds into nitrites (NO2-)
Describe the second stage of nitrification
Nitrobacter oxidises nitrites into nitrates (NO3-)
What is denitrification?
The process by which denitrifying bacteria convert nitrates in the soil back to nitrogen gas
In what conditions does denitrification take place?
Anaerobic conditions
Give an example of a denitrifying bacteria
Pseudomonas denitrificans
What is ammonification?
The process by which decomposers convert nitrogen-containing organic matter into ammonium compounds
What is the main source of carbon for land-living organisms?
The atmosphere
How is carbon removed from the atmosphere?
Carbon dioxide is converted into small organic molecules by photosynthesis by plants and other photosynthetic organisms.
After the photosynthetic organisms, where does the carbon go?
Primary consumers consume producers, and the organic molecules are subsequently passed up the food chain. Also, when both the photosynthetic organisms and the animals die, the carbon compounds in their body are released via decomposition
What does decomposition do to the levels of carbon in the atmosphere?
It increases C levels, as CO2 is released when the decomposers respire.
In what ways is carbon released into the atmosphere?
Respiration of plants, animals, and decomposers, as well as combustion of fossil fuels
How are fossil fuels formed?
By the accumulation of dead organic matter in places where decomposers are not present.
How are fossil fuels formed?
By the accumulation of dead organic matter in places where decomposers are not present.
Describe the fluctuation of atmospheric CO2
CO2 levels are higher at night than during the day, as photosynthesis takes place during the day, while respiration takes place during day and night. Also, CO2 levels are generally higher in winter rather than summer, as photosynthesis rates are lower in winter, and more fossil fuels are burnt for heating.
How has increased CO2 levels impacted temperature?
Higher CO2 levels trap more heat in the atmosphere, resulting in global warming
How does global warming impact CO2 levels?
Higher water temperatures cause less gas to be dissolved in the water, so global warming reduces the carbon bank in the oceans, releasing more CO2 into the atmosphere, causing a positive feedback loop.
What is succession?
A process by which ecosystems change over time
Why does succession occur?
It occurs as a result of changes to the environment, causing the plant and animal species present to change
What are the two types of succession?
Primary succession and secondary succession
What is primary succession?
Succession that occurs on an area of land that has been newly formed or exposed such as bare rock. There is no soil or organic material present to begin with
What is secondary succession?
Succession that occurs on an area of land where soil is present, but it contains no plant or animal species. An example is the bare earth that remains after a forest fire
Give examples of when primary succession takes place
Post volcanic eruption, when sand is blown by the wind or deposited by the sea to create new sand dunes, when silt and mud are deposited at river estuaries, and when glaciers retreat depositing rubble and exposing rock
What are the stages of succession called?
Seral stages
What are the main seral stages?
Barren land, pioneer community, intermediate community, and climax community
What is the pioneer community?
Organisms known as pioneer species colonise an inhospitable environment. The species arrive as spores or seeds carried by the wind from nearby land masses
Give examples of pioneer species
Algae and lichen
What adaptations do pioneer species have that enable them to colonise the bare environment?
The ability to produce large quantities of seeds or spores, seeds that germinate quickly, the ability to photosynthesise, tolerance to extreme environments, and the ability to fix nitrogen from the atmosphere
Describe the formation of an intermediate community
Weathering of bare rock produces particles that form the basis of a soil. Then, when organisms of the pioneer species die and decompose, small organic products are released into the soil. This organic component is known as humus. The soil becomes able to support the growth of new species of plant, known as secondary colonisers, and are often mosses. The environmental conditions continue to improve, allowing tertiary colonisers to arrive, such as ferns.
What happens after each stage of development?
The rock continues to be eroded, and the mass of organic matter increases. When organisms decompose, they contribute to a deeper, more nutrient-rich soil, which retains more water.
Describe the formation of a climax community?
The final seral stage is the climax community, when the community is in a stable state and does not change much. Generally, there will be few species that are dominant in the community, outcompeting the other species
When is biodiversity at its peak during succession?
Mid-succession when progress and growth of the ecosystem is at its fastest
Describe animal succession
Primary consumers such as insects and worms are first to colonise an area, as they consume and shelter in the mosses and lichens. Secondary consumers arrive once a suitable food source has been established. Eventually, larger organisms colonise the area when biotic conditions are favourable
What is deflected succession?
When human activities halt the natural flow of succession and prevent the ecosystem reaching a climax community. When succession is stopped artificially, the final stage that is formed is known as a phagioclimax
What is one of the main reasons deflected succession occurs?
Agriculture
