Give 2 examples of decomposers.
Explain why decomposers are important in ecosystems.
- Energy and materials are lost from a food chain when living things excrete waste or die.
- If bacteria and fungi did not break down dead organisms, energy and valuable nutrients would remain trapped within the dead organisms.
- By digesting dead and waste material, they get a supply of energy to stay alive, and they also recycle trapped nutrients/chemicals, so that it is available for other organisms in the eco system again.
- Eg. Nitrogen and carbon
How do decomposers break down dead and waste material?
- They feed saprotrophically, so they are described as saprotrophs.
- Saprotrophs secrete enzymes onto dead and waste material
- These enzymes digest the material into small molecules, which are then absorbed into the organism's body by endocytosis (usually I think).
- Having been absorbed, the molecules are stored or respired to release energy.
Living things need nitrogen for what? (2)
- To make proteins
- To make nucleic acids
Name the 4 processes microorganisms are involved in, in the nitrogen cycle.
- 1. Nitrogen fixation
- 2. Ammonification
- 3. Nitrification
- 4. Denitrification
Tell me all about nitrogen fixation and its role in the nitrogen cycle.
- Nitrogen makes up 79% of atmosphere but plants cannot use it directly. Instead, they need supply of 'fixed' nitrogen, such as ammonium ions (NH4+) and nitrate ions (NO3-).
- 3 ways of nitrogen fixation are: by lightening strikes, the Haber process (fertilizer) but most by nitrogen-fixing bacteria (such as Rhizobium), they fix nitrogen in the air to make amino acids.
- These bacteria can live freely in soil, but can also live inside root nodules of plants in bean family (legumes). It has mutualistic relationship with plant - bacteria provide fixed nitrogen and plant provides carbon compounds in return. Also the nodules keep condition anaerobic so that bacteria reduce nitrogen to ammonium ions.
Tell me all about ammonification and its role in the nitrogen cycle.
When nitrogen compounds from dead organisms and waste (like urine and faeces) are turned into ammonium compounds by decomposers.
Tell me all about nitrification and its role in the nitrogen cycle. Give the bacteria name at the end.
- Conversion of ammonium into nitrate ions.
- Ammonium ions are released by bacteria involved in ammonification.
- Chemoautotrophic/nitrifying bacteria oxdises these ammonium into nitrite ions or oxidises nitrite ions to nitrate ions. (This is how they get their energy, unlike photoautotrophic bacteria).
- Because this oxidation requires oxygen, only happen in well-aerated soils.
- Nitrate ions can be absorbed from soil by plants and used to make nucleotide bases and amino acids.
- Nitrosomonas converts ammonium ions to nitrite ions, and nitrobacter converts nitrite ions to nitrate ions.
Tell me about denitrification and its role in the nitrogen cycle.
- Denitrifying bacteria convert nitrate ions back to nitrogen gas.
- They use nitrates in soil to carry out respiration (because nitrates are source of oxygen) and produce nitrogen gas, in anaerobic conditions (eg. waterlogged soils).
- Now the whole cycle begins again!
The size of a population depends upon the __ between the __ ___ (___) and the rate of ___.
- death rate (mortality)
Explain the meaning of the term carrying capacity (SPEC).
- The maximum population size that can be maintained over a period of time in a particular habitat.
- This is the stationary phase in population growth, when the habitat cannot support a larger population, so size stays stable, or fluctuates very slightly in response to small variations in the environment. Rate of morality is equal to rate of reproduction.
Factors that limit the growth in population size are called __ __. They determine the __ __ of a population - the habitat's __ __. Give some examples of the 2 types of limiting factors.
- limiting factors
- final size
- carrying capacity
- Abiotic: eg. light, oxygen, space, temperature.
- Biotic: eg. intensity of competition for resources, both within and between species; predators, parasites etc.
Describe, using step-by-step explanation, why the population sizes of predators and prey are interlinked.
- 1. When predator population gets bigger, more prey eaten.
- 2. Prey population then gets smaller, leaving less food for predators.
- 3. With less food, fewer predators can survive and their population size reduces.
- 4. With fewer predators, fewer prey are eaten, and their population size increases.
- 5. With more prey, the predator population gets bigger, and cycle starts again.
Imagine a graph showing predator-prey relationship.
However, what do we have to remember about predator-prey relationships? In which situations is it harder to stop the graph pattern?
- We have to remember that in the wild, predators often eat more than one type of prey, and there are other limiting factors. Therefore graph of predator-prey pop.size in wild yields graph that not as well defined as the one we just showed.
- + In areas of higher species diversity, the pattern is even harder to see, beacause there are many biotic and abiotic factors that affect population size.
List the two types of competition.
- Intraspecific competition: happens between individuals of same species.
- Interspecific competition: happens between individuals of different species.
Explain what intraspecific competition is.
- Happens between individuals of the same species.
- Although there are fluctuations, intraspecific competition keeps population of a species relatively stable.
- Population increases when resources are plentiful, and as it does, there will be more individuals competing for food and space.
- Eventually, resources such as food and space become limiting - there isn't enough for all.
- The individuals better adapted to obtaining food will survive and reproduce, but other die, this slows down population and population enters stationary phase.
- (CHECK FOR RELAVENT EXAMPLE)
Explain what interspecific competition is, using examples.
- Happens between individuals of different species.
- Affects both population size and the distribution of species in an ecosystem.
- Eg. Red and grey squirrels compete for same food sources and habitats in UK.
- The two species can coexist in the same habitat. Eg. In areas where both red and grey squirrels live, the population sizes are smaller than they would be if the habitat only had one of them.
- Or a more adapted species might increase and outcompete the other, eventually leading to the other species dying out (this is more common). Eg. since grey squirrel was introduced into UK, red squirrels have died out in some large areas. Because grey ones are more adapted because they are bigger and can store more fat over winter.
- The more overlap between two species' niches, the more intense the competition - the competitive exclusion principle.
Give 2 reasons why we need to manage timber production in a sustainable way.
- To conserve species and biodiversity of ecosystems
- Also a more economic reason - to maintain a sustainable supply of wood so that timber companies can have be financially secure and satisfy human needs etc. (In other words, not just for ecosystems, but for useful for us too.)
Explain how management of small-scale timber production can provide timber in a sustainable way.
- Coppicing: Cutting trunk of deciduous (shed leaves in winter) tree. Once cut, several new shoots grow from cut surface, and eventually mature into narrow stems - these can be cut to use for fencing/firewood etc. After cutting, new shoots start to grow again, and coppice cycle continues.
- Rotational coppicing - to provide continuous supply of wood, woodland managers divide wood into sections and cut one section each year. This is very good for biodiversity, because it allows species which would otherwise have little exposure to sunlight, to grow. Some trees are left for large pieces of timber, and are called standards.
- Pollarding: like coppicing, but involves cutting trunk higher up, usually so that deer can't eat the emerging shoots.
Explain the effects of non-sustainable large-scale timber production (such as clear-felling).
- Destroy habitats
- Reduce soil mineral levels (tree has its role in nitrogen and carbon cycles).
- Leave soil susceptible to erosion (because trees remove water from soil). Soil may run off into waterways, polluting them.
Explain how management of large-scale timber production can provide timber in a sustainable way.
- If each tree supplies more wood, fewer trees will need to be harvested, therefore foresters...
- control pests/pathogens
- only plant particular tree species where they know they will grow well
- position trees at optimal distance apart.
- Modern sustainable forestry often works on principles such as:
- Any tree harvested is replaced
- The forest must still maintain its ecological function, regarding biodiversity, climate and mineral/water cycles. Also consideration for local people.
- ALSO, other technique:
- Selective cutting: involves removing only the largest, most valuable trees, so that habitat is largely unaffected.
Discuss economic reasons for conservation of biological resources.
- Direct economic value:
- Many species provide valuable food source. Genetic diversity in wild strains may also be needed in future to breed species with disease resistance etc.
- Valuable source of potentially useful drugs or clothes or other useful resources.
- Others may have a direct value that is as yet unrecognised. Letting species go extinct and reduce biodiversity means ridding ourselves of potential useful resources yet to be discovered.
- Indirect economic value:
- Wild insects are responsible for pollinating crop plants. In similar way, other communities maintain water quality, protect soil, break down waste etc. The interlinking nature of ecosystem means most biological factors have some effect on our economy.
Discuss ethical and social reasons for conservation of biological resources.
- Ethical: Argument that every species has a value in its own right, and that they have a right to live/survive. Moral responsibility to look after them.
- Moral responsibility to conserve ecosystems for future generations.
- Social: Biodiverse ecosystems have an aesthetic value. Ecotourism and birdwatching, some of which are also linked to better psychological health, play an important part in enriching people's lives.
Define biodiversity (revision from AS).
The range of habitats, communities and species that are present in an area, and the genetic variation that exists within each species.
As ecosystems are ___, conservation is also a ___ process, and methods need to be ___ to the ___ ___ that occur within ecosystems.
- constant changes
Conservation is a ___ process involving ___ (1) and ___ (2). Describe further what (1) and (2) are.
- management (1):controlling how resources are used and replaced, and also involves humans taking active role in helping an ecosystem maintain its biodiversity. Eg - Coppicing to interfere with succession; vaccinate individuals against disease, move individuals to enlarge populations.
- reclamation (2): restoring ecosystems that have been damaged or destroyed by human activity by reversing this human activity. (eg. restoring forest that has been cut down)
Distinguish between the terms conservation and preservation.
- Conservation is the management of the environment to maintain and, where possible, increase biodiversity. It is an active, dynamic process and not simply preservation.
- Preservation is leaving the ecosystem as it is, without any human interference, to protect it.
Give examples of the effects of human activities on the animal and plant populations in the Galapagos Islands.
- Habit disturbance: Dramatic increase in population and tourism has placed huge demands on water, energy and sanitation services. Pollution as well.
- Over-exploitation of resources: Giant tortoise eaten, and only one Pinta tortoise left.
- Fishing - depletion of sea cucumber population has drastic effect on under-water ecology. Shark fin also led to death of 150,000 sharks each year around islands - 14 species endangered.
- Introduced species: The agressive quinine tree, occupies highlands, and spreads rapidly, and ecosystem in the highlands has changed from low scrub and grassland to a closed forest canopy. Native Scalesia trees were out-competed.
- Goats out-competed and damaged the habitat for giant tortoise.
- Cats eat the young iguanas.
- Stats: 50% of vertebrate and 25% plant species on the islands recognised as endangered.
What methods have been put in place to try and conserve the Galapagos Islands? (2)
- Introduction of quarantine system - search foreign boats and tourists for foreign species.
- Natural predators exploited to reduce damage caused by pest populations.
- Eg. by the Charles Darwin Research Station and the National Park Service.