Ecosystem
All the living organisms and physical conditions in the area
Community
All of the organisms that living within an ecosystem
Habitat
Area where an organism lives
Population
Total number of organisms of each species
Producers
Organisms that make their own food by photosynthesis. They include all plants, and algae.
Consumers
Organisms that cannot make their own food. They have to eat other organisms to gain energy. All animals are consumers.
Decomposers
A special group of consumers. They gain their energy by feeding on dead or decaying material, for example worms and slugs.
Organisms and energy transfer
Energy from the sun is transferred by light to the chlorophyll in the cells of a producer. The plant will photosynthesise to produce glucose. Glucose is then converted to carbohydrates, proteins and lipids, which are used as energy stores, and for growth and repair. As an organism grows it increases in biomass. This is the mass of living material present.
Consumers then eat producers. Producers and consumers both respire to grow and increase in biomass.
Food web
A series of over linked food chains
Biotic and abiotic factors
Biotic factors - the living factors in an ecosystem. For example, in a woodland ecosystem, there would be squirrels, beech trees and hedgehogs.
Abiotic factors - the non-living factors in an ecosystem. For example within the woodland ecosystem, they would include the amount of rainfall or the temperature.
Biotic - food availability, pathogens & parasites, predators, and interspecific competition
- Food availability - plenty of food means successful breeding. Food shortage leads to animals struggling and often not breeding.
- Pathogens & parasites - an emergence of new pathogens / parasites means organisms have no resistance to the disease so it can potentially damage or wipe put entire populations.
- Predators - organisms may have no defences against new predators and can potentially be wiped out.
- Interspecific competition - competition between species. New species may out compete another where the number became too low for successful breeding.
Abiotic factors - light intensity, temperature, moisture level and soil pH
- Light intensity - light is required for photosynthesis. In general, the greater the light availability, the greater the success of a plant. Plants evolve to grow successfully in different light intensities. For example in areas of low light plants have larger leaves.
- Temperature - temperature has its greatest effect on the enzymes that control metabolic reactions. Plants develop more rapidly in warmer temperatures as their metabolism will be faster. This is also true for cold blooded animals like lizards, which rely on the sun to warm them up. Warm blooded animals are less affected by their external environment.
- Moisture level - typically a lack of water leads to death. A lack of water causes most plants to wilt because water i required to keep their cells turgid, which keeps the plant upright. Water is also required for photosynthesis. Animals also need water as a main component of blood plasma.
- Soil pH - the pH of soil affects the biological activity in soil and the availability of certain minerals. Some plants will grow better in acidic soils but some will grow better in alkaline soils.
Interdependence
Different organisms depend on each other within a community. This is known as interdependence.
The interactions between organisms are known as ecological relationships. There are three main types: predation, mutualism and parasitism.
Predation
Predation is the name given to the relationship between a predator and prey species. The size of the predator population directly affects the size of the prey population
- if the population of prey increases there is a larger food supply for predators. This can therefore support more predators, so more offspring survive. The growing numbers of predators eventually reduce the food supply. The number of predators starts to decrease. The prey population starts to increase once more - the cycle then begins again.
Mutualism
In a mutualistic relationship both organisms benefit from the relationship. For example, oxpeckers are small birds that live on buffalo. They are known as ‘cleaner species’ because they eat ticks and fleas living on the buffalo’s skin. They gain food, while the buffalo is free from irritation and potential disease.
Parasitism
In a parasitism relationship only one organism (the parasite) gains. The organism it lives off (the host) suffers. Examples include tapeworms in an animals digestive system, and fleas.
Pyramid of numbers
Pyramids of numbers show the population at each tropic level. Not all pyramids of numbers are pyramid shaped.
Pyramid of biomass
Pyramids of biomass are always pyramid shapes. They take into account both the number and size of the organisms present.
Calculating biomass
- samples are taken from each trophies level
- enrage mass of the organisms from each trophies level is calculated
- the average mass is multiplied by the number of organisms present to calculate the total biomass at each trophies level
scientists normally calculate the dry mass of an organism, as water content can vary between individuals. This requires the organism to be dead
When is biomass lost
Consumers at each trophies level convert around 10% of the chemical energy in their food to new body tissue. This is because biomass is lost when:
- not all of an organisms is eating, for example plant roots or animal bones
- some of the biomass is used in respiration and so transferred to the surroundings by heating
- egestion where the undirected material is lost from the body as faeces
- exertion where waste products are lost from the body
Efficiency of biomass transfer formula
Efficiency of biomass transfer = biomass available after the transfer / biomass available before the transfer x100%
What is nutrient cycling?
- plants obtain the nutrients they need for growth from the soil.
- these are passed onto animals when the plant is eaten.
- when organisms die, decomposers release the trapped nutrients back into the soil where they are absorbed by plants. Some are released into the atmosphere.
Nitrogen cycle
- plants can’t absorb nitrogen directly from the atmosphere.
- nitrogen fixing bacteria can however, so plants contain this bacteria in their roots.
- nitrogen fixing bacteria convert nitrogen in the air into nitrates in the soil, which can then be absorbed by plants.
- nitrogen fixation can also occur when lighting strikes the ground.
- the plants use the nitrates to form amino acids and proteins which can be transferred to animals when they consume the plant biomass.
- animals then release waste products back into the soil.
- plants and animals die and decomposing bacteria in the soil convert the nitrogen from the organism biomass into ammonia.
- nitrifying bacteria then convert the ammonia back into nitrates in the soil to be absorbed by the plant.
- denitrifying bacteria remove nitrates in the soil by converting them into nitrogen gas, ammonia or poisonous nitrates in the soil.
Water cycle
- as water droplets in clouds get heavier they fall as rain, snow or hail. This is known as precipitation.
- during percolation, the water trickles through gaps in soils and rocks.
- plants absorb this water, and transpiration occurs in the plants. Water vapour is lost from the plants directly to the atmosphere.
- however this water in the ground can also go into the ocean as surface run-off
- the sun heats the earths surface and this water from the ocean can turn into water vapour, forming warm moist air.
- as Morisot air rises it cools. Water vapour condenses back unto liquid water droplets producing clouds.
