organisms and their environment Flashcards
Food Chains
A food chain shows the transfer of energy from one organism to the next, starting with a producer
The source of all energy in a food chain is light energy from the Sun
The arrows in a food chain show the transfer of energy from one trophic level to the next
Energy is transferred from one organism to another by ingestion (eating)
In the food chain above:
Food Webs
A food web is a network of interconnected food chains
Food webs are more realistic ways of showing connections between organisms within an ecosystem as animals rarely exist on just one type of food source
Food webs give us a lot more information about the transfer of energy in an ecosystem
They also show interdependence – how the change in one population can affect others within the food web
For example, in the food web above, if the population of insects decreased:
The population of grass plants would increase as there are now less species feeding off them
The populations of frogs and voles would decrease significantly as insects are their only food source
The population of thrushes would decrease slightly as they eat insects but also have another food source to rely on (slugs)
Most of the changes in populations of animals and plants happen as a result of human impact – either by overharvesting of food species or by introduction of foreign species to a habitat
Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or web
Trophic Levels
Trophic levels describe the position of an organism in a food chain, web or pyramid
Animals (known as consumers) can be at different trophic levels within the same food web as they may eat both primary, secondary and / or tertiary consumers
Energy flows from the sun to the first trophic level (producers) in the form of light
Producers convert light energy into chemical energy and it flows in this form from one consumer to the next
Eventually all energy is transferred to the environment – energy is passed on from one level to the next with some being used and lost at each stage
Energy flow is a non-cyclical process – once the energy gets to the top of the food chain or web, it is not recycled but ‘lost’ to the environment
This is in direct contrast to the chemical elements that organisms are made out of, which are repeatedly recycled
Transfer of Energy
At each stage in a food chain only about …
gets passed on to the next trophic level
Why is this?
-10% of the energy received by an organism
-
In order for the energy to be passed on, it has to be consumed (eaten)
However not all of the energy grass plants receive goes into making new cells that can be eaten
The same goes for the energy the vole gets from the grass, and the energy the barn owl gets from the vole
Only the energy that is made into new cells remains with the organism to be passed on
Even then, some of this energy does not get consumed – for example few organisms eat an entire organism, including roots of plants or bones of animals – but energy is still stored in these parts and so it does not get passed on
The majority of the energy an organism receives gets ‘lost’ (or ‘used’) through:
making waste products eg (urine) that get removed from the organism
as movement
as heat (in mammals and birds that maintain a constant body temperature)
as undigested waste (faeces) that is removed from the body and provides food for decomposers
This inefficient loss of energy at each trophic level explains why food chains are rarely more than 5 organisms long
In the example above, something that preyed regularly on the barn owl would only get 0.1J of energy from each barn owl it ate
In order to survive, it would have to:
eat a huge number of them every day to get the amount of energy it needed to survive (are there that many barn owls close together?)
not expend much energy itself hunting them (is this likely?)
Energy Transfer in Human Food Chains
Humans are omnivores, obtaining energy from both plants and animals, and this gives us a choice of what we eat
These choices, however, have an impact on what we grow and how we use ecosystems
Think of the following food chains, both involving humans
wheat → cow → human
wheat → human
Given what we know about energy transfer in food chains, it is clear that if humans eat the wheat there is much more energy available to them than if they eat the cows that eat the wheat
This is because energy is lost from the cows, so there is less available to pass on to humans
Therefore, it is more energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores
In reality, we often feed animals on plants that we cannot eat (eg grass) or that are too widely distributed for us to collect (eg algae in the ocean which form the food of the fish we eat)
Pyramids of Biomass
A pyramid of biomass shows how much mass the creatures at each level would have without including all the water that is in the organisms (their ‘dry mass’)
Pyramids of biomass are ALWAYS pyramid-shaped, regardless of what the pyramid of numbers for that food chain looks like
This is because the mass of organisms has to decrease as you go up a food chain – if we take our first food chain as an example, it’s impossible to have 10kg of grass feeding 50kg of voles feeding 100kg of barn owls
Pyramids of biomass provide a much better idea of the quantity of the plant or animal material at each level of a food chain and therefore are a better way of representing interdependence within the food chain
Pyramids of Number
A pyramid of numbers shows how many organisms we are talking about at each level of a food chain.
in pyramids of number The width of the box indicates
number of organisms at that trophic level
Pyramids of Number
For example, consider the following food chain:
Ask yourself the following questions:…
-Is it likely that there would be more voles in an area than grass plants?
How many voles might one barn owl need to eat per day? If it’s more than one, is it likely that there are more barn owls in an area than voles?
So, a pyramid of numbers for this food chain would look like this:
Despite the name (and the example above), a pyramid of numbers doesn’t always have to be…
for example
This is because the… of the organism is also important – one large organism, like the oak tree in the pyramid above, contains to support many smaller organisms (the insects)
pyramid-shaped
- size
- enough energy
Rules to remember when drawing a pyramid of numbers:
You cannot change the trophic level of the organisms – they must stay in the same order as in the food chain with producers on the bottom, followed by primary consumers, then secondary consumers, then tertiary consumers
Generally, the larger an individual organism is, the less of them there are
pyramids of biomass are ALWAYS
pyramid-shaped
pyramids of number can be
any shape
Make sure you learn the rules for drawing a pyramid of numbers to get it correct.
The Carbon Cycle
Nutrients such as carbon and nitrogen are not endless resources
There is a finite amount of each element on the planet and as such, they need to be recycled in order to allow new organisms to be made and grow
Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis
It is passed on to animals (and microorganisms) by feeding
It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration
If animals and plants die in conditions where decomposing microorganisms are not present, the carbon in their bodies can be converted, over millions of years and significant pressure, into fossil fuels
When fossil fuels are burned (the process is known as combustion), the carbon combines with oxygen and carbon dioxide is released into the atmosphere
Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere
In addition, mass deforestation is reducing the amount of producers available to take carbon dioxide out of the atmosphere by photosynthesis
This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they are burnt down, releasing yet more carbon dioxide into the atmosphere
The Water Cycle
Water molecules move between various locations – such as rivers, oceans and the atmosphere – by specific processes
This is possible because water changes state at a relatively low temperature
Water enters the atmosphere as water vapour in one of two processes:
Energy from the Sun heats the Earth’s surface and water evaporates from oceans, rivers and lakes
Transpiration from plants releases water vapour into the air
The warmer air of the lower atmosphere rises, taking the water vapour with it
The moist air cools down as it rises
Water vapour condenses back into liquid water, forming clouds
Water returns to Earth in the form of precipitation
As the water droplets in the cloud get bigger and heavier, they begin to fall as rain, snow and sleet
This is called precipitation
The nitrogen cycle cycle
