4.17 understand the effects of deforestation, including leaching, sol erosion, disturbance of the water cycle and of the balance in atmospheric oxygen and carbon dioxide

Leaching

Trees leach nutrients when they are alive, but return nutrients to the soil when they die. When trees are cut down, nutrients gets leached but not returned, resulting in infertile soil.

Soil erosion

When trees are removed, soil can be washed away by rain etc as tree roots hold soil together (but there will be no tree roots, as there will be no trees).

Disturbance of the water cycle

Trees take up water, when they are cut down, water runs straight into rivers, causing flooding. also, the local climate gets drier as there is much less transpiration occurring.

Disturbance of the balance of carbon dioxide and oxygen

When trees die, carbon dioxide is naturally released. When they are burnt, all the carbon dioxide is released at once. alternatively, if wood is used in furniture etc, the carbon is stored and not released, disrupting the carbon cycle.

Fewer trees means fewer photosynthesis means less oxygen.

4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms causing depletion of oxygen

Like fertilisers, sewage also contains phosphates (from detergents) and nitrates (from faeces etc). If these are leaked into rivers, eutrophication occurs.

NOTE: Point 4.16 my help for understanding

4.16 understand that eutropication can result from leached minrals from fertiliser

Nitrates and phosphates can leak from mineral fertilisers that are put on fields. If it rains, they are easily leached into rivers and lakes. this results in eutrophication. Basically...

- The extra nutrients causes algae to grow super fast. This blocks out the light
- Plants in the river (before the algae) can not photosynthesise due to low light. They die.
- With more food (dead plants) available, microorganisms living in the water rapidly increase in number and deplete/use up all of the oxygen in the water.
- Organisms, like fish for example, that need oxygen, die.

4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences

Heat from the sun is naturally radiated off the earth and into space. Greenhouse gases naturally keep in some of the heat (otherwise we would all die of cold, basically). However, increasing the amount of greenhouse gases is blocking the heat from escaping (known as the greenhouse effect). effectively, this heats up Earth, which is global warming.

Consequences of global warming include climate change (e.g. change in rainfall pattern)

4.13 understand how human activities contribute to greenhouse gases

Okay so basically...

Contribution to carbon dioxide - Car exhausts, industrial processes (burning of fossil fuels etc), cutting down of trees

Contribution to methane - rice growing, cattle rearing

Contribution to nitrous oxides - fertilisers, vehicle engine, industrial engines

CFCS - all man-made

4.12 understand that water vapour, carbon dioxide, nitrous oxide, methane and CFCs are greenhouse gases

NOTE: You may be asked where the greenhouses originate from. Well, its not in the spec but it was in the 2015 paper so just to be safe I have included the info (its in red).

Greenhouse gases are bad as they trap heat from the sun in the earths atmosphere. Examples of greenhouse gases include...

- Water vapour
- Carbon dioxide (deforestation, industrial processes, car exhausts)
- Nitrous oxide (fertilisers, vehicle engines, natural release from bacteria)
- Methane (rotting plants, rice growing, cattle rearing)
- CFCs (NOTE: CFCS are man-made chemicals, they are basically not produced anymore but some still are and are leaking from old products that contain them)

4.11 understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide

Sulfur dioxide

When fossil fuels are burnt, sulfur dioxide is released (from sulfur impurities in the fuel). When it mixes with rain clouds is forms acid rain (dilute sulfuric acid). This kills fish and trees as it causes lakes to become more acidic and can damage leaves and release toxic substances from the soil, meaning it is hard for the tree to take up nutrients from the soil.

Carbon monoxide

When fossil fuels are not burnt with enough air (incomplete combustion), carbon monoxide is produced. this is a poisonous gas and binds to haemoglobin in red blood cells, preventing the red blood cells from carrying enough oxygen to your muscles.

4.10 describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitryfying bacteria (specific names of bacteria are not required)

Firstly, here's a diagram...



Okay so...

nitrogen fixing bacteria - this turns atmospheric nitrogen into nitrogen compounds (in the soil) that plants can use

decomposers - turns proteins and urea (from plants and animals) into ammonia

nitrifying bacteria - this turns ammonia into nitrates

denitrifying bacteria - this turns nitrates back into atmospheric nitrogen gas

The process repeats.

NOTE: Some of these bacterium live in the soil and some live on the root nodules of plants.

4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

To start, here is a diagram...



Okay so...

Respiration - breathing basically. this releases carbon dioxide back into the air.

Photosynthesis - carbon is taken in (by the plants)

Decomposition - when plants and animals die, decomposers decompose them. this introduces carbon back into the soil

Combustion - things like wood and fossil fuels are burned. This releases carbon dioxide back into the air

The carbon dioxide in the air is then taken in by plants and the cycle continues(this is why plants are so important)

4.8 describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation

Firstly, here is a diagram...


Okay, so...

Evaporation - this is where water (from  the ground) gets warmed (usually from sunlight). When this happens, the water molecules gain energy and they start to move lots more, eventually they turn into a gas.

Transpiration - all transpiration is is evaporation from plants/leaves

Condensation - When the warm water vapour is carried upwards (convection currents). However, the higher you go the colder it gets. The water vapour eventually cools down and condenses, forming clouds

Precipitation - a fancy name for rain/snow/hail

4.7 explain why only about 10% of energy is transferred from one trophic level to the next

This is mainly explained in point 4.6, but I will cover the main points again...

Much energy is lost so not all energy an organism takes in is conserved until it dies and then transferred onto he next trophic level when it is eaten. the main causes of energy loss are...

- Heat energy
- Energy needed for the 7 life processes
- Energy in indigestible foods (e.g fibre) is not 'absorbed'

this results in around 90% of the energy being used, so only 10% is passed onto he next trophic level.

4.5 understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer

Food chain
A food chain shows the flow of energy up the food chain. It can only show one organism at each trophic level, also you cannot tell whether the organism is feeding at more than one.


Here is an example of a food chain...

Food web
A food web gives a better understanding of a certain ecosystem by linking several animals within a habitat showing which organisms consumes which etc. A food web basically just shows multiple different food chains, that are all linked together. They show multiple different trophic levels including multiple prey and multiple predators. This means an organism has the potential to be a secondary or tertiary consumer at the same time.

Here is an example of a food chain...

Pyramid of numbers
A pyramid of number shows the number of each organism (of each trophic level of a certain food chain) by the area of the block in the pyramid. E.g a large block is lots of that animal, a little block means few of that animal.

Here is an example of a pyramid of numbers...

Pyramid of biomass

A pyramid of biomass is a bit like a pyramid of numbers, only it represents the dry mass of each consumer (and producer), again, by the area of a pyramid block.


Here is an example of a pyramid of biomass...

Pyramid of energy

A pyramid of energy, again looks like a pyramid of numbers/biomass, but it shows the transfer/flow of energy through the food chain.

Here is an example...

NOTE: The amount of energy transferred decreases by 10% each time, this is important (this is explained in 4.6).

4.6 understand the transfer of substances and of energy along a food chain

Plants use energy from the sun in photosynthesis, this energy makes its way through the food chain as animals eat the plants and each other.

However, not all the energy that's available to the organisms in a trophic level is passed on to the next trophic level, this is because 90% of the energy is lost in various ways. These include...

- Indigestible energy is not taken in in the first place (e.g. fibre), it is just digested out
- Lots of energy is used for the 7 life processes
- Lots of the energy is lost in heat

NOTE: Only around 10% of energy becomes biomass (e.g. it is stored for growth etc). This is transferred onto the next trophic level once the organism is eaten.

4.4 explain the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers

Producers are the first trophic level because they are at the bottom of the food chain. They turn sunlight into usable energy, in other words, the produce energy.

The second tier are known as the primary consumers, as they are the first consumer in the food chain. They consume the producers.

The third tier are known as secondary consumers as they are the second consumer in the food chain, they consume the primary consumers.

And so on.

NOTE: Eventually all of the above die, they are eaten by decomposers (who break down dead material/waste.

4.3 explain how quadrats can be used to sample the distribution of organisms in their habitats

This experiment is laid out along a line (known as a transect).

-  Mark out a line along the area you want to investigate

- Using quadrat(s) placed next to each other, collect data along the line.

That's it :)

4.2 explain how quadrats can be used to estimate the population size of an organism in two different areas

Firstly, this is a quadrat…

They are usually 1m2 and split up into 100 smaller squares. Just randomly place/throw it on the ground and count all of the organisms within the quadrat. Repeat 5 times and find the mean. Now multiply the number of that organism found with the size (in m2) of the area you are investigating.

Repeat with another area and compare.

4.1 understand the terms population, community, habitat and ecosystem

Population - All the organisms of one species in a habitat

Community - All the different species in a habitat

Habitat - The area/place in which an organism lives

Ecosystem - All of the organisms living in a particular area and all the abiotic (non-living) conditions

NOTE: You literally just need to learn these