4.18B understand the effects of deforestation, including leaching, soil erosion, disturbance of evapotranspiration and the carbon cycle, and the balance of atmospheric gases

Effects of Deforestation:

1. Eutrophication
- Loss of trees will lead to the unused nutrients and minerals remaining in the soil.
- These excess nutrients and minerals may be washed into rivers and lakes, causing eutrophication.

2. Soil Erosion
- Loss of trees will cause the soil to be loose and unstable
- Soil may be washed away by rain, inhibiting vegetative growth.

3. Disturbance in the water cycle
- As transpiration releases water vapors into air and returns via precipitation, loss of trees will result in less transpiration.

4. Unbalanced carbon cycle
- As trees carry out photosynthesis to absorb carbon dioxide and release oxygen, the loss of trees will decrease photosynthesis, therefore carbon dioxide levels will increase, and less oxygen will be produced. Oxygen levels will, therefore, decrease over time.

4.17 understand the biological consequences of eutrophication caused by leached minerals from fertiliser

Eutrophication: environment of an aquatic ecosystem that is boosted by chemical nutrients. 

Biological Consequences of Eutrophication:

1. Excessive nutrients from fertilizers in farms can be washed into rivers and lakes by rain.

2. These excessive nutrients allow the rapid growth of plants such as algae and duckweed. The growth of algae on the river surface blocks sunlight for aquatic plants, therefore they can no longer absorb sunlight via photosynthesis, which causes them to die.

3. When there is less photosynthesis, oxygen levels deplete.

4. Furthermore, decomposers breaking down the dead plants by photosynthesis can cause further depletion of oxygen. 

5. This stresses the survival of marine organisms, which potentially leads to a reduction in biodiversity.

4.16 understand the biological consequences of pollution of water by sewage

Water pollution by sewage:

- Sewage is rich in minerals and nutrients to allow organisms like decomposers to reproduce, increasing their population. This causes depletion of oxygen as decomposers will respire aerobically, so oxygen levels will decrease for other organisms. Aquatic animals can die as a result.
- Sewage is rich in phosphates which promote the growth of algae. Formation of algae can block sunlight, which prevents plants from absorbing sunlight via photosynthesis, resulting in the death of aquatic plants.
- Sewage contains bacteria respiring aerobically, which uses up oxygen levels in the water.

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

Greenhouse gases: gases responsible for global warming. Includes carbon dioxide, nitrous oxide, methane, and CFC.

Enhanced greenhouse effect: impact on the climate from the additional heat retained due to the increased amounts of greenhouse gases that humans have released into the earth's atmosphere.

1. Sun emits ultraviolet radiation which is absorbed and re-emitted as infrared radiation by the Earth's surface
2. Greenhouse gases in the atmosphere absorb and re-radiates the infrared radiation
3. As a result, this heat is kept in the atmosphere which enhances the greenhouse effect.

4.14 understand how human activities contribute to greenhouse gases

Carbon Dioxide: Humans release carbon dioxide in car exhausts, industrial processes, and fossil fuel combustion. Deforestation also increases carbon dioxide levels as fewer trees will be able to carry out photosynthesis to exchange carbon dioxide to oxygen.

Methane: Can be naturally produced from rotting plants in marshlands. Rice growing and cattle rearing also cause the release of methane.

Nitrous oxide: Released naturally by bacteria in soils and the ocean. It is also released from fertilizers and vehicle engines.

CFCs: CFCs are chlorofluorocarbons, which are man-made chemicals that once used in aerosol sprays and fridges.

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

Greenhouse gas: responsible for global warming, as they trap energy from the sun in the earth's atmosphere.
- Gases in the atmosphere absorb most heat that would normally be radiated out into space, and re-radiate it in all directions.
- If greenhouse effect didn't happen, the earth would be extremely cold.

Gas	Examples
Water vapour	Rivers, lakes, oceans
Carbon Dioxide	Deforestation
Nitrous Oxide	Fertilizers and combustion
Methane	Rice growing and cattle farming
CFC (Chlorofluorocarbons)	Chemicals in aerosol sprays and refrigerators

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

Sulfur dioxide: 
- The combustion of fuels creates sulfur dioxide. This is because fuels contain impurities such as sulfur. When this is burned at high temperature, the sulfur reacts with oxygen in the air to create sulfur dioxide.
- Sulfur dioxide dissolves in clouds to form sulfuric acid (acid rain).
Consequences of acid rain:
- Acid rain leaches minerals and nutrients out of the soil, causing the death of plants and trees.
- Damages waxy cuticle, reducing plants' ability to absorb mineral ions for growth.
- Acidifies rivers and lakes, causing the death of aquatic animals.
- Corrodes limestone and marble buildings. (acid can react with calcium carbonate/limestone)

Carbon Monoxide:
- Incomplete combustion of fossil fuels produces carbon monoxide.
Why?

From these equations, we can see that methane (CH4) reacts with oxygen during combustion. There are two types of combustion: incomplete combustion and complete combustion. While complete combustion only creates carbon dioxide and water, incomplete creates carbon monoxide, water, and carbon dioxide.



Consequences of Carbon Monoxide:
- Carbon monoxide binds to hemoglobin, thereby restricting the amount of oxygen that can be carried around the body.
- This can cause fatigue due to poor oxygen transport.
- It can also cause emphysema due to insufficient oxygen in aerobic respiration.
- If pregnant, carbon monoxide causes insufficient oxygen for respiration, which reduces the growth of the fetus.

4.11B describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of bacteria are not required)

Energy in ecosystems moves in a linear flow; that is, there is no "recycling" of energy in an ecosystem. There is no possible way that energy is recycled. Matter, on the other hand, is what's being recycled. For example, all atoms in your body have been in other organisms and will be again in the future.

- The atmosphere contains around 78% nitrogen gas. This is very unreactive so it can't be used directly by plants or animals.
- Nitrogen is needed for making proteins for growth. This is because amino acids are part of the -NH2 group, and so nitrogen is found in proteins. While animals can only get proteins by eating plants (or each other), plants can only get proteins by turning nitrogen in the air into nitrogen compounds (such as nitrates) before plants can use it.

Nitrogen Fixation: the process of turning nitrogen gas from the air into nitrogen compounds in the soil which plants can use. There are two ways of nitrogen fixation:
1. Lightning: energy in lightning allows nitrogen to react with oxygen in the air to give nitrates.
2. Nitrogen-fixing bacteria: turns atmospheric nitrogen gas to nitrogen compounds in soil that plants can use.

There are 4 different types of bacteria involved in the nitrogen cycle:
1. Decomposers: break down proteins and urea, and turns them into ammonia (nitrogen compound). This forms ammonium ions in the soil.
2. Nitrifying bacteria: turn ammonium ions in decaying matter to nitrates.
3. Nitrogen-fixing bacteria: turns atmospheric nitrogen gas to nitrogen compounds in soil for plants
4. De-nitrifying bacteria: turns nitrates back to nitrogen gas.

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

Carbon Cycle: movement of carbon molecules in the environment.


















1. Respiration
- all living organisms respire aerobically and release carbon dioxide into the atmosphere as organic compounds that are broken down to release energy.

2. Photosynthesis
- fixes carbon atoms from atmospheric carbon dioxide to organic molecules and becomes a part of complex carbon compounds in plants.

3. Decomposition
- dead organisms are broken down by decomposers and carbon in their bodies return as carbon dioxide.

4. Combustion
- Decayed plants and animals are made into fossil fuels which burn to release carbon dioxide back into the atmosphere.

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

Only 10 % of energy is transferred from one trophic level to the next as energy is lost to:

1. Respiration:
- Energy is lost as heat energy via respiration to enable the movement of an organism.

2. Incomplete consumption:
- Energy may be lost as not all of the food is consumed by an organism. For example, parts of food such as roots or bones aren't eaten as they are indigestible, so they pass through organisms and come out as waste.

3. Excretion:
- Incomplete digestion results in energy loss via egestion to produce feces, which is then broken down by decomposers.

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

- Energy enters most ecosystems via sunlight, where it is then converted to chemical energy by producers via photosynthesis.
- However! Only 10% of energy is passed from one trophic level to the next.

Energy is lost to:

1. Respiration:
- Energy is lost as heat energy via respiration to enable the movement of an organism.

2. Incomplete consumption:
- Energy may be lost as not all of the food is consumed by an organism. For example, parts of food such as roots or bones aren't eaten as they are indigestible, so they pass through organisms and come out as waste.

3. Excretion:
- Incomplete digestion results in energy loss via egestion to produce feces, which is then broken down by decomposers.

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

Food Chains:

- Show what's eaten by what.

- Food chains always start with a producer. In this case, the flower is the producer as it produces its own food using the sun's energy via photosynthesis. (photosynthesis produces glucose!)

- Producers are eaten by primary consumers, which are then eaten by secondary consumers, and secondary consumers are then eaten by tertiary consumers. 

- All these organisms die eventually and get eaten by decomposers like bacteria. 

*Each stage (e.g. producers, primary consumers...) is called a trophic level.

Food Webs:

- Shows how food chains are linked to more complex feeding relationships. 

- There are many different species in the environment. Therefore food webs can be used to show these species.

- All species in the food web are interdependent. This means that if one species changes, it affects all others. 

- e.g. if lots of water spiders died, then there would be less food for frogs, causing their numbers to decrease. The number of mayfly larvae can therefore increase, and diving beetles would have less competition therefore the number of diving beetles would increase.

Pyramids of Numbers: 

-Wider bar indicates a larger population.

- As energy is lost to surroundings from one trophic level to the next, there are usually fewer organisms with each tropic level due to decreased chances of survival.

Pyramids of Biomass:

- Shows the total mass of organisms in each trophic level. 

- Each bar represents the mass of living materials all organisms at each trophic level would "weigh" if you put them all together. 

- In this case, one fox would have big biomass and the hundreds of fleas would have very small biomass. Biomass pyramids are almost always in the right pyramid shape.

Pyramids of Energy Transfer:

- Always pyramid-shaped as energy is lost to the surroundings and only 10% of energy is passed from one trophic level to the next.

4.6 understand the names given to different trophic levels, including producers, primary, secondary and tertiary consumers and decomposers

Trophic levels: the position an organism occupies within the feeding sequence.

Producers: organisms that produce their own organic nutrients (e.g. plants produce their own food (glucose) via photosynthesis)

Primary consumers: herbivores that feed on producers (plants).

Secondary consumers: Predators that feed on primary consumers.

Tertiary consumers: Predators that feed on secondary consumers.

Decomposers: Organisms that release digestive enzymes on dead organisms for energy

4.5 understand how abiotic and biotic factors affect the population size and distribution of organisms

Abiotic Factors:
- Non-living environmental factors can affect organisms in an ecosystem.
Examples include: light intensity, soil pH, temperature, soil moisture, minerals and nutrients in the soil, oxygen levels, carbon dioxide levels, availability of water.

Biotic Factors:
- Living interactions between organisms, that will affect ALL species (as they have the vulnerability of being food to predators or host to disease).
Examples include: diseases, predation, competition for food, competition for shelter, bacteria, fungi.

4.4B practical: investigate the distribution of organisms in their habitats and measure biodiversity using quadrats

Method:

1. Place quadrat randomly within the sampling area.
2. Count the number of members of the same species within the quadrat.
3. Repeat numerous times and repeat process in other sampling areas to compare results.
4. Results can be shown on a map of the sampled area displaying which areas are densely populated by certain species.



To increase reliability:
- Randomly place quadrat by dividing the sampling area into a grid and using a random number generator to select random coordinates to place the quadrat at.
- Use quadrat of the same size with each repeat.
- Take more samples to collect larger data sizes.

4.3B understand the term biodiversity

Biodiversity: The measure of the variety of different species living in a habitat. A greater number of different species indicates greater biodiversity.

High biodiversity makes sure that ecosystems are stable, as different species depend on each other for things such as shelter and food. The species can help maintain the right physical environment for each other (e.g. acidity of the soil).

Human actions such as deforestation are reducing biodiversity.

4.2 practical: investigate the population size of an organism in two different areas using quadrats

Quadrat: square frame enclosing a known area, such as 1 meter squared

To study population size of a species:
1. Place a 1-meter squared quadrat on the ground at a random point in the sample area. This is done by dividing the sample area into a grid and using a random number generator to pick the coordinates to place your quadrats at.

2. Count all the organisms you're interested in within a quadrat.

3. Repeat steps 1 and 2 at least 3 times.

4. Find the mean (average) of the number of organisms within the sample area.

5. Calculate the population size. Population size is essentially the mean number of organisms per meter squared, so just multiply the mean number of organisms from step 4 and multiply this by total area of habitat.

To study/compare population size in 2 sample areas:
1. Place a 1-meter squared quadrat on the ground at a random point in the sample area. This is done by dividing the sample area into a grid and using a random number generator to pick the coordinates to place your quadrats at.

2. Count all the organisms you're interested in within a quadrat.

3. Repeat steps 1 and 2 at least 3 times.

4. Find the mean (average) of the number of organisms

5. Repeat steps 1 and 4 in the SECOND sample area, and take mean.

6. Compare 2 means.

4.1 understand the terms population, community, habitat and ecosystem

Population: Number of members of a single species in a habitat.
Community: Different species of organisms in a habitat.
Habitat: Where living organisms live.
Ecosystem: Population of all different species of organisms and the habitat that they live in.