Welcome to Ecosystems and Material Cycles!
In this chapter, we are going to explore how every living thing on Earth is connected. We’ll look at how plants and animals rely on each other to survive, how energy flows through the natural world, and how nature is the ultimate recycler—making sure that nothing goes to waste. This is a key part of your Paper 2 exam, so let’s dive in!
1. Levels of Organisation
To understand an ecosystem, Biologists look at it in different layers, like zooming out on a map:
1. Individual Organism: A single living thing (e.g., one fox).
2. Population: All the individuals of the same species living in one area.
3. Community: All the different populations (plants, animals, fungi) living together in an area.
4. Ecosystem: The community of living things (biotic) interacting with their non-living (abiotic) environment (like water, weather, and soil).
Quick Review Box:
Biotic = Living (think "Bio" like Biology).
Abiotic = Non-living (the "a" means "not").
Key Takeaway
An ecosystem is the highest level of organisation, including both the living community and the physical environment.
2. Factors Affecting Communities
Why do some animals live in one place but not another? It's all down to Abiotic and Biotic factors.
Abiotic Factors (Non-living)
Changing these can change where organisms can survive:
- Temperature: Most organisms have an ideal temperature range.
- Light intensity: Plants need light for photosynthesis.
- Water availability: No water usually means no life!
- Pollutants: Chemicals in the air or water can harm sensitive species.
Biotic Factors (Living)
- Competition: Organisms fight for the same resources (food, space, mates).
- Predation: If the number of predators goes up, the number of prey usually goes down.
Key Takeaway
Communities are constantly changing based on the balance of living and non-living factors around them.
3. Interdependence and Relationships
In a community, every species depends on others for things like food, shelter, and pollination. This is called interdependence. If one species is removed, it can affect the whole web!
Special Relationships
Some species have very close "roommate" deals:
- Parasitism: One organism (the parasite) lives off another (the host) and harms it. The parasite wins, the host loses. Example: Fleas on a dog.
- Mutualism: Both organisms benefit from the relationship. It's a win-win! Example: Bees and flowers (Bees get food, flowers get pollinated).
Memory Aid:
Mutualism = Mutual benefit (Me and you are both happy!).
Key Takeaway
Organisms rarely live in isolation; they are tied together through mutualism or parasitism.
4. Investigating the Environment (Core Practical)
We can’t count every single blade of grass in a field, so we use sampling techniques.
Quadrats
A quadrat is a square frame. You place it on the ground and count the organisms inside. To get a fair result, you must place it randomly to avoid bias.
Belt Transects
If you want to see how the environment changes (e.g., as you move from a sunny field into a dark forest), you use a belt transect. You lay a tape measure (the transect) and place quadrats at regular intervals along it.
Calculating Population Size
To estimate the total number of organisms in an area, use this simple formula:
\( \text{Total Population} = \frac{\text{Total Area}}{\text{Area Sampled}} \times \text{Number of organisms counted} \)
Common Mistake to Avoid:
Don't just put your quadrat where you see "interesting" things. That's not random! Close your eyes and throw it, or use a random number generator for coordinates.
Key Takeaway
Quadrats measure abundance in a uniform area; belt transects measure how abundance changes across a gradient.
5. Energy Transfer and Biomass
Energy enters most ecosystems through sunlight, which plants turn into biomass (biological material) through photosynthesis.
Trophic Levels
Energy moves through trophic levels (feeding levels):
1. Producers: Plants and algae.
2. Primary Consumers: Herbivores that eat producers.
3. Secondary Consumers: Carnivores that eat primary consumers.
4. Tertiary Consumers: Carnivores that eat secondary consumers.
Pyramids of Biomass
A Pyramid of Biomass shows how much living tissue is at each level. They are almost always pyramid-shaped because energy is lost at every step. Only about 10% of the energy is passed on to the next level!
Where does the energy go?
- Respiration: Energy is used for movement and keeping warm (heat loss).
- Waste: Not everything is eaten (bones, roots) and some is passed as faeces (poop!).
Calculating Efficiency
\( \text{Efficiency} = \frac{\text{Energy transferred to next level}}{\text{Energy available from previous level}} \times 100 \)
Key Takeaway
Energy is lost at each trophic level, which limits the length of food chains—there usually isn't enough energy left to support a 5th or 6th level!
6. Human Impact on Biodiversity
Humans interact with ecosystems in both positive and negative ways.
Fish Farming
- Why we do it: To produce more food and reduce overfishing in the wild.
- The downside: Waste from the fish can leak into the environment, and diseases can spread easily in crowded pens.
Non-Indigenous Species
These are species brought into an area where they don't naturally belong. They can outcompete local species for food and space, often causing a drop in biodiversity.
Eutrophication (The "Green Blanket")
This happens when fertilizers wash into ponds or lakes:
1. Nitrates cause algae to grow rapidly on the surface (Algal Bloom).
2. The algae block light, so plants below die.
3. Decomposers (bacteria) break down the dead plants and use up all the oxygen in the water.
4. Fish and other animals suffocate and die because there is no oxygen.
Conservation and Reforestation
We can help by protecting species (conservation) or planting new forests (reforestation) to increase biodiversity and provide habitats.
Key Takeaway
Human activities like fish farming and eutrophication can reduce biodiversity, but conservation efforts aim to restore it.
7. Material Cycles
Nature doesn't have a bin! It recycles everything using Material Cycles.
The Carbon Cycle
- Photosynthesis: Plants take \(CO_{2}\) out of the air.
- Respiration: Plants and animals put \(CO_{2}\) back into the air.
- Decomposition: Microorganisms (decomposers) break down dead matter and release \(CO_{2}\) through respiration.
- Combustion: Burning wood or fossil fuels releases \(CO_{2}\).
The Water Cycle
- Evaporation: Sun heats water into vapour.
- Transpiration: Water evaporates from plant leaves.
- Condensation: Vapour forms clouds.
- Precipitation: Rain or snow falls.
- Potable Water: In dry areas, we can get drinking water through desalination (removing salt from seawater).
The Nitrogen Cycle
Plants need nitrogen for proteins, but they can't take it from the air. They need nitrates from the soil.
- Nitrogen-fixing bacteria: Turn nitrogen gas from the air into nitrogen compounds in the soil.
- Nitrifying bacteria: Turn ammonia into nitrates.
- Denitrifying bacteria: Turn nitrates back into nitrogen gas (usually in waterlogged soil).
- Decomposers: Break down proteins in dead waste into ammonia.
Farmers help this cycle by using fertilisers or crop rotation (planting beans or peas that have nitrogen-fixing bacteria in their roots).
Key Takeaway
Carbon, water, and nitrogen are constantly cycled between the living world and the physical environment.
8. Indicator Species and Decomposition
How can we tell if an environment is polluted without expensive sensors? We look at the organisms living there!
Indicator Species
- Polluted Water: Bloodworms and Sludgeworms love low-oxygen, dirty water.
- Clean Water: Freshwater shrimps and Stonefly nymphs only live in very clean, oxygen-rich water.
- Air Quality: Different types of Lichen (crusty plants on trees) and Blackspot fungus on roses tell us how much sulfur dioxide (air pollution) is around.
Decomposition (Decay)
Decomposition is the breakdown of dead matter by bacteria and fungi. It happens faster if:
1. Temperature is warm (but not boiling).
2. There is plenty of Water (moisture).
3. There is plenty of Oxygen (for aerobic respiration).
We use this knowledge to preserve food (freezing, drying, vacuum packing) and to make compost for gardens.
Key Takeaway
Indicator species act as natural "pollution meters," and decomposition is a vital process that recycles nutrients back into the soil.
Don't worry if the cycles seem tricky at first! Just remember that most of them follow a "circle"—what goes out must eventually come back in. You've got this!