Grade 7 Science
End-of-Term Revision Guide: Ecosystems, Energy, and Biodiversity
Part 1: Ecosystem Fundamentals
Covering LOs 1, 21, 22: What is an ecosystem and how is it organized?
LO 1: Identify parts of an ecosystem.
What is an Ecosystem?
An ecosystem is a community of living organisms interacting with their non-living environment.
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Biotic Factors: The living parts of the ecosystem.
Examples: Plants, animals, fungi, bacteria. -
Abiotic Factors: The non-living parts of the ecosystem.
Examples: Sunlight, water, soil, temperature, air.
Ecosystem Diagram Concept
Imagine a forest: The **Biotic** parts (trees, animals, insects) interact with the **Abiotic** parts (soil, water in the river, sunlight).
An ecosystem is the total sum of these interactions.
LO 21: Levels of organization.
Organism
One single living individual. (e.g., one deer)
Population
A group of the same species living in the same area. (e.g., a herd of deer)
Community
All the different populations (species) in one area. (e.g., deer, rabbits, and trees)
Ecosystem
The community plus its abiotic factors. (e.g., the forest, river, and all its life)
Part 2: Chemical Reactions & Energy
Covering LOs 2, 3, 4, 5, 6, 7, 24: How life makes and uses energy.
LO 2, 3, 4, 24: Explain Photosynthesis.
Photosynthesis: Making Food
The process plants use to turn sunlight, water, and carbon dioxide into their own food (glucose/sugar) and oxygen.
Simple Formula:
Carbon Dioxide + Water --(Sunlight)--> Sugar + Oxygen
The Plant's Kitchen
Inputs: Carbon Dioxide (CO2), Water (H2O), **Light Energy**
Outputs: Glucose/Sugar (C6H12O6), Oxygen (O2)
Occurs in the chloroplasts (using chlorophyll).
LO 2, 3, 4, 24: Explain Cellular Respiration.
Cellular Respiration: Using Food
The process all living things (plants and animals) use to break down food (glucose) to release usable energy (ATP) for the cell. It uses oxygen.
Simple Formula:
Sugar + Oxygen --> Carbon Dioxide + Water + Energy
The Cell's Powerhouse
Inputs: Glucose/Sugar (C6H12O6), Oxygen (O2)
Outputs: Carbon Dioxide (CO2), Water (H2O), **ATP Energy**
Occurs in the mitochondria.
LO 5, 6, 7: Describe the flow of energy.
Producers
Make their own food, usually using sunlight (e.g., plants, algae). They are the base of the food chain.
Consumers
Eat other organisms. Primary: Herbivores (eat producers). Secondary: Carnivores/Omnivores (eat primary consumers).
Decomposers
Break down dead organisms and waste (e.g., fungi, bacteria), returning nutrients to the soil.
Energy flows in one direction: Sun → Producers → Consumers → Decomposers. Only about 10% of energy moves to the next level!
Part 3: Matter, Cycles & Changes
Covering LOs 8, 9, 10, 11, 15, 16, 17, 19, 23, 25: How ecosystems are built and how they change.
LO 8, 9, 25: Describe the cycling of matter.
The Water Cycle
Movement through the atmosphere (Condensation), back to Earth (Precipitation), and into the air (Evaporation/Transpiration).
The Carbon Cycle
Moved primarily by **Photosynthesis** (taking CO2 out) and **Respiration** (putting CO2 back in).
The Nitrogen Cycle
Requires specialized **soil bacteria** to convert atmospheric nitrogen into usable compounds for plants.
LO 10, 11, 15-17: Changes to components.
Physical (Abiotic) Changes
Changes to the non-living parts of an ecosystem that affect populations.
- Natural: Drought, flood, volcanic eruption.
- Human-caused: Pollution (spilling oil), building dams, climate change (rising temperatures).
Biological (Biotic) Changes
Changes to the living parts of an ecosystem that affect populations.
- Natural: A disease kills many of one species.
- Human-caused: Introducing an Invasive Species (like Kudzu) that outcompetes native life.
LO 19, 23: Resource Availability & Data.
Argument & Evidence
Argument (LO 19): A change to any component (like less water) will affect populations (e.g., plant populations will decrease).
Data (LO 23): If there is less food, water, or space (Limiting Factors), competition increases and the population size is restricted.
Carrying Capacity: The maximum population an ecosystem's resources can support.
Part 4: Interactions & Biodiversity
Covering LOs 12, 13, 14, 18, 20, 22: How species live together and why variety matters.
LO 12, 13, 14: Patterns of interactions.
Competition (- / -)
Organisms fighting for the same limited resource (food, mates, space).
Predation (+ / -)
One organism (predator) hunts and eats another (prey).
Symbiosis (Close Relationship)
Mutualism (+/+): Both benefit (bee & flower). Commensalism (+/0): One benefits, one is unaffected. Parasitism (+/-): One benefits, one is harmed (tick & dog).
LO 18, 22: Measuring Biodiversity.
What is Biodiversity? (LO 22)
The variety of life in an area. This includes:
- Genetic Diversity: Variety of genes (e.g., different colored chicks).
- Species Diversity: Number of different species in a community.
- Ecosystem Diversity: Variety of habitats (e.g., desert, coral reef, tundra).
How to Measure (LO 18)
Quadrat Sampling: Using a square frame to count species in a small, random area, then using math to estimate the total for the large area.
Quadrat Sampling: Estimation
Scientists place a square frame (quadrat) on the ground to count organisms within that small, defined space.
This count is then scaled up to estimate the total population or diversity in the entire field.
LO 20: Methods to maintain biodiversity.
- Habitat Restoration: Reforestation (planting trees) and Reclamation (restoring land damaged by mining).
- Reducing Pollution: Cleaning up oil spills and plastic waste; limiting harmful chemicals.
- Controlling Invasive Species: Using traps (mechanical), pesticides (chemical), or introducing natural predators (biological) to remove harmful non-native species.
- Reducing Climate Change: Using renewable energy (solar, wind) to reduce greenhouse gases that warm the planet and threaten ecosystems like coral reefs.
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