Ecosystems
Section: Biology | Syllabus: Cambridge Primary Science (0846)
Food Webs and Food Chains
- A food chain is a simple diagram showing ONE path of energy from a producer to consumers - arrows show the direction energy moves
- A food web is a diagram showing MANY connected food chains in an ecosystem
- shows that most animals eat more than one type of food
Key Vocabulary
- Producer: a green plant that makes its own food using sunlight (photosynthesis) - always starts the chain
- Consumer: an animal that eats other organisms to get energy
- Predator: an animal that hunts and eats other animals
- Prey: an animal that is hunted and eaten by predators
- Herbivore: an animal that only eats plants
- Carnivore: an animal that only eats other animals
- Omnivore: an animal that eats both plants and animals
A food web showing several connected food chains in one ecosystem
Skill: Finding Food Chains Within a Food Web
- To find a food chain inside a food web, follow ONE path from a producer to a top consumer
Worked Example: Identifying Food Chains
- Using the food web above, identify two different food chains
- Answer: Grass → Shrimp → Minnow → Otter
- Grass → Periwinkle → Crab → Gull
- Grass → Shrimp → Minnow → Gull
Use this food web to identify predators and their prey
Worked Example: Predators and Prey
- Question: in the food web above, name one predator and its prey. [2 marks]
- Answer: Predator: Dingo [1]
- Prey: Koala (or Kangaroo) [1]
Toxic Substances
- If toxic substances (like pesticides) enter a food chain, they can build up
- animals at the top of the food chain eat many smaller animals, so they end up with the highest amount of toxin
Worked Example: Toxic Substances
- Question: in the food chain Grass → Insect → Frog → Hawk, which organism will have the most toxin if the grass is sprayed with poison?
- Answer: the Hawk (the top predator)
Worked Example: Calculating Toxin Build-Up
- Question: a diagram uses dots to represent units of toxin - water plants have 2 dots, and small fish that eat the water plants have 8 dots. How many times more toxin do the small fish contain than the water plants?
- Answer: divide the two amounts: 8 ÷ 2 = 4 times more toxin
Human Impact and Reducing Pollution
- Human activities like dumping plastic, oil spills, and burning fossil fuels can pollute oceans, rivers and lakes with toxic substances
- Ways to reduce this pollution include:
- using less plastic and recycling more
- reducing the use of fossil fuels
- cleaning up litter and oil spills
- laws that ban harmful toxins and educate people about pollution
Soil and Ecosystems
- Different soil types affect which plants can grow well in an ecosystem
- Sandy soil: drains water quickly, so it dries out fast and holds fewer nutrients
- Clay soil: holds water well and is rich in minerals, but can become waterlogged
- Loam soil (a mix of sand, clay and organic matter): drains well AND holds water and nutrients - best for most plants
- Plants suited to well-draining soil (like sandy soil) can suffer in waterlogged clay soil, while plants that need lots of water and nutrients grow better in clay or loam soil
Investigating Soil
- When comparing how well different soils hold water or nutrients in a fair test, keep these variables the same: the amount of soil, the amount of water added, the type of plant/seed used, and the light and temperature conditions
- the only thing that should change is the type of soil being tested
Interactive revision notes, videos and practice questions load below.