Unit 7: Genes and inheritance
Food chains and webs — HIA International - Grade 8 Revision Notes & Topical Questions
5 min read 11 parts Lesson 3 of 9 3 quizzes
Lesson summary
Food chains and webs — HIA INTERNATIONAL notes: Construct food chains and food webs with correct arrows and use the key terms for the organisms in them.Ecology — the study of organisms in their environment and how they affect one another.Energy begins in the Sun — energy from sun…
- Energy transfer
- A food chain
- Every food chain starts with a producer
- Top predator
- A food web
- Energy is lost at every step
Part 1 of 9Where the energy in food comes from
Ecology
- Ecology the study of organisms in their environment and how they affect one another.
Energy begins in the Sun
- Energy begins in the Sun energy from sunlight reaches the Earth.
Plants use energy from sunlight to make their own food.
- Some of this energy is stored in the roots, stems, fruits and leaves of the plant.
Energy transfer
- Energy transfer when an animal eats part of a plant, it takes in the food the plant made and so gets energy.
Part 2 of 9Food chains
A food chain
- A food chain shows how energy is passed from one organism to the next by feeding.
Arrows
- Arrows point from the organism that is eaten to the organism that eats it, so they show the direction of energy transfer.
Every food chain starts with a producer
- Every food chain starts with a producer usually a green plant or alga that makes food by photosynthesis using energy from the Sun.
Order of a typical chain: Sun → grass → rabbit → fox → eagle.
- The Sun is the energy source and is shown at the start of the chain.
Part 3 of 9Producers and consumers
Producer
Producer an organism that makes its own food, such as a green plant.
Consumer
Consumer an organism that has to eat ready-made food to get energy; all animals are consumers.
Herbivore
Herbivore a consumer that eats only plants.
Carnivore
Carnivore a consumer that eats only other animals.
Omnivore
Omnivore a consumer that eats both plants and animals.
Predator
Predator an animal that catches, kills and eats other animals; the animals it eats are its prey.
Top predator
Top predator a predator with no natural predators in that food web.
Part 4 of 9Roles in a food chain
| Role | Gets energy from | Example | Trophic level |
|---|---|---|---|
| Producer | Sunlight (photosynthesis) | Grass | 1 |
| Primary consumer | Producers | Rabbit (herbivore) | 2 |
| Secondary consumer | Primary consumers | Fox (carnivore) | 3 |
| Tertiary consumer | Secondary consumers | Eagle | 4 |
| Decomposer | Dead organisms and waste | Fungi, bacteria | All levels |
Part 5 of 9Food webs
A food web
- A food web is a network of interlinked food chains in a habitat.
Most animals eat, and are eaten by, more than one type of organism, so one chain cannot show all the feeding links.
Example on the African plains: acacia tree → springbok → cheetah and grass → termite → aardvark → leopard.
- The two chains join where the same organism appears in both, for example where the leopard and cheetah both eat zebra.
Tracing a path with a finger from a producer along the arrows follows one food chain through the web.
Part 6 of 9Building a food web from descriptions
1
List the organisms in the habitat and write each name on a card.
2
Identify the producers and place them at the bottom.
3
Place each herbivore above the plants it eats and draw an arrow from the plant to the herbivore.
4
Add the carnivores above their prey with arrows pointing towards the carnivore.
5
Check that every arrow points in the direction of energy flow and label the top predator.
Part 7 of 9Energy loss and changes in populations
Energy is lost at every step
- Energy is lost at every step through movement, heat from respiration and waste, so less energy reaches each higher level.
Food chains are short
- Food chains are short they rarely have more than four or five links because too little energy is left for further consumers.
A change in one population affects the whole web.
- If a predator is removed, its prey may increase, then overeat their own food, which then decreases.
Toxic chemicals
- Toxic chemicals some pesticides build up along a food chain and harm the top predators most.
- (bioaccumulation)
Part 8 of 9Food chains and webs as models
A food chain or food web is a model
- A food chain or food web is a model it shows how organisms living in the same place depend on each other for food.
Strength: it shows clearly the direction of energy transfer and who eats whom.
Limitation: no food web is totally complete, because real feeding relationships are more numerous than any diagram.
- Decomposers are usually left out because an arrow would be needed from every organism to the decomposers.
Part 9 of 9More from the specification
Decomposer fungi and brewer's yeast
- Decomposer fungi and brewer's yeast saprotrophic microorganisms including cultivated yeast recycle nutrients by decomposing organic matter within trophic food webs.
Food chain
- Food chain arrow diagram showing the transfer of energy from a producer through consumers
Food web
- Food web linked food chains showing that organisms feed on several species
Decomposers
- Decomposers microorganisms such as fungi and bacteria that cause decay, such as mould on bread, and return nutrients to the soil
Change in a population
- Change in a population removing one organism affects others in the web, so cells and energy flow depend on the group of species present
Food chain
- Food chain arrow diagram showing the transfer of energy from a producer through consumers
Food web
- Food web linked food chains showing that organisms feed on several species
Decomposers
- Decomposers microorganisms such as fungi and bacteria that cause decay, such as mould on bread, and return nutrients to the soil
Change in a population
- Change in a population removing one organism affects others in the web, so cells and energy flow depend on the group of species present
Colony
- A visible group of cells from one microorganism.
Organic matter
- Any substance made by a living organism.
Solar eclipse
- The Moon blocks light from the Sun to Earth.
Lunar eclipse
- The Earth blocks light from the Sun to the Moon.
Microorganism
- A living thing so small that it needs a microscope to be seen clearly.
Eclipse
- When one body blocks light and casts a shadow on another.
Key terms
| Term | Meaning |
|---|---|
| Producer | An organism that makes its own food, usually a green plant. |
| Consumer | An organism that eats other organisms to get energy. |
| Herbivore | A consumer that eats only plants. |
| Carnivore | A consumer that eats only animals. |
| Predator | An animal that hunts, kills and eats other animals. |
| Prey | An animal that is hunted and eaten by a predator. |
| Food chain | A line of organisms showing how energy passes by feeding. |
| Food web | Many linked food chains in one habitat. |
Avoid these mistakes
1
Drawing arrows from the eater to the food — arrows point from the organism that is eaten to the organism that eats it.
2
Starting a food chain with an animal — every food chain starts with a producer.
3
Saying energy is recycled along a chain — energy is transferred and lost as heat at each step.
4
Thinking all animals are carnivores or predators — herbivores and omnivores are consumers too.
Marked practiceQuizzes for this lesson
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