Food Chains and Food Webs, Grade 8
The arrow in a food chain does not mean "eats". It means "energy flows to".
Grass → zebra → lion. The arrow points from the grass to the zebra, which reads backwards to most learners, because the zebra is the one doing the eating. Every mark lost on food chain diagrams comes from arrows drawn the wrong way round, and the fix is one sentence said before the first diagram, not after the first test.
This page covers food chains and food webs, the energy pyramid with numbers that actually work, and a one-square-metre fieldwork study you can run in the school grounds with equipment you already own.
Where this fits in the curriculum
| Subject | Natural Sciences |
|---|---|
| Grade | 8 |
| Term | 1 |
| Strand | Life and living |
| Topic | Topic 2, Interactions and interdependence within the environment |
| Status | Not a formally assessed practical task. The topic revision in the book is 45 marks |
| Marks | None prescribed. Our worksheet is 45 marks |
The five feeding groups, and the two that get confused
| Group | Eats | Example |
|---|---|---|
| Producer | Nothing. Makes its own food by photosynthesis | Grass, marula tree, algae, kelp |
| Herbivore | Plants only | Impala, locust, cow, aphid |
| Carnivore | Other animals | Leopard, ladybird, eagle |
| Omnivore | Both | Human, baboon, warthog |
| Decomposer | Dead material, breaking it down | Bacteria, fungi, earthworm, millipede |
Scavenger and decomposer are not the same thing. A vulture is a scavenger: it eats dead flesh whole, the way any carnivore eats. A fungus is a decomposer: it releases enzymes onto the dead material, digests it outside its own body, then absorbs the result. The vulture leaves bones. The fungus leaves nutrients in the soil.
Watch the sparrow. Textbook lists of herbivores often include sparrows. House sparrows are omnivores and they feed their chicks on insects. If a list looks tidy, check the awkward one on it.
Arrows, and the sentence that fixes them
Say this before the first diagram goes on the board:
The arrow points the way the energy travels, which is from the thing being eaten towards the thing doing the eating.
Then draw grass → zebra → lion and ask which animal the arrows point at. The lion. The lion is where the energy ends up.
A food chain always starts with a producer, because a producer is the only thing that can put new energy into the system. Everything after it is passing along energy that the sun gave to a plant.
From chain to web
A food chain is a lie you tell to get started. Nothing eats one food. A baboon eats fruit, insects, eggs and small animals, and four different things eat a locust.
A food web is several food chains drawn on top of one another, sharing organisms. It is the honest picture, and it is what the questions are actually about, because a web lets you ask what happens when one species disappears.
| Question | What it is testing |
|---|---|
| Remove all the producers | Everything collapses. Nothing is putting energy in |
| Remove one herbivore | Its predators drop or switch prey. The plants it ate increase |
| Remove the top carnivore | Herbivores increase, then the plants get eaten out, then the herbivores crash |
The good answers name the route. "The leopard would die" is worth little. "Fewer baboons are eaten, so baboon numbers rise, so more locusts and fruit are eaten" is worth the marks.
The energy pyramid, with numbers that add up
Only a small part of the energy at one level reaches the next. The rest is used for moving, breathing and growing, or lost as heat, or leaves in waste.
Here is a grassland pyramid in kilojoules per square metre per year, and the arithmetic checked:
| Level | Energy in | Passed on | Lost here | Percentage passed on |
|---|---|---|---|---|
| Producers, grass | 50 000 | 6 500 | 43 500 | 13% |
| Primary consumers, locusts | 6 500 | 310 | 6 190 | 4,8% |
| Secondary consumers, field mice | 310 | 38 | 272 | 12,3% |
| Tertiary consumer, owl | 38 | — | — | — |
Textbooks say "about 10% is transferred", then print figures like these, which are 13%, 4,8% and 12,3%. Both things are in the same book, on the same page, and learners notice. Tell them 10% is a rough rule of thumb, not a law, and that real transfer runs from about 1% to about 20%.
Why the pyramid is pyramid-shaped: each level holds less energy than the one below it, so each block is drawn narrower. The shape has nothing to do with how big the animals are or how many there are. One owl sits on top of thousands of locusts, and the owl block is the small one.
The practical: a one square metre study of the school grounds
This is the best fieldwork in Grade 8 and it needs almost nothing you do not already own.
What you need
String and four pegs · a metre stick or tape · a thermometer · hand lenses · a sieve · a field guide or identification chart · a clipboard
Method
- Choose a patch that has something living in it. A flower bed, the ground around a tap, the edge of a sports field, a strip beside a wall
- Peg out one metre by one metre with the string. That square is the whole study
- Record the abiotic factors: sun or shade, water nearby, wind exposure, temperature from the thermometer, soil colour and type, and whether the ground slopes
- Record the biotic factors: name and count every plant and animal you can find. Use the hand lenses. Turn over one stone and put it back
- Sieve a small sample of soil and look for roots, dead leaves, insects and worms
- Come back at the same time each day for a week and record again
Turning it into a food web
Your square almost certainly contains grass, an insect, a bird that visits and something in the soil. That is four organisms and a real food web, built from an actual place instead of a textbook picture.
Ask each group to draw the web for their own square, then compare the shaded square with the sunny one. Different abiotic factors, different organisms, and the class works out why without being told.
Two squares beat one. A group with a single square has a description. A group with a shaded square and a sunny square has a comparison, and a comparison is science.
Balance, and what upsets it
An ecosystem holds as many organisms as its resources allow. More food, more animals. Less food, fewer animals. Predator and prey numbers rise and fall against each other.
| Natural disruptions | Human disruptions |
|---|---|
| Fire, drought, flood, sudden temperature change | Pollution, monoculture farming, over-harvesting, poaching, alien species |
Fertiliser run-off is worth a minute of its own. The three nutrients in most fertiliser are nitrogen, phosphorus and potassium. What the crop does not use washes into rivers, feeds algae, and the algae use up the oxygen that fish need.
Rhino poaching: use the current numbers
Textbooks printed before about 2015 say rhino poaching is still rising. It has been falling for a decade.
| Year | Rhino poached in South Africa |
|---|---|
| 2009 | 122 |
| 2013 | 1 004 |
| 2014, the peak | 1 215 |
| 2024 | 420 |
| 2025 | 352, a 16% decline |
That is a better lesson than the old one, because it lets you ask what changed, rather than only how bad things are. Rhino horn is keratin, the same protein as fingernails, and it has no medicinal properties. Figures from the Department of Forestry, Fisheries and the Environment.
If it does not work
| What happens | What to do |
|---|---|
| The square has nothing in it | You chose bare paving. Move to a bed, a lawn edge or the damp ground near a tap |
| Learners cannot name anything | Naming is not the point. "Small black six-legged insect on the grass stem" is a perfectly good record. Description first, identification second |
| Arrows drawn the wrong way | Back to the one sentence. Energy travels towards the eater |
| Every web is a straight line | Ask what else eats the locust. A web with no branches is a chain |
| The pyramid is drawn upside down | They have drawn numbers of animals, not energy. One owl, thousands of locusts |
| A group has emptied the square into a jar | Stop it early. Look, count, replace. Turn one stone and put it back the way it was |
Safety
- Nothing goes in a mouth and nothing is taken home. Look, count, put it back
- Turn stones and logs towards yourself so anything underneath moves away from you, and replace them
- Hands washed before eating, always, after soil work
- Sun hats and water if the square is in the open
- Check the area for glass and sharp litter before the class kneels on it
Free worksheet and marking memo
Both free, no sign up, straight to the PDF.
- Learner worksheet, 45 marks. Part A feeding groups and arrows, Part B a food web to read and one to build, Part C the energy pyramid with the percentages calculated, Part D the fieldwork record sheet
- Marking memorandum, with the full answers and the five answers that look right and score nothing
Related practicals
- Photosynthesis and respiration, Grade 8. Where the energy at the bottom of the pyramid comes from
- Micro-organisms and the growth of yeast, Grade 8. The decomposers, up close
- Circulatory and respiratory systems, Grade 9. Where the energy goes inside one animal
What you need to run it
This is the cheapest good practical in Grade 8 and most schools already own the whole list.
The measuring side is a laboratory thermometer for the abiotic record and a metre stick or tape for the square. String and pegs come from a hardware shop for small change.
Hand lenses are what turn the square from a lawn into an ecosystem. A dual 3x and 5x magnifying glass is R35, and a folding 10x loupe is R75 and lives in a pocket. Buy one per group of four rather than one per class.
For soil work, any kitchen sieve does the job, and a glass dish holds what comes out of it.
If you want to take the square further, a stereo microscope shows soil animals at 20x to 40x with no slide preparation at all, which is the right instrument for whole insects and roots. A compound microscope is the wrong tool here; it is for thin sections and single cells.
For classroom reference, the natural science wall charts run to 121 titles at R85 each, and the ecology and food web charts are the ones that stay up all year.