The role of bacteria and fungi, plus parasitism, mutualism and commensalism with Caribbean examples.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
Leaf-cutter ants farm fungus. Ticks feed on cattle. Which one is a partnership?
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
Bacteria and fungi; saprophytic nutrition; secrete enzymes onto dead matter; release CO₂ and mineral ions for recycling.
Recycle nutrients (C, N); remove dead material/waste; make humus that improves soil.
Legumes & Rhizobium; leaf-cutter ants & fungus; coral & zooxanthellae; cattle & gut bacteria that digest cellulose.
Bromeliads/orchids on trees; remora on sharks.
Ticks, lice, tapeworm, dodder, Plasmodium. Ecto- (outside) vs endo- (inside).
Brief feeding visits and predator–prey relationships.
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Try it in your notebook first, then reveal the solution one step at a time.
Try it in your notebook first, then reveal the solution one step at a time.
| Relationship | Organism A | Organism B | Example |
|---|---|---|---|
| Mutualism | + | + | Rhizobium in legume root nodules; lichens |
| Commensalism | + | 0 | Remora on a shark; orchids growing on trees |
| Parasitism | + (parasite) | − (host) | Tick on a cow; tapeworm in a human |
Symbiosis means two species living closely together. Use + (benefits), − (harmed) and 0 (unaffected).
Mutualism = Mutual benefit (+/+). Commensalism = Company at no cost (+/0). Parasitism = Pain for the host (+/−).
Caribbean farmers often grow pigeon peas between other crops. The Rhizobium bacteria in their root nodules fix nitrogen, which enriches the soil for the next crop — a natural fertiliser.
Put a slice of damp bread in a sealed clear bag and watch it for a week (do not open the bag — mould spores can trigger allergies). Record the colour and spread of the mould each day.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Write full answers, then reveal the mark scheme and tick the points you earned (14 marks in total). Your answers are saved on this device.
Question 1 [9 marks]
Students uprooted black-eyed pea plants and found small swellings (nodules) on the roots. Elsewhere, ants cut hibiscus leaves, chew them and grow a fungus on them to feed their larvae. Small birds also feed on the hibiscus.
(a) Explain the significance of the root nodules to the pea plant. [3]
(b) Explain the nature of the relationship between the fungus and the ants. [3]
(c) Explain why the birds feeding on the hibiscus is NOT a symbiotic relationship. [3]
Question 2 [5 marks]
Decomposers are found in every food web.
(a) Name ONE decomposer and explain its role in the ecosystem. [3]
(b) Suggest TWO reasons why decomposers are important to all food webs. [2]
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.