CSEC Biology • Lesson 4 of 4Food Chains, Food Webs & Energy Flow · Myers Science Hub Student Centre
CourseCSEC Biology
Practice formatMCQ • Structured • Experimental
Your progress0% complete
Learning objectives
- Construct and interpret food chains containing at least four organisms.
- Identify producers, consumers, herbivores, carnivores, omnivores, predators and prey.
- Construct and interpret food webs and trophic levels.
- Explain the role of decomposers and the direction of energy flow.
Core notes
Feeding relationships
A food chain shows one pathway of energy transfer. Arrows point from the food to the feeder, showing the direction in which energy is transferred.
| Trophic role | Meaning | Example |
|---|---|---|
| Producer | makes organic food, usually by photosynthesis | grass, algae, seagrass |
| Primary consumer | feeds directly on a producer | grasshopper, sea urchin |
| Secondary/tertiary consumer | feeds on other consumers | frog, snapper, hawk |
| Decomposer | breaks down dead organic matter and waste | bacteria, fungi |
Food webs and Caribbean habitats
Food webs combine interconnected food chains. Removing or increasing one population can affect several others. Predator–prey relationships, competition and biological control should be interpreted in context.
Energy flow
Energy enters most ecosystems as sunlight, is stored as chemical energy by producers and moves through trophic levels. Energy flow is non-cyclic because energy is continually lost from organisms to the surroundings, especially as heat during respiration.
Video lesson
Paper 01-style MCQ
1. In the chain grass → grasshopper → lizard → hawk, the lizard is theKC • 1
2. What do the arrows in a food chain represent?KC • 1
3. If a predator population decreases sharply, the most immediate effect on its main prey is likely to beUK • 1
Paper 02-style structured questions
4. Explain the role of decomposers in an ecosystem.UK • 4
Decomposers such as bacteria and fungi feed on/break down dead organisms and waste (1); convert complex organic materials into simpler substances (1); release mineral nutrients/materials back into the environment (1); making them available again to producers and contributing to nutrient cycling (1).
5. A food web includes seagrass, parrotfish, small reef fish, grouper and barracuda. Explain why a food web gives a more realistic picture than a single food chain.UK • 3
Most organisms have more than one food source and/or predator (1); therefore energy can move through several interconnected pathways (1); a food web shows these multiple feeding relationships (1).
Experiment-type question
6. Students investigate whether the abundance of a small herbivore is related to the abundance of its plant food in a field. Design an ecological sampling investigation.XS/PD • 8
State aim/hypothesis (1); choose random/systematic quadrat sampling (1); record plant abundance and herbivore abundance in the same or paired sampling units (1); use many samples across the field (1); keep quadrat size/method consistent (1); calculate means/frequencies or plot the relationship (1); identify a limitation such as herbivore movement/time of day (1); conclude only from the observed association and avoid claiming causation without evidence (1).