Living things do not survive as isolated dots. A plant depends on light, water and suitable conditions. A herbivore may depend on that plant for food. A predator may depend on the herbivore. Two organisms may depend on the same limited resource and therefore affect one another even when neither eats the other.
This guide develops Living Together as a cumulative PSLE Science reasoning layer inside the current Primary Science syllabus. The official P6 owner is Interactions within the Environment; this page focuses specifically on the relationships pupils need to reason about when organisms share habitats, resources and food-web pathways.
Return to the Primary 6 Science Learning Hub.
The Living Together rule
WHO LIVES THERE → WHAT EACH ORGANISM NEEDS → WHAT THEY SHARE → WHO DEPENDS ON WHOM → WHAT CHANGES WHEN ONE PART CHANGES → WHAT THE EVIDENCE SUPPORTS.
This is an eduKate reasoning routine, not an official SEAB answer formula.
Part I — Start with organism, population and community
A useful P6 environmental model begins with three levels:
- Organism: one living thing.
- Population: organisms of the same kind living and reproducing in the same place and time.
- Community: many populations living together in the same place.
When a question says a pond, field, tree or mangrove supports a community, it means several populations are interacting within the same environment.
Part II — A habitat is more than a place name
“Pond” is not enough to explain survival. Ask what the habitat provides:
- water;
- light;
- temperature conditions;
- food;
- shelter;
- space;
- other organisms.
The same species may survive well in one habitat and poorly in another because these conditions differ.
Part III — Interdependence means one part affects another
Organisms can depend on other organisms for:
- food;
- shelter;
- pollination;
- seed dispersal;
- protection;
- habitat structure.
At PSLE level, the important job is not to memorise every ecological relationship. It is to identify the dependency shown in the question.
Part IV — Food is one form of interdependence
If Bird B feeds on Insect X, Bird B depends on X as a food source.
If X feeds on Plant P, then a change in P can affect X and may later affect B.
Possible chain:
fewer plants → less food for insects → fewer insects may survive or remain → less food available for the bird.
Each arrow represents a dependency that must be supported by the food web or question information.
Part V — Interdependence does not mean equal dependence
A predator may eat three prey species. One prey may form only a small part of its food supply.
If that prey decreases, the predator may still survive using alternatives.
Therefore:
dependency exists does not always mean one change causes immediate collapse.
Part VI — Competition begins when organisms share a limited resource
Competition can occur when organisms need the same resource and that resource is not unlimited.
Examples:
- two plants needing light;
- two plant populations drawing water from the same soil;
- two animal species eating the same prey;
- organisms using the same shelter or nesting space.
The shared resource must actually be relevant to the organisms in the question.
Part VII — Shared resource does not always mean strong competition
If food is extremely abundant, two species may use the same food without strongly affecting one another.
Competition becomes scientifically important when the resource is limited enough that one organism’s use reduces what remains available to another.
Part VIII — Competition within the same species
Members of the same population may compete for:
- food;
- water;
- space;
- mates;
- shelter.
Because their needs are often similar, competition within one population can be strong when resources become scarce.
Part IX — Competition between species
Different species may also compete when their needs overlap.
Example:
Bird A and Bird B both feed on Insect X.
If X decreases and neither bird has an alternative food source, both may face reduced food availability.
Part X — Food-web arrows are not competition arrows
A food-web arrow shows a feeding relationship. Competition is often inferred when two organisms share the same food source.
Do not draw or read an arrow between the competitors unless the diagram specifically defines one.
Part XI — Direct and indirect effects
A direct effect occurs at the first dependency.
An indirect effect occurs through another organism.
Example:
Plant P decreases → Insect X has less food = direct effect.
Plant P decreases → X decreases → Bird B has less food = indirect effect on B.
Part XII — Alternative pathways soften predictions
If Bird B eats X and Y, a fall in X does not guarantee a fall in B.
Before predicting:
- List all stated food sources.
- Check whether alternatives remain.
- Check whether those alternatives are also changing.
- Use “may” when several outcomes remain possible.
Part XIII — A community is a network, not a chain
Food chains are useful for showing one pathway. Communities contain many simultaneous pathways.
A more realistic question asks:
- Who eats whom?
- Who shares the same resource?
- Which populations affect habitat conditions?
- Which alternatives remain if one pathway weakens?
Part XIV — Plants compete too
Plants may compete for:
- light;
- water;
- space;
- mineral resources from soil.
If one plant grows taller and blocks light from another, the scientific relationship is not simply “the taller plant wins”. The important idea is that less light reaches the shorter plant, which can reduce the light available for photosynthesis.
Part XV — Space is a resource
Space can matter when organisms need:
- room to grow;
- a nesting site;
- a burrow;
- a territory;
- surface area exposed to light.
Do not treat “space” as empty background when the question makes it part of survival.
Part XVI — Water can be both habitat and resource
For an aquatic organism, water is part of the habitat.
For a land plant, soil water is also a resource needed for processes such as photosynthesis and transport.
The same word can therefore play different scientific roles.
Part XVII — Interdependence can involve habitat structure
A tree can provide:
- food;
- shade;
- nesting sites;
- shelter;
- surfaces for other organisms to live on.
Removing the tree may therefore affect several populations through different mechanisms, not just one food chain.
Part XVIII — Population change does not mean every individual behaves the same way
If a population decreases:
- some individuals may die;
- some may move away;
- fewer may reproduce successfully;
- new individuals may fail to enter the habitat.
Population reasoning is broader than “all organisms died”.
Part XIX — Time matters
Some relationships change immediately; others take time.
Example:
food source removed today does not always mean predator population falls today.
Population effects may appear later because organisms may use stored energy, alternative food or move elsewhere.
Part XX — Living Together and adaptation
Adaptations affect how organisms use shared environments.
A bird with a beak suited to one food type may compete differently from a bird using another food source.
A plant adapted to low light may survive beneath taller plants where another species cannot.
Adaptation therefore changes the pattern of interdependence and competition.
Part XXI — Living Together and human impact
Human activity can change community relationships by altering:
- habitat area;
- food availability;
- water quality;
- shelter;
- temperature;
- population sizes.
One human action can therefore create several indirect ecological effects.
Part XXII — Original workshop 1: two birds, one insect
Bird A and Bird B both feed on Insect X. X becomes scarce.
Question: Explain one possible effect.
Worked answer: Both bird species have less of the shared food source available. If neither has sufficient alternative food, competition for X may increase and one or both bird populations may later decrease.
Original workshop 2: two plants, one light source
Plant P grows taller and shades Plant Q.
Question: Explain how P may affect Q.
Worked answer: Plant P blocks some light from reaching Q. With less light available, Q may photosynthesise less under otherwise suitable conditions, which can reduce its growth over time.
Original workshop 3: predator alternatives
Fox F eats Rabbits R and Mice M. R decreases but M remains abundant.
Question: Why is an immediate fall in F not certain?
Worked answer: Fox F still has mice as an alternative food source, so the reduction in rabbits does not remove all available food.
Original workshop 4: nesting sites
Two bird populations use holes in old trees for nesting. Many old trees are removed.
Question: State one likely interaction change.
Worked answer: The number of suitable nesting sites decreases, so the two bird populations may face greater competition for the remaining sites.
Original workshop 5: community recovery
A pond is restored and aquatic plants increase.
Question: Give one possible community effect.
Worked answer: More aquatic plants may provide more food or shelter for organisms that depend on them, allowing some populations to increase if other conditions remain suitable.
Part XXIII — The SHARE test
- S — Species/populations: who lives together?
- H — Habitat: what conditions and resources are present?
- A — Access: which organisms use the same resource?
- R — Relationship: dependency, feeding or competition?
- E — Effect: what happens when one part changes?
This is an eduKate teaching mnemonic.
Part XXIV — The WEB test
- W — What changed?
- E — Edges: which direct relationships connect to it?
- B — Branches: what alternative pathways remain?
This is an eduKate teaching mnemonic for fast food-web reconstruction.
Part XXV — Common PSLE Living Together errors
- Assuming every shared resource creates strong competition.
- Ignoring alternative food sources.
- Reading food-web arrows as competition arrows.
- Predicting immediate population collapse.
- Ignoring time delay.
- Using “all” and “must” when several outcomes remain possible.
- Forgetting that plants also compete.
- Confusing habitat with only physical surroundings.
- Explaining one organism without tracing what it depends on.
Part XXVI — Revision matrix
| Relationship | Question to ask | Typical evidence |
|---|---|---|
| Feeding dependency | What does the organism eat? | Food chain/web |
| Competition | Which limited resource is shared? | Same food, water, light, shelter or space |
| Habitat dependency | What does the place provide? | Food, shelter, water, suitable conditions |
| Indirect effect | What changes through another population? | Two-or-more-link chain |
| Alternative pathway | What other resource remains? | Food-web branch or second habitat option |
Official boundary
The current MOE Primary Science syllabus places Interactions within the Environment in P6 Standard Science. This guide uses “Living Together” as a learner-facing integration lens for community, habitat, interdependence, competition and food-web reasoning; it does not claim “Living Together” is a separate official P6 topic heading.
MOE Primary Science Syllabus 2023
Where to connect
- Interactions Within the Environment: Food Chains, Food Webs & Survival
- Adaptation, Unfavourable Environments, Movement & Survival
- Man’s Impact on the Environment
- Recognising Interdependence in an Ecosystem
- Recognising Competition for Resources
Retrieval checklist
- I distinguish organism, population and community.
- I treat a habitat as a set of conditions and resources.
- I can identify a direct dependency.
- I can identify a shared limited resource.
- I distinguish food-web arrows from competition.
- I check alternative pathways before predicting.
- I can trace indirect effects through two or more populations.
- I include time when population effects may be delayed.
- I understand that plants can compete too.
- I can explain how one human or environmental change alters a community network.
The quiet return
Living together means every organism occupies a network of needs and relationships. The strongest environmental answer does not begin with “what happens next?” It begins with “what depends on what?”
Find the populations. Find the shared resources. Trace the dependencies. Check the branches. Predict only what the network supports.
Return to the Primary 6 Science Learning Hub.
