Last reviewed: 7 November 2026
Updated November 2026. These Grade 9 interdependence of life notes cover biotic and abiotic factors in the environment, relationships between living things (predation, parasitism, symbiosis, competition and saprophytism), food chains and food webs, and the effects of human activities. In short: living things depend on each other and on non-living factors such as light and water; energy flows from the sun to plants and then along food chains, with decomposers recycling nutrients.
The questions are original practice for Kenyan junior school learners, not an official paper. For other Grade 9 science topics, see the Grade 9 Integrated Science revision guide and the Grade 9 notes hub.
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What the Grade 9 Curriculum Covers
“The Interdependence of Life” is a sub-strand under Living Things and the Environment in the Kenya Institute of Curriculum Development’s Grade 9 Integrated Science design. It covers biotic relationships, abiotic factors (temperature, light, water, wind, atmospheric pressure, pH and salinity), energy flow through food chains and food webs, and the effects of habitat change, hunting and poaching, and introduced species. The design is listed on the KICD Grade Nine curriculum designs page.
Biotic Relationships
| Relationship | What happens | Example |
|---|---|---|
| Predation | One animal (predator) kills and eats another (prey) | Lion and zebra; chameleon and grasshopper |
| Parasitism | A parasite lives on or in a host and harms it | Ticks on cattle; tapeworm in the intestine |
| Symbiosis (mutualism) | Both organisms benefit | Bees and flowers; oxpeckers removing ticks from buffalo |
| Competition | Organisms struggle for the same limited resource | Weeds and maize competing for water and light |
| Saprophytism | Organisms feed on dead and decaying matter | Mushrooms and bacteria decomposing fallen leaves |
Abiotic Factors
- Temperature: affects which organisms survive; Mt Kenya’s upper slopes support different plants from the warm lowlands.
- Light: needed for photosynthesis; few plants grow on a dark forest floor.
- Water: plants in dry areas, such as acacias, have adaptations to reduce water loss.
- Wind: disperses seeds and pollen, but can also increase water loss.
- Atmospheric pressure: lower at high altitude, affecting breathing.
- pH and salinity: soil acidity and salt levels decide which plants and aquatic animals can live in an area; flamingos thrive in salty, alkaline lakes like Lake Nakuru.
Food Chains
A food chain shows the transfer of energy from one organism to the next. Arrows point in the direction energy flows (from the eaten to the eater). The concepts here follow OpenStax Concepts of Biology’s section on energy flow through ecosystems.
Example from a school compound: grass → grasshopper → lizard → hawk.
- Producer: grass (makes its own food by photosynthesis).
- Primary consumer (herbivore): grasshopper.
- Secondary consumer: lizard.
- Tertiary consumer: hawk.
Only part of the energy at one level passes to the next; the rest is used for life processes or lost as heat. That is why food chains are usually short.
Food Webs
A food web joins many food chains, because most animals eat more than one kind of food. In a local example: maize and grass are eaten by grasshoppers and rats; grasshoppers are eaten by spiders, toads and lizards; rats and lizards are eaten by snakes and hawks. If rats disappeared, snakes would eat more lizards and hawks would lose a food source. Food webs show how a change to one population affects others.
Decomposers
Bacteria and fungi break down dead plants, animals and wastes. This releases nutrients back into the soil for plants to use again. Without decomposers, nutrients would stay locked in dead matter.
Effects of Human Activities
- Habitat change: clearing forests for farming or settlement removes food and shelter for many species.
- Hunting and poaching: removing animals such as elephants and rhinos upsets food webs and can push species towards extinction.
- Introduction of new species: introduced plants or animals can spread quickly and out-compete local species. The water hyacinth on Lake Victoria is a well-known example of an introduced plant that spread rapidly.
Original Practice Questions With Worked Answers
- Name the relationship between a tick and a cow. Parasitism.
- Give two abiotic factors. Any two of temperature, light, water, wind, atmospheric pressure, pH, salinity.
- In grass → antelope → lion, which is the primary consumer? The antelope.
- Why are food chains rarely longer than four or five levels? Energy is lost at each level, so too little is left for further levels.
- What is the role of decomposers? They break down dead matter and return nutrients to the soil.
Cover the answers and attempt each question first. For timed practice, use the Grade 9 revision papers or the Grade 9 CBC Challenge. These notes are free; full revision access is available with the KSh 20 Day Pass or the KSh 500 Monthly Pass.
Frequently Asked Questions
What is the difference between biotic and abiotic factors?
Biotic factors are living things and their interactions; abiotic factors are non-living conditions such as light, temperature and water.
Which way do the arrows point in a food chain?
From the organism that is eaten to the organism that eats it, showing the direction of energy flow.
What is the difference between a food chain and a food web?
A food chain is a single feeding sequence; a food web shows many interconnected food chains in an ecosystem.
Give an example of symbiosis.
Bees and flowering plants: bees get nectar and the plants get pollinated.