2.4 The Interdependence of Life

• Biotic (living) components of the environment: predation, parasitism, symbiosis, competition and saprophytism.
• Abiotic (non-living) components of the environment: temperature, light, water, wind, atmospheric pressure, pH and salinity.
• Energy flow in an ecosystem: food chains and food webs.
• The effect of human activities on the environment: habitat change, hunting and poaching, and the introduction of new living things.

• explain the biotic and abiotic factors of the environment
• construct food chains and food webs in the environment
• describe the effect of human activities on the environment
• appreciate the interdependence between living and non-living factors of the environment

“What is the role of living and non-living factors in environments?”

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1. Biotic and abiotic factors
   40 min · 1 practice tasks · quiz
   Every environment has a living half and a non-living half, and each acts on the other.
2. Predation
   40 min · 1 practice tasks · quiz
   One animal hunts and eats another, and their numbers rise and fall together.
3. Competition
   40 min · 1 practice tasks · quiz
   Two organisms needing the same limited thing, and both getting less of it.
4. Parasitism and symbiosis
   40 min · 1 practice tasks · quiz
   Two organisms living closely together, and the one question that separates them.
5. Saprophytes and decay
   40 min · 1 practice tasks · quiz
   The organisms that take the dead apart and hand the pieces back.
6. Surveying our own locality
   40 min · 1 practice tasks · quiz
   Going outside, recording what is there, and naming the relationships.
7. Relationships in Kenya's parks and reserves
   40 min · 1 practice tasks · quiz
   The same four relationships, on the scale of the Mara, Amboseli and Nakuru.
8. Temperature and light
   40 min · 1 practice tasks · quiz
   Two abiotic factors that decide what can live where.
9. Water and wind
   40 min · 1 practice tasks · quiz
   How much water there is, and how hard the air moves, both shape what grows.
10. Pressure, pH and salinity
    40 min · 1 practice tasks · quiz
    Three quieter conditions, each drawing a boundary round where life can be.
11. Producers, consumers and trophic levels
    40 min · 1 practice tasks · quiz
    Feeding steps, and why each one supports far fewer than the one below.
12. Food chains
    40 min · 1 practice tasks · quiz
    A line of organisms, and an arrow that always points one way.
13. Food webs
    40 min · 1 practice tasks · quiz
    Real ecosystems are not lines. Every chain crosses several others.
14. Energy flow
    40 min · 1 practice tasks · quiz
    Only about a tenth gets through each step, which is why chains are short.
15. Recycling nutrients
    40 min · 1 practice tasks · quiz
    Energy leaves for good; the minerals go round and round.
16. Human activity: habitat change
    40 min · 1 practice tasks · quiz
    Clearing land does not remove one species. It removes the place many depended on.
17. Hunting, poaching and introduced species
    40 min · 1 practice tasks · quiz
    Taking a species out, and putting one in. Both wreck the balance.
18. Interdependence: the whole picture
    40 min · 2 practice tasks · quiz
    Living and non-living, joined into one system that people can disturb.