The interdependence of living things
- A food web can show which organisms eat other organisms in a particular habbitat.
- Different species in a particular habitat often compete for the same space or food source.
- A change which affects one species in a food web also affects other species in the same food web.
- Ecosystems can often adjust to changes but large disruptions may change an ecosystem permanently.
Maintenance of life
- Organisms need water, food and light to survive.
- Organisms need to avoid harmful chemicals, predators ad extreme temperatures in order to survive.
- They are more likely to survive if they can sense what they need, or need to avoid, in their surroundings.
- Multi - cellular organisms have sensor cells and effector cells.
- Multi - cellular animals have nervous systems.
- Nervous systems are comprised of nerve cells (neuron) which link sensor cells to effector cells.
- In humans they are linked via the central nervous system ( spinal cord and brain)
- Hormones are chemicals which travel in the blood and bring about slower longer - lasting responses.
Theory of evolution by natural selection
- The first living things developed about 3.500 million years ago from molecules that could copy themselves.
- The molecules were produced in conditions on Earth at the time.
- Evolution occurs due to natural selection.
- If conditions on Earth had been different from what they were, natural selection could have produced very different results.
- There is variation between individuals of the same species.
- Individuals with certain characteristics have a better chance of surviving, and reproducing, if the environment changes or vital resources become scarce.
- There will be more individuals with these characteristics in the next generation and so on.
-Selective breeding involves making deliberate selections based on desirable charecteristics.
- New species have evolved over a very long period of time.
- A large change in the environment may cause an entire species to become extinct.
- For some scientific questions, there is not a definite answer yet.
- An observation that agrees with a theory increases confidence in it.
- An observation that disagrees with a theory indicates that either the observation or the theory is wrong.
- Explanations cannot simply be deduced from the available data - personal background, experience or interests may influence judgements.
- Nervous and hormonal communication systems are involved in maintaining a constant internal environment (homoeostasis).
- Genes can be changes by mutation.
- Mutation can cause cancer cells.
- Mutated genes in sex cells can be passed onto offspring and produce new charecteristics.
- A new species can be produced by the combined effects of mutations, environmental changes and natural selection.