8.1.1 Key ideas in biology
What the key ideas are
- Biology is built on a small number of key ideas that appear again and again across the course.
- Learning these ideas helps you connect topics and answer synoptic questions that mix them together.
Once you understand the key ideas, an unfamiliar example is usually just a familiar principle in a new setting.
Molecules, cells and organisation
- Life processes depend on molecules whose structure is suited to their function, such as enzymes with a specific active site.
- The basic unit of every living organism is the cell.
- Cells can be specialised and grouped into tissues, organs and organ systems that carry out life processes efficiently.
A red blood cell's shape and lack of a nucleus fit its job of carrying oxygen, showing structure matched to function.
Interdependence and adaptation
Interdependence
The way each species in a community relies on other species for resources such as food, shelter, pollination and seed dispersal, so that removing one species affects the whole community.
- Organisms live in populations, communities and ecosystems, interacting with each other and their environment.
- Species are interdependent, relying on one another for food, shelter and other needs.
- Organisms show adaptations that suit them to the environment they live in.
Photosynthesis and respiration
Photosynthesis
The process in which green plants and algae use light energy to turn carbon dioxide and water into glucose and oxygen.
Cellular respiration
The reaction in every living cell that transfers energy by breaking down glucose, so the cell can carry out its life processes.
- Life on Earth depends on photosynthesis, in which plants and algae use light to turn carbon dioxide and water into glucose and oxygen.
- This traps energy from the Sun in organic compounds such as glucose.
- In cellular respiration, organisms break down these organic compounds to release energy for their life processes.
- This energy powers all the other chemical reactions a cell needs to stay alive.
- Do not think plants only photosynthesise and animals only respire.
- Plants respire all the time as well, using the glucose they make.
Cycling of chemicals
Decomposer
A microorganism, such as a bacterium or fungus, that breaks down dead organisms and waste, returning carbon dioxide to the air and mineral ions to the soil.
- The chemicals in ecosystems are cycled continually through the living and non-living world.
- Elements such as carbon, and the water itself, are used, released and then used again.
- Decomposers are essential, because they return nutrients to the soil and air.
Genome, variation and evolution
Genome
The entire genetic material, all the DNA, of an organism.
Natural selection
The process in which organisms with characteristics best suited to their environment are more likely to survive, reproduce and pass on their alleles.
- The characteristics of an organism are influenced by its genome and by its interaction with the environment.
- Variation within a species provides the raw material for evolution.
- Evolution happens by natural selection, in which organisms with useful variations are more likely to survive and pass on their alleles.
- Natural selection explains both the biodiversity of life and how all organisms are related to different degrees.
Using the key ideas in the exam
- Synoptic questions bring together content from more than one topic, often in an unfamiliar context.
- Work out which key idea a question is really testing, then apply what you already know.
- Do not treat each topic as separate, because the same key idea often carries the marks even when the organism or context is new.
- State three key ideas that run through the whole of biology.
- Why is life on Earth dependent on photosynthesis?
- What two things influence the characteristics of an organism?
- How does natural selection account for biodiversity?
- How should you approach a question about an unfamiliar organism?
