Stages 3 · 4
Biology
Life is built from cells, runs on matter and energy, and changes by variation and selection.
Seeds
BIO-1
Cells are the units of life
BIO-2
Structure fits function
BIO-3
Matter cycles, energy flows
BIO-4
Inheritance is passed on in units
BIO-5
Evolution by variation and selection
Stages
3
Structure and Evidence
How is life organised?
- Zoom into a leaf, a hand, a pond Zoom in far enough on any living thing and you find cells. Try it
- Why are cells so small? When a cell doubles in width, its volume grows eight times but its surface only four, so big cells cannot feed themselves. Try it
- Where does a tree's mass come from? Most of a plant's dry mass is carbon taken from carbon dioxide in the air by photosynthesis, not from the soil. Try it
- Where does fat go when you lose weight? Most of the mass of burned fat leaves the body as carbon dioxide you breathe out; the rest leaves as water. Try it
- Mendel's peas: why the 3 : 1? Each parent passes on one of its two copies of a gene at random, so a hidden trait comes back in about a quarter of the grandchildren. Try it
- Why does a potato shrink in salt water? Particles never stop moving; water crosses a cell membrane both ways, and the net flow is towards the side where water is scarcer, the saltier side. Try it
- The heart is two pumps Blood goes through the heart twice per lap: the right side pumps it to the lungs, the left side pumps it to the body; it is always red, bright when full of oxygen and dark when not. Try it
- Breathing is not respiration Breathing only moves air in and out of the lungs; respiration, releasing energy from glucose (almost always with oxygen), happens inside every living cell, day and night, in plants too. Try it
4
Systems and Argument
How does life continue and change?
- Who leaves more offspring? No individual changes; the mix of a population shifts because some variants leave more offspring than others. Try it
- From DNA letters to a protein Almost every cell in your body holds the same DNA; cells differ by which genes they read, three letters (a codon) per amino acid. Try it
- Hares and lynx: why do the numbers cycle? Predators and prey can rise and fall in repeating cycles with the predator peak arriving after the prey peak, because predators multiply only after food is plentiful and starve only after it is gone. Try it
- The body's thermostat Body temperature and blood sugar stay near a set point because any change switches on a response that pushes it back: negative feedback. Try it
Ideas we expect to meet
- Plants get their food and mass from the soil.
- Children are a blend of their parents, like mixing paint.
- Animals change because they need to: giraffes stretched their necks.
- When you lose weight, the fat turns into energy or heat.