A green plant builds its own food. It takes carbon dioxide from the air and water from the soil and, using energy from light trapped by chlorophyll, turns them into glucose. That glucose becomes starch, cellulose, sucrose and nectar, and mineral ions from the soil let the plant make proteins and chlorophyll itself.
Photosynthesis is the process by which plants synthesise carbohydrates from raw materials using energy from light. Carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. Chlorophyll is a green pigment found in chloroplasts; it transfers energy from light into energy in chemicals, for the synthesis of carbohydrates.
In the sim, carbon dioxide molecules drift in from the air and water molecules arrive from the xylem. Once six of each have collected in the chloroplast and the light is on, the chloroplast glows, one glucose molecule is made and six oxygen molecules leave. Untick Light and watch the raw materials pile up with nothing made.
Light and chlorophyll are written over the arrow, not as reactants. Chlorophyll is not used up and light is not a substance. Also, plants do not "make energy": chlorophyll transfers light energy into chemical energy.
Glucose is made in the leaves, but most of it does not stay as glucose. Pick each use in the sim and follow the particles: some go to the root store, some to the growing tip, some to every cell's mitochondria and some to the flower.
| Use | Turned into | Why |
|---|---|---|
| Energy store | starch | insoluble, so it does not affect osmosis; stored in leaves, roots, tubers and seeds |
| Cell walls | cellulose | long chains of glucose build the walls of new cells as the plant grows |
| Respiration | stays as glucose | respired in every living cell to release energy, day and night |
| Transport | sucrose | carried in the phloem to roots, growing tips, flowers and storage organs |
| Pollination | nectar | sugary nectar in flowers attracts insects, which carry pollen |
Glucose is not transported in the phloem: it is converted to sucrose first. And it is starch, not glucose, that is stored, because starch is insoluble.
Photosynthesis only makes carbohydrates, which contain carbon, hydrogen and oxygen. To make other molecules the plant needs mineral ions, absorbed from the soil by its roots. The sim shows three plants grown with all minerals, with no nitrate and with no magnesium.
Nitrate is for amino acids (proteins), not for chlorophyll directly; magnesium is for chlorophyll. Do not swap them, and do not say minerals give the plant energy.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the sim, what happens when the Light box is unticked?
For each glucose molecule made in the sim, how many oxygen molecules are released?
In the uses of glucose tab, which use sends sugar through the phloem to the potato-like store in the soil?
In the mineral ions tab, the plant grown without magnesium shows:
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Which statement describes photosynthesis?
What is the role of chlorophyll in photosynthesis?
Why do plants store carbohydrate as starch rather than as glucose?
A crop has stunted growth and its older leaves are yellow. Which ion is most likely lacking?
This skill is now recorded on your profile. Keep the chain going.