3.3.3Unit 3 — Life on Earth
Using the Products of Photosynthesis
5 min read 4 parts Lesson 17 of 31
Section 1 of 4The Fate of Glucose
Respiration
- Some glucose is broken down in respiration, which releases energy for the plant to carry out its life processes.
Storage
- Glucose is joined into starch, an insoluble compound that can be stored without affecting water movement in cells.
Structure
- Glucose is converted into cellulose, which forms strong cell walls that support the plant.
Other molecules
- Glucose is also used to make amino acids and lipids.
Section 2 of 4Making Other Compounds
Making Other Compounds
Cellulose
- This carbohydrate builds cell walls, so glucose is needed whenever a plant grows new cells.
Amino acids
- Glucose supplies carbon and, with nitrates from the soil, is used to make amino acids that are built into proteins.
Lipids
- Glucose can be changed into lipids, which are used in cell membranes and as an energy store in seeds.
Starch
- Starch is stored in leaves, roots, stems and seeds so that it can be broken back down to glucose when required.
| Product | Made from | Use |
|---|---|---|
| Starch | Glucose | Storage |
| Cellulose | Glucose | Cell walls |
| Amino acids | Glucose and nitrates | Proteins |
| Lipids | Glucose | Membranes and energy store |
Section 3 of 4From Leaf to Whole Plant
1
Glucose is made in the chloroplasts of leaf cells during the day.
2
Part of the glucose is used straight away in respiration to release energy.
3
Surplus glucose is converted to starch and stored in the leaf.
4
At night the stored starch is broken down to glucose and moved to where it is needed.
5
Glucose is transported to growing regions and storage organs, where it is used or stored again.
Section 4 of 4Exam Checklist & Tips
3.3.3 – Key Points for the Exam
- Respiration The process that releases energy from glucose in all living cells.
- Cellulose A carbohydrate made from glucose that forms plant cell walls.
- Starch An insoluble carbohydrate in which plants store glucose.
- Amino acid A building block of proteins that plants make using glucose and nitrates.
- Lipid A fat or oil used in membranes and as an energy store.
Common Mistakes
- Saying plants only use glucose for storage;
- it is also used in respiration and to make cellulose, amino acids and lipids.
- Thinking plants do not respire; they respire all the time, day and night.
- Writing that plants store glucose directly, when it is converted to insoluble starch first.
- Mixing up cellulose and starchcellulose is structural in cell walls, starch is for storage.
Biology 0610 & 9700 Exam Model
Limiting Factors Master
Photosynthesis: Limiting Factors & Graph Plateau
6CO2 + 6H2O → C6H12O6 + 6O2 (Light & Chlorophyll required)
- Limiting Factor Definition: Something present in the environment in such short supply that it restricts life processes.
- Graph Plateau: When rate levels off as light intensity increases, light is no longer the limiting factor; CO2 concentration or temperature has become limiting.
- High Temperature Drop: Beyond optimum temp (~40°C), enzymes (e.g. RuBisCO) denature, permanently decreasing rate.