- Photosynthesis is where green plants use light energy to convert raw materials into simple sugars. Light energy is converted to chemical bond energy in the simple sugars produced.
- The equation: carbon dioxide + water -> glucose + oxygen (6CO2 + 6H2O -> C6H12O6 + 6O2)
- Oxygen is produced as a by-product which is used in the plant's respiration, and it also diffuses into the atmosphere.
- Glucose produced is used for respiration, stored as starch, and used to make cellulose for cell walls. It is converted to sucrose for transport, used with nitrate to make amino acids, and converted to oils for energy storage in seeds.
- In order to carry out photosynthesis, green plants need: light (for energy), chlorophyll (in chloroplasts and absorbs energy), carbon dioxide (diffuses into the leaves), and water (absorbed from soil).
- Photosynthesis keeps the concentrations of gases in the atmosphere constant.
- Increased photosynthesis = higher yield of crops. Light intensity, carbon dioxide concentration, water supply and temperature affect the rate.
- Photosynthesis increases with light intensity up to a point because of the other factors restricting the rate. Chloroplasts can be damaged with light that is too strong.
- Temperature: maximum rate occurs at optimum temperature because of enzymes.
- Carbon dioxide: in glasshouses, more is added to increase yield as it is a limiting factor.
- In a glasshouse: glass stops heat from escaping, heaters are used, artificial lights/sunlight and blinds are available, natural gas can be burned, sprinklers and humidifiers are used. Sensors detect changes in the limiting factors.
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Leaves and mineral requirements
- Features: Large surface area absorbs light rays. Thin shape allows for gas diffusion. Chloroplasts absorb light. Veins support the leaf surface and carry substances in the plant.
- Structure: Cuticle is waterproof so cuts down water lost to evaporation. Upper epidermis is a layer of cells, no chloroplasts. Palisade mesophyll - photosynthesis occurs. Spongy mesophyll = lots of air spaces. Vein contains xylem and phloem. Lower epidermis has stomata allowing for diffusion.
- Stomata are holes in the epidermis - carbon dioxide diffuses in for photosynthesis, oxygen and water vapour diffuse out.
- Guard cells open and close stomata. In the day, osmosis allows them to bend so the stomata open. Water diffuses out through osmosis at night so the guard cells straighten - the stomata close.
- Plant nutrients/mineral salts are absorbed from the soil through active transport.
- Nitrate is needed for amino acids which make proteins. Deficiency = poor growth.
- Magnesium ions are used to make chlorophyll. Deficiency = chlorosis (leaves look yellow).
- Phosphate is for making compounds like DNA. Deficiency = poor root growth, younger leaves turn purple.
- Fertilisers replace missing nutrients in soil. NPK fertilisers contain nitrogen, phosphorus and potassium.
- Chemical/artificial fertilisers are used in large quantities, and the farmer can choose the nutrient ratio, but it causes water pollution.
- Natural fertilisers add humus to the soil which improves its structure, but the mass of the nutrients is unknown.
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