Photosynthesis
Process that plants use to synthesise carbohydrates (glucose) from raw materials (carbon dioxide and water) using energy from light
Word equation for photosynthesis
Caebon dioxide + water -> oxygen + glucose
- In presence of light and chlorophyll
Chemical equation for photosynthesis
6CO2^ + 6H2^O -> C6^H12^O6^ + 6O2^
Chlorophyll
Green pigment found in chloroplasts -> transfers energy from light into energy in chemicals for synthesis of carbohydrates
Products of photosynthesis
Glucose: used in respiration to provide energy
. Converted to:
. Starch as energy store
. Cellulose to make cell walls
. Sucrose for transport in phloem
. Nectar to attract insects for pollination
Investigating the need of Chlorophyll
- Get a variegated leaf (green and white)
- Test dor starch
- Only green parts will turn blue/black because the contain chlorophyll and therefore can photosynthesis and produce starch -> white part goes yellow because iodine stains it
Investigating the need of light
- Get plant that has beein in darkness for 48 hours (destarching) -> it has used up its starch stores
- Test a leaf for starch
- No colour change in leaf as no more starch has been produced by plant -> shows light is needed for photosynthesis
Investigating the need of CO2
- Remove CO2 in air surrounding plant using soda lime -> absorbs it
- Test leaf for starch
- No colour change in leaf as no starch has been produced by leaf -> shows CO2 is needed for photsynthesis
3 limiting factors in photosynthesis
. Light intensity
. Temperature
. Carbon dioxide concentratiom
Limiting factors of photosynthesis: light intensity
. Rate increases as light intensity increases until certain light intensity -> beyond that it won’t make a difference (rate remains constant)
Limiting factors of photosynthesis: temperature
. Rate increases as temperature increases up a certain point -> beyond that enzymes involved become denatured (rate rapidly decreases)
Limiting factors of photosynthesis: carbon dioxide concentration
. Rate increases as CO2 concentration increases until certain concentration -> beyond that it won’t make a difference (rate remains constant)
Leaves
. Large surface area: for light absorption
. Thin shape: gasses can diffuse in and out easily
Funtion of palisade mesopyll layer
Many chloroplasts absorb light as located near on upper surface of leaf
Funtion of upper epidermis
Transparent -> allows light to pass through
Function of vascular bundle
Delivers water and nutrients to leaf and takes away glucose produced by photosynthesis + supports leaf structure
Function of waxy cuticle
Reduces water loss by evaporation
Function of stomata
Small pores which allow O2 and CO2 to diffuse into and out the leaf in lower eppidermis
Function of large intercellular spaces
Easy for gasses to move between cells + increases surface area for gas exchange
Function of guard cells
Close stomata if plant loosing water faster than replaced by roots -> prevents plant from wilting
Plant nutrients: mineral, nitrate and magnesium ions
. Mineral ions: needed for plant growth
. Nitrate ions: make amino acids
. Magnesium ions: makes chlorophyll
Investigation of gas exchange in plants
- Add the same volume of hydrogencarbonate indicator solution into three test tubes
- Put similar sized pondweed (aquatic plant) into tubes and seal with rubber bungs
- Completely wrap one tube with aluminium foil (no light gets in), one tube in gauze (little light gets through) and one leave it uncovered -> leave for an hour
Investigation of gas exchange in plants: results
. Tube with foil: turns yellow (increased CO2) -> no photosynthesis but respiratiom still takes place
. Tube with gauze: stays red -> little photosynthesis and some respiration means roughly equal amount of CO2 is taken up and produced
. Uncovered tube: turns purple (decreased CO2) -> some respiration and a lot of photosynthesis takes place
