B8 - Photosynthesis Flashcards
What is photosynthesis
An endothermic chemical reaction that takes in light energy due to the chlorophyll in the chloroplasts
Equations for photosynthesis
carbon dioxide + water —> glucose + oxygen
6CO₂ + 6H₂O —> C6H12O6 + 6O₂
Light also goes above arrow and chlorophyll goes below
Factors that affect the rate of photosynthesis
- Conc. of CO2
- Light intensity
- Amount of chlorophyll
- Temperature
Describe the relationship between light intensity and photosynthesis rate
- As light intensity increases, so does the rate of photosynthesis if it was a limiting factor
- This is due to there being more light energy
- However, this levels off and stays constant indicating that it is no longer a limiting factor
Describe the relationship between CO2 conc. and photosynthesis rate
- As CO2 conc. increases, so does the rate of photosynthesis if it was a limiting factor
- However, this levels off and stays constant indicating that it is no longer a limiting factor
Describe the relationship between temperature and photosynthesis rate
- As temp. increases, so does the rate of photosynthesis if it was a limiting factor
- This is due to there being more collisions with enzymes
- However, if the temperature increases too much, the enzymes will denature and photosynthesis rate decreases
Describe the relationship between the amount of chlorophyll and photosynthesis rate
- As the amount of chlrophyll increases, the rate of photosynthesis also increases
- This is due to more light energy being absorbed
Leaf adaptations for light absorbtion for photosynthesis
- Large SA to absorb more light
- Palisade mesophyll cells have lots of chlorophyll in chloroplasts
- Upper epidermis is transparent to allow light through
Uses of glucose produced in photsynthesis
- Respiration to release energy
- Starch - energy store
- Lipids - energy store
- Cellulose - structure
- Amino acids - synthesise proteins for growth + repair
What is needed for plants to make proteins
- Glucose to make amino acids
- Nitrate ions absorbed from soil or from insects (carnivorous plants)
What ion is needed to make chlorophyll
Magneisum ions
How to test if a leaf has photosynthesised
- Boil the leaf to kill it
- Place in boiling alcohol to remove chlorophyll making it white
- Place the leaf in hot water to soften it
- Add drops of iodine
If starch is present, iodine will go blue/black and it means photosynthesis has occured
Relationship between light intenisty and distance from light source
Inverse square law
- As distance increases, light intensity decreases
- Light intensity is proportional to the inverse of the distance from the light squared
Method for photosynthesis practical
- Place LED 10cm away from boiling tube
- Fill boiling tube with water and sodium hydrogen carbonate (release carbon dioxide)
- Add pondweed with cut end at the top and leave to acclimatise
- After 5 mins, start a stopwatch and count the number of bubbles produced in one minute
- Repeat to find a mean
- Repeat at different distances e.g. 20cm, 30cm
Control variables for photsynthesis practical
- Temperature
- Type of light source
- Concentration of bicarbonate
- Piece of pondweed