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what is the word equation for photosynthesis
carbon dioxide + water (+ light energy) —> oxygen + glucose
What is a limiting factor?
- Factor in a reaction which is in shortest supply
- Lack of this factor is the reason why the rate of reaction no longer increases
What are the limiting factors of photosynthesis?
--Carbon dioxide
- Light intensity
- Temperature
- Increasing any of the above will increase the rate of photosynthesis until another factor becomes limiting
Why is the rate of photosynthesis low in the morning?
- Temperature is the limiting factor
- Low temperatures inhibit enzyme activity
- Carbon dioxide levels are high
Why is the rate of photosynthesis high at midday
- High temperature maximises enzyme activity
- Carbon dioxide is the limiting factor as it’s in the shortest supply
How is the leaf adapted for its role?
Waxy cuticle - prevents evaporation of water and stops pathogen entry
- Upper epidermis - transparent to allow light to enter the leaf
- Palisade mesophyll - contains lots of chloroplasts for photosynthesis
- Air spaces in spongy mesophyll - allow gases to diffuse
- Xylem - allows entry of water and mineral ions by transpiration stream
- Guard cells - control opening and closure of stomata
- Stomata - allow carbon dioxide to enter, oxygen and water to leave
- Thin and broad (large surface area)
Design an investigation to measure the effect of light intensity on the rate of photosynthesis
-Use Elodea or Camboba pondweed
- Oxygen bubbles produced by photosynthesis released
- Count number of bubbles produced over one minute to record rate
- More bubbles produced per minute = faster rate of photosynthesis
- Move a lamp different distances away from beaker to measure effect of light intensity
- Improve accuracy by collecting oxygen released in test tube over longer period of time
Give the independent variable in this investigation
- Distance of lamp from pondweed
Give the dependent variable in this investigation
Number of oxygen bubbles released per minute OR volume of oxygen collected
List some control variables in this investigation
- Species of pondweed used
- Number of leaves on pondweed
- Temperature of water
- Wattage of lamp
- Concentration of CO2 in water
- Controlled by dissolving sodium hydrogencarbonate
Describe how to test leaves for starch to show photosynthesis has taken place
- Remove leaf from plant
- Boil beaker of water using Bunsen burner- Place leaf in boiling water for 20 seconds
- Remove leaf and place into boiling tube of ethanol
- Boil ethanol by placing boiling tube in beaker of very hot water
- Remove leaf when colourless
- Wash in cold water
- Place leaf on white tile and add dilute iodine solution with a pipette
- Any starch present will turn brown iodine solution blue/black
Why is the leaf placed in boiling water?
To denature enzymes involved in cellular processes
Why is the leaf placed in boiling ethanol before testing for presence of starch
- To remove green pigment (chlorophyll) in leaf
- Colour change can be seen when iodine added
- Removes waxy cuticle
What safety precautions should be taken when boiling in ethanol?
- Use a water bath (do not heat with naked flame)
- Ethanol is flammable
- Use forceps or tongs
- Protects skin
Explain why chloroplasts appear green
Chlorophyll absorbs red / blue light
- Reflects green light
Explain why different colours of light affect the rate of photosynthesis
- Green is reflected (not absorbed)
- Results in low rate of photosynthesis
- Blue & red is absorbed
- Results in faster rate of photosynthesis
What does the plant use glucose for?
-Making cellulose cell walls
- Making proteins and DNA
- Making starch for storage
- Making sucrose for transport
Role of nitrates + deficiency
Nitrate = making amino acids + proteins, DNA, growth
deficiency = stunted growth
role of magnesium + deficiency symptom
making chlorophyll
yellow leaves
