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19 Terms

1
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what is the word equation for photosynthesis

carbon dioxide + water (+ light energy) —> oxygen + glucose

2
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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

3
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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

4
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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

5
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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

6
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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)

7
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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

8
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Give the independent variable in this investigation

- Distance of lamp from pondweed

9
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Give the dependent variable in this investigation

Number of oxygen bubbles released per minute OR volume of oxygen collected

10
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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

11
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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

12
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Why is the leaf placed in boiling water?

To denature enzymes involved in cellular processes

13
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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

14
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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

15
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Explain why chloroplasts appear green

  • Chlorophyll absorbs red / blue light

- Reflects green light

16
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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

17
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What does the plant use glucose for?

-Making cellulose cell walls

- Making proteins and DNA

- Making starch for storage

- Making sucrose for transport

18
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Role of nitrates + deficiency

Nitrate = making amino acids + proteins, DNA, growth

deficiency = stunted growth

19
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role of magnesium + deficiency symptom

making chlorophyll

yellow leaves