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  • Created by: cher
  • Created on: 29-05-13 17:32

Equations + General

Word - Carbon Dioxide + Water = Glucose + Oxygen

Symbol - CO2 +nH2O = C6H12O6 + O2

Balanced - 6CO2 + 6H2O = C6H12O6 = 6O2

Photosynthesis uses sunlight energy to transform it into chemical energy in the bonds of glucose.

CO2 + H2O produces glucose, O2 = waste product

Glucose - 

  • stored as starch
  • used in respiration for the  release of  energy 
  • turned into sucrose = transported in the phloem to the rest of the plant
  • turned into cellulose = cell walls
  • with nitrates, produces protein for growth

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  • Thin = shorter path for diffusion of carbon dioxide
  • Large surface area = maximise light absorption 
  • perpendicular to the sun
  • contain palisade cells = many chloroplast + chlorophyll for photosynthesis


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Cross section of a leaf


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Upper Epidermis -

  • upper layer of cell
  • NO chloroplast
  • secrets a waxy cuticle = barrier

Palisade Layer - 

  • chloroplast
  • long + thin ^ chloroplast = ^ photosynthsis
  • close to surface = absorbs more sunlight

Spongy Layer - 

  • main gas exchange surface, absorbs CO2 + releases O2 by diffusion

Vascular Bundles

  • xylem: transports water from root to the rest of the plant
  • phloem: transports sucrose + amino acids from leaves to the rest of the plant
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Lower Epidermis -

  • lower layer of cell contains guard cells   (with chloroplasts)
  • guard cells surround the  stomata, where gases diffuse in and out 

Palisade Cell -

  • long + thin to pack more in close to upper surface = ^ sunlight absorption
  •  contain chloroplasts = ^ photosynthesis

 Chloroplast -

  • where photosynthesis takes place
  •  contain chlorophyll green pigment: absorbs sunlight = provides chloroplast with energy  
  • chlorophyll contains magnesium(Mg)
  •  reflects green light
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  • each stomata is surrounded by a guard cell
  • in low light guard cells lose water = flaccid , causing stoma to close, this normally only happens in the dark when no CO2 is needed for photosynthesis
  • in light, the guard cells become turgid = stoma opens(
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Limiting Factors

A limiting factor is a factor that limits the rate of photosynthesis.

  • light intensity, CO2, temperature


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Effect of light on gas exchange by a leaf

  • Hydrogencarbonate indicator solution can be used to show the effect on the exchange of CO2 by a leaf.
  • If we place the same volume in a boiling tube the colour change would tell us how fast photosynethsis or respiration would be occuring; the colour change depens on the concentration of CO2 [CO2].

Condition: Indicator colour:

^CO2 (>0.04%) Yellow

CO2 of normal air (0.04%) Orange

decrease CO2 (<0.04%) Purple

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Rate of photosynthesis

  • How much CO2 enters or O2 leaves the leaf depends on the rate of photosynthsis - the more sunlight = more photosynthesis and the more CO2 will enter and the more O2 will be released
  • Net uptale of CO2 = rate of photosynthesis is greater than the rate of respiration
  • Net release of CO2 = rate of respiration is greater than the rate of photosynthesis
  • this will depend on the light intensity
  • low light intensity = respiration but low rate of photosynthesis
  • as light intensity increases- rate of photosynthesis increases
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Testing a leaf for starch(1)

        (            (

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Testing a leaf for starch(2)


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Exam questions

( factor is limiting the rate of diffusion at point X on the diagram? See next slide for the answer


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Exam question answer

Answer :Light intensity. This is because the factor on the x axis will remain the limiting factor as long as the lline continues to rise. At the point at which it starts to level off some other factor becomes the limiting factor such as temperature, or carbon dioxide availability.

Explain why the rate of photosynthesis increases as the temperature is increased from 20 to 30 degrees Centigrade.

Answer See next slide

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exam question answer 2

Answer: Photosynthesis is controlled by enzymes. As the substrate molecules move more quickly as temperature increases then the enzyme and substrate will collide more often and the rate will increase. The enzyme will be near its optimum temperature.

Name another factor that can limit the rate of photosynthesis at point Y on the graph.

See next slide for the answer

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Exam question answer 3

Answer:  Carbon dioxide concentration.

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Lorran payne

These are also very useful. Can you do some more like this x


Some useful revision cards on photosynthesis that could be used to test your knowledge of the key facts in this topic that is found in nearly all science specifications. I've added a sample examination question at the end which is a good way to test whether you have grasped the key concepts as well as testing yourself using the revision cards.

Shravya Ramaraju

really helpful

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