Photosynthesis (Introduction)

These are the main things you should know before going into more detail regarding Photosynthesis. Other things you need to know after are:

Light Dependent Reaction

Light Independent Reaction

Rates Of Photosynthesis

  • Created by: Rachelezy
  • Created on: 01-02-20 10:58

Key Terms To Know Beforehand

Photosynthesis - Process in which energy from sunlight is used to make organic molecules from inorganic molecules

Photoautotrophs - Plants, algae and some fungi (organisms which photosynthesise) - animal that cannot photosynthesise obtain organic molecules by eating autotrophic organisms like plants

Carbon fixation - Process by which carbon dioxide is converted into sugars - helps to regulate the concentration of carbon dioxide in the atmosphere

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Structure Of Chloroplasts

Structure Of Chloroplasts:

Chloroplasts - organelles where photosynthesis takes place

  • Have a double membrane (envelope) (outer + inner membrane)
  • Contains grana (stacks of flattened membrane-bound sacs known as thylakoids) and stroma (fluid-filled matrix of the chloroplast and surrounds the grana)

Stack of thylakoids provides a large surface area. Thylakoids in 1 granum can connect to thylakoids in another granum by intergranal lamellae

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Function Of The Grana and Stroma


  • Light-dependent stage of photosynthesis occurs here
  • Located within the thylakoid membrane
  • Contain photosystems - funnel-shaped structures that contain photosynthetic pigments that make plants green.
  • Contain electron carriers and ATP synthase


  • Light-independent stage of photosynthesis occurs here
  • Contains specific enzymes needed to catalyse the reactions of the light-independent stage
  • Contains a loop of DNA - codes for proteins involved in photosynthesis
  • Contains small ribosomes -  where proteins for photosynthesis are assembled
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Structure Of Photosystems

Photosynthetic Pigments - Pigments that can absorb a specific wavelength of light and trap the energy associated with the light. 

  • Each one absorbs the light of a particular wavelength and reflects other wavelengths of light
  • Light energy is captured and funnelled down to the primary pigment reaction centre (at base of photosystem and consists of a type of chlorophyll
  • It is where primary energy conversion reactions of photosynthesis take place
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Types of Photosynthetic Pigments

General Structure Of Chlorophyll - Long hydrocarbon chain + porphyrin group (containing a magnesium atom)

Chlorophyll In Primary Pigment Reaction Centre:

  • Chlorophyll A - Most abundunt in all photosynthesising plants
  • Chlrophyll B
  • Carotenoids
  • Each pigment has a different absorption spectrum
  • Different wavelenths of light that the pigment can absorb
  • Having multiple pigments allows lots more light energy to be captured than having a singular pigment
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Photosystems (More detail)

Chlorophyll A comes in two forms: P680 and P700 (p meaning peak absorption). This results in two different photosystems:

Photosystem 1:

  • Contains Chlorophyll A (P700) - Has a peak absorption of 700nm (red)

Photosytem 2:

  • Contains Chlorophyll A (P680)- Has a peak absorption of 680nm (red_
  • Contains Chlorophyll B - Absorbs wavelengths of 400-500nm (blue/green) and 650nm (red)
  • Contains Carotenoids - Absorbs blue light of wavelengths 400-500nm (reflects yellow and orange light)
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