Photosynthesis

Humans owe their continued existence to photosynthesis. The energy we used DESPITE where it is from has been captured by photosynthesis from sunlight.

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Structure of the Leaf

THE LEAF IS THE MAIN PHOTOSYNTHETIC STRUCTURE!!!!!!! The chloroplasts are the cellular organelles within the leaf where photosynthesis takes place.

Leaves are adapted to bring in (H20, C02 AND LIGHT) and remove (oxygen and glucose) They need:

  • A large surface area that collects as much sunlight as possible
  • an arrangement of leaves that avoids shadowing
  • thin leaves as most light is absorbed in the first few millimetres, diffusion distance short
  • transparent cuticle and epidermis that light light through to photosynthetic mesophyll cells
  • long narrow upper mesophyll cells packed with chloroplasts that collect sunlightr
  • numerous stomata for gaseous exchange
  • Stomata that open and close in response to changes in light intensity
  • Many air spaces in the lower mesophyll to allow diffusion of C02 AND 02
  • network of xylem that brings water to the leaf cells and PHLOEM that carries away the sugars produced in photosynthesis
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Outline of photosynthesis

                                                          light

6C02             +              6H20         >>>>>            C6 H206             +             602

Three main stages:

1. Capturing of light energy - By chloroplast pigments such as chlorophyll
2. The Light-dependant reaction- in which light energy is converted into chemical energy. electron flow is created vy the effect of light on chlorophyll and this causes water to split (PHOTOLYSIS) into PROTONS, ELECTRONS AND OXYGEN. THE PRODUCTS ARE REDUCED NADP ATP AND 02

3. The light dependant reaction- which protons (hydrogen ions) are used to reduce C02  to produce sugars and other organic molecules.

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Structure and role of chloroplasts

PHOTOSYNTHESIS TAKES PLACE ON ORGANELLES CALLED CHLOROPLASTS, THESE CHLOROPLATS ARE SURROUNDED BY A DOUBLE MEMBRANE:

TWO DISTINCT REGIONS:

  • The grana thylakoids 
    - stacks of up to 100 disc like structures called thylakoids - THIS IS WHERE THE LIGHT DEPENDANT STAGE TAKES PLACE.
  • IN THEM ARE PHOTOSYNTHETIC PIGMENT CALLED CHLOROPHYLL
  • SOME THYLAKOIDS HAVE TUBULAR EXTENTIONS WHICH JOIN UP

THE STROMA:

  • FLUID FILLED MATRIX WHERE THE LIGHT INDEPENDANT REACTION TAKES PLACE
  • NBUMBER OF OTHER STRUCTURES IN THEM SUCH AS GRAIN
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