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AQA A Level Biology - Photosynthesis and Respiration (2021-22) $13.29
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AQA A Level Biology - Photosynthesis and Respiration (2021-22)
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  • Course
  • Photosynthesis and Respiration
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  • AQA

An in-depth informative booklet, covering the 2 stages of Photosynthesis and the 4 stages of Respiration in detail. Also includes required practicals for this section, useful summary questions and the specification for both topics.

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Document information

  • September 21, 2022
  • 31
  • 2021/2022
  • Class notes
  • None
  • All classes

Subjects

  • biology
  • photosynthesis
  • respiration
  • light dependent stage
  • light independent stage
  • chloroplast
  • photosynthetic pigments
  • photosystems
  • photoionisation
  • photolysis of water
  • photophosphorylation
  • chemiosmosis

Written for

  • A/AS Level
  • AQA
  • A Level Biology
  • Photosynthesis and Respiration
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Year 2



Biology Department

Photosynthesis
& Respiration




Name:

Teacher:


1

, Photosynthesis
Photosynthesis is the process where energy from light is used to make glucose (and other complex organic
molecules) from water (H2O) and carbon dioxide (CO2 ) which are simple inorganic molecules.

Energy from sunlight

6CO2 + 6H2O C6 H12O6 + 6O2

chlorophyll


Autotrophs such as plants and algae are able to carry out photosynthesis and use simple inorganic
molecules to synthesise complex organic molecules such as glucose. Energy is obtained from light.
Heterotrophs such as animals, and fungi are organisms which obtain organic molecules by digesting and
absorbing complex organic molecules. The organic molecules are used for growth or respiration.


The above equation shows the substrates and products of photosynthesis, but in reality a whole series of
reactions take place involving many intermediate substances. The reactions can be divided into two stages;

• light-dependent stage (LDR) (in thylakoid)
• light-independent stage (LIR) ( in stroma)


Chloroplast
Photosynthesis takes place in the chloroplast of plant and algal cells.




2

, Structure Function

• Site of light dependent reactions
• Contain photosystems/photosynthetic pigments

• Stacks of thylakoid
• Stacked to maximise likelihood of light striking
photosynthetic pigments
• Site of light independent reactions
• Contain enzymes

• Store products of photosynthesis as starch

• Site of protein synthesis for the chloroplast

• Carries genes coding for proteins/enzymes found in the
chloroplast

• Enclose stroma and separate contents from cytoplasm
• Control passage of substances in and out of the
chloroplast




Photosynthetic pigments: chemicals that absorb light energy (photons), found in the thylakoid
membranes of chloroplasts, each pigment absorbs light of a particular range of wavelengths of light energy.
• There are several types of chlorophyll molecule: chlorophyll a, chlorophyll b, carotene and
xanthophyll. Each pigment is able to absorb a different range of wavelengths of light energy.
• Plants have several photosynthetic pigments so that they can absorb more wavelengths of light
for the LDR. The action spectrum is the rate of photosynthesis at each wavelength.




3

, Photosystems (light harvesting)
The photosynthetic pigment molecules are arranged in
clusters in the thylakoid membrane called
photosystems. There are two photosystems, PSII that
absorbs light best as 680nm and PS I which absorbs light
best at 700nm. Photosystems consist of two types of
photosynthetic pigments – primary pigments and
accessory pigments
• Accessory pigment molecules (such as
carotenoids) surround the primary pigments and
absorb light energy and pass the energy from one
to another and then onto the primary pigment.
• Primary pigments (usually chlorophyll a) are
reaction centres where electrons are excited to
higher energy levels during the light dependent
reaction.

Redox reactions
Redox reactions involve oxidation and reduction reactions, they occur during photosynthesis (and also
during respiration). OILRIG – Oxidation is loss of electrons (and may happen when a substance has lost
hydrogens or gained oxygen) and reduction is gain of electrons (and may happen when a substance has
gained hydrogens or lost oxygen).


Co-enzymes
These are molecules that aid the function of an enzyme. They usually work by transferring a chemical from
one molecule to another. An important co-enzyme used in photosynthesis is NADP. It transfers
hydrogens from one molecule to another.


Stages of Photosynthesis
There are two main stages of photosynthesis:
1. Light dependent reaction. (LDR) occurs in the thylakoids.
2. Light independent reaction (LIR) occurs in the stroma.


Overview of Photosynthesis




4

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