AQA A Level Biology

Revision Notes

5.1.1 Chloroplast Structures & their Functions

Chloroplast Structures & their Functions

  • Chloroplasts are the organelles in plant cells where photosynthesis occurs
  • Each chloroplast is surrounded by a double-membrane envelope
    • Each of the envelope membranes is a phospholipid bilayer
  • Chloroplasts are filled with a fluid known as the stroma
    • The stroma is the site of the light-independent stage of photosynthesis
  • A separate system of membranes is found in the stroma
    • This membrane system is the site of the light-dependent stage of photosynthesis
    • The membrane contains the pigments, enzymes and electron carriers required for the light-dependent reactions
    • This membrane system consists of a series of flattened fluid-filled sacs known as thylakoids
    • These thylakoids stack up to form structures known as grana (singular – granum)
    • Grana are connected by membranous channels called stroma lamellae, which ensure the stacks of sacs are connected but distanced from each other
    • The membranes of the grana create a large surface area to increase the number of light-dependent reactions that can occur
    • This membrane system provides a large number of pigment molecules in an arrangement that ensures as much light as necessary is absorbed
  • The stroma also contains small (70S) ribosomes, a loop of DNA and starch grains:
    • The loop of DNA codes for some of the chloroplast proteins (other chloroplast proteins are coded for by the DNA in the plant cell nucleus)
    • The proteins coded for by this loop of chloroplast DNA are produced at the 70S ribosomes
    • Sugars formed during photosynthesis are stored as starch inside starch grains

Chloroplast structures, downloadable AS & A Level Biology revision notes

An electron micrograph showing the structures within a chloroplast

Exam Tip

Make sure you can identify the structures of a chloroplast on a diagram AND that you can explain the function of each of these structures.


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top