• 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

   

An electron micrograph showing the structures within a chloroplast