• Chloroplasts are the organelles in plant cells where?photosynthesis?occurs
• Each chloroplast is surrounded by a?double-membrane?known as the?chloroplast envelope
  • Each of the envelope membranes is a?phospholipid?bilayer
• Chloroplasts are filled with a?cytoplasm-like?fluid known as the?stroma
  • The stroma contains?enzymes?and?sugars, as well as?ribosomes?and?chloroplast DNA
  • If the chloroplast has been photosynthesising there may be?starch grains?or?lipid droplets?in the stroma
• A?separate system of membranes?is found in the stroma
  • This membrane system consists of a series of flattened fluid-filled sacs known as?thylakoids, each surrounded by a?thylakoid membrane
  • Thylakoids stack up to form structures known as?grana?(singular granum)
  • Grana are connected by membranous channels called?lamellae?(singular lamella), which ensure the stacks of sacs are connected but distanced from each other
• Several components that are essential for photosynthesis are?embedded in the thylakoid membranes
  • ATP synthase enzymes
  • Proteins called?photosystems?contain?photosynthetic pigments?such as chlorophyll a, chlorophyll b, and carotene

Chloroplasts are the site of photosynthesis

Chloroplast structure is related to function

• Chloroplast envelope
  • The double membrane?encloses the chloroplast, keeping all of the components needed for photosynthesis close to each other
  • The transport proteins present in the inner membrane?control?the flow of molecules between the stroma and cytoplasm
• Stroma
  • The gel-like fluid contains?enzymes?that catalyse the reactions of photosynthesis
• DNA
  • The chloroplast DNA contains?genes?that code for some of the proteins used in photosynthesis
• Ribosomes
  • Ribosomes enable the?translation?of proteins?coded by the chloroplast DNA
• Thylakoid membrane
  • There is a space between the two membranes of this double membrane known as the?thylakoid space, in which conditions can differ from the stroma e.g. a?proton gradient?can be established between the thylakoid space and the stroma
  • The space has a very small volume so a proton gradient can develop very?quickly
• Grana
  • The grana create a?large surface area,?maximising the number of photosystems and allowing?maximum?light absorption
  • Grana also provide?more membrane area?for proteins such as electron carriers and ATP synthase enzymes, which together enable the?production of ATP
• Photosystems
  • There are two types of photosystem;?photosystem I?and?photosystem II, containing?different combinations of photosynthetic pigments?such as chlorophyll a, chlorophyll b, and carotene
  • Each photosystem absorbs?light of a different wavelength, maximising light absorption e.g. photosystem I absorbs light at a wavelength of 700 nm while photosystem II absorbs light at a wavelength of 680 nm