Photosynthesis

• Chloroplasts are small flattened organelles in plant cells where photosynthesis occurs
• Chloroplasts absorb light to carry out photosynthesis, which produces the sugar used by plants for respiration to provide energy
• How large are chloroplasts?

  Around 2-10 micrometers
• Every chloroplast is surrounded by a double membrane envelope known as the phospholipid bilayer
• The outer membrane of chloroplasts is permeable to small molecules and ions, such as water and carbon dioxide, which diffuse easily, but it is not permeable to larger molecules, such as proteins
• What is the function of the chloroplasts inner membrane?

  Regulates the passage of large substances in and out of the chloroplast through membrane bound transport proteins
• The double membrane of chloroplasts provides evidence for the endosymbiotic theory, which states that chloroplasts were once their own self supporting organism
• What does the endosymbiotic theory state about chloroplasts?

  They were once their own self-supporting organism
• Which part of the chloroplast provides evidence for the endosymbiotic theory?

  The double membrane
• The inside of a chloroplast is filled with a gel like fluid called the stroma
• What can be found in the stroma of a chloroplast?

  Enzymes, starch granules, proteins, chloroplast DNA and ribosomes
• Which stage of photosynthesis occurs in the stroma of chloroplasts?

  The light independent stage
• The thylakoid space contains the pigments, enzymes and electron carriers required for the light independent to occur
• Thylakoids are disc shape fluid filled sacs found in the thylakoid space
• Thylakoids stack to form structures known as grana
• Grana are connected by membraneous channels called lamellae
• What is the function of lamellae?

  Ensures that the grana stacks are connected but distanced from each other
• What is the function of grana membranes?

  Create a large surface area to increase the number of light dependent reactions that can occur, and provide a large number of pigment molecules arranged in a way to maximise light absorbance
• The loop of DNA in the stroma codes for some of the chloroplast proteins, whilst the rest is coded for by the plants nucleus
• Proteins coded from chloroplast DNA are produced at the 70s ribosomes
• Sugars formed during photosynthesis are stores as starch inside starch grains