Chloroplasts and Chlorophyll

• Chloroplasts are the site of photosynthesis
• Each chloroplast is surrounded by an outer and inner membrane (the space between is called the inter membrane space) known as the chloroplast envelope
• Inside the envelope is a system of membranes arranged in layers called grana. A single granum is made of layers of membrane discs known as thylakoids. This is where the green pigment chlorophyll is found. The grana are joined together by lamellae, which are extensions of the thylakoid membranes, and act as a skeleton inside the chloroplast, maintaining a distance between the grana, so that they refuse maximum light for better efficiency
• The membrane layer is surrounded by a matrix called the stroma. The stroma contains all the enzymes needed for photosynthesis. The glucose produced can be used in cellular respiration, converted to starch for storage or used in the synthesis of amino acids and lipids
• Chlorophyll is a light-capturing, photosynthetic pigment. It is a mixture of pigments, including chlorophyll a (blue-green), chlorophyll b (yellow-green), the chlorophyll carotenoids (orange carotene and yellow xanthophyll) and also a grey pigment phaeophytin, which is a breakdown product of the others
• Chlorophyll a is found in all photosynthesising plants and in the highest quality of the five pigments
• The different proportions of the pigmentd (besides chlorophyll a) gives the leaves of plants their variety of different greens. Each pigment absorbs and captured light from particular areas of the light spectrum. As a result, much more of the energy from the light falling on the plant can be used than if only one pigment is involved.
• The absorption spectrum describes the different amounts of light of different wavelengths than a photosynthetic pigment absorbs. To find the absorption spectra of different photosynthetic pigments, you measure their absorption of light through different wavelengths
• An action spectrum can be achieved to show the rate of photosynthesis according to the wavelength of light.
• Having different photosynthetic pigments makes a much bigger portion of light available to plants and therefore gives them an adaptive advantage. Different photosynthetic pigments can provide a major adaptation to the habitat, for example aquatic plants are grown so they can absorb the blue light that penetrated the water easily
• 1. 70S ribosomes
  2. thylakoid membrane
  3. thylakoid
  4. grana
  5. starch grain
  6. circular DNA
  7. outer membrane
  8. intermembrane space
  9. inner membrane
  10. lipid droplet
  11. stroma

  
• Chromatography can show the different pigmentd present in a plant. The plant‘s leaves are grounded with propanone and then filtered. Using silica gel or paper as the medium, the pigments travel to the solid medium at different speeds and are separated using a solvent. The Rf value can then be calculated.
• The Rf value is the ratio of the distance travelled by the pigment to the distance travelled by the solvent. It is always between 0 and 1.

  Rf value = distance traveled by photosynthetic pigment/distance travelled by solvent
• In chloroplasts, there are two types of photosystems; Photosystem II (PSII) and Photosystem I (PSI). PSII contains chlorophyll a and b, carotenoids and phycobilins. PSI only has chlorophyll a and some accessory pigments such as chlorophyll b and carotenoids.
• The different photostems are different sized particles attached to the membranes in the chloroplasts. PSI particles are mainly on the lamellae, whereas PSII particles are on the grana.