Photosynthesis

• Chloroplasts


  Oval-shaped plastids that mainly occur in the photosynthesising parts of the plant, i.e., in the leaves
• Chloroplasts


  • Surrounded by a double membrane, an inner and an outer membrane
  • Filled with a fluid matrix known as the Stroma
  • Contain disc-shaped membranes known as lamellae or thylakoids
  • Thylakoids form small stacks known as grana
  • Contain the green pigment chlorophyll
  • Contain enzymes that control photosynthesis, as well as starch grains, oil droplets and ribosomes
• Chloroplasts are the site of photosynthesis in plants
• Photosynthesis


  Carbon dioxide + water + radiant energy from the sun -> glucose + oxygen
• Light phase (Photolysis)


  • Occurs in the grana of the chloroplast
  • Light gets absorbed by chlorophyll
  • Causes water to be split into oxygen and hydrogen molecules
  • Energized hydrogen atoms bind to NADP to form NADPH
• Dark phase (Calvin Cycle)


  • Occurs in the stroma of the chloroplast
  • Uses the energy and hydrogen from the light phase to convert carbon dioxide into glucose
• Glucose is the product of photosynthesis and can be converted into starch, proteins, fats and oils
• Photosynthesis is important for maintaining the carbon-oxygen balance in the atmosphere and providing energy to heterotrophs
• Factors affecting photosynthesis


  • Light
  • Temperature
  • Chlorophyll
  • Carbon dioxide
• Chromoplasts


  Plastids that contain pigments called carotenoids and give yellow, orange and red colours to flowers, leaves and fruit
• Leucoplasts


  Colourless plastids that store food in an insoluble form such as starch, lipids or proteins
• Vacuoles


  Fluid-filled compartments in the cytoplasm of plant cells, enclosed by a selectively permeable membrane called the tonoplast
• Functions of vacuoles


  • Provide rigidity and structure to the plant cell
  • Store pigments, sugars and other substances
  • Promote osmosis by creating a low water potential inside the plant cell
• Contractile vacuoles


  Found in unicellular animals and play a role in osmoregulation
• Food vacuoles


  Found in simple animals and play a role in the digestion and storage of food
• Vesicles


  Small vacuoles that transport substances from the Golgi body to other parts inside and outside the cell
• Lysosomes


  Small vacuoles filled with digestive enzymes that play a role in food digestion in unicellular animals
• Centrosome


  An area in the cytoplasm near the nucleus of an animal cell that contains two centrioles
• Function of centrosome


  • In animal cells, the centrioles play a role in the formation of the spindle fibres during mitosis
• Differences between plant cells and animal cells

  • Plant cells have a cell wall, plastids, large vacuoles, no lysosomes, no centrosomes, and a fixed shape
  • Animal cells lack a cell wall, plastids, have small or no vacuoles, have lysosomes, have centrosomes, and have an irregular shape