Photosynthetic Organisms Also Known As… “All they do is make the world’s food and oxygen! Let’s Kill Em!”

Basic Photosynthesis Info  Photosynthesis is the process by which certain organisms can make energy rich compounds by using the energy in sunlight.  Photo – Light  Synthesis – To Make  Photosynthetic organisms include plants, protists, algae and cyanobacteria.  These organisms can carry out photosynthesis because they contain chlorophyll – a green pigment that is capable of harnessing the energy found in light.

Chlorophyll  Chlorophyll is made from a porphyrin ring “head” and a hydrocarbon “tail”.  There are two forms of chlorophyll – a & b. They differ in a small group added to the head of the chlorophyll molecule.  The porphyrin ring has magnesium at its centre and is surrounded by alternating double bonds.

The Overall Story  The general equation for photosynthesis is: 6CO 2 + 6H 2 0  C 6 H 12 O 6 + 6O 2  What do we get from this?  Water & carbon dioxide combine to make glucose and oxygen.  Low energy reactants are getting turned into high energy products. Energy must be getting infused from somewhere (sunlight) and somehow (chlorophyll).  Opposite of cellular respiration – look for parallels.

Leaves  Leaves are the photosynthetic organs of plants.  They have several layers and/or components that each carry out their own specific role.  Cuticle  Upper Epidermis  Palisade Mesophyll  Spongy Mesophyll  Vein  Stoma  Guard Cells  Lower Epidermis

Transpiration  The loss of water by the plant (through the stoma) is called transpiration.  Leaves will try to limit water loss but they will not stop it entirely. This seems weird because water can be scarce but a little water loss can be good. Why?  “Transpirational pull” – water exits the leaf and new water from the soil is brought in to replace it. This water will contain minerals like magnesium and it has a cooling effect that keeps the enzymes in the leafs from getting to hot and calling the whole thing off.

Guard Cell Action  The guard cells control the opening/closing of the stomata.  They do this by manipulating the concentration of potassium ions they hold.  As potassium ions move into the guard cells from the surrounding epidermal cells, water follows in via osmosis. This inflates the guard cells and opens the stoma.  As the potassium ions return to the epidermal cells, the water follows them and the guard cells are limp and move closer together to limit the size of the stomata.

When to Open or Close?  The stoma tend to be open during the day and closed during the night.  The guard cells will swell and open the stoma if the cells near them have a low CO 2 concentration.  If it is a very hot day, the guard cells will shrivel and close the stoma to minimize water loss due to evaporation. This does limit CO 2 intake but H 2 O is the more limited resource.

Chloroplasts  Chloroplasts are the photosynthetic organelles within the eukaryotic cells. They contain the chlorophyll necessary for photosynthesis.  The parts of a chloroplast include:  Outer and Inner Membrane  Thylakoids, Lumen & Grana  Stroma  Lamellae

That’s All For Now! Swamp Thing The World’s First Photosynthetic Super Hero!