PHOTOSYNTHESIS

PHOTOSYNTHESIS F Photosynthesis is ability of a plant to turn sunlight, air, and water into sugar (energy). F The overall reaction is: light chlorophyll CO 2 + H 2 O > CH 2 O + O 2 F Photosynthesis is vital to life for two reasons

–1. The oxygen in the air comes from photosynthesis. The plants continue to replenish the oxygen in the air. –2. All of our food comes directly or indirectly from photosynthesis.

Parts of a leaf Stomata epidermis palisade layer spongy layer veins chloroplast thylakoids grana stroma

EPIDERMIS F Outer layer of cell F Functions- F protection against water loss by way of transpiration,transpiration F regulation of gas exchange F coated on the outer side with a waxy cuticle that prevents water losscuticle F The epidermis is covered with pores called stomata,stomata

F consist of a pore surrounded on each side by chloroplast- containing guard cells, and two to four subsidiary cells that lack chloroplasts. F Opening and closing of the stoma complex regulates the exchange of gases and water vapor between the outside air and the interior of the leaf and plays an important role in allowing photosynthesis without letting the leaf dry out. F In a typical leaf, the stomata are more numerous over the abaxial (lower) epidermis than the adaxial (upper) epidermis and more numerous in plants from cooler climates.

chloroplasts

F The chloroplast is the organelle where photosynthesis occurs F surrounded by a double membrane. F Inside is called stroma F Embedded in the stroma is a complex network of stacked sacs. F Each stack is called a granum and each of the flattened sacs which make up the granum is called a thylakoid.

mesophyll F Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll.parenchyma chlorenchyma F This assimilation tissue is the primary location of photosynthesis in the plant.assimilation F 2 parts- (a) An upper palisade layer of tightly packed, vertically elongated cells, one to two cells thickpalisade layer long cylindrical cells, with the chloroplasts, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. This separation must be minimal to afford capillary action for water distributionchloroplastsabsorptioncapillary action

. (b) Beneath the palisade layer is the spongy layer- cells are more rounded not so tightly packed, large intercellular air spaces fewer chloroplasts than those of the palisade layer.

. F Light is captured by pigments. The main photosynthetic pigment is chlorophyll. There is chlorophyll a, b and c. Chlorophyll a is the major photosynthetic pigment and is found in all photosynthetic plants, protist, and cyanobacteria