Leaf Structure In Relation to PHOTOSYNTHESIS!

LEAF STRUCTURE In Relation to PHOTSYNTHESIS!!!

The leaf has several layers of cells:

1.     The topmost layer is a waxy cuticle covering the upper epidermis.

2.     The palisade mesophyll layer lies below the upper epidermis.

3.     The spongy mesophyll layer lies below the palisade mesophyll layer.

4.     The vascular bundles, which consist of the xylem and phloem are dispersed throughout the leaf.

5.     The lower epidermis is the last layer in the leaf . Stomata are usually present on the lower epidermis. 

 

Why is the leaf so thin?                    ---large surface area to volume ratio making it ideal
                                                                for absorption and diffusion

                                                           --- Large surface area allows more sunlight
                                                                to be absorbed 

                                                           ---Thin leaf- mesophyll cells closer to surface,
                                                               thus reduce diffusion distance of carbon dioxide

                                                               from surroundings to palisade mesophyll cells.

                                                             

 Structure                     Function

                                                       

1.Waxy Cuticle                         --Covers the whole leaf to protect the underlying cells.

                                               --Transparent to allow light to enter leaf for 
                                                  Photosynthesis.

                                               -- Prevents leaf from excessive water loss because it 
                                                 is impermeable to water.

2.Upper Epidermis                    --Only one cell layer thick 

                                               --Has No Chloroplasts

                                               -- Allows  sunlight to reach mesophyll cells containing  
                                                  chloroplast so that these photosynthesizing cells can  
                                                  photosynthesize.

                                               --Are tightly linked to each other to provide plant with 
                                                  mechanical strength and protection.

                                               -- None/very few Stomata because if gaseous exchange 
                                                   takes place, the guard cells will open and water will be
                                                   lost and made worse by the heat from the sun so if
                                                   stomata is found here, there will be direct heat from 
                                                   sunlight and excessive water loss.
                                                --However, desert plants with high surrounding
                                                  surrounding temperatures have sunken stomata
                                                  while aquatic plants have stomata on the upper
                                                  epidermis cause their lower epidermis is
                                                  in contact with water.

3.Palisade Mesophyll cells          -- Lying below the waxy cuticle

                                               --Closely packed thus allowing more cells and
                                                 more chloroplasts nearer surface for more light to be   
                                                captured.

                                               -- Contains most chloroplasts as it is an actively 
                                                    photosynthesizing cell.
                                             --  Produce Glucose and directs it to Spongy Mesophyll for 
                                                  storage

                                             --Small intercellular spaces between each other for gaseous
                                                exchange to occur.

4.Spongy Mesophyll                    -- Less chloroplasts and bigger intercellular spaces
                                                  to facilitate gaseous exchange and less chloroplasts 
                                                  to maximize storage of starch.

                                                -- For Storage of Carbohydrates produced from 
                                                   Photosynthesis like starch
                                               --Dissolved carbohydrates eg. sucrose, diffuse into 
                                                 phloem to be transported to rest of the plant.

5.Vascular tissues                        --Consists of xylem and phloem vessels.

                                                 --Xylem is at top of Phloem.They are near cells that are 
                                                   actively photosynthesizing because water can be      
                                                   transported to palisade mesophyll for photosynthesis.
                                                 --Phloem nearer to the spongy mesophyll as they 
                                                   transport sugars from the mesophyll cells to rest of
                                                  plant.

                                                --Both xylem and Phloem are vascular tissues situated in
                                                   leaf vein where fibres like collenchyma support it to
                                                  make leaf flat to maximize Photosynthesis.


                                                       
6.Lower Epidermis                    -- Guard cells that form stomata are found here.

                                              --  Stomata allows gaseous exchange to occur.
                                              --Gaseous exchange is the intake of carbon dioxide and 
                                                  the release of oxygen for Photosynthesis while 
                                                  respiration requires oxygen & releases carbon dioxide.

                                               --Guard cells control water balance by controlling the
                                                 amount of water loss through diffusion of water vapour
                                                from plant.

                                                --Guard cells are specialized epidermal cells. 

6.Stomata                         ---Guard cells control the opening and closing of the stoma, the
                                            pore where gaseous exchange takes place.

                                       ---- When the plant is photosynthesizing, the stomata will 
                                             buckle to open because of the high concentration of 
                                            sugar inside compared to outside environment thus the 
                                            thinner wall of the guard cell expands causing cell to buckle 
                                            at thicker wall. The pore is open and this is due to the 
                                           differential thickness of wall.
                                       --- Water will be lost as long as stomata opens.

                                       ----The pore (stoma) and the guard cells make up the stomata.
                                    

Pics taken from google. Info taken from Grace's notes.