Leaf structure

• Stomata are small openings on the surface of leaves, stems, and other parts of plants that allow gases to enter or exit the leaf.
• Guard cells control the opening and closing of stomata based on environmental conditions such as light intensity and humidity.
• Stomata is scattered through lower epidermis of leaf to allow CO2 to diffuse into leaf
• CO2 then moves up into the spongy mesophyll tissue which has a lot of air gas between cells allowing gas to diffuse into the next layer.
• Palisade mesophyll is the next layer where most photosynthesis happens and so palisade cells cells are packed with chloroplasts which contain chlorophyll, allowing light to be absorbed and photosynthesis to take place
• Above this is the upper epidermis which is somewhat transparent as sunlight needs to be able to pass through and get to the chloroplasts in the palisade mesophyll cells
• Once photosynthesis produces a sugar molecule, it is transported into the rest of the plant via the phloem
• What does the spongy mesophyll tissue have?

  Lots of air gas between the cells
• This is the leaf structure

  the purple part is the xylem which only carries water and mineral ions from the roots to the stem and leaves

  
• Leaves face water loss but xylem continuously supplies leaf with water from roots for palisade cells but it can also be lost from bottom or top of leaf
• To reduce water loss, the leaf has a waxy cuticle on top of its surface which is a thin waterproof layer of lipids
• At bottom of leaf, due to stomata, water has ability to easily diffuse out so leaf has a guard cell that maximises CO2 absorption but minimises water loss
• Guard cell = specialised plant cell that allows gas exchange
• guard cell is sensitive to light and will close during night when photosynthesis wont take place
• Stomata is on bottom of the leaf as it is more shaded there meaning more cooler meaning less evaporation to occur
• Why do guard cells stayed closed at night?

  They are sensitive to light