Structure

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Mesophyll

Palisade Mesophyll (栅栏状叶肉)

  • Tall, narrow, stacked upright, tightly packed - maximize surface area
  • Contain many chloroplasts - main function is photosynthesis
  • Close to the top of the leaf, so they get plenty of sunlight
  • Large Vacuole - squeeze other to the side

Spongy Mesophyll (海绵状叶肉)

  • Also contain chloroplasts
  • Not as tightly packed with air spaces between them - let CO2 diffuse

Cuticle , Upper Epidermis, Lower Epidermis

Epidermis - Outer skin 表皮

Upper Epidermis

  • Tightly packed to avoid water escaping
  • No chloroplast, relatively transparent - let light pass through to mesophyll payer
  • Secrete cuticle (分泌角质层)

Lower Epidermis

  • openings on the lower epidermis called stomata(pl. stomata, s. stoma)
  • stomata are surrounded by a pair of guard cells which can open and close.
  • Stomata allow diffusion of CO2 and O2 in and out; and water vapour out;

Cuticle

  • Not a cell
  • a waxy substance that is thin, transparent, waterproof
  • protection

Vascular bundle

  • includes xylem and phloem for transport

Features

Thin: Sunlight can pass through
Helps CO2 reach all cells quickly by diffusion
Big surface area: Large amount of sunlight fall onto leaf
Increase rate of diffusion of CO2

Practical

Test a leaf for presence of starch

  1. Boil leaf in water :to kill leaf cells
  2. boil again in ethanol: for chlorophyll to leave leaf, chlorophyll dissolves in alcohol
  3. Rinse leaf in water: to soften the leaf
  4. Spread leaf out, add iodine solution, if turns blue-black, starch is present

Test for the necessity of light, chlorophyl, and CO2

  • Light: cover leaf partly with black paper, then test starch. Parts covered yellow brown so no photosynthesis happened.
  • Chlorophyll: variegated leaf, only parts that are green show starch presence
  • CO2: use $KOH$ to remove $CO_{2}$ from atmosphere, if no $CO_{2}$, no starch present
  • De-Starching means putting a plant in the dark for a few days, so it uses up all starch storage. Do this before the experiment to make sure all starch tested are made during the experiment
  • Hydrogen-carbonate indicator: purple: no CO2, orange/red: atmospheric CO2, yellow: high CO2
  • Measuring rate of photosynthesis
    • Aquatic plant makes oxygen bubbles when photosynthesis
    • Count bubbles made
    • Improvement: collect gas made with a syringe OR an inverted measuring cylinder in water