2.6.5(cell diversity in plants)

What structures are present in the cross section of a leaf

• Waxy cuticle

• Upper epidermis

• Palisade mesophyll cell

• Xylem

• Phloem

• Lower epidermis

• Spongy mesophyll

• Guard cell

• stoma

What is the structure of a stoma surrounded by a pair of guard cells?

• It has chloroplasts

• Thickened inner wall

• Stoma

• Guard cell

How are pallisade cells adapted for photosynthesis?

• They are long and cylindrical, so they pack together closely and little space between them for air to circulate; CO2 in those spaces are able to diffuse into the cell

• They have a large vacuole so that chloroplasts are nearer the outside of the cell, which reduces the diffusion distance of CO2 and O2

• They contain many chloroplasts so a lot of photosynthesis can happen at once

• They contain cytoskeleton threats and motor proteins to move the chloroplasts - nearer to the upper surface of the leaf when sunlight intensity is low, but further down if sunlight intensity is high

Describe and explain how guard cells change so gaseous exchange and therefore, photosynthesis can take place

• Light energy is used to produce ATP, the ATP actively transports potassium ions into the guard cells from surrounding epidermal cells, causes their water potential to decrease

• This causes water to enter the guard cells from surrounding epidermal cells by osmosis

• This causes the guard cells to swell, however, the outside of the guard cells is more flexible as it has a thinner wall than the thick inner wall of the guard cells

• This causes the outer parts of the guard cells to move outwards and bulge, which causes the gap between them to enlarge

• This allows for the air to enter the leaf and into the spaces below the layer of palisade cells where gaseous exchange of CO2 and O2 - CO2 in and O2 out via diffusion

• As they use the CO2 for photosynthesis this maintains a steep concentration gradient allowing CO2 to continually diffuse into the palisade cells

• O2 from photosynthesis will diffuse out of the cells into the air spaces and move out of the leaf via the open stomata

How are root hair cells adapted for movement of water, ions?

• They have a large surface area for absorption of water and ions such as nitrates

• They have many mitochondria in order to produce sufficient ATP for energy to actively transport ions into the roots

  • This causes a decrease in water potential therefore water moves into the root hair cells via osmosis down a water potential gradient

• They have special carrier proteins in the plasma membrane in order to actively transport