Question

model 2: cross - section of a leaf

1. label the following parts of the leaf on model 2:

• spongy mesophyll
• palisade mesophyll
• epidermis
• vascular bundle

1. most photosynthesis occurs in the cells of the palisade mesophyll and the spongy mesophyll. for photosynthesis to occur, these cells must receive the reactants needed for photosynthesis and be able to allow the products to exit.

(a) draw an arrow indicating the pathway you think co₂ follows to enter the leaf.

Explanation:

1. The epidermis is the out - layer of the leaf. The palisade mesophyll is the upper layer of mesophyll cells, usually more tightly packed. The spongy mesophyll is the lower layer with more air spaces. The vascular bundle contains xylem and phloem and is usually in the middle of the leaf structure.
2. Carbon - dioxide enters the leaf through stomata, which are usually located on the lower epidermis. So the arrow should start from the outside air, go through the stomata on the lower epidermis, and then into the spongy mesophyll and palisade mesophyll.

Answer:

1. On the leaf cross - section diagram:

• The epidermis is the outermost layer (both upper and lower).
• The palisade mesophyll is the upper layer of green cells just below the upper epidermis.
• The spongy mesophyll is the lower layer of green cells with more irregular shapes and air spaces.
• The vascular bundle is the cylindrical structure (usually in the middle of the leaf cross - section).

1. (a) Draw an arrow starting from the outside air, pointing towards a stoma on the lower epidermis, and then into the interior of the leaf towards the mesophyll cells.