9,20: Structure of a leaf

Question 1

State a function of the epidermis.

Answer 1

• protects the inner layers of cells from mechanical damage or microbial infection

note:
1. if the photo also includes the cuticle layer, state prevents excessive water loss too
2. epidermal cells do not have chloroplasts but the guard cells do

Question 2

State 2 differences between lower epidermis and upper epidermis + explain the differences

(NOTE: this question can be related to water loss)

Answer 2

the upper epidermis has a thicker cuticle than the lower epidermis
- reason: the upper part of the leaf is directly exposed to sunlight - thicker cuticle to prevent excessive water loss + prevent dehydration

the lower epidermis has more stomata than the upper epidermis (THE UPPER EPIDERMIS HAS STOMATA)
- reason: less exposed to sunlight - prevent evaporation of water and dehydration

Question 3

How does the cuticle prevent excessive water loss?

Answer 3

• waxy layer; water-repellent
• traps water within the leaf for survival
• prevents excessive water loss

Question 4

Differences between palisade mesophyll and spongy mesophyll + structural adaptions for photosynthesis/gas exchange

Answer 4

palisade mesophyll:
- closely packed cylindrical cells
- narrow air spaces among cells
- contains many chloroplasts
adaptive feature:
- allows more efficient absorption of sunlight for photosynthesis

spongy mesophyll:
- loosely paked irregularly-shaped cells
- many large air spaces among cells
- contains fewer chloroplasts (can still carry out photosynthesis)
adaptive feature:
- allows rapid diffusion of gases for gas exxchange