Structure of a Leaf

Question 1

STOMATA

Answer 1

Millions of tiny openings scattered through the lower epidermis that allow for gas exchange in the leaf.

Single stomata = stoma

Question 2

GUARD CELLS

Answer 2

Control the opening and closing of the stomata.

Question 3

SPONGY MESOPHYLL TISSUE

Answer 3

Once the CO2 has diffused through the stomata, it moves up and enters the spongy mesophyll tissue.

Made up of spherical cells.
Contains lots of air spaces to allow for quick diffusion of gases, through to the next layer.
Large surface area-to-volume ratio increases gas exchange.

Question 4

PALISADE MESOPHYLL TISSUE

Answer 4

Site of photosynthesis:
Palisade cells (which make up the palisade mesophyll tissue) are packed full of chloroplasts which contain chlorophyll that absorbs light for photosynthesis.

Question 5

UPPER EPIDERMIS

Answer 5

Single layer of cells: transparent to allow light to easily and abundantly pass through to the palisade mesophyll, for photosynthesis - also slightly works to prevent water-loss however not the main role.

Question 6

WAXY CUTICLE

Answer 6

A thin water-proof layer of lipids which prevents water-loss

Question 7

Vascular Bundles: PHLOEM CELLS

Answer 7

Phloem cells transport the sugar molecule glucose produced in photosynthesis from the leaf to the rest of the plant.

Question 8

Vascular Bundles: XYLEM CELLS

Answer 8

Xylem cells bring water to be used in photosynthesis, to the palisade mesophyll from the roots.

Question 9

Water Loss: Guard Cells

Answer 9

Guard cells are sensitive to light, so at night, when photosynthesis won’t occur, close.

When a plant has plenty of water that is can afford losing, the guard cells become turgid. The cell wall on the inner surface is very thick, so it cannot stretch as much as the outer surface. So, as the guard cells swell due to excess water they curve away from each other opening the stomata. Vice versa, if the plant doesn’t have enough water, or just enough for photosynthesis, the guard cells remain flacid and keep the stomata closed.

Question 10

Stomata are on the underside of the leaf…

Answer 10

This placement reduces water loss as the underside of the leaf is shaded and cool, so water loss through evaporation is prevented.

Question 11

MERISTEM TISSUE

Answer 11

Meristem cells are stem cells found at the growing tips of roots and shoots. They can differentiate into different cell tyoes so that the plant can grow.