Structure of a leaf

Question 1

State all the main organelles of a LEAF

Answer 1

ー waxy cuticle
ー upper epidermis
ー palisade mesophyll cells
ー spongy mesophyll cells
ー lower epidermis
ー guard cells
ー stoma
ー vascular bundle (xylem + phloem)

Question 2

Functions of all the organelles in a LEAF

Answer 2

Waxy cuticle: a waterproof barrier that covers the top of the leaf and prevents the loss of water from the epidermal cells (helping to stop the plant from drying out too quickly) by evaporation.

Upper epidermis: allows as much light as possible to reach the photosynthesising cells within the leaf. Do not have chloroplasts.

Palisade mesophyll cells: where most photosynthesis takes place. Tightly packed together in the UPPERMOST half of the leaf so that lots of light can be received.

Spongy mesophyll cells: irregularly shaped with lots of air spaces in the lower part of the leaf which provide a large internal surface area:volume ratio, to allow efficient exchange of co2 and o2 between cells outside (in the air) and in the leaf.

Lower epidermis: contains guard cells which ‘guard’ the entry and exit to the leaf called the stomata/stoma. There are hundreds of stomata’s in a leaf. They allow for gas exchange.
- guard cells can open and close & change shape in order for gasses to diffuse in and out of the leaf.

Vascular bundles: contain two types of cells, xylem and phloems. These form the veins in the stem and leaf. The tick cells walls of the tissue n the bundles helps support the stem and leaf. They transport substances to and away from the leaf.

Overall:
- the leaf had a broad shape to increase SA and light
- the leaf is thin to allow rapid diffusion for gaseous exchange

Question 3

Role of the xylem

Answer 3

Transports water and dissolved minerals from the roots up the CHUTES and to the leaves in ONE direction.

• made up of dead cells which form a hollow lumen for the water to travel up through the plant.
• it is strengthened by a substance called lignin.

Question 4

Role of the phloem

Answer 4

Transports sugars, amino acids, glucose and sucrose away from the leaf to all other parts of the plants. Can flow in MULTIPLE directions.

Question 5

Active transport (root hair cells)

Answer 5

Active transport is the movement of molecules AGAINST a concentration gradient (lower to higher).
- requires energy ( from cellular respiration) and is an active process
- always takes place across a membrane
- requires special proteins

Root hair cells absorb the water and mineral ions