Mr White Biology

National 5 Biology 2.5 Transport Systems in Plants

Plant organs are roots, stems and leaves.

Structure	Function
Upper epidermis	Transparent thin layer of cell with no chloroplasts that allow light to pass through.
Palisade mesophyll cells	Cells that contain lots of chloroplasts and are closely packed together. Most photosynthesis takes place in these cells.
Spongy mesophyll cells	Round cells that contain some chloroplasts but have air spaces between cells to allow carbon dioxide to circulate and reach palisade cells.
Stomata	Tiny pores that allow carbon dioxide and water vapour to diffuse in and out of leaf.
Vein	Contains xylem and phloem which supplying all parts of the plant with water and dissolved food that is produced.
Guard cells	Cells with chloroplasts on lower epidermis that control the opening and closing of the stomata.

Xylem

Water and minerals enter the plant through the root hairs and are transported in dead xylem vessels.
Xylem cells are lignified to withstand the pressure changes as water moves through the plant.

Transpiration is the process of water moving through a plant and its evaporation through the stomata.

Water is absorbed by root hairs due to osmosis.
It travels up the xylem to the leaf.
Enters spongy mesophyll and diffuses into the air spaces.
Exits via the stomata by evaporation.

The rate of transpiration is affected by

wind speed
humidity
temperature
surface area

Factor	Effect on transpiration rate when increased
Wind speed	Increase
Humidity	Decrease
Temperature	Increase
Surface area	Increase

Phloem

Sugar is transported up and down the plant in living phloem.
Phloem cells have sieve plates and associated companion cells.

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