Plants and Photosynthesis

Tissues in a leaf and their uses

Lower Epidermis

The outermost tissue on the lower side of the leaf. It protects the leaf.

Upper Epidermis

The outermost tissue on the upper side of the leaf. It protects the leaf

Palisade mesophyll layer

Rows of elongated cells in the upper half of the leaf where photosynthesis (mainly) occurs

Stomata

Pores in the leaf between the guard cells which allow gas exchange and movement of water vapour to happen

Guard cell

Surrounds the stomata controlling the opening and closing of the stomata

Spongy mesophyll layer

Irregular shaped cells in the lower half of the leaf. They allow gases to pass through the leaf

Xylem

Found in the veins of a leaf and transport water (and minerals) up from roots to shoots

Phloem

Found in the veins of the leaf and transport sugar made by photosynthesis down from the leaves to the other parts of the plant

Roots function

Water (containing salts and minerals that plants need for healthy growth ) is absorbed through the roots and travels up the plant to the leaves. Roots are adapted for this by having root hair cells which increase surface area. They also branch out allowing them to absorb water from a large volume of soil

Stems function

Provides mechanical support for the plant

Transports water from roots to shoots through the xylem

Transports sugar from the leaves to the rest of the plant through the phloem

Leaves function

Turn light into sugar by photosynthesis and transport it to the rest of the plant

Gas exchange - absorb CO2 and release O2

Transpiration

The loss of water by evaporation through the stomata

Transpiration stream definition

The movement of water in a plant

Describe the transpiration stream in a plant

Water is absorbed by osmosis into the root hair cells. It enter the xylem and travels up the stem. It then diffuses out of the top of the leaf through the stomata

Translocation

The movement of sugar solution in a plant

How are Phloem adapted for translocation?

Long thin cells - Fewer cells to travel through

Cells are end to end - cell sap can move easily from cell to cell

Cells have pores in end walls - cell sap can move from cell to cell easily

No nucleus - more space for movement of cell sap

How is the Xylem adapted for transpiration?

Hollow tubes (dead cells) - water can move easily

Tubes are strengthened by lignin - holds the tubes open to let water flow

easily

Differences between xylem and phloem

Xylem cells are dead, Phloem cells are alive

Xylem goes up, Phloem goes both ways

Xylem has lignin, Phloem does not

Xylem carries water, Phloem carries sugar solution