, minerals and
to stay alive.
Water absorbed by
which are extensions of
Water enters these cells through the process of
and passes from cell to cell (again through the same process) until it reaches a vessel called the
Xylem vessels carry
from the roots to the rest of the plant in an
direction. Xylem vessels take water and minerals to the leaves.
Xylem vessels consist of
hollow cells. They are thick, strong tubes, because they are strengthened by
Water moves from the Xylem into the
mesophyll cells and then the water on the surface of
(inside the leaf)
evaporates and then
out of the
in the leaf. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves.
The transpiration stream
The evaporation stream
Stomata are little
(usually) on the
The opening and closing of a stomata is controlled by the two
When the guard cells become turgid
When the guard cells loose water
When the guard cells gain water
When the guard cells become flaccid
When the guard cells become plasmolysed
Decrease wind speed
Decrease light intensity
Increase wind speed
Increase light intensity
You can measure the transpiration rate by using a Bubble potometer or a
as water moves up through the plant the air bubble moves along the scale giving a measure of water absorbed by the plant over time and hence the transpiration rate.
potometers work by putting a leafy shoot in water with a layer of oil over the surface to prevent loss of water by evaporation. The test tube and shoot are weighed at the start and then again after a few hours. Any difference in weight will indicate loss of water by the shoot (due to transpiration).
The sugars are moved from the leaves through tube-shaped vessels called
Unlike xylem, the cells that make this up are alive. The sugars are moved from the leaves through tube-shaped vessels called p _ _ _ _ _. Unlike xylem, the cells that make this up are alive. Phloem consists of two main types of cell.
cells are linked top and bottom with each other and do not contain a nucleus. It is through these cells that the sugar flows. Each cell is linked to the next by a perforated cell wall called a
Each sieve tube cell has an accompanying
cell. These do contain a nucleus and are thought to control the flow of sugars in the sieve tubes.
選擇要在Apple App Store上查看的Topgrade應用程序。