Plants (organisation) Flashcards
What does the xylem tissue do?
transports water and mineral ions from the roots to the stems and leaves
Adaptations of xylem tissue?
- composed of hollow tubes strengthed by lignin adapted for the transport of water in the transpiration stream
- also has dead cells joined end to end with no end walls between them and a hole down the middle
What is transpiration caused by?
evaporation and diffusion of water from a plants surface
most transpiration happens at the leaves
What factors cause an increase in transpiration?
high light intensity
high temperature
high airflow
low humidity
How does air flow affect transpiration?
faster airflow will increase the rate, as it will blow away water vapour allowing more to evaporate as it maintains the concentration gradient.
How does humidity affect transpiration?
high humidity will cause the transpiration rate to decrease because the air contains more water vapour, so the concentration gradient for diffusion is lower.
what is translocation?
transportation of dissolved sugars through the phloem
how is the phloem adapted for its function?
- elongated linking cells with small pores in the end walls to allow cell sap to flow through
- transportation happens both ways
Stomata are small pores at the bottom of the leaf. How does this reduce water loss?
because the sun does not directly shine on the stomata so less water is evaporated
Why are the stomata closed at night?
because CO2 is not needed for photosynthesis, so closing stomata reduces water loss
What happens to the guard cells and stomata when water is plentiful?
guard cells take up water and become turgid.
this causes the stomata to open, so gases for photosynthesis are free to move in and out of the stomata along with water from transpiration
What happens to the stomata when water is scarce?
losing water causes the stomata to change shape and close as it becomes flaccid.
this stops the plant from losing water through transpiration
