Plant organisation Flashcards
What is the function (job) of the xylem in plants?
To transport water and minerals
What is the function (job) of the phloem in plants?
To transport sugars and amino acids dissolved in water
What are xylem and phloem tissues grouped into?
Vascular bundles
How are xylem and phloem organised in a root?
- Xylem forms a central column
- Phloem is towards the centre, outside the xylem
What is the main organ for photosynthesis in plants?
Leaves
Describe four ways that a leaf is adapted for photosynthesis.
- Large surface area (for maximum absorption of light and CO2)
- Very thin (so short diffusion distance)
- Large network of veins (for transporting water and sugars)
- Air spaces between cells within the leaf (for diffusion of gases)
Name the six layers of the leaf from top to bottom.
- Waxy cuticle
- Upper epidermis
- Palisade mesophyll
- Spongy mesophyll
- Lower epidermis
- Waxy cuticle
How is the palisade mesophyll adapted to absorb light efficiently?
- Packed with many chloroplasts
- Towards the upper surface of the leaf
How is the spongy mesophyll adapted for gas exchange?
Has loosely packed cells and air spaces between them
What are stomata?
Small holes in the surface of the leaf where gases diffuse into and out of
What is transpiration?
The loss of water from leaves by evaporation through open stomata
What is translocation?
The movement of dissolved material up and down the plant stem through the phloem
Which process, transpiration or translocation, requires energy?
Translocation
How does a sieve tube in the phloem obtain energy for translocation?
From companion cells
Describe in detail how water is pulled up through a plant by transpiration.
There is strong cohesion between water molecules because of hydrogen bonding.
A continuous column of water is therefore pulled up the stem in the transpiration stream by evaporation from the leaves.
As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots.
