Transcript Plants and Light

Plants and Light and Water
transport
The Leaf
• Leaves are specialised structures for photosynthesis.
They have several adaptation that suit them to this
purpose:
– They have a large surface area to volume ratio. This allows
for:
• A greater area to capture light.
• More efficient diffusion of CO2
– They have holes, called stomata (stoma/stomate
singular) that allow CO2 to get into the leaf.
– Their shape is adapted to suit the local environment and
hence come in a variety of forms. Note: the follow notes are a
generalised description of leaf structure, details may vary
depending on species.
Leaf Structure
• Cuticle – A waxy water proof layer.
• Upper epidermis – creates the waxy cuticle
• Palisade layer – Contains cells packed with
chloroplasts. These cells specialised in
photosynthesis. Small air spaces between them allow
for diffusion of CO2
• Spongy Mesophyll – contains air spaces to allow
access to CO2. Also contain vascular tissue.
• Lower Epidermis – contains stomata, creates
cuticle.
• Guard cells – surround stomata and control the pore
size. When water is low the guard cells collapse and
the hole narrows to prevent water loss. When the
water level is high the cells become kidney shaped
and open up the pore.
Veins
• Xylem: tubes that brings water and
minerals from the roots into the leaf.
• Phloem: tubes that usually move sap, with
dissolved sucrose, produced by
photosynthesis in the leaf, out of the leaf
and to other parts of the plant.
Forces moving water through
plants.
•
•
•
•
Transpiration: loss of excess water from plant
leaves
Transpiration causes enough pressure to help
pull water (& required nutrients) up stem
from roots.
As part of the water cycle, trees transpire
water back into the atmosphere.
Transpiration provides much of the daily rain in
rainforest.
Forces moving water through plants
continued
• Capillary action: the combined effect of water’s
properties of adhesion (sticking to other things)
and cohesion (sticking to itself).
• The combination of these forces means that
water is drawn up very thin tube because it sticks
to the sides of the tubes and itself.
• As the water is lost through transpiration more
water is drawn up through the xylem tubes.
Diffusion
• Diffusion is movement of molecules from a
region of HIGH concentration to LOW
concentration.
Diffusion
Osmosis
• Osmosis is the diffusion of water
molecules through a semi-permeable
membrane.
• Water moves from a less concentrated
solution (hypotonic) to a more
concentrated solution (hypertonic).
• If the concentration is the same as inside a
cell it is isotonic.
• Where might you have heard the word
isotonic before?
Plant cells in different solutions