1. Biology 3A – plants and water

2. Plant transport systems

3. Forces acting on transport

4. Forces in the leaves Transpiration – water lost from leaves
Evapo-transpiration – water lost from leaves as water evaporates
Transpiration stream – water is pulled up the stem as water is lost from the leaves in transpiration

5. Forces in the stems
Adhesion – water molecules stick to the sides of the walls in the xylem
Cohesion – water molecules stick to each other
Capillarity/capillary action – water is drawn upwards through thin tubes

6. Forces in the roots
Active transport – salts are actively absorbed, increasing the osmotic pressure within the roots
Osmosis – water is pulled in due to the concentration gradients

7. Translocation

8. Movement of sugar
Translocation – movement of sugar – the sugar is actively transported from leaf to phloem (source) and from phloem to roots (sink), thus setting up a concentration gradient from leaf to roots
Diffusion – sugar will diffuse downwards because of this concentration gradient
Osmosis – water will be pulled out of the xylem near the leaves, and move downwards, then return to the xylem near the roots, due to the concentration gradient.

9. Plant transport systems
Roles of
Leaves – carry out photosynthesis and transpiration
Stomata – allow water and gases to enter and leave the leaf. Opening is controlled by guard cells
Xylem – transports water and salts upwards
Phloem – transports sugars, mostly downward
Roots – draw in water and salts
Root hairs – increase surface area

10. Leaves and stomata 1

11. Leaves and stomata 2
Leaves are responsible for photosynthesis and exchange of gases and water
Gases and water enter and leave through the stomata
Epidermis provides protection
Palisade cells carry out photosynthesis
The spongy mesophyll layer allows storage of air and water vapour
Vascular bundles contain xylem and phloem for the transport of water, salts and sugars

12. Control of stomal opening

13. Control of stomal opening 2
Stomatal opening is controlled by turgor pressure in the guard cells
This is controlled by pumping salts into the cells, thus bringing in more water (opening stoma) or pumping salts out of the cells, thus forcing water to leave (closing stoma)
Turgor pressure increases when water availability is high
Turgor pressure decreases when water availability is low

14. Structures in the stem

15. Xylem and phloem Xylem Phloem Dead Living Thick Lignin Impermeable
Cells living/dead
Dead
Living
Cell walls:
Thickness
Material
Permeability
Thick
Lignin
Impermeable
Thin
Cellulose
Permeable
Cross walls
None
Sieve plates
Cytoplasm
Yes
Function
Carries water & salts
Carries sugars
Direction of flow
Upwards
Down and up
Special features
Fibres
Companion cells

16. Roots and water transport
Image from Purves et al., Life: The Science of Biology, 4th Edition,
by Sinauer Associates and WH Freeman

17. Root hairs and water transport
Water moves in by osmosis
Osmotic pressure in root hair cell is higher than in soil
This can be maintained by active transport of salts into the root hairs
Root hairs increase the surface area available

18. Measuring water loss This can be done with a device called a potometer
The rate of transpiration is shown by movement of a bubble of air through the tubing
Key features include – air tight seal between plant and tubing, narrow tubing, intact stem (cut under water so it will draw up water), air bubble, scale

19. Water loss in plants Factors affecting water loss Temperature Humidity
Air movement
Water availability
Light intensity
Decreasing water loss also decreases photosynthesis

20. Arid regions
Usually hot and dry eg Australian & African deserts & savannah
Can be cold & dry eg icecaps & tundra

21. Plant adaptations - arid
Problems faced
Water availability low
Humidity low
Temperature high
Light high
Air movement high
Solutions include
Increased roots – either deep or wide and shallow
Water storage (roots, leaves or stems) eg cacti, boabs
Reduced leaves
Reduced stomata in leaves
Protection for leaves – cuticle, thick epidermis, curling, sunken pits, hairs to guard stomata
Closing stomata in hot conditions

22. Arid region adaptations
Water storage
Reduced leaves
Reduced leaves
Wide shallow root system
Water storage -
succulent leaves
Water storage - trunk
Reduced leaves – loses
leaves in summer
Long deep roots

23. Coastal environments
Hot, dry, saline, moving sand which can cover plants

24. Plant adaptations - coastal
Problems faced
Water availability low
Humidity low
Temperature high
Light high
Air movement high – lots of sand and salt
Solutions include
Wide shallow root systems
Rapid growth
Can cope with burial
Rolled leaves, sunken stomata, reduced stomata and/or hairs
Succulent leaves
Salt secretion in leaves

25. Rainforest
Low light, high humidity

26. Plant adaptations - wet
Problems faced
Water availability high
Humidity high
Temperature varies -high (tropical) to medium (temperate)
Light can vary – high in the canopy, low at ground level
Air movement usually low
Solutions include
Large leaves to trap light
Deep veins to carry water away from plant
Usually many stoma and thin epidermis
Large air spaces within leaves

27. Aquatic environments
Plenty of water, problems with water logging/lack of air
Marine and estuarine plants must cope with high salinity

28. Plant adaptations - aquatic
Problems faced
Water availability high
Humidity usually high
Temperature varies
Light usually high (may vary if plant deeper under water)
Air low
Solutions include
Stomata on surfaces of leaves (eg water lilies)
Large air spaces for buoyancy and gas storage
Aerial roots (eg mangroves)
Salt secretion in leaves (mangroves)

29. Cold and arctic environments
Cold, restricted water availability in winter (snow and ice), reduced light in winter

30. Plant adaptations - cold
Problems faced
Water availability seasonal - low at some times, higher at others
Humidity seasonal - low at some times, higher at others
Temperature seasonal - low at some times, higher at others
Light seasonal - low at some times, higher at others
Air movement seasonal - low at some times, higher at others
Solutions include
Deep root systems
Annuals - rapid growth, seeding and then die over winter
Bulbs – leaves die back during winter
Rolled leaves, reduced leaves (conifers)
Dropped leaves and dormancy (deciduous trees)
Antifreeze sap or resin in conifers – prevents cells bursting when frozen

31. Leaf adaptations 1

32. Leaf adaptations 2

33. Leaf adaptations 3 Look at the stomata in these leaves.
Which of these is most likely to be adapted to arid conditions?
This one- it has fewer stomata

34. Leaf adaptations 4
What adaptations can be seen in these that allow them to survive arid conditions?
Reduced stoma
Sunken pits
Thick cuticle and epidermis
Rolled leaf
Thick cuticle and epidermis
Rolled leaf
Sunken pits
Hairs to protect stoma

35. Leaf adaptations 5
What adaptations can be seen in these that allow them to survive in aquatic conditions?