1. Xylem and Phloem

2. Things we know:
Plants need water, minerals, sugars, but they also need to get rid of waste
Multicellular = small SA:V
Diffusion is too slow
TF they need a transport system!

3. The vascular bundle
Vascular tissue is distributed throughout the plant
Vascular tissue is made up of xylem and phloem tissue
As well as the transport of substances the vascular bundle has structural support purposes

4. Transpiration System
The movement of water molecules and dissolved minerals ions
Xylem vessels
Passive process
Translocation System
The movement of sugars (Sucrose) & amino acids
Phloem vessel – sieve & companion cells
Active process

7. Xylem
The X on the root diagram, always on the inside - strongest
Transports water and mineral ions
Phloem
On the outside
Transports dissolved substances e.g. sugar
Hint: ‘f’ sound – phloem = food

8. Where? All parts of the plant!
In the root they are at the centre to provide support as it pushes through the soil
In other parts of the plant (e.g. stem) they are found around the edges – scaffolding
In the leaf we see them as veins – still supporting!

9. Xylem Continuous tubes made of cells called vessel elements.
No end walls on cells – water and mineral ions can flow (1D!)
from the root
DEAD cells = no cytoplasm
Lignin spirals INSIDE the walls – stops tube collapsing inwards
Older cells have more lignin
Water and ions move in through pits where there is no lignin (like pores)
PASSIVE TRANSPORT

10. Root pressure – passive transport
Water in xylem flows from root to tip
Osmotic pressure causes water to rise up the plant at night
Mineral ions build up in the roots, leading to a decrease in water potential
This leads to water entering the
root from the soil by osmosis
The pressure of this water pushing
on the rigid xylem cells causes the
water to rise up the stem
Fun fact: root pressure can raise
water up to 7m!

13. Phloem Also in tubes Not used for support – no lignin
Solutes flow in both directions
Two important parts for solute transport: sieve tube elements and companion cells
ACTIVE TRANSPORT

14. Phloem tissues used for transport
Sieve tube elements
Living cells that make up the tubes
Have holes on the end walls for solutes to pass through
No nucleus, very little cytoplasm, and few organelles – cannot live on their own!
So they have…
Companion cells
One for every sieve tube element
Carry out the functions for both cells to provide energy for active transport of solutes

16. Pressure Flow (Hypothesis) – active transport
Sugars travel from areas of high water potential, called sources (leaves), to regions of low water potential, called sinks (growing tissues).
Sugar -> sieve tube elements - active transport
Water -> sieve elements - osmosis
Water creates turgor pressure in the sieve elements, which forces the sugars and fluids down the phloem tubes toward the sinks
At the sinks, the sugars are actively removed from the phloem and water follows osmotically
High water potential and low turgor pressure are restored, pressure flow can continue!

18. Exam Question
(b) hint: think about the structure of the xylem cells

19. Mark Scheme