Transport in plants Flashcards
Why do plants need transport systems?
To move substances to and from cells fast
What does phloem transport?
Sugars
What does xylem transport?
Water and mineral ions
What system do xylem and phloem make up in a plant?
Vascular system
What does the Xylem look like/ where is it on the cross section of a root?
A cross in the middle of the root
What do the phloem look like/ where are they on the cross section of a root?
4 Triangle shapes in between the cross shape of the xylem
Where is the xylem located on a leaf cross section?
The top
Where is the phloem located on a leaf cross section?
The bottom
Where is the xylem located on a stem cross section?
The middle
Where is the phloem located on a stem cross section?
The outside
Describe the key feature of xylem.
• Long tube-like elements
• The cells are dead (so no cytoplasm)
• Walls thickened with lignin
• Water moves into and out of the xylem the link small pits in the walls where there’s no lignin
Describe the key features of phloem.
• Transports sugars
• Arranged in tubes
• Contains sieve tube elements and companion cells
What are the key features of sieve tube elements (in phloem)
• Living cells
• Have holes in to allow solutes to pass through
• No nucleus and very few organelles
• Thin cytoplasm
What are companion cells? What do they do?
Because sieve tubes elements don’t have a nucleus, the companion cells carry out the living functions for both themselves and the sieve tubes (eg: provide energy for active transport of sugars)
Where does water enter the plant and how?
Through the root hair cells into the roots via osmosis
How/ why does the water travel down a water potential gradient in a plant?
Because water is constantly evaporated from the leaves and absorbed via the roots, this creates a gradient that keeps water moving though from the roots (high water potential) to the leaves (low water potential)
What is the symplast pathway?
Water travels through the living parts of the cells (the cytoplasm)
What are plasmodesmata?
Small microscopic channels that connect cell cytoplasms in plants
What is the apoplast pathway?
Water goes through non-living parts of the cells (cell walls).
What is the Casparian strip and what pathway is it involved in?
A waxy strip in cell walls that forces water travelling via the apoplast pathway into the symplast pathway
What is the main water pathway and why?
The apoplast pathway because it provides the least resistance
Where does water leave the plant from?
The stomata
How do cohesion and tension help move water up plants?
Water molecules are cohesive meaning they stick together and the evaporation of water creates tension (suction) which pulls the water up the leaf
What is adhesion in transpiration?
Water molecules being attracted to the walls of the xylem vessels
What four main factors affect transportation rate?
1) Light
2) Temperature
3) Humidity
4) Wind
How does light affect the transpiration rate?
The lighter it is the faster the transpiration rate stomata open when it is light and close when it is dark
How does temperature affect the transpiration rate?
The higher the temperature the faster the transpiration rate because warmer water molecules evaporate faster
How does humidity affect the transpiration rate?
The lower the humidity the faster the transpiration rate because if the air around the plant is dry then water potential increases
How does wind affect the transpiration rate?
The windier it is the faster the transportation rate because high air movement blows away water from around the stomata
What are xerophytes?
Plants that are adapted to living in dry climates
How are cacti adapted to dry climates?
1) Thick waxy cuticles to reduce water loss via evaporation
2) Spines instead of leaves to reduce surface area for water loss
3) They close their stomata at hottest times of day when transpiration rates are highest
How is marram grass adapted to dry climates?
1) Stomata that are sunk in pits so they are sheltered from the wind
2) Hairs on epidermis to trap moist air to reduce the water potential gradient
What are hydrophytes?
Plants that are adapted to living in aquatic habitats
How are water Lillie’s adapted to living in aquatic habitats?
1) Air spaces in their tissues allow the plant to float increasing the amount of light they receive
2) Stomata on the upper surface of leaves to minimise gas exchange
3) Flexible leaves and stems to prevent damage from water currents
What is translocation?
The movement of dissolved substances (sugars) to where they’re needed in a plant
Where does translocation happen?
The phloem of a plant
Where does translocation move sugars from and to?
From their source (where it’s made) to a sink (which here it’s used up)
What is the mass flow hypothesis?
The sugars leave from the source that has a low water potential and a high pressure down the pressure gradient forcing the sap down to the sink where there is a high water potential and a low pressure
What contents and where do they enter the phloem?
Water from xylem and solutes from companion cells
What is active loading?
Used to move substances into the companion cells from surrounding tissues
