Module 3: Transport in Plants Flashcards
Why do plants need transport systems?
*multicellular
*small surface area:volume ratio
*high metabolic rate
*need substances
*need to remove waste products
*exchanging substances by direct diffusion is too slow
What tissues make up the plant’s vascular system?
Xylem and phloem
Where is the xylem found in roots?
In the centre.
Where is the phloem found in roots?
Surrounding the xylem in the centre.
What is the function of the xylem and phloem in roots?
Provide support for the root as it pushes through the soil.
Where is the xyelm and phloem found in stems?
Near the outside.
What is the function of the xylem and phloem in stems?
Provide ‘scaffolding’ to reduce bending.
Where is the xylem and phloem found in leaves?
Make up a a network of veins.
What is the function of the xylem and phloem in leaves?
Provide support to thin leaves.
What are transverse cross-sections?
Sections cut though the structure at a right angle to the length.
What are longitudinal cross-sections?
Sections cut through the sturcture along the length.
What is the main function of xylem tissue?
Transports water and minerals in solution.
Which way does movement happen in xylem tissue?
Up the plant, from the roots to the leaves.
What is the other function of xylem tissue?
Support.
What is xylem tissue made up of?
Several different types of cells.
What do xylem vessels do?
Transport the water and minerals in solution.
Describe the cells of xylem vessels.
Dead with no cytoplasm.
Describe the structure of xylem vessels.
Long, tube like structures formed from vessel elements joined end to end, with no end walls, forming a continuous tube.
What are the cell walls of xylem vessels thickened with?
Lignin.
What is lignin?
A woody substance that thickens xylem vessel cell walls.
What does lignin do?
Helps to support xylem vessels and stops them collapsing inwards.
How is lignin deposited in cell walls?
In different ways, e.g. in spirals or in distinct rings.
What happens to the lignin in a cell as it ages?
Amount increases.
How does water and ions move in and out of xylem vessels?
Through small pits in the walls where there is no lignin.
What is the only function of phloem tissue?
Transports solutes around plants.
What is the main substance that phloem tissue transports?
Sugars, such as sucrose.
Which way does transport happen in phloem tissue?
Both up and down.
What is the structure of phloem tissue?
Cells arranged in tubes.
What four things does phloem tissue contain?
*phloem fibres
*phloem parenchyma
*sieve tube elements
*companion cells
What are sieve tube elements?
Living cells joined end to end to form sieve tubes.
What is a sieve tube?
The tube in phloem tissue for transporting.
What is unusual about sieve tube elemtns?
They are living cells but have no nucleus, only a thin layer of cytoplasm and few organelles.
How is the cytoplasm of adjacent sieve tube elements joined?
Through holes in the sieve plates.
What do the end walls of the sieve tube elements form?
Sieve plates.
What is the purpose of sieve plates?
They have many holes, allowing solutes through.
What is the function of companion cells?
Carry out the living functions for their sieve cells as well as themselves.
Why are companion cells needed?
Sieve tube elements lack a nucleus and other organelles so cannot survive on their own.
What does every sieve tube element have one of?
A companion cell.
What is the method for dissecting a plant stem?
- use a scalpel to cut a cross-section of the stem as thinly as possible
- use tweezers to place the sections in water until needed
- transfer each section into a dish containing stain and leave for 1 minute
- rinse off the sections with water and mount onto a slide
When dissecting a plant stem, why are the sections placed in water until needed?
To prevent them from drying out.
What is an example of a stain used for plant stems?
Toluidine blue O (TBO)
What does toluidine blue O stain?
Lignin in xylem vessels blue-green, allowing us to see the position and structure.
What are the four factors affecting rate of transpiration?
*temperature
*light
*humidity
*wind
How does temperature affect rate of transpiration?
*increasing temperature increases rate of transpiration
*warmer water molecules have more energy, so evaporate from the cells inside the leaf faster
*this increases water potential between the inside and outside of leaf
*so water diffuses out of the leaf faster
How does light affect rate of transpiration?
*increasing light intensity increases rate of transpiration
*the stomata open when it gets light so carbon dioxide can diffuse into the leaf for photosynthesis
*when it’s dark, the stomata close so there’s little transpiration as water cannot diffuse out the stomata
How does humidity affect rate of transpiration?
*decreasing the humidity increases the rate of transpiration
*of the air around plant is dry, the water potential gradient between the leaf and air is increased
*this increases transpiration
How does wind affect rate of transpiration?
*increasing wind increases rate of transpiration
*lots of air movement blows away water molecules around the stomata
*this increases the water potential gradient
*this increases rate of transpiration
