Plant Vascular Systems & Root Transport Flashcards
Why do plants require transport systems?
To ensure all cells of the plant receive sufficient nutrition.
Plants have a relatively small SA:V ratio but a high metabolic rate making a transport system necessary. Plants with specialised transport systems are known as vascular plants.
Why is simple diffusion not viable in plants?
- large transport distance - substances cannot diffuse from exchange site to rest of the organism
- small SA:V - diffusion cannot be relied upon
- high metabolic rate - greater demand for oxygen and more waste is produced
How are plants adapted to increase SA:V?
- plants have a branching body shape
- flat and thin leaves
- roots have root hairs
What is a cotyledon?
Organs that act as food stores for the developing embryo
What are dicotyledonous plants?
Plants which make seeds that contain two cotyledons
What are the differences between monocots and dicots?
- 1 cotyledon vs 2
- fibrous roots vs tap roots
- scattered vascular systems vs ringed
- parallel leaf veins vs net-like leaf veins
- x3 flowers vs 4 / 5 flowers
What the two different types of dicots?
- herbaceous dicots (non-woody stems)
- woody dicots
What is a vascular bundle?
Xylem and phloem are the transport vessels and are arranged in vascular bundles.
What is the cambium?
A layer of meristem cells between the xylem and phloem which is involved in the production of new xylem and phloem tissue.
Where is the vascular bundle found in the roots?
It is found in the centre - the core is the xylem, edges of the core is phloem.
This helps the root withstand pulling strains as the plant transports water upwards and grows.
Where is the vascular bundle found in the stem?
Bundles are located around the outside - xylem is on the inside (closer to the stem) to help support the plant. Phloem found on outside (closer to epidermis).
Where is the vascular bundle found in the leaves?
They form the midrib and veins - they spread from the centre of the leaf in a parallel line. Xylem tissue is found on the upper side (closesr to upper epidermis). Phloem is on the lower side (closer to lower epidermis).
What is the structure of xylem?
- dead tissue - no cytoplasm and nuclei
- hollow tubes
- cell wall spiralised lignin
- pits in walls (non-lignified areas where water moves in and out of vessels
- no end walls
What is the function of the xylem?
Transports water and dissolved minerals upwards from root hair cells to leaves - called the transpiration stream.
What is the function of the lignified cell walls?
Adds strength to withstand the hydrostatic pressure so the vessels do not collapse, impermeable to water.
What is the function of xylem having no end plates?
Allows mass flow of water and solutes as cohesive and adhesive forces are not impeded.
Why does the xylem vessel being dead help it’s function?
There is no protoplasm to impede the flow of water.
Why does the xylem vessel’s small diameter help it’s function?
It helps prevent the water column from breaking and assists with capillary action.
How is the phloem tissue structured?
- living tissue
- composed of elongated cells called phloem sieve tubes
- contain sieve plates (pores in the end walls) which transport assimilates
- sieve tubes have an associated companion cell (with a nucleus, organelles, enzymes)
What is the function of the phloem vessels?
Transports assimilates (sucrose, amino acids) upwards and downwards - known as bidirectional transport
This is known as translation
Why is water needed in plants?
- raw material for photosynthesis
- mineral ions / sugars transported in aqueous solution
- cooling effect (by transpiration)
- turgor pressure (hydrostatic skeleton)
What are the adaptations of root hair cells?
- very thin surface layer - diffusion and osmosis can happen quickly
- microscopic size - penetrate between soil particles easily
- large SA:V
- concentration of solutes in the cytoplasm maintains water potential gradient between soil water and cell
What are the three pathways taken by water to reach the xylem?
- symplast
- apoplast
- vacuolar
What is the symplast pathway?
Water moves through the continuous cytoplasm of living plant cells by osmosis through the plasmodesmata.
Each cell further away from the roots has a lower water potential, meaning water is drawn through the plant.
What is the plasmodesmata?
A fine strand of cytoplasm linking adjacent cells.
What is the apoplast pathway?
The movement of water through the cell wall and intracellular spaces - cohesive and tension forces acting on the cell walls pull the water up the plant.
The apoplast pathway provides the fastest movement of water.
How does water move in the apoplast pathway?
Water moves by diffusion, as it is not crossing a partially permeable membrane.
What is the vacuolar pathway?
The same as the symplast pathway, except water moves through the cell’s vacuoles as well as the cytoplasm (through the tonoplast).
It is the slowest route for water transport.
What is the casparian strip?
The casparian strip is an impermeable layer of suberin - a waxy material.
What is the endodermis?
A continuous cylinder of endodermal cells which surround the central vascular tissue.
What happens when water reaches the endodermis from the roots?
It’s path is blocked by the casparian strip - waterproof and impermeable due to the layer of suberin.
The water in the apoplast pathway is forced to move through the cell surface membrane, through the symplast pathway.
Why is the casparian strip useful to plants?
The selectively permeable membrane of the cells can control what enters the xylem - meaning toxic solutes can be removed, and only necessary water molecules / mineral ions can enter.
The casparian strip also contributes to increasing root pressure.
