Transport in Plants Flashcards
How is water taken up into plants?
Water moves by osmosis from the soil through root hair cells
The soil has a very dilute solution of mineral ions meaning it has a high water potential and the vacuole in the root hair call contains cell sap of ions and sugars lowering water potential.
How are root hair cells adapted to their function?
The root hair cell has root hairs which increase the surface area massively meaning water can be taken up quickly.
Root hair cells have thin cell walls which decreases the diffusion pathway and increase the rate of water uptake.
What is the apoplast pathway?
Water moves in the cell walls. Cellulose fibres in the cell wall are separated by spaces through which the water moves.
What is the symplast pathway?
Water moves through the cytoplasm and plasmodesmata.
What is the vacuolar pathway?
Where water moves from vacuole to vacuole
Why does water move across the root?
There is a water potential gradient across the root cortex. It is highest in the root hair cells and lowest in the xylem, so water moves down the water potential gradient, across the root.
Describe the structure of the xylem in the roots
In roots, the xylem is central and star-shaped with phloem between groups of xylem cells.
Why are the xylem and phloem arranges the way they are in the root?
It resists vertical stress (pull) and anchors the plant in the soil
Describe the arrangement of tissues in the stem of a plant
The vascular bundles are in a ring at the periphery, with xylem towards the centre and phloem towards the outside .
Why are the xylem and phloem arranges the way they are in the stem?
This gives flexible support and resists bending
How are tracheids adapted to their function?
Their cell walls contain lignin, which is hard, strong and waterproof.
How does water travel through tracheids?
The walls have gaps, called pits, through which the water travels.
Tracheids are spindle-shaped so water takes a twisting rather than a straight path up the plant.
What plants do tracheids occur in?
Ferns, conifers and angiosperms (flowering plants)
Why can mosses not grow as tall as other plants?
They have no water-conducting tissue and are therefore poorer at transporting water.
What are the two types of conducting cell in the xylem?
Tracheids and vessels
What are the two main functions of the xylem?
1) Transport of water and dissolved minerals
2) Providing mechanical strength and support
What conducting tissue only occurs in angiosperms?
Vessels
How do vessels get the shape of a long hollow tube?
As lignin builds up in their cell walls, the contents die, leaving an empty space, the lumen. As the tissue develops, the end walls of the cells break down.
How does water climb in vessels?
Due to it having a long hollow fine, like a drainpipe, water climbs straight up the plant.
Why are angiosperms the most dominant plant on earth?
Water moving through vessels is so much more efficient than the twisting path through tracheids.
How do you identify xylem in microscope sections?
Unlike cellulose of phloem cell walls, the lignin in the xylem stains red.
Why cannot water enter the xylem from the apoplast pathway ?
Because lignin makes xylem walls waterproof, water can only pass from the symplast or vacuolar pathways.
How does water leave the apoplast pathway?
The endodermis walls are impregnated with a waxy, suberin, forming a distinctive band called the casparian strip. Suberin is waterproof so the Casparian strip prevents water moving further in the apoplast and drives it into the cytoplasm.
How does the plant achieve a lower water potential in the xylem than the endodermis cells?
1) The water potential of the endodermis cells is raised by water being driven in by the casparian strip
2) The water potential of the xylem is decreased by active transport of mineral salts, mainly sodium ions from the endodermis and pericycle into the xylem
How do minerals move into the root hair cells?
In the soil minerals are present in very low concentrations, so generally, minerals are absorbed into the cytoplasm by active transport.
How do mineral ions move through the root cortex?
Along the apoplast pathway, in solution
How do mineral ions enter the xylem from the apoplast pathway?
When the minerals reach the endodermis, the casparian strip prevents further movement in the cell walls, so they enter the cytoplasm by active transport, and then diffuse or are actively transported into the xylem.
How is active transport important at the endodermis?
It allows the plant to absorb the ions selectively