A non-living plant transport vessel that carries water and dissolved mineral ions from the roots
Describe the features of the xylem:
long continuous columns - dead cells with open ends
Pits (bordered pits) = allows water to move sideways through adjacent vessels, allows water to leave the xylem and pass into the living parts of the plant
lignin = thickens the walls, kills the cells, waterproof - withstands the pressure of water, provides strength, prevents collapsing, forms spiral patterns = stretches as the plant grows, allows some flexibility
Name the features of the xylem vessels:
long continuous columns
bordered pits
lignin
Define Bordered pits:
Gaps in the cellulose cell wall that form when lignification is not complete which allows water to move sideways through adjacent vessels
Xylem vessels are hollow: empty
Define Transpiration:
The loss of water vapour from the plant's stem and leaves via diffusion and evaporation
Outline the factors that affect the rate of transpiration:
Light intensity
Temperature
Humidity
Air movement
Water availability
Number of leaves
Number/size/positionof stomata
The presence of a waxy cuticle
Outline reasons why transpiration is important:
maintains cell turgidity
transports mineral ions up the plant
cools the surface of the plant
supplies water for growth/ cell elongation/ photosynthesis
Name the processes taken by water to leave the leaf:
osmosis
evaporation
diffusion
What is the equipment used to measure the rate of transpiration?
Potometer
Water molecules are attracted to each other by the forces of cohesion
Water molecules are attracted to the sides of the xylem vessels by the forces of adhesion
Water molecules have strong cohesive forces thanks to their ability to form hydrogen bonds with one another
The narrower the xylem, the bigger the impact of adhesion
What aids the movement of water up the xylem against the force of gravity?
cohesion
adhesion
root pressure
Water molecules adhere to the walls of the xylem
What makes the walls of the xylem narrower?
lignin
the tension caused by the water molecules being pulled up
What causes root pressure?
the upwards movement of minerals via active transport
Formula for volume of cylinders:
𝚷r2l
General formula for Rate of Transpiration:
volume/time
The rate of transpiration is the volume of a cylinder divided by the time taken. πr2l/time
What does r represent?
the radius of the capillary tube
Define Adhesion:
The attraction of water molecules to the impermeable walls of xylem tissue
Adhesion is the formation of hydrogen bonds between carbohydrates in the xylem vessel walls and water molecules
Large multicellular animals need a transport system for oxygen and carbon dioxide.
Large multicellular plants do not need a transport system for oxygen and carbon dioxide, Why?
Plant cells have a low metabolic rate
What waterproof polymer lines the walls of the xylem?