xylem transport Flashcards
transpiration
the loss of water vapour from leaves and other aerial parts of the plant which is replaced by water absorption
cuticle
Outermost layer on leaf, protects plant against water loss and insect invasion
epidermis
protects plant
Vascular Tissue
Vascular Tissue: consists of phloem and xylem. Xylem carries water to the leaves while phloem carries photosynthesis products to the rest of the plant. They occur together in veins or vascular bundles and are found in the middle.
Palisade mesophyll:
Palisade mesophyll: densely packed region of cylindrical cells in the upper portion of the leaf (where the most light is) that contain a lot of chloroplasts to carry out photosynthesis.
xylem
Complex tissue composed of many cell types
Tracheids: dead cells that taper at the ends and connect to one another to form a continuous column
Vessel elements: cells involving water transport (also dead, and have THICK LIGNIFIED SECONDARY WALLS)
It transports water from the roots to the upper parts of the plant and supports the plant(TRANSPIRATION) and any water lost is used to cool sun-drenched leaves and stems
Primary walls:
Pits or pores for lateral water movement
Secondary walls: Vessel elements (lignin) are often interrupted by areas of the primary walls
stomata
Stomata can only be closed on short term basis
They open and close to changes in turgor pressure of the surrounding guard cells
guard cells
cylindrical and with uneven cell wall thickness to control the stomata
When water enters cells, they bulge and the cell wall of the guard cell thickens which opens the stoma, when they lose water the guard cells sag and that closes the stoma
ABSCISIC ACID
ABSCISIC ACID: plant hormone that causes potassium ions to diffuse rapidly out of guard cells for stomatal closure (produced in roots during times of water deficiency)
Factors that affect stomatal opening/closing:
Carbon dioxide levels Circadian rhythms Hormonal changes Humidity and droughts Temperature
Cohesion-tension theory
That intermolecular attraction explains transpiration through the xylem
Cohesion-tension theory process
- Water is pulled from the soil into the roots
- Water is pulled from the root cortex into xylem cells
- Tension occurs in the columns of water in the xylem due to osmotic pressure
- The vessel water column is maintained by cohesion and adhesion
- Water lost by transpiration (head supplied from sun evaporates water and leads to it leaving through stomata; rate controlled by guard cells) is replaced by water from the vessels
- Water moves down concentration gradients
root and fluid movement
Water moves into root hairs through plasma membranes from soil due to the higher solute concentration within the roots (osmosis) and into the vascular cylinder (phloem and xylem)
Function of roots:
Function of roots: provide mineral ion and water uptake for the plant
Efficient: because of extension branching patterns and specialised epidermal structures (root hairs that increase surface area)
root cap
protects the apical meristem during primary growth of the root through the soil
