Transport in Plants Flashcards
(31 cards)
What is a dicotyledonous plants
Plants with two cotyledons and has a network of veins
What is the meristem
A layer of dividing cells, here it is called a pericycle
What is the need for transport systems in plants
All living things need to take substances from, and return waste to, their environment. Larger plants typically have a smaller surface area to volume ratio. Plants have a low metabolic rate so the demand for oxygen can be met by diffusion. However the demand for water and sugars is still high.
What does the xylem and phloem look like in a transverse section of a root
They xylem is a star shaped in the centre with phloem’s in between the arms. Surrounding the vascular bundle is the endodermis which helps water get into the xylem vessels.
Inside the endodermis is a layer of meristematic cells called the pericycle
What does the xylem and phloem look like in a transverse section of a stem
The vascular bundles are distributed around the edge of the stem. The phloem is the most outer layer, then the cambium then the xylem.
Aphids insert their stylet into sieve tube elements to obtain the sucrose
What does the xylem and phloem look like in a leaf
The xylem is on top then the cambium then the phloem at the bottom
What is the xylem
It’s a tissue used to transport water and mineral ions from the roots to the leaves and other parts of the plants
Describe how a xylem is formed
As xylem vessels develop lignin is deposited which impregnates the walls of the cells. This makes the cells waterproof and kills the cells.
End walls decay and fuse providing a continuous column, this also helps provide little resistance
The lignin helps prevent the vessel from collapsing under the tension
The cellulose cell walls allows adhesion of water molecules
Why is lignin deposited in patterns - spiral , annular or reticulate
What parts aren’t lignified?
This prevents the vessel from being too rigid and allows some flexibility
Some gaps aren’t lignified, providing bordered pits allowing lateral flow of the movement of water
What is the phloem
Tissue that transports assimilates from the source to the sink
The main types are sieve tube elements and the companion cells
Sucrose is able to be transported as it dissolves in the water to form sap
What is the structure of sieve tube elements
Elongated sieve tube elements lined up end to end that forms sieve tubes. They contain a small number of organelles in order to decrease resistance when mass flow occurs.
At the end of each sieve tube elements are sieve plates.
How can the sieve plates help with infection or damage
They contain sieve pores that can become blocked by deposition of callose
This prevents the loss of sap and inhibits transport of pathogens around the plant
What are companion cells
They are near to sieve tubes and involved in translocation. They contain ribosomes nucleus and many mitochondria for active transport.
The plasmodesmata allow communicational and flow of substances between cells
How are roots hair adapted to their function
Large surface area to absorb more water
Many mitochondria for active transport
Root hairs are permeable to water
How does water enter the roots from soil
Ions are pumped into the roots using ATP and this lowers the water potential. Water diffuses down the water potential gradient by osmosis into the roots.
This happens across a partially permeable membrane
How does water move from the root hairs to the cortex
what 3 routes can water take
There’s a water potential gradient again and this time water can choose to move through 3 different pathways (ions can dissolve in the water and get carried by it)
Apoplast - Water moves through the well wall between cellulose fibres
Symplast - Water moves through they cytoplasm and across plasmodesmata from one cell
to the next
Vacuolar - Water takes the symplast route but can move diffuse in and out of the vacuoles
What does the endodermis contain that is made of suberin
Casparian strip this a waxy, waterproof layer of suberin. It forces water to take the symplast pathway.
It’s though that as water has to pass the cell membrane that ion concentration can be controlled
How does water move from the endodermis to the xylem
Down the water potential gradient, water has to pass the pericycle then move through the unlignified pits in the xylem
How does root pressure arise
The action of the endodermis moving ions into the medulla and xylem by active transport draws water in.
This builds up hydrostatic pressure and pushes water a few meters up the stem
What is the cohesion tension theory
The lass of water through evaporation must be replaced by water leaving the xylem so this draws water up from the roots. creating a transpiration pull
Waters cohesive nature means it can form hydrogen bonds with other water molecules.
As water is pulled up this creates tension (negative pressure)
The lignin helps prevent the xylem vessel from collapsing
If the column is broken is one vessel this can be maintained by the bordered pits
What is capillary action
Water molecules are attracted to the sides of the xylem these forces of attraction can pull water up the sides of the vessel
What is transpiration
Loss of water vapour by evaporation
Water evaporates from the cell walls of spongy mesophyll then water vapour in the air spaces diffuse out of stomata
What are the two ways water can leave the leaf
Stomata - Diffusion of water from the air space into the atmosphere, stomata are open during gas exchange
Cuticle - A small amount of water is lost through the waxy cuticle
What factors increase the rate of transpiration
Humidity (conc of water vapour in atmosphere) - A lower humidity maintains a steep water potential gradient
Temperature - A high temperature gives water molecules a higher kinetic energy
Light intensity - A high light intensity means photolysis in light dependant stage of photosynthesis is occurring faster and that co2 is needed in Calvin cycle so stomata are open for gas exchange
Stomatal aperture - The wider the stomata the more water vapour that can diffuse out
