3.3 transport in plants Flashcards
how is sucrose removed at the sink?
Sucrose is constantly being used by surrounding cells, decreasing sucrose condentration. So sucrose diffuses out of the sieve tubes into surrounding cells via the plasmodesmata. The water potential of the phloem increases so water moves out of the phloem into surround cells, so hydrostatic pressure decreases
what is translocation?
the mass flow of assimilates down the hydrostatic pressure gradient from source to sink
what are co-transporter proteins?
a type of transport protein that can move 2 moleucles across a membrane by facilitated diffusion
explain the role of meristem tissue in the stem
meristem is a source of undifferentiated cells that are used for the growth and repair of damaged tissues
describe how oncotic pressure is established
Plasma proteins are too large to leave the capillary creating a lower water potential in the capillary than is the tissue fluid. The water moves by osmosis, down the water potential gradient, into the capillary, causing pressure.
what is a potometer?
a peice of apparatus used to estimate the rate of transpiration of a plant sample
how does light intensity affect the rate of transpiration?
more stomata are open so there is more gas exchange for photosynthesis, increasing the rate or transpiration
how does humidity affect the rate of transpiration?
a higher relative humidity in the air decreases the rate of transpiration in the air as there is a shallow water vapour potential gradient
how does air movement affect the rate of transpiration?
high wind speed maintains a steep water potential gradient, as the recently diffused water vapour is quickly carried away
how does water availability affect the rate of transpiration?
if there is little water in the soil the plant cant replace the water lost in transpiration so the stomata close and the leaves wilt
how can temperature affect the rate of transpiration?
a higher temperature will increase the rate of transpiration.
what are xerophytes?
plants that are well adapted to living in dry or arid conditions
what are hydrophytes?
plants that are well adapted to living in wet or humid conditions
why is the loss of water by transpiration unavoidable?
the stomata open for gas exchange in photosynthesis, this means the water vapour can escape when the stomata are open
what is marram grass?
a xerophyte found on sand dunes
how does a thick waxy cuticle help xerophytes?
acts as a barrier, reducing the amount of water that can evaporate from the leaf
how does rolling the leaf longitudinally help xerophytes?
air is trapped inside the leaf, making it humid, reducing the water loss from the leaf
how do spines help xerophytes?
they reduce the total surface area of leaf, reducing water loss
how do stomata in pits help xerophytes?
this reduces air movement and loss of water vapour
how do long widespread roots help xerophytes?
they can reach any rain that does fall
how do large air spaces help hydrophytes?
keeps the leaf afloat so they can absorb sunlight and are in the air
how do stomata on the upper epidermis help hydrophytes?
the stomata are more exposed to the air, allowing more gas exchange, and water loss through the stomata
how does large air spaces in the leaf stem help hydrophytes?
helps with buoyancy , and allows oxygen to quickly diffuse from the leaf to the roots for aerobic respiration
what are some adaptations of marram grass?
- thick waxy cuticle
- hairs on lower surface
- rolled leaf
- stomata in pits
how can most plants reduce the loss of water by transpiration?
- stomata are closed at night
- waxy cuticle
- lose leaves in winter
- less stomata
- stomata on the underside of the lead
what is the symplast pathway?
the movement of water through the cell cytoplasms via the plasmodesmata
what is the apoplast pathway?
the movement of water and mineral ions by mass flow, through the spaces in the cellulose cell walls
what is the vacuolar pathway?
the movement of water through the cytoplasm AND vacuoles
what is osmosis?
the movement of water from an area of less negative water potential to an area of more negative water potential
describe the movement of water from the epidermis to the xylem
Water and mineral ions travelling along the apoplast pathway are blocked by the casparian strip. Transporter proteins actively pump mineral ions into the medulla, decreasing water potential. Water moves by osmosis down the water potential gradient into the medulla
what is transpiration pull?
the movement of water up the xylem to replace water lost in the leaves
how do mineral ions and water move up the xylem?
Mineral ions and water in the medulla cause root pressure to increase in the xylem. Higher up the stem, the water and mineral ions leave the xylem and travel to other parts of the plant. The water then moves by mass flow up the xylem.
how does water move from the soil to the root hair cells?
mineral ions enter the root hair cell by active transport which lowers the water potential gradient in the root hair cell. The water moves into the root hair cell by osmosis along the water potential gradient.
what is the casparian strip?
a layer of cells in the root cortex that contains a substance called suberin which makes them impereamble and waterproof
why is the apoplast pathway used?
water with dissoleved mineral ions cant pass through the plasm membrane due to their charged ions, so the symplast and vacuolar pathway arent possible.
what is the medulla?
the inner region of the plant containing the xylem and phloem
what is the endodermis?
a cylinder of cells that forms the final boundary between the root cortex and the medulla
what is the root cortex?
the series of plant cells that extend inwards from the epidermis
what is the epidermis?
the outermost layer of the plant, containing the root hair cells
what are the adaptations of the root hair cells?
- large surface area
- no chloroplasts
- lots of mitochondria
what is water potential?
the measure of tendency of water to move
what is plasmodesmata?
thin strands of cytoplasm that link the contents of adjacent cells
how does water diffues out of the stomata?
water turns to water vapour in the stomatal air spaces, this increases water vapour potenial so water diffuses out of the stomata
what is the cohesion-tension theory?
the theory that water molecules are opulled up the xylem as a column, due to the cohesive nature of water
what is the midrib in the leaf?
the central vein in the leaf
what is cohesion?
the attraction of water molecules caused by hydrogen bonds, forming a chain of column
what is tension?
the pulling force
what is adhesion?
the attraction of water molecules to the walls of the xylem
hat are the 3 processes that move water up the xylem?
- root pressure
- transpiration pull
- capillary action
what 3 ways in water lost in the leaf?
- through the waxy cuticle
- through the stomata by transpiration
- in the palisade mesophyll by photosynthesis
what are the addition features of the xylem that enable it to cope?
- lignin strengthen the vessel so it doesnt collapse
- bordered pits connect adjacen xylem
- the xylem vessel is very narrow
what is the funtion of the phloem?
to trasnport assimilates from the source to the sink
what are examples of assimilate?
- sucrose
- amino acids
what are the parts of the phloem?
- sieve tube elements
- companion cells
- plasmodesmata
what do phloem transport?
assimilates:
- amino acids
- sucrose
what are the sieve tube elements?
the coponents of sieve tubes, they have no nucleus and little cytoplasm allowing lots of cell sap to move. They also have small perforations.
what are companion cells?
cells that load assimilates into the phloem
what are the features of companion cells?
- large nucleus
- dense cytoplasm
- lots of mitochondria
- lots of ATP
What is the xylem?
transports water and minerals in the stems of plants
what is the phloem?
transports dissolved assimilates in the stems of plants
what is meristem?
a source of undifferentiated cells
what is vascular tissue?
the cells specialised for transporting fluids by mass flow
what are dicotyledonous plants?
plants with two seed leaves
what is the structure of xylem vessels?
- bordered pits
- hollow tubes with no end walls
- lignified walls
what is the function of xylem vessels?
to transport water and mineral ions in one direction from the roots to the leaves as part of the transpiration stream.
why do plants need carbon dioxide?
for photosynthesis
why do plants need glucose?
for aerobic respiration
why do plants need magnesium?
for the synthesis of chlorophyll
why do plants need water?
for photosynthesis
what is the role of lignin?
- strengthen the xylem wall
- prevents the vessel collpasing
why is lignin deposited in a spiral?
to allow the xylem to stretch and spend
what are the plant vascular tissues?
- xylem
- phloem
what is lignification?
the waterproofic of a cell through the addition of lignin. It is incomplete so there are gaps called bordered pits
why are bordered pits important?
they allow water to leave one xylem vessel and pass into the next
what is capillary action?
the hydrogen bonds holding water molecules together and to the sides of the xylem vessel, means the water can be pulled up the xylem
what is parenchyma?
a packing tissue between the xylem and phloem
what is sclerenchyma?
dead cells that provide support to the plant
what is collenchyma?
the uneven thick cell walls formed from living cells
what is cambium?
a tissue layer that provides partially undifferentiated cells for plant growth
where is the xylem vessel and phloem found in the roots and stem?
- xylem on the inside
- phloem on the outside
where is the xylem and phloem found in the leaf?
the xylem is above the phloem
why do some plants have specialised transport systems?
they have a low surface area to volume ratio
describe active loading at the source
1- companion cells have a dense cytoplasm with lots of mitochondria to produce lots of ATP
2- the hyrolyis of ATP moleucles releases energy used to actively pump protons out of companion cells, creating a proton gradient
3- co-transporter proteins move the protons and sucrose (back) into the companion cells
4- sucrose concentration increases so the sucrose diffuses into adjancent sieve tubes via the plasmodesmata
5- sucrose lowers the water potential in the sieve tube so water moves into the phloem by osmosis.
the sucrose dissoleves in the water forming cell sap, increasing hydrostatic pressure at the source
what are the advantages of mass flow?
- shorten the diffusion distance
- allows organisms to grow larger
- moves substance quickly
Why the plants need a vascular system to support amino acid synthesis?
To transport nitrates to the leaves using xylem tissue.
Name some potential uses of stem cells in medicine.
- treatment of disease such as Alzheimer’s.
- research
