Module 3.1.3 - Transport in plants Flashcards
What is the phloem and xylem known as?
Vascular tissues which are responsible for the transport of reactants and products of the chemical reactions around the plant
What is the xylem responsible for?
Transporting water and mineral ions from roots to leaves
What does lignin do in the xylem?
- waterproofs and reinforces the xylem so it doesn’t collapse under the transportation pull
- leads to death of xylem cells (loss of cytoplasm and end walls organelles)
What is lignification?
Lignin in cell walls
What happens when lignification isn’t complete?
Leaves gaps in cell walls called bordered pits which are in 2 adjacent xylem vessels that are aligned to allow water to leave 1 and pass into the next and out of the xylem and into living parts of the plant
What is capillary action in xylem vessels?
Forces holding water molecules also attract the molecules to the side of the xylem vessels. These forces of attraction can pull the water up the sides of the vessel
What is parenchyma?
Packing tissue which fills spaces between xylem and phloem tissues,
- living tissue, acts to separate/ support the vessels
What does the phloem do?
Transports amino acids, dissolves sucrose in water to form cell sap is transported by the phloem
What are the amino acids and cell sap made from in the phloem?
From the plant using substances absorbed from the environment which then becomes part of the plant
What are sieve tube elements in the phloem?
Cells that are lined up end on end to form sieve tubes, don’t have a nucleus, very little cytoplasm which leaves lots of space for cell sap to move along the phloem vessel by mass flow
What does perforations in cross-walls (sieve plates) allow?
Cell sap to move from 1 sieve tube element to another
What does the phloem consist of?
Sieve tubes, formed of sieve tube elements lined end on end and companion cells
What do companion cells do in the phloem?
Carry out active processes which are needed to load the assimilates into the sieve tubes
Where are companion cells found?
Between sieve tubes, small cells, large nucleus, dense cytoplasm containing an abundance of mitochondria
What is the plasmodesmata?
Thin strands of cytoplasm that links contents of adjacent cells
How are companion cells and sieve tube elements linked?
Plasmodesmata which allows the flow of assimilates between the cells
What do root hair cells have?
Large surface area and a lack of cytoplasm which contains a large number of mitochondria
How do mineral ions enter the root hair cells?
Active transport - require energy from the hydrolysis of ATP to move the ions against the concentration gradient
What happens to the water potential inside the root hair cell because of ions going against the conc gradient?
Water potential decreases so water will move from higher water potential in the soil to the lower water potential in the root hair cell by osmosis
What is the epidermis?
Outermost cell layer of a plant and root hair cells are located in this outer layer in the roots
What is the root cortex?
Series of plant cells that extend inwards
What is the symplast pathway?
Water and mineral ions pass through the plasmodesmata from 1 cell to the next, down the water potential gradient
What is the vacuolar pathway?
Water and mineral ions go to cytoplasm and then pass through vacuoles too
What is the apoplast pathway?
Cell walls are fully permeable so water can move freely between cells without needing to pass through the plasma membrane. Moves by mass flow which allows dissolved mineral ions to be carried through the root cortex
What is the endodermis?
A cylinder of cells that forms the final boundary between the cortex and the inner region of a plant
Where is suberin found?
The walls of the root endodermis cells
What is suberin?
Waterproof and impermeable which creates a water tight seal known as the casparian strip
What does the casparian strip do?
Blocks the apoplast pathway between the cortex and medulla so water and mineral ions have to pass into the cytoplasm
What happens to water and mineral ions due to the apoplast pathway being blocked?
Have to pass into the cell cytoplasm
What do transporter proteins do?
Actively pump the mineral ions into the medulla, the water potential of the medulla decreases
What does movement of water and mineral ions out of the xylem and into parts of the plant higher up the stem result in?
Lower root pressure
What dies mineral ions and water in the medulla result in?
Root pressure increasing in the xylem next to the roots
What does the difference in root pressure create?
A pressure gradient which forces water to move up the xylem by mass flow
How does root pressure move water a few meters up the xylem?
Mass flow
What is transpiration?
An inevitable consequences of gas exchange because the stomata remain open during light hours of the day to allow carbon dioxide to enter for photosynthesis
What is the transpiration pull?
Water vapor that is lost must be replaces by water moving up the xylem
What does cohesion force the water molecules to do?
Stick together by hydrogen bonds. The strength of force holds water molecules together in a long chain or column
What dies adhesion do?
Attracts water molecules and walls of the xylem vessel
What is capillary action?
Attraction between water molecules and walls of xylem vessel causes column to move upwards. The narrower the vessel, the stronger the force of capillary action
What is the sub-stomatal air space?
Area of space found above the stomata
What happens to guard cells for them to open and close?
Open - swell/turgid
Close - flaccid
Where does water move into/go in a plant cell?
- some moves into palisade mesophyll cells for photosynthesis
- some will move into other cells and result in turgidity
- tiny amount will leave through the waxy cuticle
How does water go from the xylem to the spongy mesophyll layer?
By osmosis
What is formed when when water evaporates from the spongy mesophyll cells?
Water vapor
How is the low water vapor potential gradient formed?
Goes from a higher water vapor potential to a low water vapor potential
What is the active process that companion cells carry out?
Assimilates being actively loaded into the sieve tubes first from the source
What are co-transporter proteins?
Type of transport protein that are able to move 2 molecules across a membrane by facilitated diffusion by coupling the favorable movement of 1 molecule with its conc gradient. Unfavorable movement of another molecule against its conc gradient
What is hydrostatic pressure?
The pressure exerted by a fluid on its container at a given point
What are the cytoplasm of the companion cells dense in?
Mitochondria which are organelles responsible for producing the energy store ATP by aerobic respiration
Where does pressure decrease and increase?
Decrease at the sink
Increase at the source
What does the hydrolysis of ATP molecules release?
Energy which is used to actively pump protons out of the companion cells and into surrounding tissue
What is the energy from the hydrolysis of ATP used for?
To actively pump protons out of the companion cells and into surrounding tissue
What does the protons being pumped by the companion cells create?
A proton gradient across the membrane of the companion cells using co-transporter proteins
Where do the protons and sucrose move into and with what conc gradient?
Into the companion cells. Protons move with their conc gradient and sucrose moves against the conc gradient
What does the assimilate diffuse through to adjacent sieve tube element?
Plasmodesmata
What does the increase in conc of sucrose in the companion cells do?
The assimilate will diffuse into adjacent sieve tube element through the plasmodesmata
What does the presence of sucrose in the sieve tubes element do to the water potential?
Lowers the water potential which causes water to move into the phloem from surrounding tissues by osmosis
What increases the hydrostatic pressure at the source?
Sucrose dissolving in the water to form cell sap
What is translocation?
The mass flow of assimilates down the hydrostatic pressure gradient from source to sink
Are leaves sources or sinks?
Sources
Are buds, flowers, fruits and roots sources or sinks?
Sinks
Are storage organs sources or sinks?
Can be both
What do carrier proteins carry into guard cells?
Solutes
What is asymmetric configuration?
Inner walls of guard cell is thicker than outer wall, causes guard cell to bend open/turgid
What increases the rate of transpiration?
- air movement
- temperature
- relative humidity
- light intensity
- soil water availability
How does air movement increase rate of reaction?
Air trapped beneath leaf, H2O diffuses out of stomata and accumulates in layer of air, increases water potential in air layer, lowers water potential gradient, wind blows air away taking H2O with it, increasing water potential gradient
How does temperature increase rate of reaction?
Amount of water vapor in air compared to total conc of water the air can hold, high humidity: lower water potential gradient between inside of leaf and outside air, low humidity: opposite effect
How does relative humidity increase rate of reaction?
Increase in temp =increase in KE of H2O molecules, increases rate of H2O evaporating from spongy mesophyll cells into the air spaces
How does light intensity increase rate of reaction?
Increase light: more stomata open, more stomata open: more H2O molecules diffuse out
How does soil-water availability increase rate of reaction?
Lack of water in soil: plant will be under ‘water stress’, water will be conserved, rate of transpiration will decrease
What is a potometer?
Measures the rate of transpiration
- more evaporation = faster transpiration = bubble speed increases
What is a xerophyte plant?
likes dry conditions, stores water
What are the features/adaptations of marram grass?
- water drains quickly, tends to be very salty, often very windy,
- roots can be 15-20m long and leaves roll p longitudinally to trap humid air to reduce water potential gradient
- waxy cuticle on outer side of rolled leaf which reduces evaporation
- stomata only on inner surface of rolled leaf reduces evaporation
- stomata in pits are covered in hairs, reduces air movement
- spongy mesophyll is very dense, few air spaces and reduces room for evaporation
What are the features/adaptations of cacti?
- stem is ribbed or fluted so can expand to store water
- leaves are reduced to spikes to reduce SA so less water is lost
- very widespread roots to collect any rain that falls
What are the features/adaptations of water lilies?
- large air spaces in leaf keep leaf afloat so can get sunlight
- stomata on upper epidermis is exposed to air to allow for gaseous exchange
- leaf stem has many large air spaces which helps with buoyancy, allows oxygen to diffuse quickly to roots for aerobic respiration
What is a hydrophyte plant?
Better in humid/wetter conditions
How do hydrophytes transpire?
They have special features at tips of their leaves called hydathodes that release water droplets, lowers water potential within leaves generating a transpiration pull
