Plant Transport Flashcards
Why is Xylem poorly developed in Hydrophytes?
There is little need for transport tissue as the plant is surrounded by water
What is a hydrophyte?
A plant that grows submerged or partially submerged in water
Why is there little lignified tissue in hydrophytes?
The plant is supported by the water therefore not requiring the support of the lignin tissue.
Where is stomata located on hydrophytes?
On the upper surface of the leaves
How much cuticle do leaves have on hydrophytes?
Little or none
What is the function of air spaces in hydrophytes?
Stems and leaves have large air spaces which act as reservoirs for CO2 and O2. They also assist with buoyancy
What are two case study examples of a Xerophyte?
Cactus and Marram Grass
How are cacti adapted to their environment?
Cacti have succulent stems for water storage and leaves reduced to spines. Many cacti also have the ability to close the stomata during the daylight hours
How are Xerophytes adapted to their living conditions in general?
They can survive in hot, dry desert or cold regions where the soil in frozen for much of the year.
How are pine trees adapted for their environment?
Pines trees have needle leaves. This reduces the surface area over which water can be lost.
What is a mesophytes?
Plants adapted to a habitat with adequate water
Where do mesophytes survive?
Grow in well drained soil and moderately dry air
What is the cuticle like on Marram grass?
The cuticle is a thick waxy covering over the surface of the leaf which reduces water loss. The thicker this cuticle the lower the rate of cuticular transpiration.
What is the stomata like on Marram Grass?
Marram grass has sunken stomata. They are located in pits so that humid air is trapped outside the stomata. This reduces the water potential gradient between the leaf and the atmosphere and therefore reduces the rate of transpiration.
What other feature of marram grass reduces the water potential gradient?
Stiff interlocking hairs trap water vapour and reduces the water potential gradient
How does the shape of the leaves effect the characteristics of the marram grass?
The Marram grass has rolled leaves. Large thin-walled epidermal cells shrink when they lose water by transpiration causing the leaf to roll in on itself. This reduces the leafs overall area over which transpiration can occur.
What is a Xerophyte?
A plant adapted to a freshwater habitat
What are the key 5 adaptations of Xerophytes?
.Sunken stomata to create local humidity/ decreases exposure to air currents
.Presence of hairs creates local humidity next to leaf/ decreases exposure to air currents by reducing flow around the stomata.
.Thick waxy cuticle makes more waterproof/ impermeable to water.
.Stomata inside of rolled leaf creates local humidity/ decreases exposure to air currents because water vapour evaporates into air space rather than atmosphere.
.Fewer stomata decreases transpiration as this is where water is lost.
How does having a thick cuticle work?
Stops uncontrolled evaporation through leaf cells
How does having a small leaf surface area work?
Less surface area for evaporation
How does having a low stomata density work?
smaller surface area for diffusion
How does having sunken stomata work?
maintains humid air around stomata
How does having stomata hairs (trichores) work?
maintains humid air around stomata
How does having rolled leaves work?
maintains humid air around stomata
How does having extensive roots work?
Maximise water uptake
Why do plants need a transport system? (3)
- Large multicellular organisms
- Diffusion alone is too slow and inefficient
- To take materials from cells to exchange surfaces and environment (ions/ sucrose/ amino acids)
What is a plant transport system similar to?
A closed animal transport system
How does a plant transport system differ to an animal system? (5)
- Xylem and Phloem not arteries and veins
- Water instead of blood
- Hydrostatic pressure and evaporation instead of a pump (heart)
- No valves
- Pigment
What are the two visible features of root hair cells?
- Large surface area for H20 to enter by osmosis
2. Cellulose cell wall freely permeable to H20
Why do root hair cells have a large quantity of mitochondria?
To provide ATP for the active transport of mineral ions
Why do root hair cells have a large quantity of embedded protein carriers in their membrane?
For the active transport of mineral ions
What is the steele/ vascular bundle?
Consists of Xylem, phloem and cambium
What is Xylem?
Dead tissue that carries water and mineral ions up the plant
What is phloem?
Living tissue that carries dissolved organic materials e. g sucrose around the plant.
What is the epidermis?
Outer cell layer, may contain root hair cells to increase surface area for water uptake and mineral uptake
What is the cortex?
A layer packing tissue between epidermis and vascular tissue
What is the endodermis?
A layer of cells that contains a waterproof casparian strip to control movement of ions into the xylem.
Why is the water potential of soil high?
Soil water contains very weak solutions of mineral ions and so has a HIGH water potential
Why is the water potential of the vacuole of the root hair cell low?
The vacuole of the root hair cell contains a concentrated solution of dissolved substances and therefore has a low water potential
How does water move into a root hair cell?
Down a water potential gradient by osmosis
What is the Apoplast pathway?
Water soaks into cellulose fibres of the epidermal and cortical cell wall and seeps across the root from the cell without entering the cytoplasm.
What is the Symplast pathway?
When water moves into the cytoplasm of a cortical cell by osmosis across the plasma membrane and between adjacent cells via the plasmodesmata to the xylem.
What is the vacuolar pathway?
When water moves via the vacuoles in the cytoplasm, but has to cross plasma membranes - resistance is high and little water moves by this method
What is the endodermis?
A layer of cells which surrounds the pericycle within which lies in the stele- vascular bundle
What is and what is the function of the casparian band?
The casparian strip and prevents movement in the Apoplast pathway. Water and dissolved mineral ions must enter the cytoplasm of the endodermal cells and follow the Symplast pathway before entering the xylem vessels.
In what form does Nitrogen normally enter a plant?
As Nitrate ions (NO3-) or ammonium ions (NH4+)
How does Nitrogen enter a plant?
They diffuse with water along the Apoplast pathway, but at the endodermis enter the Symplast pathway by active transport against the concentration gradient, to by-pass the casparian strip.
What causes root pressure?
The active transport of mineral ions into the xylem where they lower the water potential
What is the process of the creation of root pressure?
Water is drawn into the xylem from the endodermis by osmosis This accumulation of water in the xylem, produces a positive hydrostatic pressure pushing on the rigid cells and is called root pressure.
What is the purpose of root pressure?
To provide a force, which pushes water up the stem.
What is the maximum height root pressure can work to?
The maximum root pressure measured in some plants can raise to about 7 meters
What is the arrangement on xylem and phloem in the root?
Central arrangement to anchor the plant. (X shaped)
What is the arrangement on xylem and phloem in the stem
Peripheral arrangement resists bending (Circular arrangement around the edges on the circle)
What are the two types of water conducting tissue in plants?
- Vessels
2. Tracheid
What is the structure of vessels and tracheids’?
The vessels and trahceids’ from continuous tubes, with no end walls where ells joins, a column of water travels up in one direction
What is the function of Xylem?
The transport of water
Is xylem tissue made up of dead or live tissue? How do we know this, why is it necessary?
Dead cells which lack cytoplasm making it easier for water to flow up
Why is the xylem tissue dead?
The xylem is dead because of deposition of lignin on the cellulose cell walls which makes them impermeable.
What is the function of lignin in the plant?
Provides mechanical strength, which prevents the collapse of xylem, supports the plant, and allows adhesion
In what pattern in the lignin deposited in the xylem?
Lignin is deposited as rings/ spirals which thickens the cell walls.
What are ‘pits’ in the xylem?
Areas where no lignin has been deposited, also known as plasmodesmata which allows the sideways movement between vessels.
Where are tracheids found?
In the finest branches of the xylem (in leaves and roots) and are less well adapted than vessels.
Apart from vessels and tracheids what two other cell types are found in xylem structures? What are their function?
- Fibres - provide support only, do NOT transport water
2. Parenchyma - a packing tissue, keeps all xylem elements in place
Define Transpiration?
The evaporation (loss) of water vapour from the leaves through stomata
What type of process is the movement of water up through the xylem?
A passive process
The movement of water up through the xylem is a passive process what is the exception of this idea?
Some initial movement into the xylem is due to active transport of mineral ions across the endodermis of the root creating root pressure.
What is the water movement in xylem mainly due to ?
The loss of water vapour from the leaves via transpiration reducing pressure at the top of the xylem creating a transpiration stream
Why does water evaporate from the internal leaf spaces and diffuse out of the stomata in the leaves?
Due to a water potential gradient
How does a water potential gradient cause a transpiration stream?
It draws water across the leaf from the xylem, tissue by the Apoplast, Symplast and vacuolar pathways.
Describe the Cohesion-Tension theory
As water molecules leave the xylem vessels water is pulled up from the roots due to the cohesion between polar water molecules (due to H bonding) and the adhesion between the water molecules and the hydrophilic lining of the cell walls of the xylem vessels. The water in the xylem forms a continuous column.
What is capillary action in the xylem?
As a result of many xylem cells being narrow and there are narrow spaces between cellulose molecules there is capillary action and this is important in small plants
How high can capillary action work?
Up to 1m
What equipment is used to measure the rate of transpiration?
A potometer
What are the 5 steps to using a potometer?
- Leafy shoot, cut at an angle and insert under water, ensure air tight fit and no air bubbles in xylem.
- Air bubble introduced into system
- Measure time taken for movement of bubble along scale (mm/s)
- Reservoir tap opened to return bubble to start point
- Repeat measurements taken and mean calculated
What factors affect transpiration? (4)
- Light intensity
- Temperature
- Humidity
- Air Movement
How does affect light intensity transpiration rate?
This affects the degree of opening and closure of the stomata
How does affect temperature transpiration rate?
Warm air has move kinetic energy and holds more water. It also increases the kinetic energy of the after molecules so increases the rate of evaporation from the leaves and therefore transpiration.
How does affect humidity transpiration rate?
Dry air outside the leaf creates a steeper water potential gradient between the internal air spaces and the environment thus increasing transpiration rate.
How does affect air movement transpiration rate?
This maintains a water potential gradient, by blowing away humid air which accumulates around the stomata.
Define Xerophytes
adapted to living under conditions of low water availability, modified structures to prevents excessive water loss
Define Hydrophytes
Adapted to living in water
Define Mesophytes
Adapted to living with seasonal water availability in temperature areas.
What are the 4 key characteristics of Marram Grass?
.Rolled Leaves
.Sunken Stomata
.Hairs
.Thick waxy cuticle
How are mesophytes adapted for its environment?
.Annual dormant seeds
.Underground corms/ bulbs
.Shed leaves in Autumn
How are hydrophytes adapted for its environment?
.Little/ no lignin .Poorly developed xylem .No cuticle on leaves .Stomata on upper sides of leafs .Large air spaces in stems and leaves
What are the two main cell types in the phloem?
.Sieve tubes
.Companion cells
How are sieve tubes formed?
From parenchyma cells called sieve tube elements stacked on top of each other
What are sieve pores and how are sieve plates formed?
The cell walls at the ends where they join are perforated with ‘sieve pores’ and form sieve plates which allows fluid flows through and cytoplasmic strands to link cells.
What type of cells make up sieve tubes and companion cells?
Living cells - but lack a nucleus and very little cytoplasm or organelles for easier flow.
Where are companion cells found?
Found next to each sieve elements
What is the structure and function of companion cells?
They have very dense cytoplasm containing many mitochondria which provides the ATP for active transport and ribosomes and are very metabolically active.
How are companion cells connected to the sieve elements?
Via the plasmodesmata
What is the structure and function of sieve elements?
Form main conducting tubes for transport of soluble organic products of photosynthesis - sucrose and amino acids - which can flow up and down phloem.
What are the other cell types in phloem?
.Phloem fibres - support role, no transport
.Parenchyma - packing tissue, keeps all phloem elements in place
What is the Mass Flow Hypothesis?
Products of photosynthesis are transported in the phloem away from the site of synthesis ‘source’ to the other parts of the plant where they are used for growth or storage ‘sink’
Describe the ringing experiment?
.In the ringing experiment, a ring of bark is scraped away, this also removes the phloem.
.After a while sugar is trying to be transported down the stem but it is stopped by the ring.
.A bulge of sugar forms above the ring
.This suggests that sugar moves down the stem in the phloem.
What are the specialised mouthparts on aphids called?
Stylets
Why is using aphids beneficial in experiment?
Is more accurate than a human with a syringe an the aphid’s enzymes ensure the stylet doesn’t get blocked
How is radioactivity used to track rapid phloem movement?
- Radio active labelled 14CO2 is placed into a bag surrounding an illuminated individual leaf
- The 14CO2 is incorporated into sugars and transported in the phloem
- Aphids feeding on the sugar in the phloem can be used to trace the movement of the sugar in the plant from source to sink.
What are the steps to autoradiography?
- Radioactive labelled 14CO2 is placed into a bag surrounding an illuminated individual leaf
- The ‘source’ and ‘sink’ leaves are placed firmly on photographic film in the ark for 24 hours. When the film is developed the presence of radioactivity shows up as fogging of the negatives.
- RESULT: sugar transport both up and down the stem.
What are some arguments against mass flow?
.What are the function of sieve plates? Impede flow?
.Companion cells are along the entire length of the phloem, why?
.Sucrose and amino acids move at different rates and different directions in the same tissue, how?
. Phloem has a high rate of O2 consumption/ translocation is slowed/ stopped by potassium cyanide
.Companion cells contain many mitochondria
What are some new theories for plant transport?
.Translocation is active, the loading od sucrose into the phloem.
.H+ ions are pumped out, re-enter by diffusion via a co-transporter which allows entry of sucrose
What are the 7 steps to Active Translocation?
- Hydrogen ions are pumped out of the companion cells
- Hydrogen ions return to companion cell with sucrose down the diffusion gradient. This diffusion occurs through co-transported proteins
- Sucrose diffuses into sieve tube elements through the plasmodesmata
- Water potential inside the sieve tube decreases so water moves into the sieve tube element by osmosis
- Hydrostatic pressure in the sieve tube at the sources increases
- Sugary fluid moves down sieve tubes from higher hydrostatic pressure (Source to Sink)
- Sucrose molecules move from the sieve tube into the surrounding cells by facilitated diffusion or active transport. Sucrose enters root cells (sink) to be used in respiration or to be converted into starch for storage.
- Water moves out of the sieve tube by osmosis. Hydrostatic pressure at the sink drops.
What is the cytoplasmic streaming theory?
Could be responsible for bi-directional movement in individual sieve tubes. Protein filaments pass through sieve pores and suggests that different solutes are transported along different filaments.
