Adaptations for Transport: Plants Flashcards
How are water, mineral ions and organic molecules transported in plants?
In two separate transport system
How many transport systems do plants have?
2 separate transport systems
Why are water and mineral ions transported?
(Transport of water and mineral ions
They are needed by photosynthetic cells
Where are water and mineral ions only available? (transport of water and mineral ions)
In the soil
How are water and mineral ions transported?
transported upwards in hollow tubes (formed by dead cells) called xylem tissue
what is the glucose produced during synthesis used to make? (transport of the products of photosynthesis)
The glucose produced during photosynthesis is used to make sucrose and amino acids (photosynthates)
What are of photosynthates?
sucrose and amino acids
How are the products of photosynthesis transported?
(bi-directional movement)
-These molecules must be moved from the leaves to other organs of the plant (e.g. roots and flowers/fruits/shoot tips)
-The photosynthates are transported upwards and downwards in phloem tissue (bi-directional movement)
what is the distribution of vascular tissue (xylem and phloem) in stems, leaves and roots?
The distribution differs
What is a distribution of vascular tissue in the leaf?
-Leaf has a vascular bundle arranged as a vein or midrib
what does the arrangement of the vascular bundle give the leaf?
this gives flexible strength and resists leaning strain
What are the features of a leaf?
-Cuticle
-Upper epidermis
-Palisade mesophyll
-Spongy mesophyll
-Lower epidermis
-Stomata
-Guard Cells
-Xylem and phloem (vascular bundle)
what is the distribution of vascular tissue in the stems?
vascular bundles arranged around the periphery of the stem
What does the arrangement of the vascular bundles in the stem provide it with?
Provides flexible support and bending strain
What are the functions the vascular bundles in the stem?
-Acts as a site for storage
-provide storage support for the plant
-Provide transportation between roots and leaves
What are the features of a stem?
-phloem and xylem (vascular bundles)
-Cambium
-Pith
-epidermis
-cortex
what is the distribution of vascular tissue in the root?
-Vascular tissue arranged in the centre of the root and together with the endodermis, and the pericycle is called the stele; there are no vascular bundles in the root
What are the functions of the vascular tissue in the root?
-anchors the plant
-Absorb water and mineral ions from the soil
-Act as a site for food storage
-Provides resistant to vertical strain
what are the features of the root?
-epidermis
-Root hair
-Cortex
-Stele (containing xylem and phloem)
-endodermis
-pericycle
how are mineral ions transported (roots)?
-mineral ions such as nitrates are actively transported from the soil into the root hair cells.
what do the mineral ions being actively transported from soil to root hair cells do? (roots)
-This lowers the water potential inside the root hair cells so water enters by osmosis
Why does oxygen enter the roots and what does it provide?
-Oxygen enters the roots from the soil to be used in aerobic respiration, providing ATP for active transport
what do waterlogged soils lack and what does this cause?
-Waterlogged soils, lack oxygen and so plants struggle with uptake of ions in these environmental conditions
what do water and dissolved mineral ions travel through? (uptake of water and mineral ions into the xylem)
the root cells of the cortex to the epidermis down a water potential gradient
what does transport of water across the route occur by? (uptake of water and mineral ions into the xylem)
the symplast appoplast and vascular roots
what is the Apoplast pathway?
-what is taken up by the root hair sale and moves across the cortex by cohesion via cell walls
what is the symplast pathway?
-water moves from the cytoplasm of one cell to the next by osmosis via plasmodesmata
What is the vacuolar pathway?
-water can move via the cytoplasm and vacuoles
what is the process of the uptake of water and mineral ions into the xylem?
The cell walls of all the endodermal cells contain a Casparian strip made of a waxy substance called suberin that is impermeable to water molecules and mineral ions, meaning the apoplast pathway is blocked at this point.
Water and mineral ions from the apoplast pathway are forced across the cell membrane into the symplast pathway.
Active transport is needed to move ions into the cytoplasm of the endodermal cells. Mineral ions then diffuse into the pericycle and then into the xylem.
Therefore, the only way that water and mineral ions can pass through the endodermis to the pericycle and into the xylem is by the symplast pathway.
Water follows by osmosis, down a water potential gradient.
This gives the plant greater control over which ions enter the xylem and are transported to the rest of the plant.
What is root pressure?
-when water moves from the endodermal cells of the root and into the xylem by osmosis this generates hydrostatic pressure and forces water a small distance up the xylem
With reference to role of the casparian strip, how would cyanide result in the reduction in root pressure?
-Casparian strip stops apoplast pathway, so forces ions into symplast pathway
-movement of ions into xylem requires active transport
-Cyanide is a respiratory inhibitor so prevents cells inspiring and stops ATP synthesis
-so lower water potential gradient reduces movement of water in by osmosis thus lowering the root pressure
why does the plant need to control entry of mineral ions into the xylem?
-some minerals are toxic if they are absorbed they can accumulate inside plant tissues (e.g. copper ions)
how does the plant ensure toxic ions cannot enter its cell?
-there are no carrier proteins specific to these ions on the membrane, so these ions cannot enter by facilitated diffusion.
Why do plants need to absorb nitrates from the soil?
required for synthesis of amino acids, proteins, DNA, RNA, ATP, nucleotides, nitrogenous bases
-what are some other mineral ions, absorbed by plants
-potassium ion
-Calcium ion
-Phosphate ion
-Magnesium ion
What are potassium ions required for?
required for stomatal opening
What is the use of calcium ions?
Constituent of cell walls
What is the use of phosphate ions?
Synthesis of phospholipids constituent of ATP
What is the use of magnesium ions?
Constituent of chlorophyll
what are two features of the root hair cells that are adaptations for uptake of water and mineral ions?
-Large SA for absorption of water and mineral ions
-Large numbers of mitochondria (ATP required for active transport of ions)
What is the definition of transpiration?
-transpiration is the evaporation of water from inside the leaves through the stomata and into the atmosphere.
What is the process of a transpiration stream?
-water is absorbed by the root hair cells
-water moves through the root tissue, into the xylem and is transported up the xylem in the plant stem to the leaf
-water is transported by osmosis from the xylem in the leaf to the cells of the spongy mesophyll, where it evaporates from the surface of the cells into the airspaces
-Water vapour then diffuses from the airspaces out of the leaf through the stomata down a water potential gradient
What is cohesion?
-water molecules are attracted to each other by hydrogen bonds
What is adhesion?
water molecules are attracted to the hydrophilic lining of the lignified xylem vessel walls
How does water travel up the xylem to the leaves of the plant?
The cohesion-tension theory (transpiration pull)
What is the cohesion tension theory?
-as water vapour diffusers out of the stomata of the leaf by transpiration, water molecules are drawn up from behind to replace those lost
Water molecules are drawn across the leaf up to the xylem
-This is possible because of cohesion between water molecules due to hydrogen bonds and adhesion between water molecules and the xylem vessel walls
-This upward movement of water creates tension on the xylem vessel walls
what are two other processes that help water move up the xylem a small amount?
-capillarity
-Root pressure
What is capillarity?
-The forces of adhesion and cohesion allow water molecules to rise up narrow tubes for a short distance, which is useful in small plants.
Why is capillarity not useful in large trees?
After a short distance, capillary action is opposed by gravity
What type of plant does root pressure have more effect in?
Small plants
What increases the rate of transpiration?
Any factor that increases the water potential gradient between the water vapour in the leaf and the surrounding atmosphere
What factors increase the rate of transpiration?
-increased light, intensity, temperature and wind speed
-Decreased humidity
How does temperature increase the rate of transpiration?
-A rise in temperature increases the kinetic energy of the water molecules and increases the rate of evaporation and diffusion of water vapour into the atmosphere
-The water potential of the atmosphere is also lower in higher temperatures- this increases the water potential gradient
How does wind (air movement) increase the rate of transpiration?
-still air results in a layer of water vapour around the stomata of a leaf- diffusion shell
-This reduces the water potential gradient between the inside and outside of the leaf
-Air movement blows away the diffusion shell and increases the rate of transpiration from the leaf
how does humidity increase the rate of transpiration?
-The water potential gradient between the inside and outside of the leaf decreases when there is more water vapour in atmosphere
-However, there is usually a steep water potential gradient between the inside of the leaf and the atmosphere as the leaf is saturated with water vapour
how does light intensity increase the rate of transpiration?
-Light causes the stomata to open to allow gas exchange for photosynthesis
how do the factors increasing transpiration (don’t work independently) interact with each other? (e.g. on a dry windy day)
The rate of transpiration will be higher on than on a humid windy day
what does a potometer measure?
the rate of uptake of water by the shoot, which indicates the rate of transpiration
What are the features of a potometer?
-Leaf shoot
-Bung
-granulated scale (mm) along the capillary tube
-beaker of water
-Air bubble
-Reservoir of water
why is the rate uptake on estimate of transpiration rate? (potometer)
Some water is used as a reactant for photosynthesis
how is a potometer set up?
-cut a leafy shoot underwater to prevent the entry of air bubbles into the xylem vessels as these would break hydrogen bonds, affecting cohesion
-completely filled the apparatus with water to avoid introducing air bubbles into the glassware
-Fit the leafy shoot, and seal all joints with Vaseline (petroleum jelly) so apparatus is airtight
-pat the leaves dry otherwise the water potential gradient will be reduced and this could affect the results
-Introduce one air bubble into the capillary tube (open the tap)
-Measure the distance, the air bubble moves along the scale in a specific time
-
How could you calculate the volume of water taken up from the capillary tube per minute?
Pi x rsquared xheight
how could you calculate the total surface area of the leaves and why would this be useful? (potometer)
Draw around the edge of each leaf on graph paper and calculate the total surface area of the leaves. This would allow us to express the results as the volume of water lost per cm2 per minute
how could you improve the reliability of the data collected? (potometer)
repeat to calculate a mean
How is standard deviation calculated?
-calculate the meaning for the data set
-Subtract the mean from each value
-Square each answer
-Add up all the squares
-Divide this total by the number of pieces of data minus 1
-Find the square root of that value
what does xylem tissue do?
-Transport, water and mineral ions
what are the four different types of cell xylem tissue is composed of?
-vessels
-tracheids
-fibres
-xylem parenchyma
what are vessels? (xylem tissue)
-The main cells that conduct water
what do tracheids do? (xylem tissue)
Also conduct water, but less efficient than vessels
what do fibres do in xylem tissue?
-No role in transport (support only)
What is xylem parenchyma? (xylem tissue)
Living tissue
what are vessels? (explained)
-continuous column of dead cells arranged end to end with completely dissolved cross-walls to form long, hollow tubes that transport water from roots to leaves.
what stops vessels from collapsing under pressure? (xylem tissue)
Their walls are thickened with lignin, which is impermeable to water and strengthens and supports the plant
what are tracheids? (explained)
-similar to vessels, but are more elongated with tapering ends
-The cell walls are also thickened and impregnated with lignin
what do both vessels and tracheids having pits in their side walls do?
These allow movement of water between adjacent vessels
What are pits involved in, in tracheids?
They are involved in movement of water to nearby living tissue
why is it important that vessel walls are impermeable to water and solutes?
So water keeps on moving upwards to the leaves in one unbroken stream
Why is lignin being hydrophilic important for xylem function?
-water molecules are attracted to the lignified walls of the Xylem vessels (adhesion)
what does phloem tissue transport?
Sucrose and amino acids
what is four different types of cell is phloem tissue made of?
-Sieve tubes
-Companion cells
-Phloem fibres
-Phloem parenchyma
what do sieve tubes do? (phloem tissue)
transport sucrose and amino acids up/down plant stem
What do companion cells do? (phloem tissue)
connect sieve tubes via plasmodesmata
what are phloem fibres for?
support
What is phloem parenchyma?
Living tissue
what are sieve tubes formed from?
Cells called sieve elements placed end to end
what is the thin cellulose wall at the ends if sieve cells perforated to form?
sieve plates that allow the cytoplasm from one cell to run into an adjacent cell
What runs through sieve plates?
Phloem protein (filaments in cytoplasm)
what do smaller strands of cytoplasm run through? (phloem tissue)
the side walls of sieve tube cells into adjacent companion cells through the plasmodesmata
what do companion cells not transport but provide?
-they don’t transport organic materials but they have a nucleus and they provide ATP for active transport of sugars into/out of the sieve tubes
-This is important since the sieve tube cells lose their nucleus and other organelles as they mature (eg mitochondria)
what are three ways in which sieve tube elements are adapted to their function?
•Few organelles (no nucleus, few mitochondria) – more space for transport of solutes
•They have companion cells (with organelles for metabolism, e.g ATP synthesised by mitochondria)
•End walls perforated (sieve plates) to allow passage of dissolved solutes (sucrose , amino acids)
what is translocation?
The transport of soluble organic materials produced by photosynthesis (e.g. Sucrose and amino acids in the phloem)
What are photosynthates?
-Substances that have been made in the plant
What is the movement of the molecules in translocation?
-movement of these molecules is bi-directional, i.e may be downwards (e.g. from the root or upwards e.g. from the leaves to the roots and shoot tips.)
What is the liquid inside the phloem tubes called?
Sap
what is the source? (translocation)
-The region, where the products of photosynthesis (photosynthates) are produced and exported
what is the sink? (translocation)
The region where the products of photosynthesis (Photosynthates) are stored or used for growth.
what is a source region?
Leaf
what is the sink region?
root, shoot tips. flower, fruits, seeds
what is evidence for translocation in the phloem?
-Ringing experiments
-Aphid experiments
-Radioisotope labelling
what are ringing experiments?
-Removal of a ring of outer bark tissue from a woody stem removes the phloem
-Analysis of the phloem contents just above and below show that organic compounds cannot be transported past the region where the bark has been removed
why is a bulge seen during ringing?
due to accumulated phloem sap that cannot move any further
What does the result of the ringing experiment show?
-as the phloem is round the periphery under the bark, transport of sucrose must be from above i.e. Being transported downwards.
what are aphid experiments?
Aphids are small insects that can be used to collect the contents of individual phloem sieve tube cells. Aphids, such as greenfly, have specialised mouthparts called stylets which they use to penetrate sieve tubes in order to feed on the sugary sap inside. If the aphids are anaesthetised with carbon dioxide, the stylet can be cut off and left in the stem. This means pure phloem sap can be collected through the stylet for analysis. This technique is more accurate than a human with a syringe/needle as the aphid’s enzymes ensure that the stylet doesn’t get blocked.
What is the mass flow hypothesis?
-main theory to explain translocation
-Sugars flow, passively from areas of high concentration in the leaf (source) to areas of low concentration e.g rowing tissue (sink) down the pressure gradient
How does the mass hypothesis work?
-sucrose made in photosynthesis is loaded by active transport into the sieve tubes using ATP
-Water enters the sieve tubes along a water potential gradient by osmosis
-The pressure in the sieve tubes increases and the sucrose moves down a pressure gradient through the phloem towards the sinks
-sucrose is unloaded by active transport into the cells at the sinks
-Water moves by osmosis out of the phloem as the sucrose is removed and the pressure in the phloem tissue becomes lower at the sink
what does the mad flow theory not do?
-The mass flow theory does not explain the observations that sucrose is transported in sealed tubes at the rate of 25-100 cm per hour
-Diffusion alone would give a transport rate of 0.2 mm per day
What are arguments against mass flow theory?
-No explanation of sieve plates which seem to act as barriers to flow.
-sucrose and amino acids have been observed moving at different rates and directions
-The companion cells are found all the way along the sieve tubes(not just the source and sinks) and continue numerous mitochondria for the production of ATP (energy). If companion cells purely load and unload photosynthates from sieve tubes they would not be needed anywhere but sources and sinks
-Therefore an active process within sieve tubes may be involved
What are alternative theories for the mass theory?
-streaming in the cytoplasm of sieve tubes could be responsible for bi-directional movement
-Protein filaments have been observed passing through the sieve pores, suggesting different solutes are transported by different filaments
what are mesophytes?
-Most plants in temperate regions, and most crop grown plants
where do mesophyes to grow best in?
They grow best best in well drained soils and moderately dry air
what plant behaviours allow mesophytes to survive at unfavourable times of the year?
-deciduous trees shed leaves in autumn to surviveunfavourable conditions over winter, new leaves the grow in spring
-bulbs and corms produced by non- woody plants to survive underground over winter
-Annual plants provide seeds and die in the same year, seeds survive, winter frost and germinate the next spring when conditions are more favourable
What are bulbs and corms?
-storage organs
what are hydrophytes?
Water plants that live submerged, or partially submerged in water (e.g. a water lily)
what are the features of a hydrophyte?
-Stomata on the upper epidermis
-Large air spaces
-Thin/no waxy cuticle
-poorly developed xylem tissue
-little lignin
Why do hydrophytes have stomata on the epidermis?
to allow gas exchange with the air above
why do you hydrophyte have large air spaces?
To provide buoyancy for the leaves and act as a reservoir of oxygen and carbon dioxide
Why do hydrophytes have poorly developed xylem tissue?
no need to transport large quantities of water as plants is aquatic
why do hydrophytes have little lignin?
water is a supportive medium and so little lignin is required to support the xylem tissue
what conditions are xerophytes adapted to?
Conditions of low water availability
where do xerophytes live?
in hot, dry desert conditions, regions where soil is frozen for much of the year, or exposed windy locations
what is marram grass?
-a xerophyte that specialises in living on sand dunes
What are features of marram grass? (xerophytes)
-sunken stomata (in pits)
-Hairs on surface of the leaf
-Thick cuticle
-rolled leaves
-reduced leaf size/spines
why do xerophytes have sunken stomata?
-Water vapour is trapped in the pits
-this decreases the water potential gradient between the inside and outside of the leaf
-therefore less water is lost by transpiration
why do xerophytes have hairs on surface of the leaf?
-what is a vapour is trapped between the hairs
-This decreases the water potential gradient between the inside and outside of the leaf
-Therefore, less water is lost by transpiration
why do xerophytes have rolled leaves?
-stomata are less exposed to the atmosphere
-Water vapour is also trapped and saw the water potential gradient between the inside and outside of the leaf decreases
-Less water is therefore lost by transpiration
why do xerophytes have reduced leaf size/spines?
-Reduces the surface area from which transpiration can occur
What are the xerophytic the adaptations of cacti?
-Store water in succulent stems
-Leaves are reduced to spines to reduce the surface area of a transpiration
-thick waxy cuticle
-Shallow spreading roots or long, deep roots to maximise water absorption from soil
why do pine trees have needle-like leaves?
-Greatly reduces SA of leaf available for water loss by transpiration.
-Many species (eg in Canada, alaska where ground may be frozen) have sunken stomata and thick waxy cuticle to reduce water loss
Why do many xerophytes open stomata at night and close them during the day?
To conserve water
What is casparian strip?
an impermeable barrier in the endodermis formed from suberin which blocks the the appoplast pathway
