Transport in Plants Flashcards
do multicellular plants have a high or low surface area to volume ratio?
They have a low surface area to volume ratio
Does the volume increase more rapidly than the surface area increases in size?
Yes
Why can’t multicellular organisms rely on diffusion alone for the transport of molecules?
Because they have a low surface area to volume ratio
What are the products of photosynthesis?
Oxygen and glucose
What are the reactants used in aerobic respiration?
Oxygen and glucose
What is the metabolic rate of an organism?
the amount of energy expended by that organism within a given period of time
How can the metabolic rate of an organism be measured?
-Oxygen consumption
-Carbon dioxide production
-Heat production
The higher the body mass, the higher the what?
The metabolic rate
What different apparatus can be used to measure the metabolic rate in organisms?
-Respirometers
-Oxygen/carbon dioxide probes
-Calorimeters
What 4 things do effective exchange surfaces have?
-A large surface area
-Short diffusion distance
-Good blood supply
-Ventilation mechanism
What is the nitrate ion used by plants to make?
Amino acids
What are the 2 mass transport systems in plants?
The xylem and the phloem
Can plants transport hormones from where they’re synthesised to their target tissues?
Yes
What is the embryonic seed in leaves called?
Cotyledon
What happens to the cotyledon when a seed germinates?
The cotyledon unfurls, allowing the seed to carry out photosynthesis
What is an example of a plant that only has one cotyledon?
Grass
What are plants with only one cotyledon called?
monocotyledonous
What are plants with 2 cotyledons called?
dicotyledonous
What is an example of a plant that has 2 cotyledons?
Trees
Are trees and shrubs examples of woody dicotyledonous plants?
Yes
describe woody dicotyledonous plants?
They’re long-lived and have a woody stem
are geraniums examples of woody dicotyleonous plants?
Yes
Describe herbaceous plants
they’re often fast growing and can be short-lived. unlike woody plants, they don’t have a woody stem
What are the 2 different transport systems in plants?
The xylem and the phloem
What does the xylem do?
it carries water and mineral ions from the roots of the plant up the stem to the leaves
what does the phloem do ?
The phloem transports organic molecules around a plant , from the source to the sink
are the xylem vessels and phloem vessels grouped together in vascular bundles?
Yes
is the arrangement of the vascular bundles the same in the roots, stem and leaves, or different?
Different
What is the centre of the root called?
The stele
In the roots where can the vascular bundle be found?
In the centre of the root (the stele)
where do the root hair cells in a root grow from?
A layer of external tissue called the epidermis
What does the cortex contain?
parenchyma cells
What is the vascular bundle in the root surrounded by?
A layer of cells called the endodermis
In the vascular bundle in the root, are the xylem vessels or phloem vessels in the centre of the root?
The xylem vessels are in the centre of the vascular bundle. (The phloem vessels surround the xylem)
how does the fact that xylem vessels are mechanically strong help the plant (in the root) ?
The xylem vessels are grouped together in the centre of the root and this prevents the root from being pulled out of the soil by strong winds
are xylem vessels mechanically strong?
Yes
how is the vascular bundle arranged in the stem?
The vascular bundles are arranged in a ring around the edge of the stem
What is the centre of the plant stem called?
The pith, which consists of parenchyma cells
What does the pith consist of?
parenchyma cells
What’s around the edge of the stem?
The epidermis and the cortex
in the vascular bundle in the stem, where is the phloem found?
around the edge of the stem
in the vascular bundle in the stem, where is the xylem found?
closer to the centre of the stem
What does the vascular bundle being closer to the edge of the stem help with?
helps the stem to withstand bending due to the wind
where in a leaf is the vascular bundle found?
In the midrib. This helps with transport in the leaf and helps support the leaf
is the leaf also supported by smaller vascular bundles connected to the main one?
Yes
in the vascular bundle of a leaf, where is the xylem found?
at the upper part of the vascular bundle
in the vascular bundle of a leaf, where is the phloem found?
at the lower part of the vascular bundle
Where in the plant does photosynthesis take place?
In the palisade mesophyll, which is in the upper halp of the leaf
What are the 2 main tissues does the xylem consist of?
Tracheids and xylem vessel elements,which are both types of water- conducting cells
What 4 tissues does the xylem consist of?
-Tracheids (long, narrow tapered cells with pits)
-Xylem vessel elements (large with thickened cell walls and no end plates when mature)
-Xylem parenchyma
- Sclerenchyma cells (fibres and sclereids)
What is the function of the xylem?
To carry water and dissolved minerals up the plant from the roots to the leaves
what is the function of lignified cell walls in the xylem vessel elements (mature cells)?
Adds strength to withstand the hydrostatic pressure so that the vessels don’t collapse
what is the point of xylem vessel elements having no end plates?
This allows mass flow of water and dissolved solutes as cohesive and adhesive forces aren’t a barrier
what is the point of the xylem vessel elements having no protoplasm?(with organelles)
The organelles don’t get in the way of the mass flow of water and dissolved solutes (the transpiration stream )
what is the point of xylem vessel elements having pits in their walls?
This allows for the continual flow of water, in the case of air bubbles forming in the vessels
why do the xylem vessel elements have a small diameter
Lignin is impermeable so…
it stops substances from passing through the cell wall
Can lignin be arranged in spirals and in rings?
Yes. They can also be continuous, apart from the pits
What does lignin do?
It helps support the structure of the xylem vessel
What happens when water is pulled up the xylem vessels?
Pressure in the vessels falls slightly. The lignin in the vessel walls helps to prevent the vessels from collapsing
What are xylem fibres formed from?
Long, narrow cells
Are large or small amounts of lignin found in xylem fibres?
Large amounts
Are xylem fibres used to transport water?
No
What are xylem fibres used to do?
To provide mechanical support to the plant
are xylem vessels living tissue or non living tissue?
Non-living tissue
are xylem fibres living tissue or non living tissue?
Non-living tissue
do the xylem also contain parenchyma cells?
Yes
What do the parenchyma cells in the xylem do?
They act as a store of starch. They can also deter herbivores from eating the plant.
why is it good that they xylem vessel elements has no end plates?
Because this allows the mass flow of water and dissolved solutes as cohesive (between water molecules) and adhesive forces (between water molecules and the walls) aren’t impeded.
how does the xylem vessel elements not having any protoplasm (cells are dead when mature) help the xylem?
because it doesn’t impede the mass flow of water and dissolved solutes (transpiration)
how does the xylem vessel elements having pits (non lignified sections) in the xylem walls help the xylem?
helps with the lateral movement of water and allows for continual flow in case of air bubbles forming in the vessels
What cells are the xylem made from?
Tracheids, Vessel elements, Xylem parenchyma, fibres
Can organic substances(glucose) be transported both up and down the phloem ?
Yes
What is the fluid moving in the phloem referred to as?
Phloem sap
Is phloem made up of living or dead tissue?
Living
What 2 different tissues does the phloem consist of?
Sieve tube elements and companion cells (also parenchyma for storage and strengthening fibres)
How are the sieve tube elements in the phloem arranged?
They consist of a long line of cells arranged end to end
What do the insides of sieve tube elements look like?
Almost all of the organelles have been lost , including the nucleus and the vacuole
Why do sieve tube elements have almost no organelles?
So that they have enough space to transport phloem sap and assimilates
Why are the end walls of sieve tube elements modified to contain large pores called the sieve plate?
to allow for the continuous movement of organic molecules
Why can’t sieve tube elements produce large amounts of essential molecules such as ATP?
because they’ve lost almost all of their organelles
what organelles do companion cells contain?
A nucleus and large amounts of mitochondria
why do companion cells have a large amount of mitochondria?
To provide ATP for the active transport of assimilates into or out of companion cells
What links the companion cell to the sieve tube elements?
The plasmodesmata
What is the role of the companion cells?
to provide essential molecules to the sieve tube elements cells.
why do companion cells have transport proteins in their plasma membrane?
To move assimilates in and out of the sieve tube elements
why do the sieve tube elements have a companion cell associated with it?
Because companion cells control the metabolism of the sieve tube element it’s associated with
Does the phloem have lignin in the cell walls?
No
What tissues does the phloem contain to provide it with support?
Fibres and sclereids. Both of these have thickened cell walls containing lignin
Describe the structure of fibres
they’re long and narrow
describe the structure of sclereids
they have a variety of shapes
where on the root hair cell do root hairs grow?
from the epidermis of the root hair cell (the outer layer)
does water move into the root hairs via osmosis or via active transport?
Osmosis
How do the densely packed root hairs increase the rate of osmosis into the root hair cells?
The root hairs increase the surface area to volume ratio of the root
How does the fact that the surface of the root hair only consists of the cell wall and cell membrane increase the rate of osmosis into the root hair cells?
Because this makes the surface extremely thin and this provides a short diffusion path
What mechanism do the root hairs use to increase the rate of osmosis?
Actively transport mineral ions, such as magnesium, into the root
Is the water potential inside the root hair cell higher or lower than the water potential in the soil?
The water potential inside the root hair cell is lower than the water potential inside the soil
Why does water move into the root hair cell via osmosis?
Because the water potential inside the root hair cell is lower than the water potential in the soil and water moves down a water potential gradient.
Where does water move after it has entered the roots?
From the root hair cells through the root cortex and to the xylem
Which 2 pathways can water move through the cortex?
the symplast pathway and the apoplast pathway
Describe the symplast path way in the roots
water moves from the cytoplasm of one cell to the cytoplasm of an adjacent cell. To do this, water moves through the plasmodesmata that links the adjacent cells. (osmosis )
What is the plasmodesmata?
Microscopic channels through the cell wall that connects the cytoplasm of cells
What is the symplast pathway drive by?
the water potential gradient between the root hair cells and the xylem
is the water potential of the root hair cells greater than the water potential of the cortex cells?
yes
is the symplast pathway quick or slow?
relatively slow
why is the symplast pathway relatively slow?
because the pathway for water in the cytoplasm is obscured by the organelles
describe the apoplast pathway in the roots
water moves between cell walls and the spaces between the cells by diffusion
what is the idea that water molecules are attracted to each other called?
Attraction cohesion
Why does attraction cohesion occur?
Because water molecules can form hydrogen bonds with each other and as water moves into the xylem and is carried away, more water moves along the apoplast pathway due to cohesion
which offers the least resistance to water flow- the symplast system or the apolast system?
The apoplast system
what runs around the cell wall of the endodermis of the root?
The casparian strip
What is the casparian strip?
waterproof and prevents water from moving through the apoplast pathway. Instead the water moves through the symplast pathway. This allows the cell membrane to control which substances can enter the xylem
What do cells in the endodermis of the root hair cell use to pump mineral ions into the xylem?
active transport
What happens when cells in the endodermis of the root hair cell pump mineral ions into the xylem?
the water potential of the xylem is lowered and water is triggered to move into the xylem by osmosis
Is root pressure an active or passive process?
It’s an active process, requiring energy from respiration
what happens to root pressure when you inhibit respiration using a metabolic poison such as cyanide OR when you prevent aerobic respiration by excluding oxygen?
Root pressure stops
How does water reach a leaf?
Through the xylem vessels in the vascular bundle
What does the waxy cuticle do?
It reduces water loss from the surface of the leaf by evaporation
What are the reactants in photsynthesis?
Carbon dioxide and water
What can be found on the lower surface of a leaf?
The stomata
What are the surface of the cells in a leaf covered by?
A thin layer of water. This water evaporates from the surface of the cells and because of this, the internal leaf spaces contain a high concentration of water vapour
what is the pulling effect of water on xylem vessels called?
Tension
what is the transpiration stream?
The movement of water from the roots, up the xylem and out of the leaf
Can water form hydrogen bonds with molecules in the xylem vessel walls such as carbohydrates?
Yes and this attraction is called adhesion
What is one effect of adhesion and cohesion with relation to xylem vessel?
Water can move up very thin tubes against the
What is one effect of adhesion and cohesion with relation to xylem vessel?
Water can move up very thin tubes against the forces of gravity- capillary action
What is capillary action?
When water moves up very thin tubes against the forces of gravity due to adhesive and cohesive forces
What can be used to measure the rate of water uptake into a plant?
A potometer
What does a potometer consist of?
A fine capillary tube which is filled with water. The tube is connected to a plant which has been cut at the stem. The capillary tube is also connected to a syringe filled with water.
How can you measure the rate of water uptake by a plant using a potometer?
By measuring how far the air bubble moves in a given time
What are the 2 types of ptometer?
A bubble potometer and a mass potometer
What are the 2 advantages to using a mass potometer?
- The mass potometer directly measures the rate of transpiration rather than the rate of water uptake
- Much less disruptive to the plant as it does not involve cutting the stem
what is a singular stomata referred to as?
Stoma
What is each stoma surrounded by?
2 guard cells
What are the 2 key features of guard cells?
the cellulose cell wall on the inner side of the guard cell is thinker than on the rest of the cell, and some of the cellulose microfibrils in the cell wall are arranged in ring shapes
what do light conditions trigger to move into the guard cells?
solutes such as the potassium ion K +. This lowers the water potential of the interior of the guard cells.
What happens after light triggers solutes to move into the guard cell?
Because the water potential of the guard cell has been lowered, water now moves into the guard cells by osmosis and this causes the guard cells to swell. The guard cells are now turgid
What prevents the guard cells from expanding widthwise when water enters?
The rings of cellulose. So the guard cells expand lenghtwise instead
Why are the guard cells curve shaped?
Because the thickened cell walls prevent the guard cells from expanding evenly.
What factors does the rate of transpiration depend on?
Light intensity, humidity,
what does relative humidity tell us?
The concentration of water vapour in the air as a percentage of the maximum possible
does increasing humidity of the air outside of a leaf increase or reduce the rate of transpiration?
Decreases the rate of transpiration because there’s a smaller concentration gradient and so there’s no net loss of water vapour from the leaves
why does increasing the temperature increase the rate of transpiration?
Because at higher temperatures, water molecules have more kinetic energy. So, molecules will move faster out of the leaf
why does air movement, such as wind, increase the rate of transpiration?
because air movements increase the concentration gradient of water vapour
Why can the rate of transpiration also be affected by the level of water in the soil?
Because in drought conditions, the root of a plant produces a hormone. This hormone triggers the stomata to close . this reduces the rate of transpiration and reduces water lost by a plant
what are xerophytes
plants which are adapted to hot, dry conditions
What are 2 examples of xerophytes?
Cacti and marram grass
why do cacti have spines?
-because this reduces the surface area to volume ratio of the cactus and so reduces the rate of diffusion of water from the plant.
- The spines also trap moist air near the cactus, reducing the humidity and the rate of transpiration
what does sunken stomata help with?
This traps a layer of moist air around the stomata, reducing humidity, and decreasing rate of transpiration
why do cacti have extensive shallow roots?
because this allows the cacti to absorb water after it has rained before the water evaporates. this may also allow the cacti to absorb water from lower levels of the soil
why do cacti have extensive shallow roots?
because this allows the cacti to absorb water after it has rained before the water evaporates
what are plants that can store water in their stem called?
Succulents
where is marram grass found?
In sand dunes
how is water availability in sand dunes?
Scarce
where are the stomata in maram grass found?
In sunken pits, with fine hairs projecting inwards towards the centre, ensures that moist air is trapped around the stomata, reducec conc gradient
what is glucose converted to?
The dissacharide sucrose
which is more reactive- glucose or sucrose?
Glucose
what are molecules such as sucrose that are made as a result of photosynthesis called ?
Assimilates
what transports assimilates around the plant?
The phloem
what is the transport of assimilates around a plant called?
Translocation
assimilates are transported from sources to what?
Sinks
What are sources?
Where the assimilates are produced
what are examples of sources?
Photosynthesising leaves and storage organs e.g tubers
what are sinks?
Regions where assimilates are required
What is an example of a sink?
The roots and shoots
Why are the roots an example of a sink?
Because the roots carry out active transport and require the assimilate glucose for respiration
When can storage organs act as sinks?
When they’re refilling their carbohydrate stores
Does the volume increase more rapidly than the surface area increases in size?
Yes
How can the metabolic rate of an organism be measured?
-Oxygen consumption
-Carbon dioxide production
-Heat production
