Module 3 - Transport in plants Flashcards
How many transport systems are there in a plant?
Two transport systems
What are the two type types of transport systems?
- Xylemn vessels
- Phloem vessels
What do xylem vessels transport?
They transport water and minerals from root to other plants.
What do phloem vessels transport?
They transport sugars (sucrose) and amino acids made in leaves to all other parts of the plant
what does it mean that most plants are dicotyledenous?
They have 2 seed leaves when they germinate
What does cotyledon mean in plants?
It refers to the first seed leaves present in the embryo
where can gases diffuse in and out of the plant?
gases can diffuse in and out of the plant via the stomata
why do gases diffuse fast in the stomata?
- Leaves are thin and have a big surface area
- fast enough to meet the demands of the leaf cells for oxygen (respiration) and carbon dioxide (photosynthesis)
Can gases diffuse in and out of root hair cells?
- Yes
- they are adapted to have a large surface area in order to achieve this
Do plants have high oxygen requirements than plants? why?
- No
- They are not as active animals
- so they do not need high rate of respiration
Do plants need specialized transport systems?
- yes
- to deliver water, mineral ions and organic solutes to different cells and tissues.
How does water move from the root hair, across the root, up stem, into leaf and evaporate out of the stomata?
- water moves along a water potential gradient through the plant.
- from regions of higher water potential to regions of lower water potential, starting in the root hair cells
- it eventually leaves the plants by evaporating as vapour from the stomata into the air.
What is a transpiration stream?
the movement of water up the plant
what is transpiration?
The evaporation of water vapour from the stomata.
How does water move across the root?
- Mineral ions move into the root hair cells by a combination of facilitated diffusion and active transport
- lowering the water potential inside the cells
- water then moves from the soil into the root hair cell by osmosis due to water potential gradient
what is osmosis?
Osmosis is the movement of water molecules from an area of higher water potential to an area of lower water potential across a selectively permeable membrane.
what is the apoplastic pathway?
Water moves from cell to cell through the cellulose cells walls.
what is the symplastic pathway?
water moves from cell to cell through the cytoplasm then via connections from one cytoplasm to another.
what is a casparian strip?
Water molecules move across the cortex using both of these pathways until it reaches the Endodermis of the root, forming a casparain strip
what happens if the apoplastic pathway is blocked>
- water cannot pass through this, so water has to cross the endodermal cells using the symplast route only
- this slows down the flow of water slightly, and gives the plant some control over which mineral ions pass through
where does water move up?
- the stem
- water will be carried up all the way up the leaves via the xylem vessels inside the cell
what is xylem tissue made up of?
- made up of xylem vessel elements, stacked end to end forming xylem vessels
are xylem living?
- they begin as living cells
- they differentiate and lose all of their contents and lose their end walls to become continous hollow tubes “non-living”
- these vessels are very narrow
what is inside the cellulose cell walls?
- Lignin
what is lignin?
a very strong and waterproof substance
what is there is the walls of the xylem vessels?
Tiny holes called pits in the walls of the xylem vessels
what are pits?
they allow water move water sideways into neighbourings vessels if there are any blockage/air locks
what is the mechanism by which water moves up the stem?
- when water moves across the root, it was the movement of individual molecules from cell to cell by osmosis
- it moves into the xylem vessels in the stem, by osmosis
- when water moves up the xylem in the stem, it acts as a whole column for of water together - mass flow
what is mass flow?
when water moves up the xylem in the stem, it acts as a whole column for of water together
Describe root pressure?
- low water potential inside the root cell
-water continuously enters the root, it creates a pressure - this contributes a small amount to the water entering the xylem vessels of the stem and moving upwards
describe cohesion force?
- water molecules are polar, they have a slight charge difference, attract each other and form hydrogen bonds between them
- water molecules start to move up a xylem vessel, they will attract further
-water molecules to pull behind then due to cohesion forces and hydrogen bonding - causes water to be pulled upwards against gravity as a column being stretched
describe adhesion forces?
- water molecules are attracted to different molecules
- hydrogen bonds form between the molecules
- these forces allow water molecules to crawl up the sides of the xylem vessels are so narrow.
- xylem vessels are so narrow it means more of the water molecules inside are in contact with the walls, increasing the effect
what is the capillary effect?
xylem vessels are so narrow it means more of the water molecules inside are in contact with the walls, increasing the effect
what actually moves water up the plant?
- what actually moves water up the plant is evaporation of water vapour the stomata of the leaves
is water transport passive or active?
- passive
- no ATP is needed
what is cohesion?
water molecules stick together because they are polar
what is the signiicance of them being non-living?
no cell walls between cells
explain the cohesion tension theory
- transpiration if water through stomata
- creates low pressure of the top of the xylem
- water in the xylem is pulled up creating tension
- because water molecules stick to each other - cohesion
- water molecules are sucked up to the leaves
what are the factors affecting the rate of transpiration?
- temperature
- light
- humidity
- wind
how does temperature, increase the rate of transpiration
- Higher the temperature, increases rate of respiration
- more kinetic energy
how does light, increase the rate of transpiration?
more stomata opens when there is more light
- increases rate of transpiration
how does humidity and wind increase the rate of transpiration
- affects the water vapour gradient
- the steeper the vapour gradient (dry or windy), the faster the rate of transpiration
what type of tubes are the xylem made up of?
- hollow tubes made up of dead cells
Give some adaptations of xerophytes?
- they grow in dry habitats
- have thicker cuticles
- reduced leaf surface area
- few, sunken stomata
- rolled leaves
Give some adaptations of hydrophytes?
- grow in or on water
- little or no waxy cuticle
- large, flat leaves
- minimal root systems
- air pockets to aid flotation and flexible stems
What are xerophytes
They grow in dry habitats
What are hydrophytes ?
They grow in or on water
How could you investigate transpiration ?
Using a potometer
How does a potomter work?
A cut leafy shoot is connected to a rubber tube, and a graduated capillary tube, with a water reservoir in between. The rate of water uptake is measured by the distance the bubble travels in the capillary tube, which we assume is equivalent to transpiration rate.
What type of cells is the xylem made from?
is made from dead lignified cells that form continuous tubes.
What are the pits of the xylem?
They connect one xylem vessel to another to allow lateral water movement.
How does water move through the xylem?
Water moves from the soil into the root hair cells by osmosis, then moves through the root to the xylem vessel. Water evaporates from the leaves, and surface tension causes cohesion between water molecules (cohesion-tension theory) which pulls other water molecules up the stem. Water also adheres to the side of the xylem vessels, creating a continuous transpiration stream.
How does the apoplast pathway and casparian pathway relate?
The apoplast pathway is stopped by the Casparian strip which is found in the endodermal layer of the root. This causes all water to enter cells to travel further through the plant.
What is apoplast?
Water travels between cells
What is symplast?
Water enters cells
What is vaculolar?
Water passes through the cell vacuoles
How does the loading of sucrose occur?
• At a source - usually a photosynthesising leaf - sucrose is loaded into the phloem.
• The companion cells use proton pumps to pump out hydrogen ions, using ATP, creating a higher concentration of hydrogen ions outside the companion cell.
• A co-transporter protein in the companion cell membrane then transports these hydrogen ions back into the cell in conjunction with sucrose molecules.
• Sucrose then diffuses from the companion cell into the sieve tube elements via plasmodesmata.
• Water moves via osmosis from the companion cell to the sieve tube elements, due to the water potential gradient set up by the movement of sucrose into the sieve tube elements previously.
How does the unloading of sucrose occur?
At a sink - for example, a root - the sucrose moves out of the sieve tube elements by diffusion.
• The concentration gradient is maintained by converting sucrose into glucose and fructose.
• This loading and unloading causes mass flow through the phloem via hydrostatic pressure and a pressure gradient.
What is the structure of the Phloem?
Phloem is made up of living cells called sieve tube elements, which have perforated cell walls, called sieve plates, between them and companion cells beside them.
Is phloem made up of the living or dead cells?
Living cells
What are the companion cells of the phloem?
Companion cells regulate the movement of solutes and provide ATP for active transport. Strands of cytoplasm called plasmodesmata connect the sieve tube element and companion cell.
What is translocation of the phloem?
Plants transport sucrose and other substances from sources (e.g., leaf cells) to sinks (e.g., roots, meristem).
What is translocation of the phloem?
Plants transport sucrose and other substances from sources (e.g., leaf cells) to sinks (e.g., roots, meristem).
How are the phloem and xylem arranged ?
In vascular bundles
Do the roots have a single or double vascular bundle?
Roots have a single vascular bundle, which branches into a separate arrangement of tubes up the stem, further branching into veins of xylem and phloem in the leaves.
What is the structure and supporting tissue called?
Cortex
