Transport In Plants Flashcards
Function of phloem?
Transports sugars up or down the plant.
What is the apoplast pathway?
The pathway in which water passes through the spaces in the cell walls and between cells.
What is the symplast pathway?
Water enters the cytoplasm through the plasma membrane. Water then passes from cell to cell through the plasmodesmata.
What is the vacuolar pathway?
Water is not confined to cytoplasm but can also pass through vacuoles.
Best conditions for transpiration fast rate?
High light intensity
High temperature
Windy
High water availability in soil.
What will slow down the transpiration rate?
High humidity
Function of xylem?
Transports water and minerals up the plant.
What are the 3 water pathways?
The apoplast, symplast, vacuolar.
How does water move in the apoplast pathway?
By mass flow
What is the plasmodesmata?
The gaps in the cell walls containing cytoplasm that connects one cell to the next.
Which component of the plant cell is partially permeable?
The plasma membrane
What is transpiration?
The loss of water vapour from the aerial parts of the plant, mostly through the stomata in the leaves.
Why does transpiration occur mostly in the day.
The stomata is open for gaseous exchange for photosynthesis during the day
What is the first step of water leaving the leaf?
Water enters leaf through xylem. Moves by osmosis into cells of spongy mesophyll
What is the second step of water leaving the leaf.
Water evaporates from the cell walls of the spongy mesophyll
What is the third step of water leaving the leaf?
Water vapour diffuses through the open stomata.
Why is transpiration essential?
Transports essential minerals up the cell
Maintains cell turgidity
Supplies water for growth, cell elongation and photosynthesis.
Can cool down the plant in a hot day.
Structure of companion cell?
Many organelles particularly many mitochondria for energy for active transport. A companion cell for every sieve tube.
Why does high light intensity speed up transpiration rate?
Stomata are open to allow for gaseous exchange for photosynthesis.
Why do windy conditions speed up the rate of transportation.
Wind carries away water vapour that has diffused out the leaf. This maintains a higher water vapour potential in the leaf.
Why do high temperatures speed up the transpiration rate?
Increase the rate of evaporation from cell surfaces to increase water vapour potential in the leaf.
Increases rate of diffusion through the stomata as water molecules have more kinetic energy.
Maintains a low water potential in the air.
Explain the need for a transport system in multicellular plants.
Small surface area to volume ratio- diffusion would be too slow.
Demand for water and sugars is high- need a transport system to move water and minerals up to the leaves and sugars from the leaves from the rest of the plant. Unable to absorb water from the air and sugars from the roots.
What is the structure of Xylem.
Long tube like structures. No end walls between cells. Dead cells with no cytoplasm. - to allow more space for water. Supported my lignin which strengthens and waterproofs walls.
What are the vascular tissues
Phloem tissues and xylem tissues
What are dicotyledonous plants.
Those that have two seed leaves. The vascular tissue is distributed throughout the plant. The xylem and Phloem and found in vascular bundles.
Structure of phloem?
Contains sieve tubes and companion cells.
Structure of sieve tubes?
Joined end to end by sieve plates. Has pores to allow for ease of flow of solutes. Has no nucleus and thin cytoplasm.
Structure of a root cell?
Long tip, large surface area and lots of hairs.
What is the relationship between soil and leaves?
Soil around roots have a high water potential, leaves have a low water potential.
What is cohesion.
The attraction of water molecules to eachother.
What is adhesion?
The attraction of water molecules to walls of the xylem vessel
What are the steps of xylem to leaf.
Water evaporates in the leaf and diffuses out. There is a low water potential in the lead and a low water potential in the xylem. This crates low hydrostatic pressure which creates suction to pull water molecules to the leaf. Because of cohesion other water molecules follow.
What measures transpiration?
A potometer
What are the steps to measuring transpiration.
Cut shoot under water
Check for air bubbles
Insert shoot into apparatus under water
Make potometer air right and water tight
Dry leaves and allow plant to acclimatise
Measure distance of air bubbles in a set time
What is a xerophyte?
A plant adapted to living in dry conditions.
What are examples of xerophytes?
Cacti and marram grass
Adaptations of xerophytes?
Stomata are sunk in pits. Reduced no. stomata Thick waxy cuticle Hairs on epidermis Curled leaves Spikes instead of leaves Stomatal closure
What is translocation?
The transportation of assimilates around the plant
Describe the first part of active loading?
H ions and actively transported out of the companion cell. Then diffuse back in using a cotransporter protein accompanied by sucrose. The sucrose creates a concentration gradient therefore sucrose moves through plasmodesmata into sieve tubes.
Describe the second part of active loading.
As sucrose enters sieve tubes this decreases water potential. Water moves into sieve tube by osmosis. This increases hydrostatic pressure at the source. At the sink sucrose is being transported to surrounding cells that need it. This increases the water potential so water diffuses out of the sink lowering the pressure. Therefore water a solutes move down the pressure gradient.
What is the evidence for translocation?
Companion cells have many mitochondria. Aphids eat from phloem
Reasons against translocation?
Not all solutes move at the same rate. Sucrose is moved to many sinks.
What is the source?
The site where assimilates are loaded.
What is the sink?
The site where assimilates are removed.
Where is cambium found
In between the xylem and phloem vessel in the stem
Where is the vascular bundle found in the young root?
The centre
Xylem in an X shape
Phloem in between the arms of the X shape
Why is the vascular bundle arranged this way in the young root
To provide strength to withstand pulling forces
What surrounds the vascular bundle in the young root?
Sheath of cells called endodermis which plays a key role of getting water into the xylem vessels
What is found inside the endodermis?
A layer of Meristem cells called the pericycle
Where are the vascular bundles found in the stem?
Near the outer edge
How are the bundles found in non-woody plants?
Separate and discreet
What changes in woody plants as they age?
The bundles become a continuous ring
Why are the bundles arranged this way in the stem?
To provide strength and flexibly to withstand bending forces
How is the phloem and xylem found in the stem?
The xylem is found in the inside and the phloem on the outside
In between the two is a layer of cambium
What do the vascular bundles form in a leaf?
The midrib and veins which get smaller as they spread away from the midrib
How is the xylem and phloem arranged in the midrib?
The xylem is located ontop of the phloem.
What are the patterns lignin can be?
Angular, reticulate or spiral
Describe the gaps in the xylem cell wall?
When lignification is not complete
Bordered pits
Lateral movement from one vessel to the next or to living parts of plant
What is the casparian strip?
An impermeable substance in the endodermal wall which prevents water entering the xylem vessel via the apoplast pathway
Describe the movement of water from the root?
Water moves across root cortex by osmosis to the endodermis of the vascular bundle.
What happens at the endodermis?
Water can travel via the apoplast pathway as far as the endodermis, but then must enter the symplast pathway due to the caspian strip.
How is the water potential maintained in the root?
Mineral ions are actively transported to make the water potential more negetive
Movement of water up the stem processes?
Root pressure
Transpiration pull
Capillary action
Describe root pressure?
Transporter proteins pump minerals into the medulla which draws water in by osmosis. Pressure in the root builds up forcing water up the xylem. Limited only to a few metres up the stem.
Describe the transpiration pull?
Due to cohesion, water molecules are held together in a long chain. As water molecules are lost at the top of the column the whole chain is pulled up. This pull from above creates tension.
Describe capillary action?
Adhesion forces can pull the water up the sides of the xylem vessel.
Adaptations of marram grass?
Leaf is rolled longitudinally to create humidity
Thick waxy cuticle
Stomata are on inner side of the rolled leaf
Stomata are in pits covered by hairs
Spongy mesophyll is dense with few air spaces
Adaptations of cacti
Succulents- store water in stems which can expand when water is available
Leaves are reduced to spines
Roots are widespread
What are hydrophytes?
Plants that live in water
Adaptions of a water lily?
Many large air spaces in leaf- to keep leaf affloat
Stomata are on upper epidermis for air exposure for gaseous exchange
Leaf stem has large air spaces- for buoyancy and to allow oxygen to quickly diffuse to the roots for respiration
How do hydrophytes transpire?
They contain hydathodes at the tips or margins of the leaf which can release water droplets which can then evaporate
