Chapter 3: Transport in plants Flashcards
What is the role of the parenchyma in roots?
To store starch
Explain the difference between the role of xylem and phloem
Xylem: Transports water and dissolved mineral salts
Phloem: Transports products of photosynthesis eg. sugars
What is the casparian strip?
Located in the endodermis in the root, the cell wall helps to contain water movement into the xylem
Out of the xylem and phloem, which is on the outside of which?
Phloem
State three characteristics of a xylem vessel
- Transports water and mineral salts
- Transported from roots to leaves and shoots
- Transport is passive and driven by transpiration
- Cells are elongated and tubes are hollow and dead
- Cells are strengthened with lignin
What is the tracheid in the xylem?
Tapered ends with bordered pits that line up to allow water to pass through
Give three features of the sieve tube element in the phloem
- Transports organic solutes eg. glucose
- Sugars are transported from leaves to the roots and growing regions
- Thin cytoplasm, no nucleus and few organelles
- Perforated end wall helps flow (sieve plate)
Give two features of a companion cell in phloem
- Contains a nucleus, cytoplasm and all other organelles
- Connected to sieve tube elements by plasmodesmata
Why are mitochondria particularly important in companion cells?
They provide all the energy requirements for translocation
What is the plasmodesmata?
Gated plant cell wall channels that allow the trafficking of molecules between cells
Give two examples of ions absorbed in roots
Potassium and nitrate
What happens to the water potential in a root when ions are absorbed?
It lowers
What’s the apoplast pathway?
Water passes through the spaces in the cell wall and the cohesive properties of water pulls more along behind it
In three points, what’s the symplast pathway?
- Water passes through the plasmodesmata and into cells, making the water potential higher
- Higher potential adjacent cell = water passes down potential gradient into next cell
- Lowers water potential in first cell so water enters by osmosis from the soil
What’s the vacuolar pathway?
Water passes down water potential gradient through the vacuoles of adjacent cell
How does water enter the xylem?
Water enters endodermis via apoplast pathway - stops going further due to casparian strip
Nitrates are pumped into the xylem by active transport, lowering the water potential
Define transpiration
Consequence of gaseous exchange as water evaporates through the stomata
What are the four aspects of transpiration?
- Osmosis from xylem to mesophyll cells
- Evaporation from the cells into the intracellular spaces
- Diffusion of water vapour out of the leaf via stomata
- Water moves through the plant via the transpiration stream (water lost at the top is replaced by water from the bottom)
What are two unique properties of water and what do they mean?
Cohesive: Water molecules form hydrogen bonds with each other and stick together
Adhesive: Water molecules stick to the side of xylem vessels - the water is pulled up the sides of the vessels
What are mesophyll cells role in gaseous exchange?
- Covered by a thin layer of water
- Gases dissolve in this water as they move into and out of the cells. When the plant is photosynthesising during the day, these features allow carbon dioxide to diffuse into the spongy mesophyll cells, and oxygen to diffuse out of them.
Outline the cohesion tension theory
- Water evaporates from mesophyll cells - lowering their water potential
- Water moves down the water potential gradient
- By the forces of cohesion, continuous columns of water are pulled down from the xylem towards the mesophyll cells
- Water adhesives to the sides of the xylem vessels, forming a continual transpiration stream
In the potometer PAG, why is the shoot cut at an angle?
Prevents the crushing of xylem and increases the surface area
What is a Xerophyte? And give two examples of one, and where they can be located
Plants adapted to living in dry places eg. cactus, marram grass
Places found: Tundra, Deserts
Give three adaptations and their purpose of a hydrophyte
- Thick waxy cuticle - reduces water loss
- Rolling up their leaves - to conserve water
- Hairy leaves - hairs trap a layer of water vapour
What is a hydrophyte? And give two examples of it
A plant adapted to living in fresh water
Outline three adaptations of a hydrophyte
- Stomata mainly on top to maximise gaseous exchange
- Large air sacs to store oxygen and help with buoyancy
- Thin waxy cuticle
What’s a potometer?
A device for measuring loss of water from a plant
In 4 steps, outline the first stage of translocation (loading)?
- Hydrogen ions actively pumped out of companion cell using ATP
- H+ ions return to companion cell through co-transporter protein
- Increased concentration of sucrose in companion cell as it’s co-transported with H+ ion
- Sucrose diffuses into sieve tube, causing water to move into the phloem - increases turgor
Is mass flow passive or active?
Passive
In translocation, outline the process of mass flow
- Increase in hydrostatic pressure causing pressure gradient to build up
- Where sucrose is unloaded = lower pressure at sink
Outline the process of unloading
- Unloaded in sinks
- Sucrose leaves phloem via diffusion
- Invertase breaks down sucrose into glucose + fructose which is either respired or metabolised
- This reduces the solute concentration, increases water potential and helps maintain pressure gradient
