Chapter 6b Transport in plants Flashcards
What is the primary role of the transport system in multicellular plants?
To meet metabolic demands and cope with size requirements and SA:vol restrictions.
What are the metabolic demands that the plant transport system needs to meet?
- Supply of oxygen and glucose to all cells
- Remove waste products of metabolism
- Transport growth plant regulators (‘hormones’)
- Take up and transport mineral ions
What is turgor pressure and its role in plants?
Hydrostatic pressure that provides skeleton support and causes cell expansion.
What is transpiration stream?
Movement of water from roots to leaves via mass flow and transpiration.
What are the main components involved in the transpiration stream?
- Cohesion
- Tension
- Adhesion
What is the role of phloem in plants?
Transports assimilates around the plant.
What substances does xylem transport?
Water and mineral ions (nitrates, phosphates, sulphates, magnesium).
What are the main types of cells found in phloem?
- Sieve tube elements
- Phloem fibres
- Phloem parenchyma
- Companion cells
What unique features do xylem vessels have?
Hollow, dead cells supported by living parenchyma cells.
What are the stages of transpiration?
- Transpiration at the leaves
- Water transport through the stem
- Water uptake in roots via root hair cells
Fill in the blank: Transpiration is the loss of _______ from the underside of the leaf via the open stomata.
[water vapour]
What are the characteristics of monocotyledons?
- Parallel leaf venation
- Fibrous roots
- Single-pored pollen
What are the characteristics of dicotyledons?
- Reticulated leaf venation
- Main tap root with lateral branches
- Three-pored or furrowed pollen
What factors affect the rate of transpiration?
- Temperature
- Light intensity
- Humidity
- Wind speed
- Number of leaves
- Cuticle thickness
- Arrangement of stomata
- Soil water availability
How do guard cells control the opening and closing of stomata?
By changing turgidity through ion and water movement.
True or False: Lenticels require ATP input to facilitate gas exchange.
False
What is the main function of lenticels in plants?
To take in O2 for respiration and remove CO2.
What adaptations do root hair cells have for their role in transpiration?
- Extended cytoplasm and cell wall for increased surface area
- Thin cell wall for reduced distance for water entry
- Higher number of mitochondria for active transport
- Absence of chloroplasts
What is the main function of lenticels?
Take in O2 for respiration and remove CO2
What is the main function of stomata?
Gas exchange for photosynthesis
Why are lenticels necessary for woody stems?
Because stems develop bark which is impermeable to gases
What do both lenticels and stomata have in common?
Carry out gas exchange by diffusion
What is a potometer used for?
To estimate the rate of transpiration
What does a potometer actually measure?
Water uptake and assumes it is related to transpiration
What is the first step in the procedure for using a potometer?
Cut the shoot underwater to prevent air lock
What angle should the shoot be cut at for a potometer?
45 degrees (oblique cut)
What does the rate of air bubble movement in a potometer estimate?
The transpiration rate
Fill in the blank: Volume of water absorbed (mm3) = _______.
πr² x distance moved (in mm)
What is the formula for calculating rate of water uptake?
rate of water uptake (mm3 s-1) = volume of water absorbed (mm3) / time (s)
What is translocation?
Movement of dissolved organic solutes through the phloem
What are the main molecules transported by translocation?
- Sucrose
- Amino acids
What is the main source of sucrose in plants?
Sites of photosynthesis, primarily green leaves and stems
Define ‘sink’ in the context of translocation.
Site of assimilate storage
What are the main sinks in plants?
- Roots
- Meristems
- Developing seeds and fruits
What is phloem loading?
The process of loading sucrose into phloem from source cells
What are the two main routes for phloem loading?
- Symplast route
- Apoplast route
True or False: The symplast route for phloem loading is a passive process.
True
What is the role of protons in the apoplast route of phloem loading?
Protons are actively pumped out and then co-transported back with sucrose
What is phloem unloading?
The process of unloading sucrose from phloem into surrounding tissues
What happens to sucrose during phloem unloading?
- Hydrolyzed into glucose and fructose
- Condensed into starch
What does the mass flow hypothesis explain?
The movement of solutes through the phloem due to pressure gradients
What experimental evidence supports the mass flow hypothesis?
Contents of sieve tubes are under pressure and exude when cut
What is a limitation of the mass flow hypothesis?
Sieve plates may act as barriers to mass flow
How can aphids be used to measure phloem transport?
By extracting sap from phloem at various sites along the plant
What is the significance of using radioactively-labelled CO2 in phloem transport studies?
It allows tracking of sucrose produced and transported in the plant
