Plant Systems Flashcards
What does the phloem tissue transport?
Organic products- sugar
Dissolvable products of photosynthesis
From the leaves to other parts of the plant
What do xylem tissues transport?
Water
Dissolved minerals
From the soil -> roots -> stem -> leaves
Define mass transport
The movement of materials over a large distance due to pressure differences
Describe the structure of the xylem
Hollow
Made up of dead cells = hollow lumen with little resistance
Strengthened by lignin = waterproof and strength against tension
No end walls = continuous column of water movement
Define transpiration
Evaporation of water from the stomata in the leaves
Factors that affect the rate of transpiration
Windspeed
Humidity
Temperature
Light Intensity
How does windspeed affect the transpiration rate?
Positive correlation
Pushes air containing water vapour away from stomata
Maintains water potential gradient
How does humidity affect the transpiration rate?
Negative correlation
Air containing more water vapour
Decrease the water potential gradient
How does temperature affect the transpiration rate?
Positive correlation
Molecules have more kinetic energy so move faster
More water evaporation
How does light intensity affect the transpiration rate?
Positive correlation
More stomata are open due to increased photosynthesis
Provides a larger surface area for evaporation
Describe the mass flow theory (source)
Sucrose is actively transported from source -> companion cells-> phloem (active loading)
(Requires ATP and carrier proteins)
High sucrose concentration/ low water potential = water moves from xylem to phloem via osmosis (hwp-> lwp) = high hydrostatic pressure due to high volume of water
Describe the mass flow theory (sink)
Sucrose is actively transported from phloem -> companion cells -> source (active loading)
(Requires ATP and carrier proteins)
Low sucrose concentration/ high water potential = water moves from phloem to xylem via osmosis (hwp-> lwp) = low hydrostatic pressure
Pressure gradient created = substances will travel from a high pressure to a lower pressure
Why is glucose converted into sucrose?
Sucrose is less reactive than glucose
Won’t be chemically altered
Why is it necessary to transport sucrose and amino acids from one part of the plant to another?
Only leaves photosynthesise to produce sugars
The rest of the plant require sugars for respiration
Amino acids are required for protein synthesis
Structural features of the phloem tissue
1) Sieve tube element links to next via sieve plate which is perforated with pores
2) Sieve tube has little cytoplasm, no nucleus, no vacuole and few organelles = easier flow
3) Sieve tubes are alive due to plasmodesmata
4) Companion cells contain a nucleus, many mitochondria and other organelles
Define sink
Where organic solutes (sugar) are used up and therefore at a low concentration
Define source
Where organic solutes are made
High concentration of organic solute
Define hydrostatic pressure
The pressure exerted by the volume of water
Where is ATP produced for the active transport of sucrose?
Produced in companion cells
Name 4 xerophytic adaptations
Trapped humid air in air spaces
Thick waxy cuticle
Hairs on lower epidermis
Stomata sunken in pits
How does trapped humid air in air spaces reduce the rate of transpiration?
Reduces the water potential gradient between the air spaces and the atmosphere so less diffusion
How does a thick waxy cuticle reduce the rate of transpiration?
Prevents water loss
Thickness increases the distance of the diffusion pathway
How do hairs on the lower epidermis reduce the rate of transpiration?
Trap water vapour
Reduces the water potential gradient
How do stomata sunken in pits reduce the rate of transpiration?
Reduce the water potential gradient between the leaves and the atmosphere
Less diffusion can occur
