Exchange and Mass Transport - Plants Flashcards
What is the order of layers in a plant leaf cell?
(top to bottom)
Waxy Cuticle
Upper Epidermis
Palisade Mesophyll
Spongy Mesophyll and Vascular Bundle
Lower Epidermis
Waxy Cuticle
What is the function of the waxy cuticle?
contains lipids so waterproofs the leaf to prevent water loss
What is the function of the upper epidermis?
To provide an extra layer of protection and contains a few stomata for gas exchange
What is the function of the palisade mesophyll?
Main site of photosynthesis
What is the function of spongy mesophyll?
Increases the surface area of the leaf for efficient gas exchange
What is the function of the vascular bundle?
Transport of minerals and water (phloem and xylem)
What is the function of the lower epidermis?
Adds an extra layer of protection and has more stomata to allow for gas exchange
Why does the lower epidermis contain more stomata than the upper epidermis?
The underside of a leaf is cooler, so less water is lost by evaporation.
What is each stomata surrounded by?
2 guard cells
How and why does a guard cell close?
To conserve water:
K+ ions diffuse into cell when it is turgid
Water potential inside of cell increases
Cell becomes flaccid and less curved
Stomata pore closes, reducing airflow and transpiration
How and why does a guard cell open?
To lose water and allow for gas exchange:
K+ ions diffuse out of cell when it is flaccid
Water potential inside cell decreases
Cell becomes turgid and more curved
Stomata pore opens, increasing airflow and transpiration
What happens to the concentrations of CO2 and O2 when photosynthesis is taking place?
CO2 conc decreases
O2 conc increases
What happens to the concentrations of CO2 and O2 when respiration is taking place?
CO2 increases
O2 decreases
Define a xerophyte
Plants adapted to dry habitats
What are the adaptations of cacti to warm environments?
- Being as thin as vertically possible
- Roots spread sideways not downwards
- Spines formed by rolled leaves
- Fuz between spines
- Projections from the main body
How does being thin vertically help a cactus?
It allows the cactus to catch as little sunlight as possible, keeping it cooler.
Why do the roots spread sideways in cacti?
When it rains, the roots can catch as much water as possible
What are the advantages of spines on cacti?
- Produces their own microclimate inside the leaf - the water gets trapped inside the leaf which decreases transpiration
- They can concentrate to provide protection from the sun
- Reduced SA:V
What are the advantages of cacti having fuz between their spines?
- Protection from the sun
- Captures water in mists / rain
What are the advantages of cacti having projections from the main stem?
Only a few at a time will catch the sun, allowing the rest of the plant to be in the shade
What is the function of xylem?
to transport water and ions up the plant
What is the structure of xylem vessels?
narrow tubes consisting of dead, empty cells
cells have no end walls
walls strengthened by lignin
What features of a xylem vessel reduces resistance?
empty, dead cells
no end walls
What is cohesion?
a force resulting from attraction between molecules of the same substance
What is adhesion?
a force resulting from attraction between molecules of different substances
Where is adhesion found in xylem vessels?
between water molecules and the sides of the xylem
What is the cohesion tension theory?
water is drawn out of xylem vessels, developing tension and a water potential gradient
water is drawn up the xylem in a continous column due to cohesive forces
adhesive forces prevents water dropping under gravity
this mechanism is called the transpiration pull
