Plant Biology Flashcards
(37 cards)
What are the five layers of a leaf?
waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll and lower epidermis.
What is the purpose of the waxy cuticle?
A waterproofing layer
Stops water evaporating out of leaf
What is the purpose of the upper epidermis?
A protective barrier against pathogens and damage
Translucent so it lets light through to palisade mesophyll
What is the purpose of the palisade mesophyll?
Site of photosynthesis
Regular box like structure to maximise photosynthesis
roughly 80% of chloroplasts located here
chloroplasts are nearer to top of leaf
What is the purpose of the spongy mesophyll?
Site of gas exchange
lots of air spaces
less tightly packed
irregular shape
about 20% chorophyll
What is the purpose of the vascular bundle?
Contains xylem (for transportation of water+mineral ions)
Contains phloem (for transportation of amino acids and dissolved sugars-sucrose)
What is the purpose of the lower epidermis?
A protective layer
What is the purpose of the guard cells?
To open and close stomata
Open-let in CO2 for photosynthesis
and O2 for respiration
Close-To stop water loss
What is the stomata?
Tiny openings or pores in plant tissue that allow for gas exchange
What are the xylem?
Xylem are elongated dead cells, arranged end to end to form continuous vessels (tubes). They are involved in a process that carries water and mineral ions from roots to leaves(ONE DIRECTION) called the TRANSPIRATION STREAM.
What do the xylem look like/ contain?
There is no cytoplasm
have tough walls containing a woody material called lignin which builds in spirals in cell walls
Lignin makes spirals very strong to withstand pressure from water+ provide support
The contents+end walls break down to form a hollow centre or the lumen.
What happens to guard cells in bright light?
Potassium ions move into cell via active transport
Mitochondria in cell release energy
This makes cell less dilute than surroundings
Water moves in cell via osmosis across PPM
Cells swells unevenly because thicker inner cell wall is less flexible than thinner outer wall so they become TURGID
OPPOSITE OCCURS FOR DIM LIGHT
How do you measure rate of photosynthesis?
Number of air bubbles/time
Ex:2 bubbles per minute
What are some issues with the potometer experiment?
It actually measures uptake of water, not amount of transpiration out of leaf. Some water taken up is used in photosynthesis so is not lost by transpiration.
How do you calculate the rate of transpiration?
Distance air moved by our bubble/time
How does light intensity affect the rate of transpiration?
increased light=increased rate of photosynthesis
plant needs more CO2 so stomata opens to let gas in
more stomata open= more water lost by transpiration
How does temperature affect the rate of transpiration?
increase in temp=increase in kinetic energy
water molecules move more and are more likely to leave leaf via transpiration.
How does wind speed affect the rate of transpiration?
increase windspeed=high conc. gradient as lots of water inside leaf none outside
water leaves by transpiration down conc. gradient
How does humidity affect the rate of transpiration?
high humidity= nearer equilibrium so low conc. gradient
slows down evaporation so transpiration rate slows down
What are the phloem?
LIVING cells lined up end to end with perforated sieve plates containing cytoplasm. Transports sucrose and amino acids UP AND DOWN plant. This is called TRANSLOCATION.Substances are either stored in roots as starch or are used.
Describe the process of translocation.
1.Sugars made in leaf cell by photosynthesis.Glucose converted to starch.
2.Sucrose moved into companion cell from leaf.requires energy from mitochondria
3.From companion cells sugar diffuse to phloem vessel
4. high conc. sugars at top cause water to enter phloem vessel by osmosis from nearby xylem
5.Movement of water into phloem causes translocation of sugars to root.
6.In root sucrose leaves phloem vessel and is stored as starch
What are companion cells?
Found along outside of phloem vessel.Contains nuclei and many mitochondria to provide energy for translocation.
What can reduce the resistance of flow in translocation?
Limited amount of cytoplasm and no nucleus or vacuole.
What are some differences between xylem and phloem?
Xylem: dead,continuous,one way,transports minerals and water,transpiration
Phloem:alive,discontinuous,two way,transports sucrose and amino acids,translocation
