Topic 9 - Plant Biology Flashcards
1
Q
cuticle
A
- waxy outermost layer of a leaf
- protects it against water loss and insect invasion
2
Q
palisade mesophyll
A
- located in upper portion of leaf (where light is most available)
- chloroplast-rich to allow max photosynthesis
3
Q
vascular bundles
A
- the “veins” of a plant
- contains the xylem and phloem tubes
- distributed throughout the leaf to transport raw materials and products of photosynthesis
- occur roughly in the middle of the leaf so they’re near all the leaf cells
4
Q
spongy mesophyll
A
- contains many air spaces for gas exchange
- located just superior to the stomata
- to allow continuous channels for gas exchange
5
Q
stomatal pores
A
- on the bottom surface of the leaf
- receives less light so the temp is lower than on the upper surface
- lower temp minimizes water loss from the pores and the plant
- so the lower epidermis usually has a thinner cuticle than the upper epidermis
- positioning of the epidermis allows the remaining structures of the leaf to be protected and supported
6
Q
xylem
A
- supports the plant
- also specialized water-conducting tissue of terrestrial plants
- composed of multiple cell types
- their primary walls include pits or pores to allow water to move laterally
7
Q
types of xylem cells
A
- tracheids
- vessel elements
8
Q
vessel elements
A
- most important xylem cells
- dead cells with thick, lignified secondary walls
- these secondary walls are interrupted by primary walls that contain pores to allow water movement
- vessel elements are attached end to end to form continuous columns, like the tracheids
- ends of vessel elements have pores to allow water to move freely up the plant
9
Q
tracheids
A
- dead cells that taper at the ends
- they connect to one another to form a continuous column
10
Q
evolution of xylem tube
A
- ancient plants only had tracheids
- modern flowering plants only have vessel elements
- vessel elements are more effective at their function
11
Q
why stomatas must open and close
A
- stomata can only be closed on a short-term basis
- as CO2 must enter the mesophyll region so photosynthesis can occur
- changes in the turgor pressure of the guard cells that surrounds the stomata can affect whether they open and close
12
Q
how stomatas open and close
A
- guard cells are cylindrical and their cell wall thickness is uneven
- thickened area of the guard cell wall is oriented
towards the stoma - when guard cells take in water and swell, they bulge more to the outside, opening the stoma
- when the guard cells lose water, they sag towards each other and close the stoma
13
Q
what affects guard cell activity?
A
- transport of potassium ions cause guard cells to open
- blue light triggers the activity of ATP-powered proton pumps in the plasma membrane of guard cells
- thus triggering active transport of K+ into cell
- higher solute concentration within the guard cells causes inward water movement by osmosis
- when potassium ions passively leave the cells, water also leaves
- abscisic acid (hormone) can cause guard cells to close
- they cause potassium ions to diffuse rapidly out of the guard cells
- this hormone is produced in the roots during times of water deficiency
- other factors include CO2 levels and even circadian rhythm
14
Q
cohesion-tension theory
A
- transpiration occurs bc water moves down a concentration gradient: from leaf air spaces (high) to atmosphere (low)
- water lost via transpiration is replaced by water from vessels due to concentration gradient
- vessel water column is maintained by cohesion (H bonds between H2O molecules) and adhesion (H bonds between H2O and vessel walls)
- continuous tension in column due to continuous transpiration –> replacement cycles
- water is pulled from root cortex into xylem cells and from soil into root due to the tension
15
Q
adaptations of roots for their function
A
- the main function of roots is to provide mineral ion and water uptake for the plant
- roots are efficient due to an extensive branching pattern with specialized epidermal structures (root hairs)
- root hairs increase SA so absorption can occur 3x more efficiently
16
Q
importance of root cap
A
it protects the apical meristem during primary growth of root through the soil
17
Q
types of root zones
A
- zone of cell division (M phase of cell cycle): new undifferentiated cells form
- zone of elongation (G1 phase): cells enlarge in size
- zone of maturation: when the cells become fully functional parts of the plant
18
Q
movement of water into a plant
A
- moves from soil to root hairs via osmosis
- because root hairs have a higher solute concentration
- water then moves to the vascular cylinder (which contains xylem and phloem tubes)
19
Q
movement of mineral ions into a plant
A
- mineral ions diffuse in
- when there’s a higher conc. of mineral solutes in water outside the root, it may diffuse in
- some may also move via osmosis
20
Q
bulk flow
A
AKA mass flow
- passive movement of water and its mineral ion solutes
21
Q
active transport of minerals into a plant
A
- occurs if solute conc in plant is higher
- or if the ion can’t cross the lipid bilayer
- results in hypertonic state, also increasing amount of water absorbed
22
Q
factors affecting plant transpiration
A
- light
- humidity
- wind: humid air near the stomata is carried away so it increases transpiration
- temperature
- soil water: if soil is water-deficient, turgor loss occurs
- CO2 conc.: causes guard cells to lose turgor, so stomata closes
23
Q
succulents
A
plants that store water to survive
24
Q
xerophytes
A
plants adapted to live in arid climates
25
Q
xerophyte adaptations to arid conditions
A
- Small, thick leaves with decreased SA
- reduced no of stomata
- stomata located in crypts/pits on leaf surface (to cause high humidity around stomata)
- thickened, waxy cuticle (impenetrable barrier to water)
- Hair-like cells on leaf surface trap a layer of water vapour (maintains higher humidity near stomata)
- desert plants shed their leaves and/or become dormant in the driest months
- succulents can store water in their fleshy, watery stems
- xerophytes can use alternative photosynthetic processes
- can close stomata with guard cells
26
Q
types of photosynthesis
A
- C3 photosynthetic pathway (most common)
- CAM photosynthesis
- C4 photosynthesis
27
Q
CAM photosynthesis (brief)
A
CAM plants close their stomata during the day and store CO2 at night
28
Q
C4 photosynthesis
A
C4 plants open their stomata during the day but take in CO2 far quicker than other plants
29
Q
halophytes
A
plants adapted to grow in water with high salinity levels
30
Q
halophyte adaptations to saline conditions
A
- many are succulents and store water (thus diluting the salt concs)
- some species (e.g. mangrove) secrete salt through salt glands
- some species compartmentalize Na+ and Cl– in cell vacuoles to prevent NaCl toxicity
- sunken stomata (higher humidity around stomata)
- thickened leaves with developed cuticle to minimize water loss
- reduced leaf SA
- can close stomata with guard cells
31
Q
types of phloem cells
A
- sieve elements
- companion cells
32
Q
sieve elements
A
- connected by sieve plates
- forms sieve tubes
- sieve plates have pores to allow movement of water and dissolved organic molecules throughout the plant
33
Q
translocation
A
movement of organic molecules in plants
34
Q
organic molecules in phloem sap
A
- sugars
- amino acids
- plant hormones
- small RNA molecules (possibly to aid communication)
35
Q
pressure-flow hypothesis for movement of phloem sap
A
- sugar loads into sieve tube at the source (leaf cells) via active transport
- reduces the relative water conc. in the sieve tube members, causing osmosis from the surrounding cells
- water uptake causes hydrostatic pressure, resulting in bulk flow of phloem sap.
- hydrostatic pressure is diminished by removal of sugar (active transport) from the sieve tube at the sink (destination)
- the sugars are changed at the sink (storage cells in roots) to starch
- as starch is insoluble, it exerts no osmotic effect
- xylem then recycles the relatively pure water by carrying it from the sink back to the source
