Transport in Plants Flashcards
1
Q
Evidence for active transport in root pressure (4 pieces)
A
- Cyanide reduces root pressure
- Cell sap forced out of pores (guttation) when cut
- Root pressure increases with temperature (chemical reactions involved)
- Root pressure decreases with limited oxygen/ respiratory substrates
2
Q
Evidence for cohesion-tension theory (3 pieces)
A
- Water cannot be moved up the stem when the xylem is broken as it forms an air lock
- When cutting a stem, air moves in, water doesn’t leak out
- When transpiration is low, xylem tension is low and the diameter of steams/trees increases
3
Q
Factors affecting rate of transpiration (5)
A
- temperature (in 2 ways)
- humidity
- air movement
- soil-water availability
- light
4
Q
Evidence for active transport in translocation (4 pieces)
A
- Aphids puncture phloem, cell sap leaks out due to positive pressure
- Translocation stops if mitochondria is poisoned
- Sugars flow about 10,000 times faster than if they were to flow by diffusion alone
- Advances in microscopy
5
Q
where are the vascular bundles in the stem of a herbaceous dicotyledon and why?
A
around the outside to provide structural support
6
Q
cross section of a stem (herbaceous dicotyledon) from the outside in
A
- epidermis
- cortex
- phloem (withing cortex)
- xylem (within parenchyma)
- parenchyma
7
Q
cross section of a root (herbaceous dicotyledon) from the outside in
A
- root hair
- exodermis
- epidermis
- cortex
- endodermis (ring around vascular bundles)
- phloem
- xylem (x shaped)
8
Q
where are the vascular bundles located in the root of a herbaceous dicotyledon and why?
A
middle to hell the plant withstand tugging strains which comes as a result of stems and leaves blowing in the wind
9
Q
what is the main vein of a leaf called?
A
midrib
10
Q
cotyledon
A
organ that acts as a food store (for a developing embryo)
11
Q
what are the two types of dicots and compare them?
A
herbaceous dicots:
- softer tissue
- shorter life cycles
woody dicots:
- more lignified tissue
- longer life cycles
12
Q
three functions of the xylem
A
- transporting water and minerals
- strengthening tissue/structural support
- storage of starch in fibres and parenchyma
13
Q
function of phloem
A
- transport organic solutes (sucrose, amino acids etc)
14
Q
structure of the xylem and their functions
A
- lumen/hollow tube (composed mainly of dead cells)
- thick lignified walls
- non-lignified bordered pits (allow water to diffuse out via osmosis
- xylem parenchyma and fibres between xylem vessels (store food and tanin deposits)
15
Q
three ways which lignin can form around the xylem
A
- rings
- spirals
- solid tubes
16
Q
how is the phone formed?
A
- seive tube elements joined together
- joined cell walls perforate (form pores) to form sieve plates
- tonoplast (vacuole membrane), nucleus and other organelles breakdown
- phloem tube fills with phloem sap
- connected to companion cells via plasmodesmata
17
Q
plasmodesmata
A
microscopic channels through cellulose cell walls linking the cytoplasm of adjacent cells (found between sieve tube elements and companion cells)
18
Q
what tissues support the phloem?
A
- fibres
- sclereids
- cells with extremely thick walls
19
Q
five reasons why water is important for plants?
A
- turgor pressure (provides structural support)
- turgor pressure (drives cell expansion)
- cooling (loss of water via transportation and evaporation)
- transport mineral ions (acts as a solvent)
- water is a reactant in photosynthesis
20
Q
root hair and root hair cell
A
root hair - a long, thin extension growing from a root hair cell
root hair cell - specialized epidermal cell found near the growing root tip
21
Q
four adaptations of root hair cells
A
- long and thin provides greater SA:V for osmosis
- microscopic size allows them to penetrate soil particles to reach more water
- only a cell wall and plasma membrane provides a short diffusion distance
- high [solute] in cytoplasm and vascular sap maintains a Ψ gradient
22
Q
symplast pathway
A
movement of water through the continuous cytoplasm of living plant cells (connected via plasmodesmata)
23
Q
apoplast pathways
A
movement of water through cell walls and intracellular spaces
24
Q
how does water move through the symplast pathway?
A
- root hair cell Ψ > adjacent cells Ψ
- water moves down a Ψ gradient via osmosis
- those cells now have a greater Ψ than the next adjacent cells
- water continuous to move down a Ψ gradient via osmosis
25
how does water move through the apoplast pathway?
- water fills spaces between cells
- as water moves into intracellular spaces, cohesive forces pull other water molecules through the apoplast
- also a pull from water moving up the xylem
- creates a tension and a continuous flow
26
Casparian strip
waxy layer made of suberin that wraps around the endodermal cells (tissue surrounding vascular bundles) which forms a waterproof layer
27
function of the Casparian strip
- forces water in the apoplast pathways to move into the symplast pathway
- water must diffuse through the selectively permeable membrane to get into the xylem
- prevents toxic solutes from entering
28
how does the water enters the xylem and name of process?
root pressure
- minerals are actively pumped into the xylem which lowers Ψ
- water diffuses down a Ψ gradient into the xylem via osmosis (the symplast pathway)
29
transpiration
loss of water vapour from stems and leaves of a plant as a result of evaporation from cell surfaces inside the leaf and diffusion down a concentration gradient out through the stomata
30
when and why are stomata open?
- open at day so more CO2 can diffuse in for photosynthesis
- still open at night (but less) as little/no O2 is being produced from photosynthesis so plants must take in O2 from the air
31
transpiration stream
movement of water through a plant from the roots until it is lost by evaporation from the leaves
32
transpiration stream sequence
- water evaapoarates off the mesophyll cells (in leaf) and diffuse through the air spaces out of the stomata down a concentration gradient
- loss of water lowers Ψ of mesophyll cell
- water moves down a Ψ gradient from adjacent cells via apoplast and symplast pathway
- water moves out of xylem into mesophyll cells via osmosis
- cohesive and adhesive forces cause capillary action and pull water up the xylem
- tension is created which pulls water across the roots into the xylem (transportation pull)
33
capillary action
movement of water up a narrow tube against the force of gravity
34
transpiration pull
process of pulling water up through the xylem vessels to replace water lost by evaporation
35
cohesive vs adhesive forces
- cohesive forces form from H bonds between molecules
- adhesive forces form from H bonds between water and carbohydrates in xylem wall
36
five factors affecting rate of transpiration
- temperature
- humidity
- air movement
- light intensity
- water availability
37
how does temperature affect rate of transpiration?
- increase in temperature, increases rate of transpirstion
- rate of evaporation increases as water molecules have more kinetic energy
- AND air can hold a greater volume of water vapour before becoming saturated
38
how does light intensity affect transpiration?
- increase in light intensity increases rate of transpiration
- rate of photosynthesis increases with light intensity
- greater number of stomata open to allow more CO2 to diffuse in
- increase in evaporation of water vapour out of stomata
39
how does humidity affect rate of transpiration?
- increase in humidity decreases rate of transpiration
- Ψ gradient decreases
- rate of diffusion of water vapour decreases
40
how does air movement affect rate of transpiration?
- increase in air movement increases rate of transpiration
- decreases humidity around stomata
- increases Ψ gradient
- rate of evaporation increases
(each leaf has a layer of still air around it trapped by leaf shape/hairs)
41
how does water availability affect rate of transpiration?
- increase in water availability increases rate of transpiration
(plants may go into water stress if availability is low/ABA hormone)
42
assimilates
products of photosynthesis transported through the phloem via translocation
43
direction of transportation vs translocation
transpiration is unidirectional, translocation is multidirectional
44
three examples of sources
- cotyledons
- green leaves and stems
- storage organs (roots, tubers etc)
45
two examples of sinks
- actively growing shoots
- dividing meridtematic tissue (cambium etc)
46
what is the main assimilate transported via translocation?
- sucrose
47
what two ways can assimilates be loaded into the phloem?
- apoplast pathway (active)
- symplast pathway (passive, not in spec)
48
two adaptations of the companion cells
- lots of mitochondria (produce lots of ATP for the H+ pumps)
- infolds in plasma membrane (increase SA for diffusion of sucrose into cell)
49
apoplast pathway (translocation)
- H+ ions actively pumped out of companion cells at source
- H+ diffuse down a concentration gradient back into companion cells via a co-transporter with sucrose
- Ψ of companion cell decreases
- water diffuses into companion cells down a Ψ gradient
- turgor pressure increases (due to rigid cell walls)
- water containing dissolved assimilates move down a pressure gradient into phloem
50
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