3.1.3 Transport In Plants Flashcards
1
Q
why do plants need a transport system?
A
- small SA:V ratio
- rate of diffusion into plant is slow
- high metabolic rate
2
Q
what is transpiration?
A
evaporation of water from the stomata
3
Q
what’s transpiration stream?
A
movement of water up the xylem
4
Q
what are the steps of transpiration?
A
- osmosis of water from the xylem into the mesophyll
- evaporation from surface of mesophyll into air space in the leaf
- diffusion out of the stomata
5
Q
what are the factors affecting transpiration?
A
- temperature
- humidity
- light
- air movement
- number and position of stomata
- presence of waxy cuticle
- water availability
6
Q
how does temp affect transpiration?
A
- high temp = more KE for water
- more evaporation of water through stomata
7
Q
how does humidity affect transpiration?
A
- more water surrounding stomata so less steep diffusion distance
- less water leaves via evaporation
8
Q
how does light affect photosynthesis?
A
- higher rate of photosynthesis
- so more gas exchange needed
- O2 out and CO2 into the stomata
- stomata opened more so more evaporation of water
9
Q
how does air movement affect transpiration rate?
A
- more air = less water vapour surrounding the stomata as it’s blown away
- steeper water gradient and more water evaporates thru stomata
10
Q
how does no. and position of stomata affect transpiration rate?
A
- more stomata = more water evaporated
- stomata on top of leaf = more water lost
11
Q
how does the presence of waxy cuticle affect transpiration rate?
A
- thicker waxy cuticle= less water evaporates
- waxy cuticle is water proof
12
Q
what are the steps of using a potometer?
A
- select healthy plant
- cut stem under water at an angle
- dry the leaves
- use same species of plant and same SA of leaves
- set up potometer under the water
- introduce an air bubble
13
Q
what’s disadvantages of a potometer?
A
- some water uses turgod pressure
- some water uses photosynthesis
14
Q
how do u calculate water uptake?
A
SA of circle * length bubble has moved
15
Q
how does water move into root hair cell?
A
- lower water potential in root hair cell
- due to higher conc. of solutes
- water moves into root hair cell
- by osmosis
16
Q
what are the two pathways water can take to go from roots to xylem?
A
- apoplast —> thru cell wall
- symplast —> thru cytoplasm
17
Q
how does symplast pathway work?
A
- water goes through cytoplasm
- cytoplasms of neighbouring cells connect through plasmodesmata
- water moves by osmosis
18
Q
how does the apoplast pathway work?
A
- water goes through cell wall
- diffuses from an area of high hydrostatic pressure to low hydrostatic pressure
19
Q
what does the casparian strip do?
A
blocks water going through apoplast pathway and makes it go through symplast
20
Q
why is the main pathway apoplast?
A
least resistance
21
Q
what is the cohesion adhesion tension theory?
A
- high hydrostatic pressure in the roots
- low hydrostatic pressure in the leaves
- as water evaporates through the stomata
- creates tension in the xylem
- water moves up xylem along the hydrostatic pressure gradient
- by cohesion and adhesion and capillary action
- by mass flow
22
Q
what are some adaptations of xerophytes?
A
ROLLED/HAIRY LEAVES
- reduced SA for evaporation
- traps a layer of water vapour
- creating high water vapour potential outside stomata
- reducing water vapour potential gradient
- reduces evaporation of water from leaf
23
Q
what are other adaptations of xerophytes to reduce water loss?
A
- less stomata closed during day
- thicker waxy cuticle, waterproof and prevents water evaporating
- long deep roots for water intake, high solute conc in root hair cells
24
Q
what are hydrophytes?
A
cells that live in areas of high water concentration
25
what are some adaptations of hydrophytes?
1. plant tissue with **air spaces**
—> allows **buoyancy** to float
2. large SA
—> increase **rate of photosynthesis**
26
what is translocation?
- **movement of sugars** from its **sources to its sink** (where it’s needed for **respiration**)
- requires **energy**
- happens in **phloem**
27
how do substances enter the phloem?
1. **H+ ions** in **companion cells** are **actively transported** into **surrounding cells**
2. H+ ions **move back into companion cell with sucrose**, using a **co-transport protein** —> facilitated diffusion
3. **sucrose diffuses through plasmodesmata** into **sieve tube** in phloem
28
how are solutes transported in the phloem?
- move **down hydrostatic pressure gradient** by **mass flow**
1. sucrose **lowers water potential** of sieve tube so **water moves into** it **from xylem by osmosis**
2. causes an **increase of hydrostatic pressure** at the **source**
3. at the **sink, solutes are removed** from phloem to be used up which **increases water potential**, so **water leaves** by osmosis, **decreasing hydrostatic pressure**
29
how are root hair cells able to absorb water by osmosis?
- has low water potential cos of **solutes**
- this **establishes** a **water potential gradient**
30
why is sucrose used in translocation instead of other carbohydrates?
- **soluble** so can be **transported in sap**
- **metabolically inactive** so **removed during transport**
31
what’s a similarity between phloem and xylem?
both use **mass flow**
32
why’s starch not transported in sap?
not soluble
33
what assumption about the water is made in transpiration?
**none of the water** is **used** up
34
how can transpiration rates be compared from 2 plants?
compare transpiration rate **per unit area**
35
why is a control experiment used?
to see effect of IV
36
how is a colorimeter calibrated?
set colorimeter to **zero absorbance** using **water**
37
why is a colorimeter calibrated?
so that **values** are **all comparable**
38
what would happen to genetic biodiversity if population decreases?
- decreases
- **smaller gene pool**
- **loss** of **alleles**
- **new alleles** may arise by **mutations**
39
what would happen to species diversity if population is decreased?
- the species **may go extinct**
- **former prey species** may **return**
- affects **food chain**
40
how do you make sure no air is in the potometer apparatus?
1. set up **apparatus under water**
—> so **no air** is present
2. **joints** must be **sealed**
—> obtain **continuous water** column**
3. do not allow bubble to **move far**
—> so **doesn’t enter xylem**
4. keep **shoot still**
—> to **avoid column breaking**
41
why would some organisms need to expel water in fresh water?
- **maintain water potential**
- water potential **higher outside cell**
42
what are some adaptations of xylem?
1. have **bordered pits**
—> allow **water to move** into **other cells**
2. walls have **lignin**
—> to provide **structural support**
3. **no end walls**
—> for **continuous column** of water
