9.1 transport in dicotyledonous plants

Question 1

the need for transport systems in multicellular plants x3

Answer 1

• metabolic demand
• size
• surface area and volume

Question 2

plants need transport systems due to metabolic demands

Answer 2

Photosynthesis 🡪 glucose and oxygen
Glucose is then respired to produce ATP.
ATP needed by all cells for active transport, chemical reactions, cell division.
but
Internal and underground parts of plants don’t photosynthesise (no light)
Oxygen and glucose, hormones, proteins and ions transported around the plant to where they are needed.

Question 3

plants need transport systems due to their size beacuse

Answer 3

Several layers of cells.
Only outermost cells get to use substances diffusing in.
Transport systems move substances to internal cells.

Question 4

plants need a transport system because of their SA:V ratio

Answer 4

Leaves are adapted to have high SA:V
but
When considering stems, trunks and roots, they have small SA:V and cannot rely on diffusion alone

Question 5

Vascular tissue/bundle

Answer 5

Made up of xylem and phloem tissue.
Each makes up a different transport system.
Distributed differently in different areas of the plant.

Question 6

Transpiration System

Function?
medium?
passiv/active?

Answer 6

• The movement of water molecules and dissolved minerals ions
• Xylem vessels
• Passive - does not req metabolic energy

Question 7

Translocation System
role?
transport medium?
active/passive?

Answer 7

The movement of sugars (Sucrose) & amino acids
Phloem vessel – sieve & companion cells
Active - reqs metabolic energy

Question 8

Draw and compare cross section of vascular bundle in root,stem,leaf

Answer 8

root - +shape of xylem and triangular phloem and root hairs
stem- ploem on outside and xylem on inner seperated by the cambium
leaf - ploem below xylem on top

The phLOem sits beLOw the xylem tissue in the Leaf.

Question 9

Xylem structure and function

Answer 9

Mostly non-living tissue
Functions
- transport water and mineral ions
- support
Several different cell types
**Vessel elements **
Joined end to end in several columns
No end walls, no cytoplasm
Cell walls thickened by woody substance called lignin (organic polymer)
Amount of lignin increases as plant get older
Water and mineral ions move in/out through non-lignified pits
Xylem parenchyma
Thick walled
Packed around vessel elements
Store of food
Stores tannin – protection against attack from herbivores

Distinct patterns of lignin spirals around the lumen
– mechanical strength
- allows flexibility
- prevents breaking and collapsing

Question 10

phloem structure and function

Answer 10

Living tissue
Functions
* transport organic solutes (assimilates) around plant from the leaves where they are a product of photosynthesis
* supplies non-photosynthetic cells with sugars (for respiration) and amino acids (for synthesis of nitrogen containing compounds)
* Formed from cells arranged in tubes
* Not used for support
- Sieve tube elements
-Companion cells

Question 11

Sieve tube elements

Answer 11

Living cells
Joined end to end
Sieve parts are the end walls with hole to allow solutes to pass through
No nucleus
Very thin layer of cytoplasm
Few organelles
The cytoplasm of adjacent cells is connected through holes in the sieve plates

Question 12

Companion cells

Answer 12

The lack of nucleus in the sieve tube elements mean they cannot survive on their own.

Companion cells carry out ‘living functions’ for themselves and their sieve cells.

E.g. provide energy for active transport

Question 13

plants vascular bundles we learn about are called

Answer 13

herbaceous dicotyledonous plants.

flowering and seeding plants witout bark

Question 14

The cambium layer contains

Answer 14

meristem cells.

Question 15

explanation to roots structure

Answer 15

As plants grow, their roots ‘push’ through soil.
Xylem tissues is the strongest so is in the centre – X structure
Phloem in four separate sections.

Question 16

Stain
Toluidine blue O (TBO)

Answer 16

Lignin
blue/green

Phloem and rest of tissue varying shades of pink

Question 17

which stain

Lignin
blue/green

Phloem and rest of tissue varying shades of pink

Answer 17

Toluidine blue O (TBO)

Question 18

Transpiration

Answer 18

The term given to the movement through and loss of water from plants.

Question 19

transpiration mechanism

Answer 19

• Water evaporates to become water vapour.
• Water vapour diffuses out the stomata.
• Water potential of the air space decreases.
• Water osmotes from the adjacent cells into the air spaces.
• Water osmotes out of the xylem into the cells of the leaf.
• Water molecules ‘hydrogen bonds’ to itself (cohesion) resulting in tension.
• Water molecules bond to the walls of the xylem vessel (adhesion) resulting in capillary action.
• Water loss from the leaves causes transpiration.
• Thus, the rate of water loss determines the rate of transpiration.
• Most water is lost from the underside of a leaf, where there are stomata.
• Most plants control their water intake by opening and closing their stomata.
• Water levels change in the guard cells around each stoma.
• Water levels change either passively by osmosis, or by active transport of solutes.
• Transpiration rates also vary naturally in response to environmental factors such as temperature and humidity.

Question 20

how do plants Reduce water loss

Answer 20

Wilting
* Loss of turgor pressure causes cells to be flaccid. The plant will wilt.
* The leaves collapse and hang down. This reduces the surface area for water to be lost from.
* Wilting gives protection against further water loss.
Stomata close
* This prevents water loss by diffusion but stops photosynthesis.

Question 21

Why does water move? x3

Answer 21

Osmosis: water moves from areas of high water concentration to areas of low water concentration. KE of molecules.

Mass flow: water also moves from areas of high hydrostatic pressure to areas of low hydrostatic pressure.

It is also affected by gravity and electrostatic forces, such as those that cause surface tension.

Question 22

Evidence to support Cohesion-tension Theory

Answer 22

Changes in tree diameter – at high transpiration rates (e.g. warmer temps) tree diameter decreases. Higher rates of evaporation from the leaf cause extra tension. At night, during low transpiration rate, diameter increases.
**
Cut flowers** – often they draw air in rather than leaking water out, as water continues to move up the cut stem.

Broken xylems – broken or cut xylems stops drawing up water as the air drawn in breaks the transpiration stream – cohesion between water molecules.

Question 23

time of day rate of water flow and tree trunk diameter graph analysis

Answer 23

D1: decrease in diameter
E1:
increase in rate of diffusion from leaf
causes more tension in the water column.
water moves up the xylem faster
creating lower pressure.
This draws the sides of the xylem inwards,
reducing diameter(and overall diameter of the trunk).

D2: increase in diameter
E2: decrease in rate of diffusion from leaf
causes less tension in the water column.
Water moves up the xylem slower.
The sides of the xylem are not drawn inwards, increasing diameter (and overall diameter of the trunk).

Question 25

Capillary action

Answer 25

Capillary action occurs when the water molecule adhere to the walls of the xylem vessel.

Question 26

Conclusion: The narrower the tube, the higher a liquid can settle.

Answer 26

This is a plausible explanation for plants having many narrow xylem vessels, rather than fewer wide xylem vessels.
Narrower xylem vessels offer a survival advantage. They are selected for by Natural Selection.

Question 27

Root pressure

Answer 27

Root hair cells actively pump ions from the soil into the cells.
This creates a water potential gradient between soil and cytoplasm.
Water then osmotes from the soil to the cell.
This increases the hydrostatic pressure from below.
Water is ‘pushed’ up the xylem.

Question 28

Evidence for Active Transport in Root Pressure x4

Answer 28

The effect of cyanide – Cyanide stops mitochondria from working.
The effect of changing temperature – respiration is an enzyme controlled chemical reaction.
The effect of changing reactant availability – oxygen is respiratory substrate.
Guttation – sap and water will move out of cut stems, suggesting they are actively pumped out not drawn up by transpiration.

Question 29

Transpiration mechanisms

Answer 29

Three processes caused by changes in concentration and attractions pull water up the xylem

Root Pressure & osmosis [Active Process]
Transpiration Pull (Cohesion – tension theory)
Capillary Action (Adhesion)

Question 30

three routes of water from root hair to xzylem

Answer 30

Symplast
* this is the movement of water through the living spaces of the cell – cytoplasm
* Changing cells through the plasmodesmata.
* Each cell further away from the roots has a lower water potential so water is drawn up the plant
Vacuolar pathway
* is the same as the symplast pathway when the water moves through the cells vacuoles in addition to the cytoplasm
This is the slowest route
Apoplast
* This is the movement of water through the cell wall and intracellular spaces
* Cohesive and tension forces acting on the cell walls pulls the water up the plant
* This is the fastest movement of water

Question 31

Estimating the rate of transpiration

Answer 31

A potometer actually measures the rate of water uptake by the plant.
If cells are turgid, > 95% of water taken up is lost by transpiration, so this gives a reasonable estimate of transpiration rate.

Question 32

rate of transpiration formula

Answer 32

rate = change/time taken

Water vapour lost by the leaves is replaced from the water in the capillary tube.

The movement of the meniscus at the end of the water column can be measured.

Question 33

what do we use to measure transpiration

Answer 33

potometer

Question 34

how to increase validity of transpiration rate pag

Answer 34

It is important to take certain precautions to ensure the results are valid:
Set it up under water to make sure there are no air bubbles inside the apparatus.
Cut the stem under water to prevent air entering the xylem.
Cut the stem at an angle to provide a large surface area in contact with the water.
Dry the leaves.

Question 35

Species of xerophyte and description of adaptation

Answer 35

Marram grass - curved leaf
Marram grass - sunken stomata
Marram grass - hairs around the stomata
Cactus - spines instead of leaves
Cactus - succulent stems and ‘leaves’
Cactus - many shallow roots

Question 36

Marram grass - curved leaf decreases the rate of diffusion becuase….

Answer 36

The curved leaf means the stomata are not exposed to moving air.
The curved leaf traps water diffusing out of the leaf. Decreases gradient between inside and outside leaf.
Reduces rate of diffusion of water out of the leaf and so water uptake.

Question 37

Marram grass - sunken stomata decreases the rate of diffusion how?

Answer 37

The ‘dip’ means the stomata are not exposed to moving air.
The ‘dip’ traps water diffusing out of the leaf.
Reduces rate of diffusion of water out of the leaf and so water uptake.

Question 38

Marram grass - hairs around the stomata decreases the rate of diffusion how?

Answer 38

he hairs trap water diffusing out of the leaf.
Reduces rate of diffusion of water out of the leaf and so water uptake.

Question 39

Cactus - spines instead of leaves
decreases rate of diffusion how

Answer 39

By not having leaves, cacti reduce their surface area to volume ratio.
Reduces rate of diffusion of water out of the leaf and so water uptake.

Question 40

Cactus - succulent stems and ‘leaves’
decreases rate of diffusion how?

Answer 40

Having succulent stems and leaves increases the pathway for diffusion of water from the plant to the environment.
Reduces rate of diffusion of water out of the leaf and so water uptake.

Question 41

Cactus - many shallow roots

Answer 41

Can absorb a higher volume of surface water by osmosis.

Question 42

Hydrophytes

Answer 42

Hydrophytes are plants that live in water.

Question 43

Sinks

Answer 43

Parts of the plant which require sucrose.
Sucrose in low concentration.
Food storage organs (roots/tubers).
Meristems.

Question 44

Sources

Answer 44

Parts of the plant where sucrose is made or stored.
Sucrose in high concentration.
Photosynthesising leaves.
Sometimes food storage organs.

Question 45

relation between sinks and sources

Answer 45

During different growing seasons, sources and sinks can alternate.
The sink will always have the lower concentration of sucrose and the source will always have the higher concentration.

Question 46

LOADING

Answer 46

H+ ions actively pumped out of the companion cell.
H+ ions diffuse back into the companion cells.
down their concentration gradient, through a co-transporter protein, with sucrose.
Sucrose molecules diffuse into the phloem.
Concentration of sucrose increases in the phloem, decreasing the water potential.
Water osmotes into the phloem from the xylem.
Water and sucrose diffuse into the sieve tube through plasmodesmata (passive).

Question 47

UNLOADING

Answer 47

Cells of the sink convert sucrose to glucose to respire or convert sucrose to starch to store.

This maintains a concentration gradient for sucrose.

Sucrose diffuses out of the phloem into the companion cell, then to the sink cells.
This increases the water potential in the phloem.
Water osmotes back the the xylem.
This reduces the hydrostatic pressure.

Question 48

MASS FLOW

Answer 48

Water osmotes from the xylem into the sieve tubes. This increases (hydrostatic) pressure near the source.
At the sink, sucrose diffuses out of the phloem. This creates a lower hydrostatic pressure at the sink.
Sucrose solution flows from high hydrostatic pressure to low hydrostatic pressure.

Question 49

evidence for translocation

Answer 49

Ringing a tree causes sugars to collect above the ring

Aphids plug their piercing mouthparts (stylets) into sieve cells, and the pressure in the phloem pushes its contents into the insect’s gut – sometimes so quickly that it exudes from the aphid’s anus.
The contents of sieve cells are under positive pressure, as is shown by the feeding of aphids.

Question 50

plants adapted to reduce water loss

Answer 50

Xerophytes

Question 51

plants adapted to survive in water

Answer 51

Hydrophytes

Question 52

Hydrophytes adaptations to….

Answer 52

help cope with low O2 levels
- air spaces help them float and store of O2
- Stomata only present on top
- flexible leaves and stem so supported by water and prevents damage from currents

Question 53

Factors that affect transpiration rate

Answer 53

light
temp
humidity
wind

Question 54

affect of light on transpiration

Answer 54

light stimulates the opening of the stomata (mechanism). Light also speeds up transpiration by warming the leaf. Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises.

Question 55

affect of temp on transpiration

Answer 55

higher temp the faster the transpiration rate, warmer water molecules have more energy to evaporate this increases the water potential gradient between inside and outside of leaf making the water diffuse out the leaf faster