adaptations for transport in plants

Question 1

xylem

issue implantts

Answer 1

Tissue implants conducting water and dissolved minerals upwards

Question 2

Phloem

plan issue

Answer 2

Plant tissue containing sleeve tube elements and companion cells, translocating sucrose and amino acids from the leaves to the rest of the plant

Question 3

in the roots

Answer 3

xylem is central and star shaped with phloem between groups of Xylem cells
Arrangement resists vertical stresses (pull) and anchors the plant in the soil
Root hair
Epidermis
Cortex
pericycle, phloem, xylem (Steele)

Question 4

In stems

Answer 4

Vascular bundles are in a ring at the periphery, with xylem towards centre and phloem towards outside
Gives flexible support and resists bending
Epidermis
Collenchyma
Fibres (vascular bundles) P,X
Cortex
Medulla

Question 5

in leaves

Answer 5

Vascular tissue is in the mid rib and in a network of veins, giving flexible strength and resistance to tearing
adaxial surface, facing central axis of the plant
adaxial surface facing away from central axis of the plant
Vascular bundle in the leaf vein
collenchyma- compacted parenchyma, P, X

Question 6

Vessels

Answer 6

water conducting structures in angiosperms Comprising cells fused end to end making hollow tubes, with thick, lignified cell walls

Question 7

Tracheid’s

spindle shaped

Answer 7

Spindle shaped, water conducting cells in the xylem of ferns, conifers and angiosperms

Question 8

cell type in xylem- vessels

Answer 8

Occur only in angiosperms.
As Liggin built up in the cell walls, the contents die, leaving an empty space, the lumen
As the tissue develops the N walls of cells break down, leaving a long hollow tube through which water climbs straight up the plant
The liggin is laid down in a characteristic spiral pattern and stains red so xylem is easy to identify in microscope sections

Question 9

cell type in xylem- tracheid’s

Answer 9

Occurs in ferns, conifers and angiosperms but not mosses
Mosses have no water conducting tissue and therefore poorer at transporting water and cannot grow tall as other plants

Question 10

Functions of Xylem

Answer 10

• transport of water and dissolved minerals
• Providing mechanical strength and support

Question 11

Transport in the xylem - Water uptake by the roots

Answer 11

Water is taken up from the soil through the roots and transported to the leaves where it maintains turgidity and is a reactant in photosynthesis
But much water is lost through this the stomata in transpiration
Loss must be offset by constant replacement from the soil.
Region of greatest water uptake is the root hair zone, where surface area of root is enormously increased by presence of root hairs and water uptake is enhanced by the thin cell walls

Question 12

Soilwater

Answer 12

Contains a very dilute solution of mineral salt and has a high water potential
Vacuole and cytoplasm of root hair cell contain a concentrated solution of solute and have a lower, more negative, water potential
Water passes into the root hairstyle by osmosis down a water potential gradient

Question 13

Apoplast pathway

Answer 13

Pathway of water through non living spaces between cells and in cell walls outside the cell membrane

Question 14

symplast pathway

Answer 14

Pathway of water through plant within cells in which molecules diffuse through the cytoplasm and plasmodesmata

Question 15

movement of water through root

ino xlem

Answer 15

Water must move into xylem to be distributed around the plant, Can travel there across the cells of the root cortex
- apoplast pathway: Water moves in the cell walls. Those fibres in cell wall are separated by spaces through which water moves
- symplast pathway: Water moves through the cytoplasm and plasmodesmata.
- Vacuolar pathway: Water moves from vacuole to vacuole.

Question 16

Plasmodesmata in symplast

Answer 16

They are strands of cytoplasm through pits in the cell wall joining adjacent cells so the symplast is a continual pathway across the root cortex

Question 17

Endodermis

Answer 17

Single layer of cells around the pericycle and vascular tissue of the root. Has an impermeable waterproof barrier in its cell wall

Question 18

Casparian strip

Answer 18

Impermeable band of suberin in the cell walls of endodermal cells, blocking the movement of water in the apoplast, so it moves into the cytoplasm

Question 19

Structure and role of the endodermis

Answer 19

Water can only pass into the xylem from the symplast or vacuolar pathways- So it must leave the apoplast pathway
Vascular tissue is surrounded by a region- pericycle
Pericycle is surrounded by a single layer of cells - endodermis
Endodermic cell walls are impregnated with a waxy material suberin forming a distinctive band on the radical and tangential walls- casparian strip
Suberin is hydrophobic so casparian strip prevents water moving further in the apple plus. water And dissolve minerals it contains leave the apoplast then enter the cytoplasm before they move further across the root

Question 20

Movement of water from roots to the leaves

Answer 20

Water always moves down a water potential gradient
It has a very low water potential and soil water, a very dilute solution has a very high water potential
So water moves from the soil through the plant into the air
3 mechanisms: Cohesion tension, capillarity, root pressure

Question 21

cohesion

Answer 21

Attraction of water molecule for each other, seen as hydrogen bonds, resulting from the dipole structure of water molecule

Question 22

Adhesion

Answer 22

Attraction between water molecules and hydrophilic molecules in the cells walls of Xylem

Question 23

Cohesion tension theory

Answer 23

The theory of the mechanism by which water moves up the xylem, as a result of the cohesion and adhesion of water molecules and tension in the water column, All resulting from waters dipole structure

Question 24

Capillarity

Answer 24

movement of water up narrow tubes by capillary action

Question 25

Root pressure

Answer 25

Upward force on water in roots, derived from osmotic movement of water into the root xylem

Question 26

Cohesion tension process

Answer 26

Transpiration, water evaporates from leaf cells into the air spaces and diffuses out through the stomata into the atmosphere.
This draws water across the cells of the leaf in the apoplast, symplast and vaculoar pathways from the xylem
As water molecules leave xylem cells in the leaf, they pull up other water molecules behind them in the xylem. The water molecules all move because they show cohesion. Continuous pull produces tension in the water column

Question 27

Capilarity process

Answer 27

Cohesion between water molecules generate surface tension and combined with their attraction to the walls of the xylem vessels (adhesion), draws the water up.
Capillarity only operates over short distances. May have a role in transporting water in Mosses but only makes a small contribution to water movement in plants

Question 28

root pressure process

Answer 28

Operates over short distances in living plants and is a consequence of movement water from the endodermal cells into the xylem pushing water already there further up.
Caused by the osmotic movement of water down the water potential gradient across the root and into the base of the xylem

Question 29

Transpiration

Answer 29

Evaporation of water vapour from the leaves and other above ground parts of the plant out through stomata into the atmosphere

Question 30

Transpiration stream

Answer 30

The transpiration stream, which is the movement of water up the stem enables processes
such as photosynthesis, growth and elongation as it supplies the plant with water which is
necessary for all these processes. Apart from this, the transpiration stream supplies the plant
with the required minerals, whilst enabling it to control its temperature via evaporation of
water.

Question 31

Effect of temperature on the rates of transpiration

Answer 31

Temperature increase lowers water potential of atmosphere
Increasing kinetic energy of water molecules, accelerating their rate of evaporation from the walls of the mesophll cells and if the stomata are open, it speeds up the rate of diffusion out into the atmosphere
Higher temp causes the water molecule to diffuse away from the lethal quickly reducing water potential around leaf

Question 32

Effects of humidity on weights of transpiration

Answer 32

The air inside leaf is saturated with water vapour so relative humidity is 100%. Humidity of atmosphere surrounding leaf varies but isn’t greater than 100%
transpiration in still air results in accumulation of a layer of saturated air at the surfaces of leaves.
In still air the diffusion shells remain on leaf surface but wind will blow them away , increasing the water potential gradient
The higher the humidity the higher the water potential, water vapour diffuses down this gradient of relative humidity which is also a gradient of water potential away from the leaf

Question 33

Effect of airspeed on the rate of transpiration

Answer 33

Movement of surrounding air blows away a layer of humid air at leaf surface
Water potential gradient between inside and outside of leaf consequently increases and water vapour diffuses out through stomata more quickly
The faster the air is moving, the faster the concentric shells of water vapour get blown away, the faster transpirtation occurs

Question 34

Effect of light intensity on the rate of transpiration

Answer 34

In most plants, stomata opens wider as light intensity increases, increasing rate of transpiration

Question 35

mesophytes

Answer 35

Land plant adapted to neither wet nor dry environments
Although they lose a lot of water it is readily replaced by the uptake
from soil
If plant loses too much water it wilts and leaves droop, the stomata close and leaf surface area available for absorbing light is reduced so photosynthesis is less efficient

Question 36

Xerophytes

Answer 36

Land plant adapted environments with little available liquid water

Question 37

hydrophytes

Answer 37

Plant adapted to living in aquatic environment

Question 38

how mesophytes survived unfavourable times of year

Answer 38

• Many shed their leaves before winter so they don’t lose water by transpiration, when liquid water may be scarce
• The aerial parts of many non woody plants die off in winter so they are not exposed to frost or cold winds, But underground organs survive
• Most annual mesophytes over-winter
  as dormant seeds, w low metabolic rate that no water is required

Question 39

Modifications of xerophytes

Answer 39

Rolled leaves
sunken stomata
stiff hairs
Thick, waxy cuticle
Stiff fibres of sclerenchyma

Question 40

Rolled leaves

Answer 40

Large thin walled epidermal cells at base of grooves - called hinge cells
They are plasmaalized when they lose water from excessive transpiration and leaf roles with its adaxial surface inwards
Reduces leaf area exposed the air, so reduces transpiration

Question 41

Sunken stomata

Answer 41

Occurs in grooves on the adaxial surface but not outer (abaxial) surface of leaf
Somata lies in pits or depressions and humid airs trapped in the pits outside it, Reduces water potential gradient between inside of leaf and outside so reduces rate of diffusion of water out through the stomata

Question 42

Stiff hairs

Answer 42

Interlocking hair traps water vapour and reduces water potential gradient between the inside of the leaf and outside

Question 43

thick waxy cuticle

Answer 43

Waxy covering over abaxial leaf surface
Wax is waterproof and reduces water loss, the thicker the cuticle the lower the rate of transpiration through cuticle

Question 44

Stiff fibres of sclerenchyma

Answer 44

So leaf shape is maintained even when the cells become flaccid

Question 45

Adaptations of hydrophytes

Answer 45

• Water is a supported medium so they have little or no lignified support tissues
• Surrounded by water, there is little need for transport tissue so xylem is poorly developed
• Leaves have little or no cuticle because there’s no need to reduce water loss
• Stomata are on the upper surface of floating leaves because lower surface is in the water
• Stems and leaves have a large air spaces, continuous down to their roots forming a reservoir of O2 and CO2 which provide buoyancy

Question 46

Translocation

Answer 46

The movement of soluble products are photosynthesis ( Like Sucrose and amino acids) thru phloem from sources to sinks

Question 47

Sleeve tube elements

Answer 47

Component of phloem, Lack in a nucleus, but with cellulose cell walls perforated by sleeve plates, through which products of photosynthesis are conducted up, down or sideways through a plant

Question 48

Sucrose entering phloem

Answer 48

Sucrose enters the phloem in a process known as
active loading where companion cells use ATP to
transport hydrogen ions into the surrounding tissue,
thus creating a diffusion gradient, which causes
the H+ ions to diffuse back into the companion
cells. It is a form of facilitated diffusion involving
cotransporter proteins which allows the returning H+ ions to bring sucrose molecules into the
companion cells, thus causing the concentration of
sucrose in the companion cells to increase. As a
result of that, the sucrose diffuses out of the companion cells down the concentration gradient
into the sieve tube elements through links known
as plasmodesmata.

Question 49

As Sucrose enters sleeve tube elements

Answer 49

As sucrose enters the sieve tube elements, the water potential inside the tube is reduced,
therefore causing water to enter via osmosis, as a result increasing the hydrostatic pressure of the sieve tube. Therefore, water moves down the sieve tube from an area of higher pressure to an area of lower pressure. Eventually, sucrose is removed from the sieve tube elements by diffusion or active transport into the surrounding cells, thus increasing the water potential in the sieve
tube. This in turn means that water leaves the sieve tube by osmosis, as a result reducing the
pressure in the phloem at the sink.

Question 50

Ringing experiments- transport in the phloem

Answer 50

Early evidence was obtained from rigging experiments with cylinders of outer bark tissue was removed from all the way around woody stem in a ring removing phloem
Above the ring there was a lot of Sucrose suggesting it had been translocated in phloem
Below the ring there was no sucrose suggesting it had been used by the plant tissues but not replaced because ring prevented it from being moved downwards
bark swelled slightly because solutes were accumulating as they could not move down below the ring

Question 51

Radioactive tracers and autoradiography

Answer 51

A plant’s photosynthesis in the presence of a radioactive isotope eh C14
Stem section is placed on a photographic film which is fogged if there’s a radiation source producing an auto radiograph. Position of fogging and therefore the radioactivity coincides with position phloem indicating that it is the phloem that translocates the sucrose made from 14CO2 in photosynthesis

Question 52

Aphid experiments

Answer 52

An aphid has a hollow needle like mouthpart - stylet
This is inserted into a sieve tube and phloem contents, the sap, exude under pressure into the aphids stylet
In some experiments the acid was anesthetised and removed. Stylet remained embedded in the phloem. As the sap in phloem is under pressure it exuded from the stylet and was collected and analysis showed presence of sucrose

Question 53

Aphids and radioactive tracers

Answer 53

Aphid experiments were extended to plants which had been photosynthesizing with 14CO2
These showed that the radioactivity and therefore the sucrose made in photosynthesis, moved at 0.5-1 m h^-1
This is much faster than the rate of diffusion alone so some additional mechanism had to be considered