Plant Transport pdf.

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1

Plant Acquisition of Resources

Success depends on ability
to gather and conservere sources from environment
Transport of materials is
critical to a plant’s integrated functioning

2

Transport of Substances

Plants have developed mechanisms for
transporting substances over short or long distances

The vascular system...Allows extensive root and shoot systems. Provides long-distance transport. Results in competition for light, water, nutrients

3

Xylem

Transports water and minerals
from roots to shoots

4

Phloem

Transports photosynthetic
products from where they are made or stored (sources) to where they are required (sinks)

5

Adaptations in each species represent ?

compromises between enhancing photosynthesis and minimizing water loss

6

Two principal compartments of plant tissue

Apoplast

Symplast

7

Apoplast

Consists of everything external to plasma membrane

▪Cell walls, extracellular spaces, and the interior of vessel
elements and tracheids

8

Symplast

Consists of the cytosol of the living cells as well as the
plasmodesmata
▪Plasmodesma (singular) – a microscopic channel that crosses the cell walls of plant cells allowing transport and communication between them.

9

Three transport
routes for water and solutes

Apoplastic route -Through cell walls and extracellular spaces

Symplastic route -Through the cytosol

Transmembrane route -Across cell walls

10

Short-distance transport across plasma
membranes

Solutes

Water

11

Long-distance transport

Bulk flow

12

How short-distance works

 Plasma membrane
permeability controls short-distance movement of substances
 Both active and passive
transport occur in plants
 Membrane potential is established through pumping H+ by proton pumps
Animals – movement of
Na+ by Na+ K+ pumps

Plant cells use the energy of H+ gradients to cotransport other solutes by active transport

Plant cell membranes have ion channels that allow only certain ions to pass

13

To survive, plants must balance

water uptake and loss.

Osmosis
Determines net uptake or water loss by a cell
Affected by solute concentration and pressure

14
card image

A

15
card image

A. increase

16

Water potential

Measurement that combines the effects of...Solute concentration & Pressure
Determines the direction of movement of water

Water flows from regions of higher water
potential to regions of lower water potential
Potential refers to water’s capacity to
perform work

17

Water Potential is measured ?

Measured in megapascal (MPa)

(Y) = 0 MPa Pure water at sea level, room temperature

18

How solutes and pressure affect water potential

Pressure & solute conc. affect water potential (Y)=(Y)S+(Y)P

(Y)S = solute potential

▪Proportional to molarity ▪Also called osmotic potential

(Y)P = pressure potential

▪Physical pressure on a solution

19

Turgor pressure

The pressure exerted by
▪The plasma membraneagainst the cell wall
▪The cell wall against the protoplast (living part of cell, which also includes the plasma membrane)

20

Water movement across the plant cell membranes

Water potential affects uptake and loss of water by plant cells
If a flaccid (limp) cell is placed in an
environment with a higher solute concentration, the cell will lose water and undergo plasmolysis
Plasmolysis occurs when the protoplast
shrinks and pulls away from the cell wall

Turgor loss causes wilting Reversed when the plant is watered

21

Aquaporins

Transport proteins in cell membrane that allow H2O passage

Affect rate of water movement across the membrane

22

The role of Bulk flow

Movement of a fluid driven by pressure

Allows efficient long-distance transport

 Water and solutes move together through tracheids and vessel elements of xylem and sieve-tube elements of phloem
 Efficient movement is possible because

Mature tracheids and vessel elements have no cytoplasm

Sieve-tube elements have few organelles in cytoplasm

23

A flaccid (limp) cell is placed in an environment with higher solute concentration....what will occur to the cell ?

the cell will lose water and undergo plasmolysis

the protoplast shrinks and pulls away from the cell wall

24

Which of the following is a correct statement about a difference between xylem and phloem transport?

Xylem sap moves up; phloem sap moves up or down.

Xylem sap moves from sugar source to sink, but phloem sap does not.

Active transport moves xylem sap but not phloem sap.

Phloem carries water and minerals; xylem carries organic molecules.

Transpiration moves phloem sap but not xylem sap.

Xylem sap moves up; phloem sap moves up or down.

*The direction of movement in xylem is from roots to leaves. Phloem sap is transported throughout the plant from source to sink.

25

Which of the following statements about xylem is incorrect?

It conducts material from root tips to leaves.

The conducting cells are part of the apoplast.

No energy input is required for transport.

It typically has a lower water potential than is found in soil.

It transports mainly sugars and amino acids.

It transports mainly sugars and amino acids.

26

Plants do not have a circulatory system like that of some animals. If a water molecule did "circulate" (that is, go from one point in a plant to another and back in the same day), it would require the activity of

only the phloem.

both the xylem and the phloem.

only the xylem.

only the endodermis.

both the xylem and the endodermis

both the xylem and the phloem.

27

The proton pump _____.

releases kinetic energy

is a passive process

uses the energy of a proton gradient to generate ATP

operates by osmosis

uses the energy stored in ATP to produce a hydrogen ion gradient across membranes.

uses the energy stored in ATP to produce a hydrogen ion gradient across membranes.

*This proton gradient occurs across a membrane.

28

A plant cell placed in a solution with a lower (more negative) water potential will _____.

gain water and become turgid

lose water and plasmolyze

lose water and burst

lose water and become turgid

gain water and plasmolyze

lose water and plasmolyze

*Water moves from a region of higher water potential to a region of lower water potential. Loss of water pulls the plasma membrane away from the cell wall, producing plasmolysis.

29

The solute most abundant in phloem sap is __________.

amino acids

water

sugar

minerals

hormones

sugar

*Phloem transports sugar from a sugar source to a sugar sink.

30

A student is performing a chemical analysis of xylem sap. This student should not expect to find much __________.

phosphorus

potassium

nitrogen

water

sugar

sugar

* Phloem, not xylem, transports sugar.

31

Which one of the following refers to the loss of water through the stomata in a plant's leaves? bulk flow

transpiration

osmosis

respiration

guttation

transpiration

*The stomata in the leaves are entry points for the carbon dioxide necessary for photosynthesis, but they are also exit points for the evaporation of water by transpiration.

32

All of the following are involved in movement of sucrose into the phloem in most plants except __________.

cotransport

proton pumping

active transport

concentration gradients

facilitated diffusion

facilitated diffusion

*Proton pumping, cotransport of H+ and sucrose, and active transport all describe the movement of sucrose into phloem because sucrose is more concentrated in sieve-tube elements than in mesophyll. Facilitated diffusion is a form of passive transport using the substance’s concentration gradient to move it across a biological membrane from high concentration to low concentration.

33

The proton pump __________.uses the energy of a proton gradient to generate ATP

is a passive process

releases kinetic energy

operates by osmosis

uses the energy stored in ATP to produce a hydrogen ion gradient across membranes.

uses the energy stored in ATP to produce a hydrogen ion gradient across membranes.

*This proton gradient occurs across a membrane.

34

Nitrogen-fixing bacteria in the soil __________.

convert nitrate to ammonium

use nitrates to make amino acids that plants can use

change ammonium into nitrates

convert atmospheric nitrogen to ammonia convert nitrates to N2

convert atmospheric nitrogen to ammonia

*Nitrogen fixation is the conversion of N2 (atmospheric nitrogen) to NH3.

35

The relationship between legumes and Rhizobium is __________.

parasitic

commensalistic

predatory

competitive

mutualistic

mutualistic

*Both the legume and the Rhizobium benefit from this relationship. The legume gains a supply of fixed nitrogen from Rhizobium, and Rhizobium gains organic nutrients from the legume.

36

Plants must always compromise between __________ and __________.

maximizing access to light ... minimizing intake of CO2

maximizing photosynthesis ... minimizing water loss

maximizing water loss ... minimizing H+ protons

maximizing transport of minerals ... minimizing transport of sugars

maximizing water absorption ... minimizing leaf area

maximizing photosynthesis ... minimizing water loss

*Structures, such as broad leaves, that enhance photosynthesis also maximize water loss. Plant form is generally a compromise between the two, depending on the plant's environment.