Chapter 36 Transport in Plants - PowerPoint PPT Presentation

1 / 38
About This Presentation
Title:

Chapter 36 Transport in Plants

Description:

H2O H2O H2O H2O H2O Xerophyte Adaptations That Reduce Transpiration Xerophytes are plants adapted to arid climates They have various leaf modifications that reduce ... – PowerPoint PPT presentation

Number of Views:164
Avg rating:3.0/5.0
Slides: 39
Provided by: Glas2
Category:

less

Transcript and Presenter's Notes

Title: Chapter 36 Transport in Plants


1
Chapter 36Transport in Plants
2
  • For vascular plants the evolutionary movement
    onto land involved the differentiation of the
    plant body into roots and shoots
  • Vascular tissue transports nutrients throughout a
    plant this transport may occur over long
    distances

3
Transport Scale/Distance
  • Transport in vascular plants occurs on three
    scales
  • Transport of water and solutes by individual
    cells, such as root hairs
  • Short-distance transport of substances from cell
    to cell at the levels of tissues and organs
  • Long-distance transport within xylem and phloem
    at the level of the whole plant

4
Overview of Transport in Plants
CO2
O2
Light
H2O
Sugar
Sugars are transported as phloem sap to
roots and other parts of the plant.
O2
H2O
CO2
Minerals
5
Selective Permeability of Membranes
  • The selective permeability of a the plasma
    membrane controls the movement of solutes into
    and out of the cell
  • Specific transport proteins are involved in
    movement of solutes

6
Proton Pumps
  • Proton pumps create a hydrogen ion gradient that
    is a form of potential energy that can be
    harnessed to do work
  • Contribute to a voltage known as a membrane
    potential

7
  • Plant cells use energy stored in the proton
    gradient and membrane potential to drive the
    transport of many different solutes

8
Cotransport
  • In cotransport a transport protein couples the
    passage of one solute to the passage of another

9
Sucrose uptake
  • The cotransport is also responsible for the
    uptake of the sugar sucrose by plant cells

10
Happy 200th Birthday Mr. Darwin
Feb 12th 1809
11
Water Potential
  • To survive plants must balance water uptake and
    loss
  • Remember Osmosis is the passive transport of
    water across a membrane
  • Water potential is a measurement that combines
    the effects of solute concentration and physical
    pressure (due the presence of the plant cell
    wall) and determines the direction of movement of
    water
  • Water flows from regions of high water potential
    to regions of low water potential

12
Plasmolysis
  • If a flaccid cell (not firm) is placed in an
    environment with a higher solute concentration
    (Hypertonic)
  • The cell will lose water and become plasmolyzed

13
Turgidity
  • If the same flaccid cell is placed in a solution
    with a lower solute concentration (Hypotonic)
  • The cell will gain water and become turgid
  • Healthy plant cells are turgid most of the time

Turgidity helps support nonwoody plant parts
14
Wilting
  • Turgor loss in plants causes wilting which can be
    reversed when the plant is watered

15
Aquaporins
  • Water molecules are small enough to move across
    the lipid bilayer of the plasma membrane, but
    they also move through specific channels for the
    passive diffusion of water across the
    membraneAquaporins
  • Aquaporins dont effect the direction of water
    flow, but rather the rate of diffusion.

16
Three Major Compartments of Vacuolated Plant Cells
  • Transport is also regulated by the compartmental
    structure of plant cells (3 compartments)
  • Cell Wall
  • The plasma membrane controls the traffic of
    molecules into and out of the protoplast and is
    the barrier between the cell wall and the cytosol
  • Cytosol
  • Vacuole

17
Vacuole
  • The vacuole is a large organelle that can occupy
    as much as 90 of more of the protoplasts volume
  • The vacuolar membrane
  • Regulates transport between the cytosol and the
    vacuole

18
Cell-to-cell continuity
  • The cell walls and cytosol are continuous from
    cell to cell in most plant tissues
  • The cytoplasmic continuum is called the symplast
  • The cell wall continuum is called the apoplast

19
Short Distance Transport of Water/Solutes in
Tissues and Organs
  • Water and minerals can travel through a plant by
    one of three routes
  • Out of one cell, across a cell wall, and into
    another cell (transmembrane route)
  • Via the symplast (symplastic route)
  • Along the apoplast (apoplastic route)

20
Bulk Flow in Long-Distance Transport
  • In bulk flow movement of fluid in the xylem and
    phloem is driven by pressure differences at
    opposite ends of the xylem vessels and sieve
    tubes
  • Transpiration (evaporation of water from a leaf)
    reduces pressure in the leaf xylem. This creates
    a tension (negative pressure) that pulls material
    up the xylem
  • In phloem, hydrostatic pressure (pressure exerted
    upon the tube from the surrounding tissue) is
    generated at one end of a sieve tube, which
    forces sap to the other end of the tube

21
Roots absorb water and minerals from the soil
  • Water and mineral salts from the soil enter the
    plant through the epidermis of roots and
    ultimately flow to the shoot system
  • Soil solution?Root Hair Epidermis?Root Cortex
    ?Root Xylem
  • Root Hairs
  • Much of the absorption of water and minerals
    occurs near root tips, where the epidermis is
    permeable to water and where root hairs are
    located
  • Root hairs account for much of the surface area
    of roots

22
Root growth
Movie
23
Lateral transport of minerals and water in roots
24
Mycorrhizae
  • Most plants form mutually beneficial
    relationships with fungi, which facilitate the
    absorption of water and minerals from the soil
  • Roots and fungi form mycorrhizae, symbiotic
    structures consisting of plant roots united with
    fungal hyphae

White mycelium of the fungus around this pine
root provides a vast surface area for absorption
of water and minerals from the soil.
25
The Endodermis
  • Is the innermost layer of cells in the root
    cortex
  • Surrounds the vascular cylinder and functions as
    the last checkpoint for the selective passage of
    minerals from the cortex into the vascular tissue
  • Water can cross the cortex via the symplast or
    apoplast
  • The waxy Casparian strip of the endodermal wall
    blocks apoplastic transfer (but not symplastic)
    of water and minerals from the cortex to the
    vascular cylinder

26
Ascent of Xylem Sap
  • Plants lose an enormous amount of water through
    transpiration and the transpired water must be
    replaced by water transported up from the roots
  • Xylem sap rises to heights of more than 100 m in
    the tallest plants

27
Pushing Xylem Sap Root Pressure
  • At night, when transpiration is very low, root
    cells continue pumping mineral ions into the
    xylem of the vascular cylinder, which lowers
    water potential
  • Water flows in from the root cortex generating a
    positive pressure that forces fluid up the xylem.
    This is upward push is called root pressure

28
Root Pressure-Gluttation
  • Root pressure sometimes results in guttation,
    (the exudation of water droplets on tips of grass
    blades or the leaf margins of some small,
    herbaceous dicots in the morning). More water
    enters the leaves than is transpired, and the
    excess is forced out of the leaf.

29
Pulling Xylem Sap
  • The Transpiration-Cohesion-Tension Mechanism
  • Transpirational Pull
  • Water vapor in the airspaces of a leaf diffuses
    down its water potential gradient and exits the
    leaf via stomata
  • Transpiration produces negative pressure
    (tension) in the leaf which exerts a pulling
    force on water in the xylem, pulling water into
    the leaf

30
Cohesion and Adhesion in the Ascent of Xylem Sap
  • The transpirational pull on xylem sap
  • Is transmitted all the way from the leaves to the
    root tips and even into the soil solution
  • It is facilitated by the cohesion and adhesion
    properties of water

31
Transpiration Control
  • Stomata help regulate the rate of transpiration
  • Leaves generally have broad surface areas and
    high surface-to-volume ratios
  • These characteristics (1) increase photosynthesis
    (2) Increase water loss through stomata

32
Effects of Transpiration on Wilting and Leaf
Temperature
  • Plants lose a large amount of water by
    transpiration. If the lost water is not replaced
    by absorption through the roots the plant will
    lose water and wilt
  • Transpiration also results in evaporative
    coolingwhich can lower the temperature of a leaf
    and prevent the denaturation of various enzymes
    involved in photosynthesis and other metabolic
    processes

33
  • About 90 of the water a plant loses escapes
    through stomata
  • Each stoma is flanked by guard cells which
    control the diameter of the stoma by changing
    shape

Guard Cells
34
  • Changes in turgor pressure that open and close
    stomata result primarily from the reversible
    uptake and loss of potassium ions by the guard
    cells

35
Xerophyte Adaptations That Reduce Transpiration
  • Xerophytes are plants adapted to arid climates
  • They have various leaf modifications that reduce
    the rate of transpiration
  • The stomata of xerophytes
  • Are concentrated on the lower leaf surface
  • Are often located in depressions that shelter the
    pores from the dry wind

Stomata in recessed crypts of Oleander plant
36
Translocation of Phloem Sap
  • Organic nutrients are translocated through the
    phloem (translocation is the transport of organic
    nutrients in the plant)
  • Phloem sap
  • Is an aqueous solution that is mostly sucrose
  • Travels from a sugar source to a sugar sink
  • A sugar source is a plant organ that is a net
    producer of sugar, such as mature leaves
  • A sugar sink is an organ that is a net consumer
    or storer of sugar, such as a tuber or bulb

37
Seasonal Changes in Translocation
  • A storage organ such as a tuber or bulb may be a
    sugar sink in summer as it stockpiles
    carbohydrates.
  • After breaking dormancy in the spring the storage
    organ may become a source as its stored starch is
    broken down to sugar and carried away in phloem
    to the growing buds of the shoot system

38
Phloem loading
  • Sugar from mesophyll leaf cells must be loaded
    into sieve-tube members before being exported to
    sinks
  • Depending upon the species, sugar moves by
    symplastic and apoplastic pathways

In many plants phloem loading requires active
transport. Proton pumping and cotransport of
sucrose and H enable the cells to accumulate
sucrose.
Write a Comment
User Comments (0)
About PowerShow.com