Week 10 Flashcards
Plasmolysis would occur when
a cell is placed in a very concentrated solution.
Water will move
from a location with a higher water potential to a location with a lower water potential.
A cell that is swollen with water is said to be
turgid
The hydrostatic pressure that builds as water enters plant cells and presses on the cell wall, is called _________
pressure.
turgor
Choose all components of the water potential of a solution in a plant cell.
Gravity
Pressure
Solute concentration
If a cell loses water, the cell membrane pulls away from the wall in a process called
plasmolysis
If the water potential outside a cell is -0.3 MPa and the water potential inside the cell is -0.5 MPa, will water move and in what direction?
Water will move into the cell.
Reason: Water moves from a high water potential to a low water potential. The water potential outside the cell is higher (a larger number) than inside the cell.
The solute potential of pure water is
Zero
A turgid cell is
stiff
Under mild drought conditions, plants may be stunted because
stomata are closed so carbon dioxide is not taken in for photosynthesis.
Turgor pressure requires
cell walls to constrain the expansion of cells as they take up water
The water potential of a solution has two components: _________
forces (such as pressure, or gravity), and the concentration of ________
in the solution.
Blank 1: physical
Blank 2: solutes
Select all functions of stomata.
Minimize water loss
Admit carbon dioxide
The addition of solutes to water
decreases the water potential.
The cells that border stomata are called _________
cells.
Blank 1: guard
Plants are always dealing with the trade-off between open stomata, in which CO2 is taken in but _________
is lost, and closed stomata, in which the same compound is retained, but CO2 is not taken in.
water
The gravitropic response is
negative in shoots and positive in roots.
The first step in the root gravitropic response is the perception of gravity. The last step is differential ______.
cell elongation
In gravitropism, a ________
signal is converted into a ________
signal.
mechanical
physiological
Structural features on leaf epidermal cells, called _______
, have evolved to minimize water loss, while allowing carbon dioxide uptake.
stomata
In shoots, gravity appears to be sensed along the length of the stem in ______.
endodermal cells
What feature of guard cells allows them to open stomata when turgor pressure in them changes?
Their cells are thicker on the inside and thiner elsewhere.
In negative gravitropism, how do cells respond to auxin?
Cells on the lower side of a stem grow more rapidly than cells on the upper side
Plant roots are ________
gravitropic, and plant stems are ________
gravitropic.
Blank 1: positively
Blank 2: negatively
The roots and stems of plants bend in response to gravity due to ______.
differential growth
Which type of signal transduction occurs in gravitropism?
A mechanical signal is transduced into a physiological signal.
In roots, gravity is sensed by cells in which area?
Root cap
When a stem is placed on its side, auxin
causes the lower cells to elongate.
What happens due to low turgor pressure?
stomata closes
What is tropism?
directional growth response to external cue
What is negative phototropism?
Negative- growing away from the cue.
What is the difference between negative and positive gravitropism?
Negative gravitropism
(away from gravity vector)
Positive gravitropism
(towards gravity vector)
What happens due to shoot gravitropism in trees?
• Trees on steep mountain slopes can be pushed sideways by snow and avalanches • To regain vertical shoot growth, lower side puts on more growth – visible in growth rings
What is the process of Shoot gravitropism?
Signal to Signal perception to Signal transduction to Response.
What is required for differential growth?
Differential growth:
Auxin (plant hormone) is
required for shoot growth
What does auxin lead to?
Auxin leads to cell elongation in the coleoptile
Where is signal perception in shoot gravitropism?
Signal perception is in a specific cell layer
containing amyloplasts
When do plants show no shoot gravitropism?
Plants without endodermis show no shoot gravitropism
Outline shoot gravitropism: Signal transduction
Undisturbed shoot growth:
• High auxin concentration at the tip of the
shoot (shoot apical meristem)
• Auxin is transported equilaterally from the tip
to the bottom of the shoot (coleoptile)
• Growth of shoot is driven by auxin in a dosedependent relationship
What happens due to Undisturbed shoot growth?
auxin transported
from the tip of the coleoptile to the bottom
What happens due to Gravitropism signal transduction?
Statolith
movement leads to change in auxin flow.
Experiment with coleoptile tip on two agar
blocks.
Auxin transported from the shoot tip
accumulates in agar blocks.
• Gravistimulated shoot: Auxin flow is redirected
laterally, more auxin flows to the lower half of
the shoot.
• Agar block placed on coleoptile with tip
removed (no source of auxin).
• Coleoptile with agar block from lower half of tip
shows increased differential growth (bending).
Differential growth is needed for
gravitropic
bending
How does the shoot bend?
Cells on the lower side of the root grow more
than on the upper side: shoot bends
What is the amount of growth dependent on?
Amount of growth depends on amount of auxin:
in shoot tissue, more auxin = more growth
Auxin leads to
cell growth
Outline the Acid-induced growth of plant cells
• Acidification of cell wall leads to loosening of cross links between cellulose microfibrils • If cell wall strength is reduced, turgor pressure can drive cell growth
What is the Acid growth hypothesis?
Auxin causes the acidification of cell walls
This is still somewhat controversial and
there are probably other factors that
contribute to cell wall acidification.
Gravity signal perception is through
movement of
amyloplasts in the endodermis layer
Signal transduction is through
changes in auxin
transport: more auxin is transported to the lower side of
the shoot
Changes in auxin transport lead to
differential growth:
more growth on lower side of shoot
Acid growth hypothesis links
links auxin to increased cell wall acidification, which leads to changes in cellulose microfibril crosslinks, which allow turgor pressure to
drive cell growth
What happens if you have an acidic cell wall?
If you have an acidic cell wall you have some plant cells that have a better ability to grow as it affects how the cellulose microfibrils are bond/ crosslinked together- high tensile strength which enables them to withstand the turgor pressure.
Plants are acutely aware of their _____ and produce very specific _______.
Blank 1- environment
Blank 2- responses
What are some biotic plant responses to their environment?
Herbivory diseases causes a signal transduction making defence response compounds.
What are some abiotic plant responses to their environment?
light, water, gravity, nutrients and temperature lead to a signal transduction that causes responses such as
What are all plants surrounded by?
A cell wall
What is the cell wall?
• Cell wall is extracellular matrix:
outside the plasma membrane
• Rigid structure that provides support and protection
• Cells are fixed in their position and cannot migrate
The cell wall has
several layers
What do the cell wall layers suggest?
Cell wall is built in layers, oldest layer is
furthest away from the cell
What is the middle lamella?
oldest layer of cell wall
(derived from cell plate, cell division).
contact zone between cell
walls of two cells, Pectin (polysaccharide)
What happens during cytokinesis in plants?
- Rigid cell wall prevents migration of cells or division by cleavage of plant cells
- Golgi-derived vesicles move along microtubules towards middle of cell
- Vesicle coalesce to form cell plate (new compartment surrounded by membrane)
- Cell wall forms inside cell plate
What is the primary cell wall?
second oldest layer of cell
wall
What is the secondary cell wall?
(not all cells have this):
youngest layer of cell wall
What is the main structural component of the primary and secondary cell wall?
Main structural component of primary and secondary cell wall are cellulose fibres
What is a major component of a cell wall?
Cellulose fibres
Explain the cellulose cell walls?
- Made of glucose molecules
- Long chains of glucose molecules
- Cellulose molecules are tightly packed together in cellulose microfibrils
What are cellulose microfibrils made by?
made by cellulose
synthase complexes in the plasma membrane
Where are the new cellulose microfibrils deposited?
deposited outside the cell
What are the enzyme complex (multimer) linked to?
Enzyme complex (multimer) is linked to microtubule in the cytosol and is pushed along it during synthesis
What is the orientation of cellulose microfibril?
Orientation of cellulose microfibril is parallel to microtubule
What does the orientation of cellulose microfibrils determine?
Orientation of cellulose microfibrils determines growth and cell shape
responses to the environment
The cell wall is a
complex structure
What are the properties of the complex structure of the cell wall?
• Cellulose microfibrils
crosslinked with other glycans (rigidity) several layers orientation of fibres is important
• Proteins (e.g. extensins, change rigidity)
• Lignin (polymer, improves rigidity)
• Suberin (wax, water proofing)
Cell walls give plant cells
specific shapes and structures
Cellulose microfibril orientation in the cell wall is controlled by
the cell
What are the several layers that the plant cells are built from?
middle lamella, primary and secondary walls
Cellulose microfibrils synthesized from
glucose are the major
structural component of the cell wall
Cellulose microfibrils are synthesized by
a multimeric cellulose
synthase enzyme complex in the plasma membrane
Association of the cellulose synthase enzyme complex with microtubules determines the
the orientation of cellulose microfibrils
What is essential for plant cell shape?
Water
What happens when plants cannot take up water?
If plants cannot take up water from their growth medium (environment), cells (and whole plant) will lose their shape.
Water movement across a semi-permeable
membrane depends on
solute concentration
What is a property of the plasma membrane?
The plasma membrane is semi-permeable: water moves more easily across than larger molecules (solutes).
What happens if teh solute concentration is different between compartments separated by plasma membranes?
water will move to
compartment with higher solute concentration.
Rigid cell walls lead to
to turgor pressure in plant cells
What happens when plants are under normal growth conditions?
Under normal growth
conditions, plant cells are
pressurised.
What does Turgor pressure contribute to?
Turgor pressure contributes to cell (and plant) shape
What happens during Plasmolysis?
• Cell volume shrinks
• plasma membrane
detaches from cell
wall
What happens when there is turgor pressure?
• Cell volume increases
• Volume increase is
resisted by rigid cell wall
What is water potential used to describe?
Water potential (ψ, psi) is used to describe the
direction of water movement in plants (and
environment)
Where does water always move to?
Water always moves from cells or parts of the plant
with high ψ to cells or part of the plant with lower ψ.
What does water potential also determine?
Water potential also determines water uptake from soil and transpiration.
How is water potential measured?
Measured as a pressure (megapascals, MPa)