BIO225 Ch. 35
A plant is introduced to a new environment where the soil solute potential is Ψs= -0.45. If the water potential in the root is Ψw= -0.1 and the Ψp= 0.2, what will happen when we add water to the plant?
-0.1 = 0.2 + Ψs -0.3 = Ψs for root Water exits the root because Ψs is lower in soil
If ΨP= 0.3 MPa and ΨS= −0.45 MPa, the resulting Ψwis ________.
-0.15
What are the five events that explains the mass flow of materials in the phloem?
1. Leaf cells produce sugar by photosynthesis 2. Water diffuses into the sieve tubes 3. Sugar is transported from cell to companion cell in the leaf 4. Solutes are transported into sieve tubes 5. Sugar moves down or up the stem
How does a flaccid cell differ from a turgid cell?
A flaccid cell has lower pressure potential.
Water potential (ΨW) can be thought of as the tendency for water to move from one place to another. In plants, it is made up mainly of solute potential and pressure potential. Hypothetical plant cells A and B are adjacent to each other. The solute potential (ΨS) of cell A is -0.35MPa, and its pressure potential (ΨP) is 0.15MPa. The solute potential (ΨS) of cell B is -0.30MPa, and its pressure potential (ΨP) is 0.05MPa. In which direction will net water movement occur? ΨW = ΨS - ΨP
A: YW = -0.35 + 0.15 YW = -0.20 B: YW = -0.30 + 0.05 YW = -0.25 From cell A to cell B
Which of the following transmembrane transport mechanisms requires the expenditure of energy?
Antiporter
What would enhance water uptake by a plant cell?
Decrease the Ψs of the cytoplasm
Which cells in a root form a protective barrier to the vascular system where all materials must move through?
Endodermis
Which of the following has the lowest (most negative) water potential?
Leaf air spaces.
In the pressure-flow mechanism, loading of sucrose from companion cells to sieve-tube elements takes place through ________.
Plasmodesmata
What would enhance water uptake by a plant cell?
Positive pressure on the surrounding solution
Water flows into the source end of a sieve tube because...
Sucrose has been actively transported into the sieve tube, making it hypertonic.
Which of the following supports the finding that sugar translocation from mesophyll cells into companion cells is an active process?
Sucrose occurs in higher concentrations in companion cells than in the mesophyll cells where it is produced
What drives the flow of water through the xylem?
The evaporation of water from the leaves
If isolated plant cells with a water potential averaging −0.5 MPaare placed into a solution with a water potential of −0.3 MPa, which of the following would be the most likely outcome?
The pressure potential of the cells would increase.
When an animal cell is placed in a hypotonic solution and water enters the cell via osmosis, the volume of the cell increases until it bursts. This does NOT happen to plant cells, because...
They have cell walls, which provide pressure to counteract the pressure of the incoming water.
The value for Ψwin root tissue was found to be −0.15 MPa. If you take the root tissue and place it in a 0.1M solution of sucrose (Ψw= −0.23 MPa), the net water flow would...
be from the tissue into the sucrose solution
Compared to plants from other environments, the cells of many desert plants contain high concentrations of solutes. This helps them survive in their arid surroundings because the high solute concentrations create relatively ________ solute potential, which help reduce water loss.
low
______ is to xylem as _____ is to phloem
vessel element; sieve-tube member
As an undergraduate research assistant, your duties involve measuring water potential in experimental soil-plant-atmosphere systems. Assume you make a series of measurements in a system under normal daylight conditions, with stomata open and photosynthesis occurring. What depicts the trend your measurement data should follow if the cohesion-tension mechanism is operating?
Ψatmosphere < Ψleaves < Ψroots < Ψsoil
