Osmosis and water potential

What is a HYPOtonic solution?

(less concentrated solution) - the concentration of solutes is lower outside the cell

Compare diffusion and osmosis

- Diffusion is the movement of molecules from an area of high concentration to an area of low concentration - both solute and solvent move - Osmosis is the movement of solvent (water) across a semipermeable membrane from high to low solvent concentration - ONLY SOLVENT MOVES

Why is it important for animal cells to be in an isotonic solution?

If animal cells are in a hypertonic solution (cytoplasm has higher WP compared to solution outside of the cell), water will leave by osmosis causing the cell to shrink and for little spikes to appear on the cell membrane

What happens at the stoma?

gaseous exchange

How does water move in a hypotonic solution?

into the cell

How does water move in osmosis? (in terms of solute concentration)

moving from a low-conc. solution to a high-conc. solution

What is water potential?

the ability of a cell to draw water into itself (water pressure)

Healthy plant cells are ___________.

turgid

What is carbon dioxide and oxygen needed for in plants (in leaf cells)?

- carbon dioxide is needed for photosynthesis - oxygen is needed for cell respiration

What can overhydration result in? (3)

1) Headache 2) Nerve function and dysfunction 3) sometimes death

In a plant cell where the water potential inside and outside is the same (isotonic solution), what must be done to make it healthy?

1) equal water potential inside and outside the cell 2) increased pressure potential until the cell turns turgid

Why is the cell wall important in a plant? (2)

1) it prevents the cell from bursting when it gains water 2) the pressure of water in the cytoplasm against the cell wall provides strength for the plant, making it stand upright with its leaves out to catch sunlight

What do guard cells control?

1) the opening and closing of stoma 2) the rate of gaseous exchange (CO2 in, O2 out)

In a wilting plant cell, the extracellular liquid is higher in 3 things. What are they?

1) water potential 2) water pressure 3) osmotic potential (which the inside of the cell will have lower amounts of)

What is the mortality rate of people suffering with burr cells?

27% mortality rate

What do you call an animal/ plant cell in an isotonic solution?

Animal: Plant: flaccid

What do you call an animal/ plant cell in a hypotonic solution?

Animal: lysed Plant: turgid (normal)

What do you call an animal/ plant cell in a hypertonic solution?

Animal: shrivelled Plant: plasmolyzed

When is an animal/ plant cell normal?

Animal: when in an isotonic solution Plant: When in a hypotonic solution (turgid)

Why can water molecules pass through the lipid bilayer of the membrane despite being polar?

Because they are very small

Water molecules always move from a HWC to a ________

LWC

Is there any movement of water when the concentrations of the two solutions are equal?

No

Will a plant cell burst when it gains water?

No, because the cell wall pushes against the cytoplasm, creating high turgor pressure

Are the solutions inside and outside cells the same?

No, in cells we can think of the inside and outside solutions as two separate solutions which are relative (opposite) to each other.

Is water potential ever positive?

No, it has a maximum value of zero, which is that of pure water

Is overhydration common?

No, it is quite rare as the kidney gets rid of excess water

When a cell loses water, does the whole cell shrink?

No, just the cytoplasm

Does the entire plant cell shrink when it loses water?

No, only the cytoplasm shrinks. The whole cell does not shrink because the cell wall maintains the cell shape.

Does osmosis only happen in the root hair cells of a plant?

No, osmosis continues from the surface root hair cells, deeper and deeper into the root tissue until the water molecules reach the xylem vessels

Do only plant cells gain and lose water as a result of osmosis?

No, the same happens in animal cells

What does plasmolyzed mean?

That a cell has lost a lot of water, causing the cytoplasm to shrink so that it starts to pull away from the inside of the cell membrane (creating little pockets of space between the plasma membrane and cell wall)

What does flaccid mean?

That a cell in between plasmolyzed and turgid, so the cell membrane is not pushing up against the cell wall, neither is the plant showing any signs of wilting

What does turgid mean?

That a cell that is full of water so the cytoplasm pushes against cell membrane

Plant cells have cell walls that are completely permeable. What does this mean?

That water and solutes pass easily through them

What happens if a plant cell is placed in a dilute solution (hypotonic solution)?

The concentration of the cytoplasm will be hypertonic (higher solute conc) compared to the surrounding solution which will cause a net movement of water is from the surrounding solution (high water conc) into the cell (lower water conc), therefore the plant cell gains water and the cytoplasm swells

Why would a plant cell lose water?

There would be a high concentration of water in the plant compared to the outside causing a net movement of water from the cells to the surrounding solution

Why do patients suffering from liver or kidney disease have these burr cells?

They are unable to clear waste products out of their blood which causes the RBC to always be in a hypertonic environment (water moves out so the cells look abnormal)

What happens if animal cells take in too much water?

They might burst (lyse) as they do not have cell walls to protect them

Describe osmosis in root hair cells

Water will cross the cell membrane of the root hair cells and enter the plant as a result of osmosis

What happens if the cytoplasm of an animal cell has a lower water potential compared to solution outside of cell?

Water will enter by osmosis causing the Animal cell to swell

What does lysed mean?

When a cell splits open if they become too turgid. (this is due to the swelling of the vacuole, creating a pressure on the walls of the cell - animal cells don't have a cell wall which means they cannot handle the pressure)

Why will water molecules cross the cell membrane of root hair cells into the other cells?

When water enters the root hair cells, their concentration of water molecules will increase to become higher than the concentration of water molecules in surrounding cells, so water molecules will cross the cell membrane of the root hair cells into the other cells

Is osmosis a type of diffusion?

Yes, osmosis is a special form of diffusion of only water molecules

Are water molecules in constant motion?

Yes, this is due to kinetic energy

What is a HYPERtonic solution?

a more concentrated solution, so the concentration of solutes is higher outside the cell

What are each stoma surrounded by?

a pair of kidney-shaped guard cells

What does the swelling of brain cells cause?

an increase in the brain volume, cutting off the blood supply

Why can the effects of osmosis be more dramatic in animal cells than in plant cells?

animal cells do not have a supporting cell wall

How does water move in an isotonic solution?

both in and out of the cell

What do you call an animal cell that has lost water?

crenated

What are burr cells?

crenated red blood cells which are common in patients suffering from liver or kidney disease

Compare the membranes required in diffusion and osmosis

diffusion requires a fully permeable membrane (both solute and solvent move) osmosis requires a semi-permeable membrane (only solvent - water - moves)

a low concentration of water molecules means a high concentration of ...

dissolved solutes (i.e. concentrated solution)

Do water molecules move up or down the water potential gradient?

down (always dilute to concentrated)

Why will water moves up plants?

due to decreasing water potential

Why will a plant cell shrink?

due to the cell wall controlling the structure of the cell

When does the swelling and bending of the guard cells usually happen?

during the day

When do guard cells usually lose water?

during the night

What does ISOtonic mean?

equal concentrations of two solutions

What are stomata (sing: stoma)?

holes in the surface of the leaf - usually the lower surface)

If a plant cell is placed in a concentrated solution (hypertonic solution), what will the concentration of the cytoplasm be in comparison to the surrounding solution?

hypotonic (lower solute conc.)

Describe the water potential in a hypotonic solution

hypotonic solution has a higher water potential than the cell, so the cytoplasm has a lower water potential

How will a plant cell look like when it loses water?

it will show wilting and plasmolysis

A hypertonic solution has a __________ water potential than the cell

lower

Does a concentrated sugar solution have a higher or lower water potential than pure water?

lower water potential (more negative)

How does water move in a hypertonic solution?

out of the cell

What do you call the wilting of plant cells?

plasmolysis (plant cells become plasmolyzed)

What are plant roots surrounded by?

soil water

What is water potential measured in?

the Greek letter Ψ (Psi) (symbol); its units are: kilopascals (kPa)

Why are brain cells particularly sensitive to large amounts of water?

the brain has limited space due to the skull surrounding it making it easy for brain cells to swell

What do we usually refer to when talking about the concentration of a solution?

the concentration of the solute

Compare the concentration of water inside the root hair cells to the soil

the cytoplasm inside root hair cells have a lower concentration of water molecules (more negative water potential) than the soil water

What is osmosis?

the diffusion (net movement) of water molecules from an area of higher water concentration to a region of lower water concentration, through a partially permeable membrane

What happens to the water potential as more solutes are added?

the water potential becomes more negative

Describe the water potential of a cell (in the cytoplasm) in a hypertonic solution

the water potential is higher inside the cell in comparison to the solution outside the cell

What is the water potential like in an isotonic solution?

the water potential is the same inside and outside the cell

What happens if someone drinks a very large volume of water very quickly?

the water will move into the blood and from the blood, it will move into the body cells by osmosis

Describe the net movement of water when the concentration of solutes is lower outside the cell (hypotonic solution)

there will be a net movement to hypertonic solution (higher concentration inside the cell) until the solutions become isotonic and there is no net movement of water

Describe the wall of the guard cells

they are thick and non elastic

What happens when guard cells lose water by osmosis?

they lose their turgidity causing them to shrink and straighten which closes the stoma

What happens when the guard cells gain water by osmosis from surrounding cells?

they swell up and bend, opening the stoma (become turgid)

What do you call a plant cell that has gained water?

turgid

The process of water molecules entering other cells continues as the water travels ...

up the plant

A low concentration of dissolved solutes means a high concentration of ...

water molecules (i.e. dilute solution)

What happens when two regions of different water potential are separated by a partially permeable membrane?

water moves from the region of higher water potential (high water conc - dilute) to lower water potential (lower water conc. - concentrated)

What do we often use to talk about the movement of water (osmosis)?

water potential

What's another way to think about osmosis?

water potential

Inevitably, what else is lost by the leaves through the stomata?

water vapour

What is the water potential of pure water?

zero