Transport across membranes Flashcards

Chp 6

How/what type of solutes move across membranes?

Some solutes (small uncharged molecules) move by simple diffusion across a membrane, some require active transport (large charged molecules)

Define Diffusion

• The movement of a solute from an area of high concentration to an area of low concentration

• Move down the concentration gradient

• Movement across a selectively permeable membrane

Define Concentration gradient

difference in concentration of a solute across a membrane

what is facilitated diffusion?

Diffusion of large charged molecules across a membrane through transport proteins

Osmosis

• Focuses on the movement of water across a selectively permeable membrane

• Area of lower solute concentration to higher solute concentration

Define Isotonic solution

Solutions that have same solute concentration as another concentration thus having no net movement

Define hypertonic solutions

Solution that has a greater solute concentration over the other solution

Define Hypotonic solutions

Solution that has a lower solute concentration over the other solution

Define Crenation

When an animal cell is placed in a hypertonic solution where water leaves the cell, causing it to shrink (i.e. crenate)

Define Lysing or Lysed and why is it not ideal for animal cells?

• When animal cell is placed in a hypotonic solution where water enters the cell leading it swell up and burst (i.e lysed)

• Not ideal as it has no cell wall to hold it together

When is a plant cell flaccid?

• When plants are placed in a isotonic solution, thus no net movement and no water to keep it rigid.

• This causes plants to wilt therefore cells are flaccid

What is plasmolysis?

When a plant cell is placed in a hypertonic which leads water to leave the plant cell.

This makes the plasma membrane pull away from the cell wall

What is turgid and what does it mean for a plant?

• When a plant is placed in a hypotonic solution, water enters the cell and causes it to be rigid

• This is an ideal or a plants happy state

• Plants do not explode due to the cell wall

What are the 3 types of tonicity?

Hypertonic, Hypotonic, and Isotonic

What is a dialysis membrane (tubing)?

• It is a artificial membrane that allows only certain sizes of molecules to cross

In the dialysis tube experiment, which molecules were small enough to diffuse by simple diffusion across a dialysis membrane?
glucose, starch, I2KI, water?

✅ Molecules small enough to diffuse across:

• Water

• Glucose

• I₂KI (iodine-potassium iodide)

❌ Molecules too large to diffuse:

• Starch

In the dialysis tube experiment, how could we know I₂Kl diffused?

• It entered the dialysis bag and reacted with starch inside the bag turning it into a blue-black colour, indicating diffusion.

• Starch did not leave the bag, because the outside solution did not change color.

How do we know glucose diffused?

• The outside solution was tested with glucose test strips.

• The strip changed color, showing that glucose exited the bag and was present in the surrounding solution.

What is the role of water in this experiment?

• Water moves by osmosis across the membrane.

• It moves toward the higher solute concentration (into or out of the bag, depending on the solution).

Difference between plasma membrane and dialysis membrane in terms of diffusion?

Plasma membrane found in living cells is selectively permeable based on the polar charge and size of molecule

Dialysis membrane is artificial and permeable to molecules of certain sizes