1.4 Membrane transport

Question 1

What is diffusion?

Is it an active or passive process? What type of energy to particles use when diffusing?

Answer 1

The net movement of molecules from a region of higher concentration -> region of lower concentration down a concentration gradient

It is a passive process meaning an ion or molecule passes through a cell wall via a concentration gradient which does not require any energy.

Kinetic energy is used when diffusing

Question 2

Name two examples of substances that cells need to obtain from the extracellular environment?
How about substances that cells need to remove from their cytoplasm?

Answer 2

Obtain: Oxygen, glucose and water

Remove: Water, carbo dioxide and urea

Question 3

Which molecules can diffuse across plasma membranes using simple diffusion alone?

Answer 3

Small molecules, nonpolar molecules, lipid soluble molecules

Question 4

What affects the rate of diffusion? (5)

Answer 4

Temperature, diffusion distance, surface area, concentration gradient, sides of diffusing molecules

Question 5

What is osmosis?

Answer 5

The net movement of water molecules down the water potential gradient, from a region of high water potential to area of low water potential, across a partially permeable membrane

Question 6

What does tonicity refer to? What are the 3 terms?

Answer 6

Tonicity refers to the concentration of one solution relative to another.

1) isotonic -
when two solutions have equal concentration across a semi permeable membrane

2) hypertonic - when a solution has a higher concentration of solutes
3) hypotonic - a solution having a low amount or concentration of solutes in comparison to other solution across a partially permeable membrane

Question 7

What happens to a plant cell when it is put in: a hypotonic solution, isotonic solution, a hypertonic solution?

Answer 7

Hypotonic solution: do you having a low concentration of solute, more of the solution consists of water. Concentration gradient of water is higher in a solution and lower in the cell, the water will pass through the membrane and cause a plant to swallow up and become turgid

Isotonic solution: same concentration so no change. Water leaves and enters at the same rate the cell is flaccid,
meaning it is weak, soft plasma not tightly pressed against the wall

Hypertonic solution: more solute outside with less water. Water in the soul we moved to the area of lower concentration so the cell would shrink and contract. The cell is plasmolysed.

Question 8

Differentiate between turgid, flaccid, plasmolyzed.

What is it used to describe?

Answer 8

Describes plant cells

Turgid cell is is swollen from water intake (normal)

Facet cell is weak, soft because the plasma is not tightly pressed against the wall

Plasmolyzed cell is shrunken/contract because water has left the cell

Question 9

Differentiate between lysed, normal, crenated

What is it used to describe?

Answer 9

Describes animal cells
Lysed: happens in hypotonic solutions when one cell swells up and burst (no cell wall like plants to prevent it from bursting)

Normal: In isotonic solution. Not change.

Crenated: Happens in hypertonic solution when cell shrinks because the water travelled out the cell

Question 10

What is active transport?

Where does the energy come from? Why does it need energy?

Answer 10

The movement of substances against their concentration gradient (from low to high concentration of that substance) across a partially permeable membrane. Need energy.

Release energy by hydrolyzing ATP

Question 11

Why is the role of active transport important in digestion in animals?

Answer 11

As glucose molecules have to be moved across the wall into the blood, the villi absorb the soluble nutrients and ultimately it will reach an equilibrium with the concentration in the gut. Active transport is used to continue the transport of the remaining nutrients against the concentration gradient with energy.

Question 12

How is facilitated diffusion different from simple diffusion?
Why can’t polar molecules enter through simple diffusion? What do transport proteins regulate?

Answer 12

Using transport proteins to allow polar molecules to enter the cell. Polar molecules such as ions have an electrical charge, are insoluble in lipid because they cannot interact with the hydrophobic tails of the lipid bilayer.

They regulate the movement of larger and polar molecules through the membrane.

Question 13

What is the difference between channel protein carrier proteins?

Answer 13

Channel proteins is a passive process

Carrier proteins can be passive or active (specific for particular ions/molecules)

Question 14

What is facilitated diffusion?

Answer 14

Facilitated diffusion involves channel proteins and carrier proteins embedded within plasma membranes. Facilitated diffusion moves polar, lipid–insoluble molecules across membranes, from an area of high concentration, to an area of low concentration, down their concentration gradient

Question 15

What are the factors that affect the rate of facilitated diffusion?

Answer 15

• Diffusion distance
• temperature
• Steepness of concentration gradient
• SA:V ratio - affect the number of transport proteins
• Size of molecules (larger=heavier-> more energy)

Question 16

How is osmosis and diffusion similar?

Answer 16

What is the passive process similar to diffusion but it is in reference to the passage of water molecules

Question 17

How are water molecules able to pass through the phospholipid by layer?
What channel protein does osmosis have that allows water molecules across the membrane more rapidly?

Answer 17

Water molecules can pass directly through the phospholipid bilayer. Some membranes have aquaporins - channel proteins that allow water molecules to cross the membrane more rapidly.

Question 18

Diffusion is concerned with ______ molecules

Osmosis is concerned with ______ molecules

Answer 18

Diffusion is concerned with solute molecules

Osmosis is concerned with solvent molecules

Question 19

Diffusion is concerned with ______ molecules

Osmosis is concerned with ______ molecules

Answer 19

Diffusion is concerned with solute molecules

Osmosis is concerned with solvent molecules

Question 20

In osmosis what is able to cross the partially permeable membrane and what molecules are too large?

Answer 20

Only solvent (water) molecules can cross the partially permeable membrane, solute molecules are too large

Question 21

What is osmolarity? What is it measured in?

Answer 21

The total concentration of osmotically active solutes. Measured in milliosmoles (mOsm). Kind of another word for concentration.

Question 22

What is the osmolarity in terms of isotonic, hypotonic, hypertonic?

Answer 22

An isotonic solution has the same osmolarity as a tissue

A hypertonic (high conc. of soluted) solution has a higher osmolarity

A hypotonic (Low conc. of solute) solution has a lower osmolarity

Question 23

Why is it important to be human tissues in saline solution?

Answer 23

Saline solution is isotonic. Helps ensure the osmolarity of the cells is unaffected - the cells do not lyse or become crenated

Question 24

What is the pattern between diffusion, facilitated diffusion, and osmosis vs active transport?

Answer 24

Diffusion, facilitated diffusion, and osmosis are all from high concentration -> low concentration down a concentration gradient

Active transport is from low concentration -> high concentration, against a concentration gradient.

Question 25

What is the role of carrier proteins and active transport?

Answer 25

Carrier proteins have specific sites that combine reversibly with specific solute molecules or ions.

They also have a binding site for ATP or hydrolysis of a molecule of ATP releases energy that helps change their conformation (shape), carrying the ion from one side of the membrane to the other.

Question 26

What is an example of a carrier portein that uses active transport?

Answer 26

sodium-potassium pumps

Question 27

What is an example of channel proteins? What membrane transport do they use?

Answer 27

sodium channels and potassium channels which use facilitated diffusion

Question 28

What would be the effect on active transport of metabolic poison e.g. cyanide that inhibit enzymes required for respiration?

Answer 28

Active transport would be inhibited as no ATP can be produced by respiration

Question 29

as active transport is dependent upon a supply of ATP from aerobic respiration, what other factors could affect this mechanism?

Answer 29

• Oxygen concentration
• Glucose concentration
• Temperature

Question 30

How is bulk transport used?

What are some examples?

Answer 30

Bulk transport is used to transport large molecules and particles that are too large to pass through transport proteins in the plasma membrane.

Examples include exocytosis and endocytosis.

Question 31

Why do endocytosis and exocytosis require ATP?

Answer 31

Movement of vesicles along microtubules (cytoskeleton) using motor proteins require ATP