Lecture 7

Question 1

Plasma membrane function

Answer 1

The membrane that encloses a cell and controls the traffic of molecules in and out of the cell. The plasma membrane allows things to be kept in one place and create an environment and confines all organelles into one area.The plasma membrane is the interface between the inside and the extracellular fluid

Question 2

What are cells regulating in and out of the cell to maintain cell shape?

Answer 2

Water

Question 3

Concentration gradient

Answer 3

A concentration gradient occurs when a solute is more concentrated in one area than another.

Question 4

Osmosis

Answer 4

Osmosis is the movement of a solvent across a semipermeable membrane toward a higher concentration of solute (lower concentration of solvent)

Question 5

Intracellular fluid

Answer 5

This fluid is located within the cell membrane and contains water, electrolytes and proteins.

Question 6

Extracellular fluid

Answer 6

Extracellular fluid denotes all body fluid outside the cells of any multicellular organism.

Question 7

Interstitial fluid

Answer 7

Interstitial fluid is a thin layer of fluid (salty water) which surrounds the body’s cells.

Question 8

Tonicity

Answer 8

The water potential of two solutions separated by a semipermeable cell membrane. Tonicity is the relative concentration of solutes dissolved in solution which determine the direction and extent of diffusion.

Question 9

Isotonic

Answer 9

This is a homeostatically stable situation.When two environments are isotonic, the total molar concentration of dissolved solutes is the same in both of them. When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell.

This state allows for the free movement of water across the membrane without changing the concentration of solutes on either side.

When you place a cell into this kind of solution, the cell does not shrink or swell as there will be no net gain or loss in water.

Question 10

Hypertonic

Answer 10

A hypertonic solution is a particular type of solution that has a greater concentration of solutes on the outside of a cell when compared with the inside of a cell. There is an osmotic water shift from the ICF into the ECF which restores osmotic equilibrium but decreases the volume of the ICF.

Question 11

Hypotonic

Answer 11

A hypotonic solution has a lower concentration of solutes than another solution. In biology, a solution outside of a cell is called hypotonic if it has a lower concentration of solutes relative to the cytosol. Due to osmotic pressure, water diffuses into the cell, and the cell often appears swollen.

Question 12

What is hyponatremia and an explanation of it ….

Answer 12

Too much Na+

One or more factors — ranging from an underlying medical condition to drinking too much water — cause the sodium in your body to become diluted. When this happens, your body’s water levels rise, and your cells begin to swell. This swelling can cause many health problems, from mild to life-threatening.

There is not enough sodium in the extracellular space in relation to the amount of water which results in water flooding into the cell causing them to well and they swell and can eventually burst.

Question 13

Red blood cells in isotonic, hypotonic and hypertonic solution

Answer 13

Biconcave cells (there normal appearance) in an isotonic solution

In a hypotonic solution the cell would swell (hypOtonic as it looks like the letter O)

In a hypertonic solution the water is drawn out of the cells to dilute the solute in the ECM

Question 14

Excitable cells

Answer 14

Refers to the ability of some cells to be electrically excited resulting in the generation of action potentials. Neurons, muscle cells, and some endocrine cells are excitable cells.

Question 15

Cellular membrane potential relies on _____ and ____ separation

Answer 15

K+ and Na+

Question 16

Lipid bilayer is an …

Answer 16

Insulator to prevent the free flow of cations and anions

Question 17

What is the resting membrane potential? What causes this?

Answer 17

There is a charged separation between K+ and Na+. This charge separation across the membrane creates a voltage difference where the cell is said to be, by convention, inside negative in relation to the outside and this is called the resting membrane potential. The resting membrane potential in living cells is about -70mV. At rest, there are relatively more sodium ions outside and more potassium ions inside the cell.

Question 18

What are ion channels and how are they used in terms of K+ and Na+?

Answer 18

Proteins that are inserted into the phospholipid bilayer in the cell membrane are called ion channels (or pores). They have an aqueous pore, which becomes accessible to ions after a conformational change in the protein structure that causes the ion channel to open.

Question 19

Describe why the resting membrane potential is negative

Answer 19

The resting membrane potential is -70mV which indicates that the cell is negative on the inside in relation to the outside. Negative because you are using energy at the sodium potassium pump, ATP is being spilt into ADP and Pi at the pump. The cell is always busily swapping K+ and Na+, to keep sodium high outside the cell and to keep potassium high inside the cell so you are using energy to establish and maintain these concentration gradients and in doing so you have a negative inside in relation to the outside.

Question 20

Na+ gradient in a cell and what would happen if the cell membrane became permeable to Na+?

Answer 20

We have a concentration gradient for the movement of sodium, high concentration outside and low concentration inside the cell, so if the membrane were to become permeable, then it would suddenly allow sodium from the outside go inside. Sodium is positively charged and the inside of the cell is negative, opposite charges attract so if the channel was to suddenly open we would have a concentration and electrical gradient. Electrochemical gradient would, if the cell membrane was permeable, drive sodium into the cell carrying the positive charge with it. For sodium, the electrical and chemical gradients are inwards so if the membrane were to become permeable to sodium then there would be a very strong, rapid movement of positive charge into the cell

Question 21

K+ gradient in a cell and what would happen if the cell membrane became permeable to K+?

Answer 21

Potassium is high inside the cell and is low outside the cell. If the membrane were to be permeable to potassium, the potassium would move out of the cell carrying positive charge with it out of the cell but the inside of the cell is negative and the outside of the cell is positive so at rest the electrical gradient is into the cell for potassium.

Question 22

Potassium chemical, electrical and electrochemical gradients

Answer 22

Chemical - Out of the cell
Electrical - Into the cell
Electrochemical - Out of the cell

Question 23

Sodium chemical, electrical and electrochemical gradients

Answer 23

Chemical - Into the cell
Electrical - Into the cell
Electrochemical - Into the cell

Question 24

What are the Na+ levels inside and outside as well as the K+ levels inside and outside of the cell?

Answer 24

Outside has …. High Na+ and low K+

Inside has …. High K+ and low Na+

Question 25

What is an electrochemical gradient?

Answer 25

An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of, the chemical gradient, or difference in solute concentration across a membrane, and the electrical gradient, or difference in charge across a membrane.

Question 26

What is depolarisation?

Answer 26

Depolarisation refers to a sudden change in membrane potential – usually from a (relatively) negative to positive internal charge. In response to this chemical stimulus, sodium channels open within the membrane.

Question 27

What is repolarisation?

Answer 27

Repolarisation refers to the restoration of a membrane potential following depolarisation (i.e. restoring a negative internal charge). Following an influx of sodium, potassium channels open within the membrane. The efflux of potassium causes the membrane potential to return to a more negative internal differential.

Question 28

What is hyperpolarisation?

Answer 28

Hyperpolarization is when the membrane potential becomes more negative. It is the opposite of depolarisation.

At this level the sodium channels begin to close and voltage gated potassium channels begin to open. After hyperpolarization the potassium channels close and the natural permeability of the neuron to sodium and potassium allows the return to resting membrane potential.

Question 29

Basal surface and apical surface

Answer 29

The basal side of the cell is the side that faces the basement membrane, i.e. the connective tissue layer the cell lives on. The apical side is the side that faces the opposite direction, usually towards the lumen (inside) of a tube.

Question 30

Red blood cells are what shape?

Answer 30

Biconcave