Movement Across the Cell Membrane

Question 1

What is diffusion?

Answer 1

The passive movement of a substance from an area of high concentration to an area of low concentration until equilibrium is reached

Question 2

Why is diffusion considered a passive process?

Answer 2

It does not require energy to take place

Question 3

What is equilibrium?

Answer 3

The situation where there is no net movement of molecules in either direction, they move equally in both. Also occurs when the substance is evenly distributed.

Question 4

Which molecules can easily move through the cell membrane via simple diffusion?

Answer 4

Oxygen and carbon dioxide

Question 5

What process maintains oxygen’s concentration gradient along the cell membrane?

Answer 5

As oxygen is continually used in cellular respiration, it is constantly diffusing into the cell as the inside of the cell has a low oxygen concentration.

Question 6

What is facilitated diffusion?

Answer 6

The passive diffusion of polar molecules across the cell membrane through proteins. These molecules are either too large, or are charged and cannot diffuse through lipid bilayer.

Question 7

Describe carrier facilitated diffusion

Answer 7

Carrier proteins embedded in the membrane bind to molecules on one side of the membrane. They change shape and release the molecules on the other side. Used for sugars and amino acids.

Question 8

Describe channel facilitated diffusion

Answer 8

Channel proteins provide narrow passage ways through the membrane for small ions (e.g sodium ions).

Question 9

What is osmosis?

Answer 9

the passive movement of water from an area of high water concentration to an area of low water concentration across a semi-permeable membrane.

Question 10

How does water diffuse across the cell membrane?

Answer 10

They travel through protein channels called aquaporins.

Question 11

Describe what occurs when water is concentrated more highly on the outside of the cell (solute concentration high inside)

Answer 11

Water will move into the cell by osmosis through the cell membrane, and the cell may swell (become turgid)

Question 12

Describe what occurs when water is concentrated more highly on the inside of the cell (solute concentration high outside)

Answer 12

Water will move out of the cell, and it may shrink (flaccid)

Question 13

What is a hypotonic solution?

Answer 13

When cells are surrounded by a solution that contains lower solute concentrations that the cytoplasm, the external solution is hypotonic.

Question 14

What is an isotonic solution?

Answer 14

Isotonic solution occurs when fluids inside and outside of cell have equal solute concentration

Question 15

What is a hypertonic solution?

Answer 15

External solution is hypertonic when it is of a higher solute concentration than the cytoplasm.

Question 16

Describe osmoregulation in fish

Answer 16

Freshwater fish absorb water by osmosis, do not drink water, excrete large volumes of diluted urine.

Saltwater fish lose water by osmosis, drink saltwater, and excrete highly concentrated urine.

Question 17

What is active transport?

Answer 17

The movement of molecules from a region of low concentration to a region of high concentration, requiring the input of energy (ATP). This process requires carrier proteins.

Question 18

Provide an example of active transport

Answer 18

Sodium-potassium pump: a single unit of this ‘pump’ has two proteins, with one open at a time, pumping sodium out of the cell, and potassium into the cell

Question 19

Describe how active transport is utilised in kidneys

Answer 19

At the proximal tubule, substances such as amino acids and glucose are reabsorbed into the blood by active transport.

Question 20

Describe the process of endocytosis

Answer 20

Membrane pinches around substance and engulfs it to bring it into the cell by placing it in a vesicle.

Question 21

What is phagocytosis?

Answer 21

Endocytosis, where a solid particle(s) is taken into the cell. (Eg. amoeba feeds on a smaller organism)

Question 22

What is pinocytosis?

Answer 22

The cell membrane engulfs extracellular fluid, including dissolved chemicals

Question 23

What is receptor mediated endocytosis?

Answer 23

Receptor molecules on the membrane target specific chemicals, the membrane encapsulates the receptor coated pit into a vesicle.

Question 24

What is exocytosis?

Answer 24

Moving substances out of the cell.
Secretion - substances released for useful purposes
These substances are packaged by golgi body in vesicles
Excretion - removal of wastes, encapsulated in vesicles to protect cell

Question 25

Do endo/exocytosis require energy?

Answer 25

Yes, they are active transport processes.