5-Membrane Structure transport Function

Question 1

What does plasma membrane exhibits, why does this help?

Answer 1

The plasma membrane exhibits selective
permeability, allowing some substances to cross it
more easily than others

Question 2

Which is the most abudant lipid in the plasma membrane?

Answer 2

Phospholipids

Question 3

What does the mosaic model states?

Answer 3

 The fluid mosaic model states that a membrane is a fluid structure with a mosaic of various proteins embedded in it.

Question 4

All membranes are made of a bilayer of phospholipids?.

Answer 4

yes

Question 5

What is diffusion?

Answer 5

The passive movement of molecules from a higher to a lower concentration until equaibrium is reached.

Example: Gases move through plasma membranes by diffusion.

Question 6

How can the rate of diffusion be determined

Answer 6

The rate of diffusion is determined by 4 factors:

The steepness of the concentration gradient.

The bigger the difference between the two sides of the membrane the quicker the rate of the diffusion.

Temperature.

Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster.

The surface area.

The greater the surface area the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any one moment.

The type of molecule or ion diffusing.

Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar

Question 7

What is facilitated diffusion?

Answer 7

 Large polar molecules such as glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also ions such as Na¬+ and CI+ cannot pass.

 These molecules pass through protein channels instead. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low concentration.

Question 8

What is Osmosis

Answer 8

The diffusion of water from an area of high concentration of water molecules (high water potential) to an area of low concentration of water (low water potential) across a partially permeable membrane.

Question 9

Why the term ‘tonicity’ is used?

Answer 9

 Refers to the concentration of SOLUTES
 Is a RELATIVE term, comparing two different solutions

 Hypertonic
 Hypotonic
 Isotonic

Question 10

What is a Hypertonic solution?

Answer 10

A solution with greater solute concentration compared to another solution.
In a hypertonic solution, water leaves the cell, which shrivels (crenation)

Question 11

What is a Hypotonic solution?

Answer 11

A solution with a lower solute concentration compared to another solution.
In a hypotonic solution, water enters the cell, which may burst (lysis).

Question 12

What is a Isotonic solution?

Answer 12

A solution with an equal concentration compared to another solution.
In an isotonic solution, there is no net movement of water.(see slide 45)

Question 13

How can active transport occur?

Answer 13

Cells must maintain very high or low levels of some molecules.

Passive transport can’t do this!!!

Question 14

• Facilitated transport—passive
• Active transport

Which does require energy and which doesn’t?

Answer 14

• Facilitated transport—passive

- Active transport— requires energy (ATP)

Question 15

Diffusion
Osmosis
Facilitated Diffusion
Active Transport

Characterize the above procedures as active or passive

Answer 15

Diffusion=passive
Osmosis=Passive
Facilitated Diffusion=Passive
Active Transpor=Active

Question 16

What is bulk transport?

Answer 16

Bulk Transport: The movement of macromolecules such as proteins or polysaccharides into or out of the cell is called bulk transport.

Question 17

Exocytosis
Phagocytosis
Pinocytosis
Receptor-mediated Endocytosis
See slides (18-21)

Answer 17

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