Cell Membrane and Transport

Question 1

What is the cell membrane?

Answer 1

Forms the boundary between the internal environment of the cell - the cytoplasm - and its external environment.

Question 1

What are the functions of the cell membrane?

Answer 1

Functions include the recognition of other cells, the transportation of materials into and out of the cell, the provision of attachment sites for enzymes and hormones added nerve cells the transmission of neural impulses.

Question 2

What are 2 properties/structure of the cell membrane?

Answer 2

• It is selectively permeable meaning that it is able to control the movement of substances into and out of the cell and it is able to exclude unwanted substances.
• It is a flexible structure.

Question 3

What are the membranes of organelles like?

Answer 3

Organelle membranes have the same general structure as cell membranes.

Question 4

Describe the fluid mosaic model.

Answer 4

The fluid mosaic model describes membranes as a phospholipid bilayer, with the ability to flow and change shape, like a two dimensional fluid. Specialised protein molecules are embedded in the lipid in various patterns, like a mosaic. Some of the proteins can move laterally and others are fixed in position. Both proteins and phospholipids help take control the exchange of materials between the internal an external environments.

Question 5

What is the fluid part of the fluid mosaic model?

Answer 5

Fluid refers to the flexible fluid bilayer of phospholipids that enable the membrane to expand and contract.

Question 6

What is the mosaic part of the fluid mosaic model?

Answer 6

Mosaic refers to the mosaic of components including cholesterol protein and carbohydrates.

Question 7

What do transport proteins do?

Answer 7

They allow interaction and communication between cells and exchange of substances between cells and the external environment.

Question 8

What are the 2 main types of transport proteins?

Answer 8

• Channel proteins (ion channels)
• Carrier proteins (transporters)

Question 9

What do channel proteins do?

Answer 9

Catalyse the movement of specific ions and some super molecules such as water down each substances own electrochemical gradient. They help move these substances across the membrane via passive transport in a process called facilitated diffusion.

Question 10

Give an example of a channel protein.

Answer 10

Channel proteins that facilitate the transport of water are called aquaporins they selectively allow water to pass along its concentration gradient.

Question 11

What do carrier proteins do?

Answer 11

Have to change shape to pass a molecule across the membrane. Many use ATP to transport specific small molecules or ions against their concentration gradient. Some carrier proteins can move ions or molecules for example glucose along their concentration gradient through passive transport.

Question 12

Give an example of a carrier protein.

Answer 12

The sodium potassium pump maintains the electrochemical gradient and the correct concentrations of sodium and
potassium ions in cells.

Question 13

What do adhesion proteins do?

Answer 13

Link cells together to maintain both 3 dimensional structure and the normal functioning of tissues.

Question 14

What do receptor proteins do?

Answer 14

Bind hormones and other substances that cause changes to cells activities. Different types of cells have different receptor proteins, enabling them to respond to only certain signals and so carry out specific functions.

Question 15

What are the 2 types of transports that materials can be moved across a cell membrane with?

Answer 15

Active and passive transport.

Question 16

What is the difference between active and passive transport?

Answer 16

Active transport processes require energy (ATP), passive transport processes do not.

Question 17

What are the different types of active transport?

Answer 17

• Active transport
• Endocytosis
• Exocytosis

Question 18

What are the different types of passive transport?

Answer 18

• Simple diffusion
• Facilitated diffusion
• Osmosis

Question 19

What is a concentration gradient?

Answer 19

The difference in concentration between two regions.

Question 20

What is simple diffusion and how does it occur?

Answer 20

The net movement of particles from a region of high particle concentration to a region of lower particle concentration. Diffusion occurs because of the random kinetic movement of the particles, it’s effects are seen when a concentration gradient exists until the particles are evenly distributed through the system
(equilibrium).

Question 21

What materials can be moved by simple diffusion?

Answer 21

• Small uncharged molecules such as oxygen, water and carbon dioxide.
• Alcohols

Question 22

What is facilitated diffusion?

Answer 22

Diffusion from high to low concentration. Charged particles such as sodium and chlorine ions and relatively large molecules such as glucose and amino acids do not readily pass through the phospholipid bilayer. In the cell membrane, Carrier and channel proteins assist such particles to diffuse into the cell.

Question 23

What materials can be moved by facilitated diffusion?

Answer 23

• Charged particles such as sodium and chlorine ions.
• Large molecules such as glucose and amino acids.

Question 24

How does facilitated diffusion occur with carrier proteins?

Answer 24

Carrier proteins bind to specific molecules on one side of the membrane change shape and release the substance on the other side.

Question 25

How does facilitated diffusion occur with channel proteins?

Answer 25

Channel proteins form narrow passageways through which small ions can diffuse rapidly from high ion concentration to lower ion concentration. Only ions of a specific size and shape can pass through a particular channel protein.

Question 26

What is active transport?

Answer 26

Active transport is the movement of dissolved molecules into or out of a cell through the cell membrane, from a region of lower concentration to a region of higher concentration. The particles move against the concentration gradient, using energy released during respiration.

Question 27

Give an example of active transport.

Answer 27

Uptake of glucose by epithelial cells in the villi of the small intestine.

Question 28

What is endocytosis?

Answer 28

When large particles (eg polysaccharides or proteins) or even whole cells need to be moved across the cell membrane.
Endocytosis is the process by which cells take in substances from outside of the cell by engulfing them in a vesicle.

Question 29

How does endocytosis occur?

Answer 29

Endocytosis occurs when a portion of the cell membrane folds in on itself, encircling extracellular fluid and various molecules or microorganisms. The resulting vesicle breaks off and is transported within the cell.

Question 30

What are the two types of endocytosis?

Answer 30

• Phagocytosis
• Pinocytosis

Question 31

What is phagocytosis?

Answer 31

Phagocytosis, also known as cell eating, is the process by which cells internalize large particles or cells, like damaged cells and bacteria.

Question 32

What is pinocytosis?

Answer 32

Pinocytosis, also known as cell drinking, is
common in plant and animal cells. During pinocytosis, the cell takes in substances from the extracellular fluid that it needs to function. These include things like water and nutrients.

Question 33

What is exocytosis?

Answer 33

Exocytosis is the process by which cells move materials from within the cell into the extracellular fluid.

Question 34

How does exocytosis occur?

Answer 34

Exocytosis occurs when a vesicle fuses with the plasma membrane, allowing its contents to be released outside the cell.

Question 35

What are the factors that effect the exchange of materials?

Answer 35

• Chemical properties of substances
• Concentration gradient
• Physical properties of substances
• Size and shape of cells

Question 36

How does the chemical properties of substances effect the exchange of materials?

Answer 36

Charged molecules that are hydrophilic cannot pass through the hydrophobic interior of the membrane.

Question 37

How does the physical properties of substances effect the exchange of materials?

Answer 37

Small molecules such as water and oxygen can slip between the phospholipids.

Question 38

How does the size and shape of cells effect the exchange of materials?

Answer 38

More smaller cells have a larger surface area than one larger cell. This means that a substance does not need to travel as far to reach the center or the edge of the cell. Faster movement of substances means more efficient metabolic processes.

Question 39

How does the concentration gradient effect the exchange of materials?

Answer 39

If higher the concentration gradient the substance will diffuse more rapidly. Maintaining a steep concentration gradient can be achieved by removing substances or converting them to something else (eg liver converts glucose to glycogen).

Question 40

What is osmosis?

Answer 40

The diffusion of water through a semipermeable membrane, from an area of high water concentration (low solute) to an area of low water concentration (high solute).
Cell membranes are selectively permeable, meaning that water molecules pass through them easily but solutes do not. If the concentration of water molecules inside the cell is lower than the concentration outside, water
would diffuse into the cell until the balance is reached.
Osmosis is a special type of diffusion in which water molecules move passively via small gaps between phospholipids and through aquaporins. It doesn’t require an input of energy.

Question 41

What is an isotonic solution?

Answer 41

Solutions that are isotonic have the same concentration of solutes. If there is a selectively permeable membrane between them water will move between the two solutions but there will be no net change in the amount of water in either solution.

Question 42

What is a hypotonic solution?

Answer 42

When cells are surrounded by solution that contains a lower solute concentration than their cytoplasm, the external solution is said to be hypotonic to the cells. Water molecules will diffuse through the membrane into the cells because the cells have a lower concentration of solvent (water).

Question 43

What is a hypertonic solution?

Answer 43

When cells are surrounded by a solution of higher solute concentration; the external solution is described as hypertonic to the cells, and water molecules will diffuse out.

Question 44

If a solution has equal amounts of solutes what type of solution is it?

Answer 44

Isotonic

Question 45

If a cell has more solute than the outside what type of solution is it?

Answer 45

Solution is hypotonic to cell.

Question 46

If a cell has less solute than the outside what type of solution is it?

Answer 46

Solution is hypertonic to cell.

Question 47

Describe the phospholipid bilayer.

Answer 47

The lipid bilayer is composed of subunits called phospholipids. Each phospholipid can be represented by a head and two tails.
The phosphate group on the head makes this end hydrophilic, meaning that it is able to absorb water or dissolve in water.
The fatty acid tails hydrophilic, meaning that they’re water avoiding or unable to dissolve in water.
The molecules spontaneously form a bilayer, with the fatty acid tails turned inwards away from the watery environment of the cytosol.