Cell Membrane

Question 1

What is the cell membrane and what does it do?

Answer 1

• gateway into the cell
• allow molecules to enter and exit the cell (nutrients, wastes)
• molecules must pass through the cell membrane (hydrophobic, hydrophilic)
• all living cells are surrounded by cell membranes

Question 2

Describe the fluid mosaic model

Answer 2

• a double layer of phospholipid molecules with the cosistency of light machine oil
• has proteins embedded in phospholipid bilayer
• membrane is selectively permeable; can discriminate between different molecules that are the same size

Question 3

Role of cholesterol

Answer 3

• maintains fluidity
• strung together in chains and are attached to proteins(glycoproteins) or lipids(glycolipids) of membrane
• identification markers for cell recognition(identify which cells belong to body and which are invaders

Question 4

Role of integral proteins

Answer 4

passage to interior of cell for polar substances

Question 5

Role of peripheral proteins

Answer 5

anchor for glycogen(carbohydrate chain) to attach for cell markers

Question 6

Proteins functions(in cell membrane)

Answer 6

• act as hormone binding sites
• facilitate enzymatic reactions
• serve as anchors for cell adhesion
• act in cell to cell communication
• be channells for passive transport
• be pumps for active transport

Question 7

Describe the cell wall and what does it do?

Answer 7

• thickness of cell wall varies with cell function
• primary cell wall is outermost layer, composed of threadlike cellulose microfibrils; a sticky substance called middle lamella binds cells together
• freely permeable(anything small enough to fit through will get through)
• keeps cell from bursting; important for plant cells to retain erect positions

Question 8

What is diffusion and what can affect the rate of diffusion?

Answer 8

• law of diffusion states that particles move from the area of greater concentration to the area of lesser concentration until equally distributed
• requires no energy
• a slow process
• rate of diffusion is affected by:
• ->the concentration gradient(difference in [ ] of the diffusing molecules between the regions
• ->the size & shape of the molecules
• ->the temperature(faster in gas, slower in liquid)

Question 9

What is osmosis?

Answer 9

-diffusion of water into and out of cells
across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration

Question 10

What is solute?

Answer 10

particles which are dissolved in water

Question 11

What is solvent?

Answer 11

liquid which dissolves the solute

Question 12

What is solution

Answer 12

combination of solute and solvent

Question 13

What is osmotic pressure

Answer 13

• the pressure due to the flow of water from the area of greater concentration to the area of lesser concentration
• the greater the difference across the membrane, the greater the osmotic pressure

Question 14

Isotonicty

Answer 14

• no net movement of water across membrane

- same number of solute molecules per unit volume

Question 15

Hypertonic

Answer 15

• greater concentration of solute than the cell(and therefore a lesser concentration of water)
• if a cell is placed in a hypertonic solution, water will leave the cell and the cell will shrivel up(cell is hypertonic)
• this called crenation in animal cells

Question 16

Hypotonic

Answer 16

• solutions have lower concentration of solute than the cell contents
• if a cell is placed in hypotonic solution, water will enter the cell and it will swell, possibly causing it to burst(cell is hypertonic)
• this is called lysis in animal cells

Question 17

How does tonicity work in plants?

Answer 17

• hypertonic solutions cause plasmolysis; the central vacuole loses water and cell membrane shrinks pulling away from cell wall
• -hypotonic solution causes turgor pressure; occurs when plant cells admit water; as water enters, pressure builds up inside the cell

Question 18

What molecules will pass and not pass through the cell membrane with ease?

Answer 18

• hydrocarbons and oxygen will pass through the membrane with ease as they can dissolve in the lipid bilayer
• small polar uncharged molecules such as water, nitrogen, and CO2 will pass
• large polar uncharged molecules like sugar and ions like H, Na, & Cl will need proteins to transport them into and out of the cell
• steroids & alcohols can diffuse directly because the membrane itself is made of lipids

Question 19

Facilitated transport

Answer 19

• protein carriers control the passage of molecules in and out of the cell
• each carrier passes only 1 type of molecule
• molecules only pass along concentration gradient(high to low)
• requires no energy
• this is how lipid-insoluble molecules like glucose and amino acids cross the membrane

Question 20

Active transport

Answer 20

• transport performed by protein carriers
• requires ATP energy and a change in the shape of the protein
• moves molecules against the concentration gradient (low to high)
• sodium + potassium transport by active transport

Question 21

Endocytosis

Answer 21

• endocytosis: cell membrane forms a vesicle around the substance to be taken in and it requires ATP
• phagocytosis: (eating)when large particles are taken in; can be seen with a light microscope
• pinocytosis: (drinking) solutions are taken in; requires electron microscope to see

Question 22

Exocytosis

Answer 22

• reverse of endocytosis
• vacuole fuses with cell membrane
• the vacuole contents are deposited on the outside
• important in secretion and excretion in cells