Section 5 reading guide

Question 1

What are the major functions of the plasma membrane?

Answer 1

Defines the cell, outlines its borders, determines the nature of its interaction with its environment

Question 2

How does the fluid mosaic model apply to plasma membranes? What types of biomolecules are in the plasma membrane?

Answer 2

The fluid mosaic model applies to plasma membranes because it best describes the structure and function of the plasma membrane. The biomolecules in the plasma membrane are carbohydrates, proteins, cholesterol, and phospholipids.

Question 3

What does it mean that phospholipids are amphipathic? Which part of phospholipids are hydrophobic? Hydrophilic?

Answer 3

Phospholipids are hydrophobic and hydrophilic. They have hydrophilic heads that interact with water, and hydrophobic tails that interact with other hydrophobic tails.

Question 4

How do phospholipids arrange themselves in solution?

Answer 4

Phospholipids arrange themselves so the hydrophobic tails are facing each other and the hydrophilic heads are facing outwards, making contact with the water.

Question 5

How does temperature affect membrane fluidity?

Answer 5

increased temperature leads to increased membrane fluidity, and decreased temperature leads to decreased fluidity

Question 6

How does saturation level of fatty acids affect membrane fluidity?

Answer 6

a higher degree of saturation (more saturated fatty acids) leads to a less fluid membrane, while a higher degree of unsaturation (more unsaturated fatty acids) results in a more fluid membrane

Question 7

How does cholesterol affect membrane fluidity?

Answer 7

Cholesterol acts as a “buffer” to regulate membrane fluidity, preventing excessive fluidity at high temperatures and preventing excessive rigidity at low temperatures by inserting itself between phospholipids and preventing them from packing too tightly together

Question 8

What do we mean when we say the plasma membrane is selectively permeable?

Answer 8

The membrane allows certain substances to pass through the membrane and disallows the entrance of other substances.

Question 9

What types of molecules can cross the lipid bilayer without extra help? Why can they do this?

Answer 9

small, nonpolar molecules like oxygen, carbon dioxide, and nitrogen gas. These molecules can pass through because they are hydrophobic like the tails of phospholipids.

Question 10

What types of molecules cannot cross the lipid bilayer on their own? Why can’t they?

Answer 10

Large, charged, and polar molecules are not able to pass through the lipid bilayer because they have an opposite polarity than the hydrophobic tails, so they cannot interact with each other.

Question 11

1) What is diffusion?
2) How is this an example of passive transport?
3) How does a solute’s concentration gradient affect the direction that a solute diffuses?

Answer 11

1)the movement of molecules from an area of high concentration of the molecules to an area with a lower concentration
2) does not require any additional energy from the cell
3) Higher the concentration gradient, the faster the rate of diffusion

Question 12

How is facilitated diffusion different from passive transport?

Answer 12

facilitated diffusion utilizes transport proteins (like channels or carriers) embedded in the membrane to help specific molecules move down their concentration gradient

Question 13

Explain the roles of channel proteins in facilitated transport

Answer 13

hydrophilic domains inside of the protein, hydrophobic domains outside of the protein, allows polar compounds to pass through without interacting with the nonpolar side, open all the time

Question 14

Explain the roles of carrier proteins in facilitated transport

Answer 14

binds to a substance and changes shape to move the molecule from the cells outside to its interior, for a specific single substance

Question 15

How does osmosis work? How is it similar yet different from diffusion?

Answer 15

Osmosis moves free water molecules through a semipermeable membrane. It is similar yet different from diffusion because they both transport material across the membrane, but osmosis transports only water.

Question 16

Describe an animal cell in a hypotonic solution

Answer 16

A red blood cell will have a lower concentration of water outside, so water will go into the cell and cause it to swell/burst

Question 17

Describe an animal cell in isotonic solution

Answer 17

A red blood cell will have an equal amount of water outside of the cell and inside of it. There will be no net loss/gain of water in the cell.

Question 18

Describe an animal cell in hypertonic solution

Answer 18

A red blood cell will have a higher concentration of water inside of the cell, so it will leave the cell and cause it to shrivel/shrink.

Question 19

Describe a plant cell in hypotonic solution

Answer 19

When there is a higher concentration of water outside of the plant cell, the cell wall prevents the plasma membrane from expanding too much, so the cell does not burst/swell.

Question 20

Describe a plant cell in isotonic solution

Answer 20

The plant cell well not lose water or gain water.

Question 21

Describe a plant cell in hypertonic solution

Answer 21

The cytoplasm in plants always causes the cell to be slightly hypertonic, so water always enters the cell when it is available. This strengthens the cell wall by producing turgor pressure. The cell wall is not flexible, so even if water tries to leave, it can’t.

Question 22

1)What is active transport? 2)How is it similar yet different to passive transport and facilitated transport?
3)What is required for active transport to work?

Answer 22

1) the process of moving molecules across a cellular membrane through the use of cellular energy
2)all three methods move molecules across a cell membrane, but the key difference is that active transport requires energy to move molecules against their concentration gradient, while passive transport and facilitated transport do not
3)energy in the form of ATP

Question 23

How can active transport move molecules against their concentration gradients?

Answer 23

The cell has to use energy to move substances against their concentration gradient. ATP is generated through the cell’s metabolism, and pumps help work against gradients.

Question 24

What is the difference between primary active transport and secondary active transport?

Answer 24

primary active transport directly uses energy from ATP to move molecules against their concentration gradient, while secondary active transport uses the energy stored in an existing electrochemical gradient, typically created by primary active transport, to move molecules against their gradient

Question 25

What is endocytosis?

Answer 25

the taking in of matter by a living cell by invagination of its membrane to form a vacuole

Question 26

What is exocytosis?

Answer 26

a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane