Text C Biology 8.1 Membrane Properties

Question 1

Why do cells need membranes?

Answer 1

To separate their interior from their surroundings and allow survival as individual units of life.

Membranes define the inside versus the outside of cells, creating a controlled environment for cellular functions.

Question 2

What is the primary composition of cell membranes?

Answer 2

A double layer of phospholipids, with embedded proteins and other molecules.

Phospholipids are a type of lipid that form the structural basis of cell membranes.

Question 3

How do cell membranes allow materials to move in and out?

Answer 3

Materials must cross the cell membrane, which changes according to each cell’s needs.

This dynamic nature allows cells to function as open systems.

Question 4

What happens when lipids, such as cooking oil, are mixed with water?

Answer 4

They do not dissolve and instead form small droplets that float back to the surface.

This behavior is similar to phospholipids in water, which form thin layers.

Question 5

Fill in the blank: Cell membranes are primarily composed of a double layer of _______.

Answer 5

[phospholipids]

Question 6

What is one function of a cell membrane related to the environment?

Answer 6

To regulate the flow of materials entering or exiting the cell.

This is analogous to the maintenance of an aquarium for tropical fish.

Question 7

True or False: Cell membranes are rigid and do not change.

Answer 7

False

Cell membranes are flexible and adapt to the needs of the cell.

Question 8

In what way is an aquarium similar to a cell?

Answer 8

Both maintain a controlled environment for their inhabitants.

An aquarium holds water and maintains conditions for fish, similar to how a cell maintains conditions for its processes.

Question 9

What is the significance of membranes in terms of cellular systems?

Answer 9

They allow cells to survive and function as open systems by regulating material exchange.

This is crucial for processes like nutrient uptake and waste removal.

Question 10

What are the two ends of a phospholipid molecule?

Answer 10

Head and tail

Question 11

What term describes the head end of a phospholipid?

Answer 11

Hydrophilic

Question 12

What is the characteristic of hydrophilic molecules?

Answer 12

Dissolve easily in water

Question 13

What term describes the tail end of a phospholipid?

Answer 13

Hydrophobic

Question 14

What is the characteristic of hydrophobic molecules?

Answer 14

Do not dissolve readily in water

Question 15

What do water molecules do to the tail end of a phospholipid?

Answer 15

Repel, or push away

Question 16

What structure do phospholipid molecules automatically form?

Answer 16

Phospholipid bilayers

Question 17

What orientation do the hydrophilic heads have in a phospholipid bilayer?

Answer 17

Point toward the water

Question 18

Where are the hydrophobic tails located in a phospholipid bilayer?

Answer 18

Sandwiched in the middle

Question 19

How thick are the layers formed by phospholipid molecules?

Answer 19

Two molecules thick

Question 20

What do the two layers of phospholipid molecules look like when viewed from the side?

Answer 20

Almost like mirror images of one another

Question 21

Fill in the blank: The hydrophilic head group of a phospholipid contains a _______.

Answer 21

Phosphate group

Question 22

What additional group may be present in the hydrophilic head of some phospholipids?

Answer 22

Nitrogen group

Question 23

What type of environment do the phospholipid bilayers typically surround?

Answer 23

Water

Question 24

What do cell membranes contain that helps move substances across them?

Answer 24

Embedded proteins

These proteins also carry out chemical reactions.

Question 25

What is the role of marker molecules on membrane proteins?

Answer 25

Allow cells to recognize each other and may protect from infection ## Footnote They also act as attachment sites for messenger molecules.

Question 26

What are messenger molecules used for in cells?

Answer 26

Cell-to-cell communication and control of cell functions.

Question 27

How do cell membranes appear under a microscope?

Answer 27

They may appear motionless.

Question 28

What model describes the fluid nature of cell membranes?

Answer 28

Fluid-mosaic model.

Question 29

What is the analogy used to describe the fluidity of membrane components?

Answer 29

Canoes on a lake.

Question 30

What does the fluidity of membranes allow proteins to do?

Answer 30

Move within the membrane.

Question 31

What additional feature do membranes gain from their fluidity?

Answer 31

Flexibility, allowing cells to change shape.

Question 32

What are carbohydrates attached to on the membrane's outer surface?

Answer 32

Lipids and proteins.

Question 33

What is the function of carbohydrates in cell membranes?

Answer 33

Involved in cell-to-cell communication.

Question 34

What forms the biological mosaic of the membrane?

Answer 34

Proteins, lipids, and carbohydrates.

Question 35

What supports the membrane from the inside of the cell?

Answer 35

The cytoskeleton.

Question 36

What distinguishes each type of cell from others?

Answer 36

Unique 'fingerprint' of carbohydrate chains on the outer surface.

Question 37

Fill in the blank: The model that describes the structure of membranes is called the _______.

Answer 37

Fluid-mosaic model.

Question 38

True or False: The proteins in cell membranes are static and do not move.

Answer 38

False.

Question 39

What do the filaments of the cytoskeleton do in relation to the membrane?

Answer 39

Support the membrane.

Question 40

What is the primary function of the cell membrane?

Answer 40

The cell membrane prevents many substances from entering a cell.

Question 41

What types of chemicals are found in the fluids that bathe cells?

Answer 41

* Salts * Sugar * Proteins * Electrically charged molecules and ions

Question 42

How do membranes contribute to the organization of cells?

Answer 42

Membranes organize the insides of cells into many smaller compartments.

Question 43

What is the role of organelles in relation to membranes?

Answer 43

Most organelles are surrounded by membranes, and chemical reactions take place within these organelles.

Question 44

What would happen if lysosomal enzymes were not contained within a membrane?

Answer 44

The enzymes would digest everything they contacted, which would kill the cell.

Question 45

What process involves the release of lysosomal contents into a cell?

Answer 45

Apoptosis

Question 46

How is a cell membrane similar to a plastic zip-up freezer bag?

Answer 46

Both can regulate what enters and leaves their contained space.

Question 47

What does it mean for a cell membrane to be semi-permeable?

Answer 47

It allows some materials to cross while excluding others.

Question 48

What is an example of a semi-permeable fabric?

Answer 48

The fabric used in a jacket, such as Gore-Tex.

Question 49

What is a key factor that determines whether particles can cross the cell membrane?

Answer 49

Particle size

Question 50

What happens to small molecules like oxygen gas or water in relation to the cell membrane?

Answer 50

They can cross the membrane by slipping between phospholipid molecules.

Question 51

What is an example of a membrane that is permeable to some particles but not to others?

Answer 51

A window screen

Question 52

How do membrane proteins contribute to the semi-permeability of the cell membrane?

Answer 52

They may bind to specific chemicals based on their shape or electrical charge and transport them across the membrane.

Question 53

Fill in the blank: The process by which a cell digests itself from the inside is called _______.

Answer 53

apoptosis

Question 54

True or False: Cell membranes are fully permeable to all substances.

Answer 54

False

Question 55

What is the consequence of lysosomes releasing their enzymes at the wrong time?

Answer 55

It could lead to the digestion of the cell itself.

Question 56

What technique is used to study membrane proteins?

Answer 56

Freeze-fracture ## Footnote Freeze-fracture allows researchers to visualize the distribution of proteins in cell membranes.

Question 57

What happens to specimens during the freeze-fracture process?

Answer 57

Specimens are frozen in liquid nitrogen and then cracked with a cold knife ## Footnote This process causes the cells to shatter along a line of least resistance.

Question 58

What does the fracture line in freeze-fracture sometimes follow?

Answer 58

The line falls between the cell membrane's two phospholipid layers ## Footnote This separation makes membrane proteins visible.

Question 59

What is applied to the fractured specimen for examination?

Answer 59

Coated with platinum ## Footnote This coating is necessary for visualization under an electron microscope.

Question 60

What do electron micrographs of freeze-fractured membranes resemble?

Answer 60

Miniature moonscapes ## Footnote The appearance is due to the proteins creating bumpy hills and craters.

Question 61

What model of membrane structure has freeze-fracture provided evidence for?

Answer 61

Fluid-mosaic model ## Footnote This model describes the dynamic and flexible nature of cell membranes.

Question 62

What are the two main components of cell membranes?

Answer 62

Double layer of phospholipids ## Footnote Each phospholipid has a hydrophobic fatty acid tail and a hydrophilic head.

Question 63

What characteristic of cell membranes allows only certain substances to pass through?

Answer 63

Semi-permeable ## Footnote This property restricts movement based on size and other factors.

Question 64

What role do protein molecules embedded in the cell membrane play?

Answer 64

Transport certain substances through the membrane ## Footnote They function like passageways for materials entering or exiting the cell.

Question 65

What is the state of the lipids, proteins, and carbohydrates in the cell membrane?

Answer 65

In constant motion ## Footnote This movement contributes to the membrane's fluid and flexible nature.

Question 66

Fill in the blank: The model of membrane structure that describes its dynamic nature is called the _______.

Answer 66

fluid-mosaic model