Cell Structure - Cell membranes

Question 1

Why is the cell membrane structure knows as fluid mosaic

Answer 1

• Fluid - The components can move around within the membrane
• Mosaic - Due to the pattern produced by the proteins embedded throughout the membrane

Question 2

What are glycoproteins

Answer 2

Carbohydrate bound to a protein

Question 3

What is the role of glycoproteins

Answer 3

The carbohydrate acts as a recognition site

Question 4

What are glycolipids

Answer 4

Carbohydrate bound to a phospholipid

Question 5

What is the role of glycolipids

Answer 5

The carbohydrate acts as a recognition site

Question 6

What is the role of cholesterol

Answer 6

• Reduces the fluidity of the membrane by restricting the movement of other molecules
• Makes the membrane more rigid and less permeable
• Maintains the shape of the membrane

Question 7

What is the role of phospholipids

Answer 7

• Forms a bilayer
• Allows lipid soluble and small, non-polar molecules to diffuse through
• Prevents the passage of charged and water soluble molecules

Question 8

Define diffusion

Answer 8

The passive net movement of small non-polar or lipid soluble molecules from a higher concentration to a lower concentration down a concentration gradient

Question 9

Define osmosis

Answer 9

The net movement of water molecules from a high water potential to a low water potential through a partially permeable membrane

Question 10

Define facillitated diffusion

Answer 10

The passive net movement of water-soluble and charged molecules from a higher concentration to a lower concentration through channel proteins or carrier proteins

Question 11

Define co-transport

Answer 11

When 2 molecules are moved across the membrane by the same protein at the same time

Question 12

Define active transport

Answer 12

The movement of molecules across the membrane against the concentration gradient via a specific carrier protein. Requires energy from the hydrolysis of ATP

Question 13

Contrast active transport and facillitated diffusion

Answer 13

• Active transport uses energy from the hydrolysis of ATP, whereas facilitated diffusion does not
• Active transport uses carrier proteins only, whereas facilitated diffusion uses carrier proteins and channel proteins
• In active transport, molecules are moved against a concentration gradient whereas in facilitated diffusion molecules are moved down a concentration gradient

Question 14

Compare active transport and facillitated diffusion

Answer 14

• Both use carrier proteins

Question 15

Step by step process of active transport

Answer 15

• The molecule binds to the carrier protein
• The carrier protein changes shape, and energy from the hydrolysis of ATP is used to transport the molecule against its concentration gradient

Question 16

What is a hypotonic solution

Answer 16

• Higher water potential outside the cell
• Lower water potential inside the cell

Question 17

What is a hypertonic solution

Answer 17

• Higher water potential inside the cell
• Lower water potential outside the cell

Question 18

What is an isotonic solution

Answer 18

Water potential inside the cell = Water potential outside the cell

Question 19

What happens to animal cells in a hypotonic solution

Answer 19

Osmotic lysis (cell bursts because of too much water)

Question 20

What happens to plant cells in a hypotonic solution

Answer 20

• Cell becomes turgid
• Cell does not burst due to the cellulose cell wall

Question 21

What happens to animal cells in a hypertonic solution

Answer 21

Crenation (cell shrivels)

Question 22

What happens to plant cells in a hypertonic solution

Answer 22

• Cell becomes flaccid
• Plasmolysis occurs (cell membrane can come away from the cell wall due to large amounts of water leaving)

Question 23

What happens to animal cells in an isotonic solution

Answer 23

No effect due to no net movement

Question 24

What happens to plant cells in an isotonic solution

Answer 24

No effect due to no net movement

Question 25

What facors can cause the rate of movement across a membrane to increase

Answer 25

• Higher temperature
• Greater surface area
• Higher concentration gradient
• More carrier/channel proteins

Question 26

How does temperature affect the rate of movement across a membrane

Answer 26

• Higher temperature increases the kinetic energy of molecules
• Faster rate of diffusion

Question 27

How does surface area affect the rate of movement across a membrane

Answer 27

• More phospholipids for diffusion
• More carrier/channel proteins for facilitated diffusion

Question 28

How does concentration gradient affect the rate of movement across a membrane

Answer 28

As the concentration difference increases, the rate of diffusion increases

Question 29

How does the number of carrier/transport proteins affect the rate of movement across a mambrane

Answer 29

There are more proteins for molecules to pass through

Question 30

How does temperature affect membrane permeability and why

Answer 30

• Makes the membrane more permeable
• Higher temperatures make the phospholipids more fluid by increasing their kinetic energy

Question 31

How does very high temperture affect membrane permeabilty

Answer 31

• Makes the membrane very permeable
• Channel/carrier proteins denature, so are non-selective, allowing any molecule through

Question 32

How does alcohol affect membrane permeability and why

Answer 32

• Makes the membrane more permeable
• Dissolves the phospholipid bilayer

Question 33

How does acid affect membrane permeability and why

Answer 33

• Makes the membrane more permeable
• Channel/carrier proteins denature, so they are non-selective, allowing any molecule through

Question 34

Step by step process for co-transport

Answer 34

• Sodium ions are actively transported from the epithelial cells into the blood using a specific carrier protein and energy from the hydrolysis of ATP
• A sodium ion concentration gradient is established between the lumen and epithelial cell
• Glucose/amino acid and sodium ions are co-transported from the lumen of the small intestine into the epithelial cell via facilitated diffusion using a specific carrier protein
• The glucose/amino acid molecule moves into the blood via facilitated diffusion using a specific carrier protein

Question 35

Adaptations of epithelial cells

Answer 35

• Microvilli for large surface area
• Many carrier proteins for active transport, facilitated diffusion and co-transport
• Many mitochondria to produce more ATP for active transport
• Epithelial lining is one squamous epithelial cell thick therefore a short diffusion pathway