Chapter 4 - Transport Across Cell Membranes

Question 1

What is a cell surface membrane

Answer 1

A phospholipid bilayer

Question 2

How are the phospholipids structured in a cell surface membrane

Answer 2

• Hydrophilic heads outwards, hydrophobic tails inwards

Question 3

What is meant by the fluid mosaic model

Answer 3

Because phospholipids are able to slide over each other, the membrane is flexible and so can constantly change shape

Question 4

What molecules can diffuse through a cell surface membrane and why

Answer 4

Small, non-polar molecules, as these are lipid soluble

Question 5

Water can’t diffuse through a cell surface membrane, what does this stop from leaving and entering cells

Answer 5

Water soluble substance

Question 6

What does water move through to enter cells

Answer 6

Aquaporins / water channels

Question 7

What are the 2 types of transport protein

Answer 7

Protein channels

Carrier proteins

Question 8

What do protein channels do

Answer 8

They form water-filled tubes to allow water-solubles ions to diffuse across the membrane

Question 9

What do carrier proteins do

Answer 9

Bind to ions or molecules (eg glucose and amino acids), then change shape in order to move the molecules across the membrane

Question 10

What type of transport occurs in carrier proteins

Answer 10

Active transport

Question 11

What other uses do proteins have in a cell surface membrane

Answer 11

• Provide structural support
• Form cell surface resettles to identify cells
• Help cells adhere together
• Act as receptors eg for hormones

Question 12

What is the function of cholesterol in cell surface membranes and how do they do this

Answer 12

Reduce lateral movement of other molecules by binding to hydrophobic tails, making it less flexible and more rigid

Question 13

How does cholesterol helps animals cells especially

Answer 13

Provide strength and support, as animals don’t have cell walls

Question 14

Why does cholesterol prevent loss of water

Answer 14

It is hydrophobic

Question 15

What are glycolipids made up of

Answer 15

Carbohydrates covalently bonded with a lipid

Question 16

What do glycoplipids do in a cell surface membrane

Answer 16

• Act as recognition sites (cell-surface receptors)
• Help cells attach to each other to form tissue
• Help maintain stability of a membrane

Question 17

What are glycoproteins

Answer 17

Carbohydrate chains attached to extrinsic proteins on outer surface of the cell membrane

Question 18

What functions do glycoproteins do

Answer 18

• Act as recognition sites
• Help cells attach to each other to form tissues
• Allow cells to recognise each other (eg lymphocytes recognise own cells)

Question 19

What is diffusion

Answer 19

The net movement of molecules from high to low concentration, until evenly distributed

Question 20

What is diffusion an example of

Answer 20

Passive transport

Question 21

What is meant by passive transport

Answer 21

No external source of energy is used, such as ATP

Question 22

What should be considered when thinking about diffusion

Answer 22

Fick’s law

Question 23

What are the three parts to fick’s law

Answer 23

Concentration gradient
Diffusion distance
Surface area of membrane

Question 24

What do the parts of fick’s law effect

Answer 24

The rate of diffusion

Question 25

What is facilitated diffusion

Answer 25

Movement of molecules across the cell membrane vie specific transmembrane proteins

Question 26

What is facilitated diffusion an example of

Answer 26

Passive transport

Question 27

What are transmembrane proteins

Answer 27

Protein channels | Carrier proteins

Question 28

Explain how protein channels work

Answer 28

- Water filled hydrophilic channels - Allow water soluble, small, charged ions to pass across membrane - Have to be charged as otherwise can just diffuse across

Question 29

What do carrier proteins do

Answer 29

Carry large molecules across cell surface membrane

Question 30

How do carrier proteins work

Answer 30

- Bind with protein | - Change shape so that molecule is released on the inside of the membrane

Question 31

What concentration gradient does facilitated diffusion occur at

Answer 31

High to low

Question 32

What is meant by transmembrane proteins being specific

Answer 32

Each molecule has its own transport protein

Question 33

What can transmembrane proteins also be used for

Answer 33

Active transport with ATP

Question 34

What is osmosis

Answer 34

Movement of water molecules from a high water potential to a low water potential across a partially permeable membrane

Question 35

What is osmosis an example of

Answer 35

Passive transport

Question 36

What is meant be a selectively/partially permeable membrane

Answer 36

A membrane that is permeable to water molecules and a few other small molecules, but not larger molecules

Question 37

What is meant by hypotonic

Answer 37

A solution with a high water potential

Question 38

What is meant by hypertonic

Answer 38

Solution with a low water potential

Question 39

What is meant by isotonic

Answer 39

A solution with the same water potential as the cell

Question 40

What value does the water potential of a solution always have

Answer 40

A negative value

Question 41

What kind of value will a high water potential have

Answer 41

A less negative one

Question 42

What kind of value will a low water potential have

Answer 42

A more negative one

Question 43

What value of water potential will pure water have

Answer 43

0

Question 44

What can water potential cause to happen with animal cells

Answer 44

Animal cells can shrink or burst as they have no cell wall

Question 45

What is active transport

Answer 45

Movement of molecules or ions across cell surface membranes from low concentration to a high concentration using ATP energy and carrier proteins

Question 46

How does active transport work

Answer 46

- Molecule binds to receptor sites in carrier protein - On inside of the cell, ATP bonds to the carrier protein, causing it to break down into ADP + Pi - Protein Changes shape and opens on the other side of the membrane - Molecule is released inside

Question 47

How does co-transport work

Answer 47

- 2 molecules move at once, via carrier protein - One moves with the concentration gradient, one moves against it - The molecule against the gradient uses energy from the molecule using facilitated diffusion

Question 48

What is an example of co-transport in the human body

Answer 48

Absolution of glucose in the ileum

Question 49

Where does the absorption of glucose take place

Answer 49

For diagram: Ileum at the top, epithelial cell middle, blood capillary at the bottom

Question 50

What is the ileum

Answer 50

Part of the small intestine

Question 52

Explain how glucose is absorbed into the blood

Answer 52

- Sodium moves out of epithelial cell into blood, through sodium-potassium pump via active transport, so there is a low concentration of sodium in the epithelial cell - Sodium moves with the concentration gradient from ileum into epithelial cell, co-transport occurs for glucose to also enter - Glucose is absorbed into blood through facilitated diffusion, via a carrier protein

Question 53

What is the epithelial cell

Answer 53

The outer cell of the small intestine