As Biology Wjec Eduqas Component 1 Ch3

Front 1

What is a phospholipid

Back 1

Phospholipids are important components of cell-surface membranes and form the basis of membrane structure. They consist of a lipid (3 fatty acids and a glycerol molecule) attached to a phosphate ion.

Front 2

State 2 properties of phospholipids

Back 2

Any of the following:

1. Phospholipids can form bilayers

2. Inner layer of phospholipids has hydrophobic heads pointing inwards

3. Outer layer of phospholipids has hydrophilic heads pointing outwards

4. Phospholipids allow lipid-soluble molecules across, but not water-soluble molecules

Front 3

State what an extrinsic protein is

Back 3

Extrinsic proteins are on either surface of phospholipid bilayers. They provide structural support and form recognition/receptor sites for hormone attachment

Front 4

State what an intrinsic protein is

Back 4

Intrinsic proteins extend across both layers of the bilayer. Some are carrier proteins, which transport water-soluble substances across the membrane. Others are channel protein that transport ions by active transport

Front 5

What is the currently accepted model for cell membranes known as and why?

Back 5

The fluid-mosaic model was hypothesized by Singer and Nicolson in 1972. The membrane is known as fluid since phospholipids can move relative to each other. It is mosaic since the membrane contains many different molecules: phospholipids, proteins, glycoproteins/lipids and cholesterol

Front 6

Why can polar molecules not move directly across biological membranes?

Back 6

They must pass through intrinsic proteins because the phospholipids are selectively permeable due to their hydrophobic tails

Front 7

Define diffusion

Back 7

The passive movement of a molecule or ion down a concentration gradient, from a region of high concentration to a region of low concentration.

Front 8

Define passive

Back 8

Not requiring energy provided by the cell

Front 9

State the equation for rate of diffusion

Back 9

Surface area x difference in concentration/

length of the diffusion path

Front 10

Give 2 factors that effect rate of diffusion

Back 10

Any of the following:

1. The size of the diffusing molecule

2. The nature of diffusing molecule

3. Temperature

Front 11

Define facilitated diffusion

Back 11

The passive transfer of molecules or ions down a concentration gradient, across a membrane, by protein carrier molecules in the membrane.

Front 12

The two types of protein that perform facilitated diffusion are:

Back 12

1. Channel proteins: transport ions and water-soluble molecules over the membrane selectively

2. Carrier proteins: transport larger polar molecules across the membrane selectively

Front 13

Define active transport

Back 13

The movement of molecules or ions across a membrane against a concentration gradient, using energy from the hydrolysis of ATP made by the cell in respriation

Front 14

What are the features of active transport?

Back 14

1. Ions or molecules are moved against the concentration gradient

2. The process requires energy from ATP

3. The process occurs through intrinsic carrier proteins spanning the membrane

4. The rate is limited by the number of carrier proteins available

Front 15

Describe the process of active uptake of a single molecule or ion

Back 15

1. The molecule or ion combines with a specific carrier protein on the outside of the membrane

2. ATP transfers a phosphate group to the carrier protein of the inside of the membrane

3. The carrier protein changes shape and carries the molecule across the membrane, to the inside of the cell.

4. The molecule is released into the cytoplasm

5. The phosphate ion is released from the carrier protein

6. The carrier protein regains its original shape

Front 16

What is co-transport?

Back 16

Another type of facilitated diffusion that brings molecules and ions into cells together on the same transport protein molecule

Front 17

Describe the process of co-transport

Back 17

1. Glucose molecule and two sodium ions attach to a carrier protein

2. The carrier protein changes shape and deposits the glucose and sodium inside the cell

3. The glucose molecule and sodium ions separately diffuse through the cell to the opposite membrane

Front 18

Define osmosis

Back 18

The diffusion of water, from a region of higher water potential to a region of lower water potential, through a selectively permeable membrane

Front 19

Define water potential

Back 19

A measure of the free energy of water molecules, measured in kilopascals (kPa)

Front 20

Explain what solute potential is

Back 20

A measurement of how easily water molecules move out of a solution. The more solute present, the more tightly water molecules are held, the lower the tendency of water to move out. The higher the concentration, the more negative the solute potential

Front 21

Define turgid

Back 21

A plant cell that holds as much water as possible. Further entry of water is prevented as the cell wall cannot expand further

Front 22

Define pressure potential

Back 22

A force which increases the tendency of water to move out

Front 23

State the equation for the water potential of a cell

Back 23

Water potential of cell = pressure potential + solute potential

Front 24

Describe what happens to a cell when the external solution is hypotonic to the cell

Back 24

If the water potential of the external solution is less negative than the solution inside the cell, it is hypotonic to the cell and water flows into the cell

Front 25

Describe what happens to a cell when the external solution is hypertonic to the cell

Back 25

If the water potential of the external solution is more negative than the solution inside the cell, it is hypertonic to the cell and water flows out of the cell

Front 26

Describe what happens to a cell when the external solution is isotonic to the cell

Back 26

If the cell has the same water potential as the surrounding solution, the external solution and the cell are isotonic and there will be no net water movement

Front 27

The point at which the vacuole shrinks completely in a hypertonic solution is known as __________.

Back 27

Plasmolysis

Front 28

Define flaccid

Back 28

"Floppy" - such cells cannot provide support so the plant wilts

Front 29

What is the point of incipient plasmolysis?

Back 29

The point at which the membrane begins to pull away from the cell wall

Front 30

What is haemolysis?

Back 30

When red blood cells are placed in a hypotonic solution, water flows into them by osmosis and they burst

Front 31

When do red blood cells become crenated?

Back 31

When red blood cells are placed in a hypertonic solution, water flows out of the them by osmosis and they become crenated. They appear shrunken and bumpy

Front 32

What is endocytosis?

Back 32

Endocytosis occurs when material is engulfed by extensions of the plasma membrane and cytoplasm, surrounding it, making a vesicle

Front 33

What are the two types of endocytosis?

Back 33

1. Phagocytosis

2. Pinocytosis

Front 34

What is exocytosis?

Back 34

The process by which substances may leave the cell, having been transported through the cytoplasm in a vesicle, which fuses with the cell membrane. Digestive enzymes are often secreted in this way