2.1.5 biological membranes

Question 1

describe the fluid Mosaic model of membranes

Answer 1

fluid: phospholipid bilayer in which individual phospholipids can move which means that the membrane has flexible shape

Mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded

Question 2

Explain the role of cholesterol and glycolipids in membranes

Answer 2

cholesterol: steroid molecule in some plasma membranes, connects phospholipids and reduces fluidity to make bilayer more stable

Glycolipids: cell signalling and cell recognition

Question 3

Explain the function of extrinsic and transmembrane proteins in membranes

Answer 3

binding sites/receptors e.g. for hormones and drugs: antigens (glycoproteins), bind cells together and involved in cell signalling

Question 4

Explain the functions of intrinsic transmembrane proteins in membranes

Answer 4

electron carriers (respiration/photosynthesis)

Channel proteins: facilitated diffusion

Carrier proteins: facilitated diffusion and active transport

Question 5

Explain the functions of membranes within cells

Answer 5

provide internal transport system

selectively permeable to regulate passage of molecules into and out of organelles or within organelles

provide reaction surface

Isolate organelles from cytoplasm for specific metabolic reactions

Question 6

Explain the functions of the cell surface membrane

Answer 6

isolate Cytoplasm from extra cellular environment

selectively permeable to regulate transport of substances

involved in cell signalling/cell recognition

Question 7

Name and explain three factors that affect membrane permeability

Answer 7

temperature: high temperature denatures membrane proteins/phospholipid molecules have more kinetic energy and move further apart

PH: changes tertiary structure of membrane proteins

Use of a solvent: may dissolve membrane

Question 8

What are the three factors that affect the permeability of the cell membrane

Answer 8

ethanol: dissolves the lipid components of membrane, makes membrane more permeable

PH: if extreme, denatures the membranes proteins

Heat: more movement in the phospholipid bilayer which creates gaps. When cold, ice crystals damage the membrane. The kinetic energy of phospholipid bilayer increases fluidity

Question 9

Describe the five functions of the cell surface membrane and give examples

Answer 9

partially permeable: allow small, un charged particles to pass through it

Produce different compartments inside cells: mitochondria surrounded by two membranes, which isolate the reactions taking place inside from reactions in the cytoplasm

important in cell signalling: a substance produced by one cell docs into a receptor in membrane of another, causing something to happen in second cell

can allow electrical signals to pass along them: the membrane of the axon of a motoneuron transmits action potential from the CNS to a muscle

Provides attachment sites for enzymes and other molecules involved in metabolism: the inner membrane of the mitochondrion contains my molecules need for the production of ATP. The inner membrane of a chloroplast contains chlorophyll

Question 10

Describe a phospholipid

Answer 10

phospholipids have a hydrophilic head which contain a phosphate group connected to a glycerol by phosphodiester bond

They also have a hydrophobic tail which include 2 fatty acids that are connected to the glycerol by Ester bond

Question 11

Describe cell signalling

Answer 11

receptor activation: the binding of a signalling molecule causes a change in receptor that activates its function

Signal transduction: the activated receptor stimulates a series of proteins that form a signal transduction pathway

Cellular response

Question 12

Describe hormone receptors

Answer 12

Hormones are chemical messengers. Any cell with a receptor for the hormone molecules is a target cell. A hormone binds to receptor on a target cell surface membrane as they have a complimentary shape. The binding of the hormone receptor causes the target cell to respond in a certain way

Question 13

What affects the rate of diffusion

Answer 13

temperature: the higher the temperature, the greater rate of diffusion

concentration gradient

surface area of membrane: the larger the surface area, the greater rate of diffusion

size of particle: larger the particle, slower rate of diffusion

Chemical nature of particle: nonpolar particles diffuse faster than polar

Question 15

Describe simple diffusion

Answer 15

The net movement from high concentration to low concentration through the phospholipid bilayer. Small uncharged molecules go through e.g. carbon dioxide

Passive process requires no energy from ATP hydrolysis

Question 16

Describe facilitated diffusion

Answer 16

The net movement from high concentration to low concentration through an intrinsic protein. Large, charged molecules can move through e.g. glucose

Passive process

Question 17

Describe active transport

Answer 17

The movement from low concentration to high concentration. It is an energy requiring process and it moves the molecule from one side of the membrane to another. These molecules would be minerals in root hair cells or glucose in the small intestine

Question 18

Describe water potential

Answer 18

water potential is the amount of solutes in a solvent. You cannot have a water potential higher than zero so if you have pure water it is 0 kPa.

The most solvents, the lower the kPa is

At high water potential, water molecules have more energy because they are less restricted by the presence of solutes and vice versa. More water molecules can diffuse from high to low more than low to high

Question 19

Define osmosis

Answer 19

The net movement of water from an area of high water potential to a low water potential across a partially permeable membrane

Question 20

What is water potential measured in

Answer 20

kPa

Question 21

What is the water potential of pure water

Answer 21

0 kPa

Question 24

How does osmosis affects plant and animal cells

Answer 24

animal: when there is too much water red blood cells will burst (lysis). When there is not enough water the red blood cell will become crenated and shrivel
plant: when there is too much water the plant will become turgid as the protoplast swells. When there is not enough water the plant becomes flaccid and this occurs due to plasmolysis when the membrane comes away from the cell wall

Question 25

define hypertonic

Answer 25

this is when the solution is more concentrated: more solute : water ratio

lower water potential as less water

Question 26

Describe endocytosis

Answer 26

Food particles/even whole cells, are taken into the cell and digested

Question 27

Define exocytosis

Answer 27

Large amount of some substances transported out of the cell and requires energy

Question 28

What is it meant by cell signalling

Answer 28

The process of cellular communication within the body by cells releasing and receiving hormones and other signalling molecules

Question 29

How do hormones and drugs bind to target cells

Answer 29

A hormone will have a specific shape for the receptor(complimentary binding)

Question 30

Describe the role of phospholipids

Answer 30

Provide barriers in cellular membranes to protect the cell

Question 31

describe the role of cholesterol

Answer 31

Maintains fluidity of membrane and gives the membrane of some eukaryotic cells mechanical stability

Question 32

describe The role of proteins (intrinsic)

Answer 32

Channel proteins move ions and large molecules down diffusion gradient and carrier proteins transport large molecules against a concentration gradient

Question 33

Describe the role of glycoproteins

Answer 33

Cell to cell recognition and adhesion

Question 34

Describe the role of glycolipids

Answer 34

Maintain stability of cell membrane and facilitate cellular recognition

Question 35

outline how colorimetry Could be used to investigate membrane permeability

Answer 35

use plant tissue with soluble pigment in vacuole. Tonoplast and cell-surface membrane disrupted which increases permeability and pigment diffuses into solution

select colorimeter filter with complimentary colour

use distilled water to set colorimeter to 0. Measure absorbance/percentage transmission value of solution

High absorbance/low transmission means there’s more pigment in solution

Question 36

ppq: Suggest why galactose and glucose cannot pass through the plasma membrane by simple diffusion through the phospholipid bilayer

Answer 36

They are too large

Question 37

ppq: What two substances are required To break the glycosidic bond in lactose

Answer 37

Enzymes and water

Question 38

ppq: Which component of the plasma membrane act as a barrier to mineral irons entering the cell

Answer 38

Phospholipid bilayer

Question 39

ppq: Describe roles of the membrane in single celled organisms e.g. amoeba

Answer 39

Compartmentalisation and controls what enters and exits organelles

Question 40

ppq: Describe the structure of a plasma cell surface membrane

Answer 40

hydrophilic phosphate heads point outwards, hydrophobic fatty acid tails point inwards

There is cholesterol in amongst it (between phospholipids) and also has extrinsic and intrinsic proteins on the surface

Question 41

ppq: One molecule that crosses membranes easily is the steroid hormone progesterone which is produced in the ovaries from cholesterol. Explain why progesterone can move across membranes

Answer 41

Because they are fat and soluble and they are hydrophobic which means they can diffuse through the phospholipid bilayer

Question 42

ppq: describe the arrangement and functions of two named components of a cell surface membrane

Answer 42

phospholipid bilayer: phospholipid hydrophobic tails point inwards and hydrophilic heads point outwards. this provides a barrier to large polar molecules

proteins embedded in the bilayer are for active transport/facilitated diffusion

cholesterol molecules fit within the bilayer and they regulate fluidity

Glycoproteins/glycolipids on the surface for cell signalling

Question 43

ppq: Which component of a cell membrane becomes more fluid as temperature increases

Answer 43

Phospholipid bilayer

Question 44

ppq: Which component of a cell membrane denatures as temperature increases

Answer 44

Proteins e.g. glycoproteins

Question 45

ppq: State the term used to describe a membrane through which some substances can pass freely but others cannot

Answer 45

Partially permeable

Question 46

ppq: Complete the following paragraph about cell membranes

The model of cell membrane structure is called the ____ ___ model. phospholipid bilayer is with specific membrane proteins account for the ability of the membrane to allow both passive and ____ transport mechanisms. ions and most polar molecules are insoluble in the phospholipid bilayer. However, the bilayer allows diffusion of most nonpolar molecules such as ___. protein channels, which may be gated, and _____ proteins and able to sell to control the movement of most polar substances

Answer 46

Fluid Mosaic

Active

Oxygen

Carrier

Question 47

ppq: Explain how cell-surface membranes contribute to the process of cell signalling

Answer 47

The release of signal molecule by exocytosis. Proteins e.g. glycoproteins or glycolipid have receptors and this receptor is specific. The shape of receptor and signal are complimentary and the attachment of the signal molecule causes change and the cell surface membrane allows entry of some signal molecules

Question 48

ppq: State three roles of membranes inside cells

Answer 48

to make compartments for organelles within a cell

to isolate the contents of an organelle e.g. hydrolytic enzymes

Provide selective permeability

Site for attachment of enzymes

Question 49

How do you find percentage change

Answer 49

Find the difference, divide by original, multiplied by 100

Question 50

define isotonic

Answer 50

same amount of water : solute ratio

Question 51

define hypotonic

Answer 51

solution is less concentrated. There is more water : solute ratio

Question 52

ppq: The proteins embedded in the membranes of vesicles have different functions. COPI and COPII proteins are known as “address proteins”. vesicles that transport materials from the golgi to the rer are coated in COPI proteins. vesicles that transport materials to the golgi from the RER are coated in COPII proteins

suggest how these proteins ensure that a vesicle is transported to the correct target organelle

Answer 52

The receptor is found only on the correct target. The address protein provides a way of labelling/identifying the vesicles. The COPI has a specific shape and therefore the address proteins are complimentary to the receptor and the receptor will then fit the shape of the protein (COPI)

Question 53

ppq: State two examples of active transport in cells. For each example, you should name the substance that is transported and the cell involved

Answer 53

mineral ions e.g. into root hair cells

hydrogen ions out of companion cells

Mineral ions e.g. across endodermis

Question 54

ppq: State how each of these substances crosses the cell surface membrane

release of enzymes into the gut

plant cell taking up water

calcium ions entering a nerve cell down a concentration gradient

Oxygen entering a red blood cell

Answer 54

bulk transport

Osmosis

facilitated diffusion

Diffusion

Question 55

ppq: Describe the routes that water molecules take through the cell surface membrane

Answer 55

water molecules fit between phospholipid is through the phospholipid bilayer via Protein channels

Question 56

ppq: explain why plant cells do not burst when they are left in pure water

Answer 56

Due to the cell wall which provides strength and limits the uptake of water

Question 57

ppq: Explain how a glycoprotein can act as a receptor

Answer 57

Receptors have a specific shape and I’ll complimentary to the shape of trigger and this trigger binds to receptor