F211 Cell Membranes

Question 0

Partially Permeable Membranes

Answer 0

Cell membranes that are permeable to water and some solutes are described as partially permeable membranes
e.g. plasma (cell surface) membranes

Question 1

Roles of Membranes Within Cells

Answer 1

Separating cell contents from the outside environment
Separating cell components from the cytoplasm
Cell recognition and signalling
Holding the components of some metabolic pathways in place
Regulating the transport of materials into or out of cells

Question 2

Permeability

Water

Answer 2

All membranes are permeable to water molecules because water molecules can diffuse through the lipid bilayer

Question 3

Fluid Mosaic Model

Answer 3

A bilayer of phospholipid molecules for s the basic structure
Various protein molecules float in the bilayer some are completely free others are bound
Extrinsic proteins are partially embedded in the bilayer on the inside or the outside of the cell
Intrinsic proteins completely span the bilayer
Cholesterol, glycolipids and glycoproteins

Question 4

Phospholipid

Definition

Answer 4

A molecule consisting of a glycerol molecule, two fatty acid molecules and a phosphate group covalently bonded together

Question 5

Phospholipid

Role in the Cell Membrane

Answer 5

The hydrophobic layer formed by the phospholipid tails creates a barrier to many molecules and separates the cell contents from the outside
The thin layer of oil is ideal as most metabolic reactions take place in water

Question 6

Cholesterol

Role in the Cell Membrane

Answer 6

Gives the membranes of some eukaryotic cells mechanical stability
Fits between fatty acid tails to make the barrier more complete so that larger molecules cannot pass through easily
Regulates fluidity

Question 7

Glycolipid

Definition

Answer 7

A carbohydrate part attached to a phospholipid molecule

Question 8

Glycolipids

Role in the Cell Membrane

Answer 8

Receptor sites allowing hormones to with the cell so that a response can be carried out
Receptors are specific to certain hormones
Also allow drugs to bind so effect cell metabolism
Can be involved in signalling to allow recognition by the immune system
Markers for cellular recognition

Question 9

Proteins - Channel Proteins

Role in the Cell Membrane

Answer 9

Allow the movement of some substances (that are too large or hydrophilic to pass through the phospholipid bilayer) across the membrane by diffusion
Can be gated, opened or closed

Question 10

Glycoprotein

Definition

Answer 10

A carbohydrate part attached to a protein molecule

Question 10

Proteins - Carrier Proteins

Role in the Cell Membrane

Answer 10

Actively move some substances across the membrane
A specific molecule binds with the protein causing it’s shape to change
The molecule is released on to the other side of the membrane
Kinetic energy of molecules is the only energy required but movement still depends on concentration gradient

Question 12

Glycoproteins

Role in the Cell Membrane

Answer 12

Receptor sites allowing hormones to bind with the cell so that a response can be carried out
Important for allowing drugs to bind which effect cell metabolism
Can involved to allow recognition by the immune system
Can bind cells together in tissues

Question 12

Increasing Temperature

Effect on the Cell Membrane

Answer 12

Gives molecules more kinetic energy so they move faster
Higher chance of gaps being created
Fluidity increased
Destroys semipermeable nature of membrane
Proteins in the membrane denature meaning they are unable to control the movement of molecules through the membrane

Question 13

Cell Signalling

Answer 13

Cells communicate with each other by sending signals between and within cells

Question 13

Cell Signalling

Purpose

Answer 13

To detect nutrients in unicellular organisms
Between cells that make up tissues and organs in multicellular organisms
Cells are involved in a complex system of communication with each other

Question 14

Cell Signalling

Receptors

Answer 14

Cells detect signals with receptors (usually glycolipids or glycoproteins) on the cell surface membrane
The signalling molecule binds to the complimentary receptor and changes its shape
This instigates a chain of reaction within the cell causing a response

Question 15

Endocrine Signalling

Answer 15

Over long distances

Signalling molecule often transported in the circulatory system

Question 16

Paracrine Signalling

Answer 16

Signalling between cells that are close together
Sometimes directly
Sometimes by extracellular fluid

Question 17

Autocrine Signalling

Answer 17

A cell releases signals for its own receptors

Stimulates a response within the cell

Question 19

Mechanisms of Cell Signalling

Ion Channels

Answer 19

The signal is a chemical
It attaches to a protein or glycoprotein acting as an ion channel
When the chemical attaches it opens the ion channel
Ions are able to get into the cell bringing about a response

Question 20

Mechanisms of Cell Signalling

G - Proteins

Answer 20

Receptor in the membrane interacts with G - protein
Signal molecule attaches to receptor which activates the G- protein
The G - protein activates an enzyme to bring about a reaction inside the cell

Question 20

Mechanisms of Cell Signalling

Enzymes

Answer 20

Receptor is an enzyme
The receptor is made of two parts and the signal molecule joins the together
This forms an active enzyme
The enzyme brings about reactions in the cell

Question 21

Insulin

Answer 21

A hormone released f on beta cells in Islets of Langerhans in the pancreas
Released as a response to high blood sugar
Insulin attaches to receptors on cells causing more glucose channels in the membrane to open
Glucose moves from the blood into cells reducing blood sugar

Question 22

Medicinal Drugs

Answer 22

Some drugs bind with complimentary receptor sites to block signalling molecules
Some drugs mimic signalling molecules to bing with a receptor and trigger a response

Question 23

Viruses

Answer 23

Invade cells by binding to receptor sites to prevent cell signalling and therefore normal function from taking place
Some poisons also work like this

Question 24

Hormones

Answer 24

Often used as cell signalling molecules
Move through the blood
Bind to receptor sites on the target cell and trigger a response

Question 26

Diffusion

Answer 26

A passive process

Movement of molecules from a high concentration to a low concentration across a concentration gradient

Question 28

Facilitated Diffusion

Answer 28

A passive process
Movement of molecules from a high to a low concentration across a concentration gradient via channel or carrier proteins
For hydrophobic molecules and ions which can’t pass through the phospholipid bilayer

Question 29

Factors Affecting Rate of Diffusion

Answer 29

Temperature
Concentration Gradient 
Stirring/Movement 
Surface Area 
Distance
Size of Molecule

Question 30

Endocytosis

Answer 30

Bulk transport of materials into a cell via vesicles which can fuse with the cell plasma membrane

Question 31

Exocytosis

Answer 31

Bulk transport of materials out of a cell via vesicles which can break from the cell

Question 32

Active Transport

Answer 32

Requires ATP, energy

Movement of molecules against a concentration gradient

Question 33

Osmosis

Answer 33

Diffusion of water from an area of high water potential to an area of low water potential

Question 34

Water Potential

Answer 34

The number of free water molecules

Question 35

Animal Cell

In Pure Water

Answer 35

Water moves into the cell by osmosis

Cell bursts, lysis

Question 36

Animal Cell

In a Concentrated Sugar Solution

Answer 36

Water moves out of the cell by osmosis

Cell becomes crenated

Question 37

Plant Cell

In Pure Water

Answer 37

Water moves in by osmosis
Cell membrane presses against cell wall
Cell wall is strong enough to with stand the pressure
Cell become turgid

Question 38

Plant Cell

In a Concentrated Sugar Solution

Answer 38

Water moves out of the cell by osmosis
The membrane pulls away from the cell membrane
Cell is plasmolysed