B4 Cell Transport Mechanism

Question 1

What’s the cell surface membrane or plasma membrane

Answer 1

• they enter or exist molecules in cells that are controlled by the cell surface membrane or plasma
• surrounded by cytoplasm of the cell
• membrane is described as partially/semi/ selective permeable
• cells membrane have a specific structure to enable the movement of substances from one place to another

Question 2

The fluid - mosaic model

Answer 2

• the cell membrane that consists of proteins, glycoproteins, phosolipids and carbohydrates
• phospholipids molecules form a double layer that’s bilayer that are constantly moving around relative to one another
• giving the membrane fluid structure
• proteins molecules are unevenly distributed throughout the membrane
• forming a mosaic
• selective permeability of the cell surface membrane is related to the types and distribution of specific proteins and phospholipids molecules that are present in the membrane

Question 3

What are intrinsic proteins

Answer 3

Are the membrane proteins which are embedded completely or party through the lipid bilayer of the membrane

Question 4

Extrinsic proteins

Answer 4

Are loosely bound to proteins that are located outside of the membrane

Question 5

Explain why the model for membrane structure is known as the fluid mosaic model

Answer 5

• phospholipids molecules moves the freely with respect to one another making members be fluid
• proteins are distributed throughout the membrane unevenly and in a mosaic pattern when viewed above
• agreed structure is based on experimental/ chemically evidences and classed as a model

Question 6

Function of phospholipids

Answer 6

• hydrophobic tails of the phospholipids molecules are attracted towards each other
• hydrophilic heads are inwards to the cytoplasm or outwards towards the watery extra cellular fluids
• most abundant molecules found in all membrane
• the phospholipids bilayer allows lipid soluble non polar molecules to pass through the simple diffusion but prevents the passage of small polar molecules like irons

Question 7

Cholesterol functions

Answer 7

• decrease permeability and increases stability
• more cholesterol less fluidity of membrane
• different tries of cells have different proportions of cholesterol

Question 8

Channel proteins functions

Answer 8

• channel proteins are like pores within the membrane and only allow specific charged ions or small molecules to move across the membrane by facilitated diffusion
• can open and close and are intrinsic
• proteins have specific tertiary structure
• specific and can only transport molecules that are complementary to the shape

Question 9

Carrier proteins functions

Answer 9

• carrier proteins aid to transport of ions / polar molecules and large molecules
• example glucose and amino acids by facilitated diffusion sand active transport

Question 10

Receptor of proteins functions

Answer 10

• other proteins act as specific receptors for complementary molecules
• example hormones such as insulin, may bind to the insulin receptors proteins
• this allows cell to respond by increasing the cell’s permeability to glucose
• • specific cells have specific receptors

Question 11

Enzymes proteins functions

Answer 11

• enzymes are also found embedded in the cells membrane
• example Maltese and dipeptidases
• the shape of the enzymes active site of specific and complementary to its substrate
• Allowing them to bind to form enzyme substrate complexes

Question 12

Glycoproteins functions

Answer 12

• glycoproteins are composed of carbohydrates and proteins
• the outer surface of the membrane and are important in cell recognition often act as antigens
• immune system detects specific shape of glycoproteins
• to identify the cells as self or if they’re are non self
• produced by Golgi body with cell that display them

Question 13

Aquaporins functions

Answer 13

• aquaporins are special types of challenges proteins
• to specific water
• a lot of aquaporins is said to be very permeable to water and will carry out osmosis easily

Question 14

Diffusion simplified

Answer 14

• is a passive process
• doesn’t require ATP
• net diffusion will stop when there are equal number of that specific molecules on either side of the membrane
• when molecules have reached equilibrium
• doesn’t require specific proteins and involve non - polar
• small lipid soluble molecule
• example O2 , CO2, and oestrogen
• diffusion is the net movement of molecules from an area of higher concentration to a lower concentration across a partially permeable membrane

Question 15

Factors that affect rate of diffusion

Answer 15

Temperature - increases kinetic energy therefore faster rate of diffusion of molecules
Surface area - large surface area which provides more space for molecules to pass through therefore faster. This allows for more particles to be present. Microvilli increases surface area of a cell
Concentrated gradient - concentration differences increases, rate of diffusion increases
Diffusion distance - shorter diffusion distances, the faster molecules will travel through it

Question 16

Definition of facilitated

Answer 16

Facilitate means to help or aid so proteins help molecules to pass through the phospholipids bilayer

Question 17

Facilitated diffusion

Answer 17

• hydrophilic which is water soluble charged or large substances that cannot pass between hydrophobic tails of the phospholipids bilayer
• this is because of the fatty acid tails are non polar and they repel polar molecules
• enter and exist cells water soluble molecules move through the membrane through channel proteins or carrier proteins
• channel and carrier proteins are a specific shape
• only transport specific molecules that are complementary to the binding site

Question 18

Osmosis definition

Answer 18

Osmosis is the net movement of water molecules for a region of low solute concentration (high concentration) to a region of high solute concentration (low water concentration) across a partially permeable membrane

Question 19

Active transport step by step

Answer 19

1) used to transport molecules across the membrane against their concentration gradient
2) for low concentration to high concentration
3) active transport only use carrier proteins
4) requires specifically shaped carrier proteins with complementary binding site
5) requires source of energy supplies by ATP this is produced during respiration its an active process
6) molecules transport bind to the binding site of the specific carrier proteins
7) hydrolysis of the ATP into ADP + Pi provides small amount of energy. This causes the proteins to change shape
8) change in proteins shape transport the molecules across the membrane into the are where the concentration of the molecules is relatively high

Question 20

Other forms of active transport exocytosis

Answer 20

• the prefix exo means outside
• transport uses Golgi vesicles to move very large quantities of molecules like enzymes and other proteins like insulin and neurotransmitter from inside the cell to outside of the cell
• ATP is required to move the vesicles to the surface membrane and the vesicles fuse with the membrane

Question 21

Other from of active transport endocytosis

Answer 21

• the prefix ends means inside
• the cell surface membrane is pulled inwards to create a vesicles
• molecules next to that part of the membrane are enclosed within the vesicles
• the movement of the vesicles into the cells also requires the breakdown of the ATP into ADP and Pi

Question 22

Yeh surface area of the cell = cell membrane

Answer 22

• the cell membrane is the last of the cell which exchange materials with the surroundings
• it is partially permeable I.e. let some substances in and out of but not others
• only very small molecules can diffuse through such as oxygen, glucose, amino acids, water
• it’s passive process

Question 23

What does passive means

Answer 23

Big molecules like stretch and proteins can’t fit through the membrane

Question 24

The volume of the cell = cytoplasm

Answer 24

• the cytoplasm is the part of the cell where chemicals reactions takes place
• it is full of enzyme which control the chemicals reactions such as respiration

Question 25

How to calculate surface area

Answer 25

Length x width

Question 26

How to calculate volume

Answer 26

Length x width x height

Question 27

How can a cell specialise to increase its surface area

Question 28

Fick law

Answer 28

Rate of diffusion = surface areas x concentration gradient / diffusion distances

Question 29

Solution type is they lower solute concentration than tissue / organelle description

Answer 29

• animal cells - swelling and lysis occurs this will bursting destroying the cell and it’s content are lost
• plant cells swell increasing mass the cellulose cell wall prevent lysis
• water moves in by osmosis

Question 30

Solution type higher solute concentration than tissue / organelle description

Answer 30

• results in animal cells shrivelling crenatation
• plant cell membrane pull away from the cell wall plasmolysed
• water moves out by osmosis mass is lost

Question 31

Solution type isotonic equal solute concentration description

Answer 31

• no net movement of water in or out of cells
• solute concentrations inside cell = solute concentration outside cells
• no concentration gradient = no gain in mass