transport across cell membrane

Question 1

what re plasma membranes?

Answer 1

all membranes around and within cells as they have the same basic structure.

Question 2

why is the phospholipids an important component in the cell surface membrane?

Answer 2

their hydrophilic heads mean that the layers point in different directions as they both attracted to the water on the outside and the inside of the cell.
their hydrophobic tails mean that the inside the other side of both layers pints inwards as they are repelled by the water.

Question 3

what is the function of phospholipids in he membrane?

Answer 3

• to allow phosphor-lipid soluble materials to enter and leave the cell.
• to prevent water-soluble materials from entering and leaving the cell.
• to make the membrane flexible and self sealing.

Question 4

what are the functions of proteins in the membrane?

Answer 4

.provide structural support
.act as channels transporting water-soluble substances across the membrane
.allow active transport across the membrane through carrier proteins
.form cell-surface receptors used for identifying cells
.helo cells adhere to each other
.act as receptors, for example for hormones

Question 5

what are the functions of cholesterol in the membrane?

Answer 5

to reduce lateral movement of other molecules including phospholipids
make to the membrane less fluid at high temperatures
prevent leakage of water and dissolve ops from the cell

Question 6

what are the functions of glycoproteins in the cell membrane?

Answer 6

act as recognition sites
help maintain the stability of the membrane
help cells to attach to one another and so form tissues

Question 7

what is the function of glycoproteins in the membrane?

Answer 7

act as recognition sites
help cells to attack to one anther and so form tissues
allows cells to recognise one another, for example lymphocytes can recognise an organisms own cells

Question 8

why do most molecules not freely diffuse across the the cell-surface membrane?

Answer 8

many are:
not soluble in lipids and therefore cannot pass through the phospholipid layer
too large to pass through the channels in the membrane
of the same charge as the charge on the protein channel and so, even if they are small enough to pass through they will be repelled
electrical uncharged and therefore have difficulty passing through the non-polar hydrophobic tails in the phospholipid bilayer

Question 9

why is the cell surface model of the cell called a fluid-mosaic model?

Answer 9

fluid because the individual phospholipid molecules can move relative o one another. this gives the membrane a flexible structure that is always changing shape
mosaic because the proteins that are embedded in the bilayer vary m shape, size and pattern

Question 10

what is simple diffusion?

Answer 10

the net movement of molecules or ions from a region where they are more highly concentrated to region where they are less highly concentrated until evenly distributed.

Question 11

what is facilitated diffusion?

Answer 11

the movement of charged ions and polar molecules through transmembrane channels and carriers that span the membrane. the process is passive and relies on inbuilt kinetic energy of the diffusing molecules, there is no external input.

Question 12

what are protein channels?

Answer 12

proteins that form water filled hydrophilic channels across the membrane allowing specific water soluble ions to pass through. the channels are selective.

Question 13

what are protein carriers?

Answer 13

when a molecule is present that is specific to the protein, it binds with the protein. this causes the protein to change shape in such a way that the molecule is released into the inside of the membrane - no external energy is needed.

Question 14

what is osmosis?

Answer 14

the movement of water from a region of high water potential to a region of low water potential through selectively permeable membrane.

Question 15

what is water potential?

Answer 15

the pressure created by water molecules

pure water is said to have a water potential of zero under standard conditions.

Question 16

explain what follows the water potential?

Answer 16

the addition of solute to pure water will lower its water potential
the water potential of a solution must always be less than 0
the more solute that is added , the lower the water potential
ware will move by osmosis from a region of higher to one of lower water potential

Question 17

what is active transport?

Answer 17

the movement of molecules from a region o low concentration to a region of high concentration using ATP and carrier proteins.

Question 18

in active transport what is ATP used for?

Answer 18

to directly move molecules
individual move molecules using a concentration gradient which has already been set up by (direct) active transport. this is known as co-transport.

Question 19

how does active transport differ from passive transport?

Answer 19

metabolic energy in the form of ATP is needed
substances new moved against the concentration gradient, that is from a lower to a higher concentration.
carrier protein molecules which act as a pump are involved
the process is very selective, with specific proteins being transported.

Question 20

what is the direct transport of a single molecule or ion?

Answer 20

the carrier protein spans the whole width of the membrane and bind to the molecule to me transported on one side of it.
the molecule or ion binds to the receptor sites of the protein
on the inside of the cell, ATP bind to the protein, causing it to split into ADP and a phosphate molecule as a result the protein molecule changes shape and opens up on the other side of the membrane
the molecule or ion is then released onto the other side of the membrane
the phosphate molecule is released from the protein which causes the protein to revert to its, original shape, ready for the process to be repeated. the phosphate molecule then rejoins with the ADP to form ATP during respiration.

Question 21

what is the difference between active transport and facilitated diffusion?

Answer 21

facilitated diffusion occurs down the concentration gradient where as active transport occurs against it.

Question 22

when the ATP changes to ATP what is this called?

Answer 22

phosphorylation.

when it goes back this is called dephosphorylation

Question 23

what is a fluid mosaic structure?

Answer 23

the membrane is a phospholipid bilayer, it is fluid as they are always moving and it is a mosaic as it has proteins scattered through the bi layer.

Question 24

what is the head of a phospholipid?

Answer 24

hydrophilic

Question 25

what is the the tail of a phospholipid?

Answer 25

hydrophobic

Question 26

what is the role of cholesterol in the phospholipid bilayer?

Answer 26

it is a typ elf lipid that provides membrane stability. it binds between the tails of the phospholipids. it causes them to more closely pick together restricting their movement - makes the membrane less fluid mosaic.

Question 27

what does increasing the temperature do to membrane permeability?

Answer 27

increases membrane permeability.
at temperatures below 0 the phospholipids don’t have much energy so they can’t move very much - the membrane is rigs. channel proteins and carrier proteins however deform increasing the permeability of the membrane
temperature between 0-45 the membrane is partially permeable, as the temperature increases the phospholipids move quicker increasing the permeability of the membrane.
above 45 the phospholipid bilayer starts to brake downed the membrane becomes more permeable - proteins deform so they can’t control whet enters and leaves the cell

Question 28

what is an intrinsic protein?

Answer 28

a protein that spas the whole length of the phospholipid bilayer

Question 29

what is a glycolipid?

Answer 29

they are made up of carbohydrates covalently bonded to lipid. the carbohydrate portion extends from the phospholipid bilayer into the watery environment outside the cell where it acts as a cell surface receptor.

Question 30

what are the functions of phospholipids in the membrane?

Answer 30

t act as a recognition site
to help maintain the stability of the membrane
helps cells attach to each other and so form tissue

Question 31

what does simple diffusion depend on?

Answer 31

the concentration gradient - the higher the concentration gradient the taste the rate of diffusion
the thickness f the exchange surface
the surface area

Question 32

what does facilitated diffusion depend on?

Answer 32

the concentration gradient - the higher the quicker

the number of channel or carrier proteins

Question 33

what does the rat of osmosis depend on?

Answer 33

the water potential gradient - the higher the faster the rate
the thickness of the exchange surface
the surface area of the exchange surface

Question 34

what is the experiment that you can do to investigate the water potential?

Answer 34

add 10cm3 of 2M sucrose solution to a test tube and then make 4 others with 5cm3 of distilled water in them. trasfer 5ml from 1 and transfer it to to + mixing and then 2-3, 3-4,4-5.

us using potato cylinders

Question 35

what are co transporters?

Answer 35

a type of carrier protein that bind two molecules at a time. the cincentrion gradient of one of the molecules is use to move the other molecule against its own concentration gradient

Question 36

what happens with the movement of water in hypotonic cells ?

Answer 36

when water moves into the cell

ion animal cells it is called cytolysis and in RBCs it is called imolosys. it causes plants to become turgid.

Question 37

what happens with the movement of water in isotonic cells?

Answer 37

the same about of water that comes into the cell goes out meaning that the cell remains the same shape

Question 38

what happens with the movement of water in hypertonic cells?

Answer 38

when water moves from the cell into the surrounding solution, in RBCs it is called crenation and in plants it plasmolyses the cell.

Question 39

what does hypotonic mean?

Answer 39

the concentration of solutes is greater inside the cell than it is outside

Question 40

what does isotonic mean?

Answer 40

the concentration of solutes is the same in the cell as it is outside the cell in the solution.

Question 41

what does hypertonic mean?

Answer 41

concentration of solutes is greater outside the cell than inside.