Transport Across Membranes

Question 1

Investigating osmosis why should the experiment be taken out at 30 rather than 20

Answer 1

Faster levels of osmosis / larger difference in mass
Warmer water means more kinetic energy

Question 2

Describe how you would test for the presence of a lipid

Answer 2

Add ethanol
Add water
Then shake / mix
White milky emulsion

Question 3

Name and describe 5 ways substances can move across the cell s-membrane into a cell

Answer 3

Simple diffusion - small, non polar cells and moving these particles from a high concentration to a low concentration
Facilitated diffiucion use of a carrier / channel protein to move non-polar substances from high to low concentration
Osmosis - moves water particle from an area of high wp to an area of low wp across
Active transport which moves molecules from a low to high concentration via carrier proteins
Co transport - bringing 2 molecules at a time by using the generated concentration gradient of one molecule and with the use of ATP releasing energy needed to the protein to bind to the other molecule

Question 4

How does the movement of na out of a cells allow teh absorption of glucose into the cell lining the ileum

Answer 4

Sodium ions moving out generates a conc gradient to allow glucose to move back into the cell lining
Using co-transport

Question 5

Describe and explain 2 features you would expect to find in a cell specialised for absorption

Answer 5

Higher number of channel/ carrier proteins to allow a faster rate of absorption and quicker movement of molecules
More folds in the membrane / microvilli to increase the SA leading to quicker movements of particles and a faster rate of absorption

Question 6

Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other

Answer 6

One amine group joins to a carboxyl group to form a peptide bind
So there is a free amine group at one end and a free carboxyl at the otehr

Question 7

One way a student can ensure beetroot cylinders were kept at 25 throughout experiment

Answer 7

Measure temperature at intervals and use appropriate corrective measure

Question 8

Describe how phospholipids are arranged in a plasma membrane

Answer 8

2 fatty acid hydrophobic tails and hydrophilic heads, in a bilayer

Question 9

Mucus contains protein, what organelle would you expect to find in a mucus secreting cell and describe its role in the production of mucus

Answer 9

Golgi
Forms peptide bonds to process the protein

Question 10

Function of a glycoprotein

Answer 10

Cell recognition, act as recognition sites
Bind to hormones
Help cells attach to one another and so form tissues
Allow cells to recognise each other - eg lymphocytes

Question 11

How does a bilayer affect entry and exit of substances

Answer 11

Allows lipid soluble molecules to diffuse through
Hydrophobic tail prevents large polar molecules to diffuse through

Question 12

Why is bilayer described as fluid mosaic

Answer 12

Phospholipids are constantly moving
Proteins and phospholipids are scattered throughout the bilayer

Question 13

How does a bacteria molecule maintain a constant shape in its CSM with no chloresterol

Answer 13

Cell unable to change shape as the cell has
a cell wall
Wall is rigid, made of Muriel

Question 14

What the function of cholesterol

Answer 14

Reduce lateral movement of other molecules including phospholipids
Makes the membrane less fluid at high temperatures
Prevents leakage of water and dissolves ions from the cell

Question 15

How does cholesterol limit movement

Answer 15

Pull together the fatty acid tails of the phospholipid molecules

Question 16

What is a glycolipid

Answer 16

A carbohydrate covalently bonded with a lipid

Question 17

Functions of a glycolipid

Answer 17

Act as recognition sites
Help maintain the stability of the membrane
Help cells attach to one another and so can form tissues

Question 18

Explain how 3 features of a plasma membrane adapt it for its functions

Answer 18

Compartmentalisation of organelles so that specific metabolic reactions can occur
Channel proteins let water soluble molecules through via active transport
Phospholipids are constantly moving giving membrane fluidity
Can bend to take up different shapes for phagocytosis

Question 19

What type of process is facilitated diffusion, why

Answer 19

Passive, relies only on the kinetic energy of the diffusing molecules no input from ATP from respiration

Question 20

How does a channel proteins move an ion across a membrane

Answer 20

Ion binds with the protein causing it to change shape in a way that closes it to one side of the membrane and open it to the other side

Question 21

What is water potential

Answer 21

Pressure created by water molecules

Question 22

What happens to phospholipids below temp of 0

Answer 22

Packed closely together and the membrane is rigid
Channel and carrier proteins ca denature which increases the permeability of the membrane
Ice crystals can form which can pierce the membrane making it more permeable when it thaws

Question 23

Phospholipids between 0-45

Answer 23

Phospholipids can move around freely and membrane is partially permeable
As temp increases kinetic energy increases and makes the membrane more permeable

Question 24

Phospholipids above 45 degrees

Answer 24

Phospholipids start to melt and the membrane becomes more permeable
Water inside the cell expands and puts pressure on the membrane
Channel + carrier proteins denature increasing the permeability of the membrane

Question 25

How do ethanol / solvents enter the bilayer

Answer 25

Form hydrogen bonds with a phospholipid molecule near the ester bonds Pushing phospholipids out of their orderly placement and increases their movement Disrupting membrane structure and increasing its permeability Solvents also denature proteins by disrupting bonds

Question 26

What is a colorimeter

Answer 26

A machine that passes light of a specific wavelength through a liquid and measures how much light is absorbed

Question 27

When will more light be absorbed in a colorimeter

Answer 27

When the concentration of the solution is greater

Question 28

CSM can be seen with a TEM but not an optical microscope , why

Answer 28

Has a higher resolution

Question 29

How do substances move across a CSM by facilitated diffusion

Answer 29

By channel proteins which are specific / complementary to a substance Substance moves down a concentration gradient

Question 30

Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes

Answer 30

They are small non- polar molecules Carry no charge

Question 31

2 reasons for keeping fluid at 40 rather than room temperature

Answer 31

Closer to body temperature Prevents cooling of the blood

Question 32

What is the water potential of pure water , why

Answer 32

Wp of 0 because no water will diffuse into this solution but there is a high chance that water will leave

Question 33

Any solution containing a solvent dissolved in water will have what type of water potential, compared to pure watre

Answer 33

More negative (lower) wp than pure water

Question 34

What does it mean about the concentration if a solution if the wp is more negative

Answer 34

Solution is more concentrated

Question 35

What happens to the wp of pure water when you add a solute

Answer 35

Lower its wp

Question 36

Water will move by osmosis into what water potential

Answer 36

A region of higher (less negative) wp to a lower (more negative ) wp

Question 37

What is the highest value of wp

Answer 37

0

Question 38

What happens when a RBC is placed in pure water

Answer 38

Will absorb water by osmosis because it has a lower wp

Question 39

What happens when an animal cell is placed in pure water

Answer 39

Animal cell swells up and will burst / lyse as their cell membrane is not string enough to withstand the pressure

Question 40

What happens to a plant cell when placed in a hypotonic solution

Answer 40

Swell up but do not burst because their cell wall protects them , their vacuoles expand , they become turgid as the cell membrane pushes on the cell wall

Question 41

What happens to plant cells when places in isotonic solution

Answer 41

No net movement of water , cell stays the same size Maintain the cells size and function

Question 42

What happens to a plant cell when placed in isotonic solution

Answer 42

Cell becomes flaccid Not ideal for plant cells , prefer hypotonic

Question 43

What happens to an animal when placed in a hypertonic solution

Answer 43

Shrivel as they lose water from the cytoplasm

Question 44

What happens to a plant cell when placed in hypotonic solution

Answer 44

Water moves out by osmosis , plant cells are protected from shrinking but their vacuoles shrink and eventual their cell membranes pull away form the cell walls = plasmolysis

Question 45

What are 3 factors affecting rate of osmosis

Answer 45

Wp gradient , membrane thickness and surface area

Question 46

How does glucose move from inside the ileum into the blood

Answer 46

Facilitated diffusion

Question 47

Explain the first step of co transport involving sodium and glucose

Answer 47

Sodium ions are actively transported out of epithelial cell , by sodium -potassium pump into the blood Takes place in one type of protein-carrier molecule found in the CSM of epithelial cells

Question 48

Step 2 of co transport

Question 49

Why are sodium ions actively transported out of epithelial cells

Answer 49

To maintain a much higher concentration of sodium ions in the lumen of the intestine than inside the epithelial cells

Question 50

Step 2 of co transport

Answer 50

Sodium ions diffuse into the epithelial cells down this concentration gradient through a different protein - co-transport protein in the CSM As the sodium ions diffuse in through this second carrier protein , they either carry amino acid molecules or glucose molecules with them

Question 51

Last step of co transport

Answer 51

The glucose / amino acids pass into the blood plasma by facilitated diffusion using another type of carrier

Question 52

What powers the movement of glucose and amino acids into the cells

Answer 52

The sodium ion concentration gradient , rather than ATP directly

Question 54

What factors affect the rate of active transport

Answer 54

Speed of carrier proteins Number of carrier proteins Rate of respirating , more mitochondria

Question 55

What is endocytosis

Answer 55

Various types of active transport that move particles into a cell by enclosing them in a vesicles made out of plasma membrane

Question 56

Describe endocytosis

Answer 56

Plasma membrane invaginate forming a pocket around the target particle/ particles Pocket then pinches off with the help of specialised proteins leaving the particle trapped in a newly created vesicle/vacuole inside the cell