3.2.3 Transport across cell membranes

Question 2

in which cells are organelles membrane bound?

Answer 2

eukaryotes

Question 3

what are cell surface membranes?

Answer 3

they surround cells to act as a barrier between the cell and its environment, controlling which substances enter and leave the cell

Question 4

cell-surface membranes are partially permeable. what does this mean?

Answer 4

they let some molecules through but not others

Question 5

what are cell membranes made of?

Answer 5

lipids -phospholipids-
proteins
carbohydrates

Question 6

what model is used to describe the structure of a cell membrane?

Answer 6

the fluid mosaic model

Question 7

what does the fluid part of the fluid mosaic model refer to?

Answer 7

the phospholipids -which form a continuous double layer called a bilayer- are constantly moving

Question 8

what does the mosaic part of the fluid mosaic model refer to?

Answer 8

the proteins of different shapes and sizes which are embedded into the phospholipid bilayer

Question 9

what kind of proteins are found in the phospholipid bilayer (span completely across the membrane) and what are they used for?

Answer 9

channel proteins
carrier proteins
allow large molecules and ions to pass through the membrane

Question 10

what proteins are found on the surface of the membrane (they never extend completely across the membrane) and what are they used for?

Answer 10

receptor proteins
they allow cell to detect chemicals released from other cells which signal the cell to respond in a certain way
can also provide structural support

Question 11

what is it called when a carbohydrate is attached to a protein?

Answer 11

glycoproteins

Question 12

what is it called when a lipid is attached to a protein?

Answer 12

glycolipids

Question 13

what are the components of a cell membrane

Answer 13

phospholipids
proteins
glycoproteins
glycolipids
cholesterol

Question 14

what is a phospholipid molecule made of?

Answer 14

hydrophilic phosphate head
hydrophobic fatty acid tails

Question 15

how are the phospholipids arranged to form a bilayer?

Answer 15

the tails face inward creating a hydrophobic centre so water soluble molecules cannot pass through
the phosphate heads face outward (towards the water)

Question 16

what is the function of phospholipids in the cell?

Answer 16

to prevent water soluble molecules from entering and leaving cell
allows lipid soluble substance to enter cell as it can dissolve in the bilayer

Question 17

Why is it important that the phospholipid bilayer of the cell membrane regulates water movement rather than allowing water to flow freely?

Answer 17

Because uncontrolled water flow could cause the cell to swell and burst or shrink and shrivel. The phospholipid bilayer helps maintain osmotic balance by allowing selective and regulated water movement, protecting the cell’s internal environment

Question 18

what is the functions of cholesterol in the membrane?

Answer 18

gives membrane stability by binding to the hydrophobic tails causing them to pack more closely together
cholesterol has hydrophobic regions further supporting the barrier to polar molecules

Question 19

why is cholesterol useful in animal cells and other cells?

Answer 19

• helps to maintain shape as it does not have a cell wall
• in other cells that are not supported by other cells eg ref blood cells the cholesterol is important for stability

Question 20

what is the function go glycolipids in a membrane?

Answer 20

acts as recognition sites (for cells to communicate)
maintains stability of membrane
acts as recognition sites (for cells to communicate)

Question 21

what is the function of glycoproteins in a membrane?

Answer 21

acts as recognition sites (for cells to communicate)
acts as recognition sites (for cells to communicate)
allows cells to recognise one another

Question 22

define diffusion

Answer 22

the net movement of particles from an area of higher concentration to an area of lower concentration down the concentration gradient

Question 23

what kind of process is diffusion

Answer 23

passive - does not require energy

Question 24

what is simple diffusion?

Answer 24

when molecules can diffuse directly through a cell membrane

Question 25

Oxygen and carbon dioxide can diffuse into cells via __________

Answer 25

simple diffusion.

Question 26

what kind of molecules can exhibit simple diffusion?

Answer 26

small - can pass through the spaces between phospholipids non-polar - can dissolve in the hydrophobic core of the cell membrane

Question 27

how do larger molecules diffuse across a membrane?

Answer 27

through facilitated diffusion

Question 28

what 2 proteins are involved in facilitated diffusion?

Answer 28

channel proteins carrier proteins

Question 29

what process is facilitated diffusion?

Answer 29

passive process

Question 30

describe the process of facilitated diffusion through carrier proteins

Answer 30

a large molecule specific to the carrier protein binds to it causing the carrier protein to change shape the carrier protein then releases the molecule on the opposite side of the membrane

Question 31

describe the process of facilitated diffusion through channel proteins

Answer 31

channel proteins form pores in the membrane allowing specific ions to pass through

Question 32

what are the factors affecting the rate of diffusion?

Answer 32

Temperature - At higher temperatures, particles have more kinetic energy and diffuse faster. Concentration gradient - The steeper the concentration gradient, the faster the rate of diffusion. Thickness of membrane - The particles travel shorter distances through thin exchange surfaces, so diffuse faster. Surface area - Larger surface areas mean more particles can cross the membrane at once, making diffusion faster. Number of carrier or channel proteins - The more of these proteins, the faster the rate of facilitated diffusion.

Question 33

define osmosis

Answer 33

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

Question 34

define water potential

Answer 34

the tendency of water molecules to diffuse in and out of a solution

Question 35

what water potential does pure water have?

Answer 35

0KPa

Question 36

What happens to an animal cell in a hypotonic solution?

Answer 36

Water moves into the cell due to higher water potential outside, causing the cell to swell and possibly burst

Question 37

What happens to an animal cell in an isotonic solution?

Answer 37

There is no net movement of water. Water enters and exits equally, so the cell stays the same size

Question 38

What happens to an animal cell in a hypertonic solution?

Answer 38

Water moves out of the cell due to lower water potential outside, causing the cell to shrink

Question 39

what are factors affecting the rate of osmosis?

Answer 39

Temperature - At higher temperatures, water molecules have more kinetic energy and diffuse faster. Water potential gradient - The steeper the gradient, the faster the rate of osmosis. Thickness of membrane - Water molecules travel shorter distances through thin exchange surfaces, so diffuse faster. Surface area - Larger surface areas mean more water molecules can cross the membrane at once, making osmosis faster.

Question 40

What happens to a plant cell in a hypotonic solution?

Answer 40

Water moves into the cell (higher water potential outside), causing it to swell and become turgid—a healthy state for plant cells

Question 41

What happens to a plant cell in an isotonic solution?

Answer 41

There is no net movement of water. The cell remains the same size, not turgid or plasmolysed

Question 42

What happens to a plant cell in a hypertonic solution?

Answer 42

Water moves out of the cell (lower water potential outside), causing the cell to shrink and become plasmolysed—the membrane pulls away from the cell wall

Question 43

define active transport

Answer 43

movement of particles from an area of low concentration to an area of high concentration against the concentration gradient using energy from ATP released during respiration

Question 44

what process is active transport?

Answer 44

active process

Question 45

what are the differences between active transport and facilitated diffusion?

Answer 45

active transport usually moves solutes from a low to high concentration - on facilitated diffusion they move from an area of high to low active transport requires energy while facilitated diffusion does not

Question 46

describe the process of active transport using a carrier protien

Answer 46

the molecule or ion binds to the carrier protein ATP binds to the carrier protein Hydrolysis of ATP to ADP and phosphate (Pi) causes the carrier protein to change shape. This releases the molecule or ion on the opposite side of the membrane The phosphate (Pi) is released from the carrier protein, causing the carrier protein to return to its original shape, ready to be used again

Question 47

what are the factors affecting active transport?

Answer 47

Temperature - At higher temperatures, particles have more kinetic energy and travel faster. Respiration also increases with temperature. Very high temperatures denature carrier proteins, decreasing the rate of active transport. Thickness of membrane - Particles travel shorter distances through thin exchange surfaces, so travel faster. Number of carrier proteins - The more of these proteins, the faster the rate of active transport. Rate of respiration - The more respiration, the more ATP available for active transport.

Question 48

what are co-transporters?

Answer 48

a type of carrier protein that can bind 2 molecules at once They use the concentration gradient of one molecule to move the other molecule against its own concentration gradient

Question 49

how is glucose absorbed from the lumen of small intestine into the bloodstream?

Answer 49

co-transport

Question 50

The co-transport of glucose involves three different proteins what are they and what do the do?

Answer 50

Sodium-potassium pumps - These actively transport sodium (Na+) and potassium (K+) ions Sodium-glucose co-transporter proteins - These use facilitated diffusion to transport Na+ ions and glucose molecules Glucose protein channels - These use facilitated diffusion to transport glucose molecules

Question 51

why can't glucose just diffuse into the blood stream why does it need to go through co transport?

Answer 51

diffusion can only result in equal glucose concentrations, so not all the glucose will be absorbed

Question 52

what is the first step in the co transport of sodium and glucose?

Answer 52

Na+ is actively transported out of epithelial cells into the blood by the sodium-potassium pump. This pump transports three Na+ out for every two K+ in. This creates a concentration gradient as there is now a higher concentration of Na+ in the lumen than in the epithelial cells.

Question 53

what is the second step in the co transport of sodium and glucose?

Answer 53

Na+ diffuses from a high concentration in the lumen to a low concentration in the epithelial cells. It is transported via sodium-glucose co-transporter proteins, which also carry glucose molecules. This causes the concentration of glucose inside the epithelial cells to increase

Question 54

what is the final step in the co transport of sodium and glucose?

Answer 54

There is now a higher glucose concentration in the epithelial cells than in the blood. So, glucose diffuses out of epithelial cells and into the blood via facilitated diffusion.

Question 55

where else is the co transport via sodium ions used?

Answer 55

to absorb amino acids in the small intestine

Question 56

what is the role of ATP in co-transport of glucose

Answer 56

ATP is used to maintain the concentration gradient of sodium ions between the lumen and the epithelial cells of the ileum