Lipids, diffusion, active transport, osmosis, co-transport

Question 1

What are lipids and what do they contain?

Answer 1

they are hydrophobic compounds that are insoluble in water, and contain carbon/hydrogen/oxygen

Question 2

What are lipids soluble in?

Answer 2

organic solvents like ethanol/alcohols/acetone

Question 3

What are the two most important types of lipids?

Answer 3

triglycerides (fats and oils)
phospholipids

Question 4

What are lipids used for?

Answer 4

source of energy
waterproofing
insulation
protection

Question 5

What are triglycerides?

Answer 5

made up of 3 fatty acids (R-COOH) and glycerol (CH2OH)

Question 6

Where are the ester bonds in triglycerides and how are they formed?

Answer 6

each fatty acid forms an ester bond with glycerol in a condensation reaction

Question 7

What is the benefit of triglycerides having a high ratio of hydrogen to oxygen atoms?

Answer 7

they release water when oxidised, therefore providing an important source of water (especially for organisms living in dry conditions)

Question 8

What is the benefit of triglycerides having a low mass to energy ratio?

Answer 8

makes them good storage molecules because a lot of energy can be stored in a small volume

Question 9

What is the benefit of triglycerides being large, non-polar molecules?

Answer 9

they are insoluble in water, so their storage does not affect osmosis in cells or the water potential of them

Question 10

How many condensation reactions and therefore water molecules are made during the production of a triglyceride?

Answer 10

3

Question 11

Draw the reaction for the formation of a triglyceride

Answer 11

(drawing, google to check answer)

Question 12

What is the R group in fatty acids?

Answer 12

a hydrocarbon chain

Question 13

Why are there differences in properties of the fats and oils?

Answer 13

due to variations of the R group

Question 14

How do you test for a lipid?

Answer 14

add ethanol and shake
pour into another test tube that contains water
if a milky white emulsion is formed then a lipid is present

Question 15

What are phospholipids?

Answer 15

the main components of the phospholipid bilayer in the cell membrane

Question 16

What are phospholipids made up of?

Answer 16

2 fatty acids, a glycerol, and a phosphate group

Question 17

Which parts of phospholipids are hydrophobic/hydrophilic and why?

Answer 17

the phosphate heads are hydrophilic as they are highly polar, and the fatty acids are hydrophobic as they are non-polar (making the centre hydrophobic also so water soluble substances can’t easily pass through)

Question 18

What are triglycerides mainly used for?

Answer 18

as energy storage molecules because
-they have long tails of hydrocarbons which contain a lot of chemical energy, containing about twice as much energy per gram as carbohydrates
-they also are insoluble in water so won’t affect the water potential in cells or osmosis

Question 19

Why do triglycerides bundle together as insoluble droplets?

Answer 19

due to their structure- the hydrophobic tails want to be as far away from the water as possible, so they face inwards to shield themselves

Question 20

When exposed to water, what happens to phospholipids?

Answer 20

they will form either a micelle (more circular) or a bilayer

Question 21

What properties do phospholipids have that make them useful in cell-surface membranes?

Answer 21

-they make the membrane selectively permeable as they allow lipid soluble substances to enter/leave the cell
-small non-polar molecules (O2/CO2) are able to pass across the membrane quickly
-large, polar molecules (Na+/Cl-) are unlikely to diffuse across the membrane`

Question 22

What are the two main types of proteins found in the phospholipid bilayer and how do you differentiate them?

Answer 22

extrinsic (confined to outer/inner surface only) and intrinsic (span the whole membrane width)

Question 23

What is the main function of extrinsic proteins?

Answer 23

they combine with carbohydrate groups to form glycoproteins/glycolipids which can act as chemical receptors

Question 24

What is the main function of intrinsic proteins?

Answer 24

sites of facilitated diffusion, co-transport, and active transport
can be enzymes
act as hydrophilic pores through which water-soluble substances can pass

Question 25

What is cholesterol’s role in the cell membrane?

Answer 25

cholesterol is a type of lipid that is important in controlling cell membrane fluidity; the more cholesterol the less fluid and the less permeable the membrane is

also prevents the leakage of water and dissolved ions from the cell

Question 26

Why is the cell membrane described as fluid-mosaic?

Answer 26

fluid- the proteins and phospholipids can move around
mosaic- made up of different components of different sizes and shapes (phospholipids/proteins/glycoproteins/cholesterol)

Question 27

What is facilitated diffusion?

Answer 27

when specific carrier proteins or channel proteins in the cell membrane have their complementary molecules bind to them, which makes the binding site of the protein temporarily change shape, allowing the molecule to pass through into the cell

it is the net movement of particles from a region of high to low concentration with the help of these transport proteins, and is a passive process

Question 28

What molecules are transported in facilitated diffusion?

Answer 28

large, lipid-insoluble molecules such as glucose/amino acids

Question 29

Describe and explain the curve on a graph showing the rate of facilitated diffusion for glucose

Answer 29

initially, as the concentration of the external concentration of glucose increases, the rate of facilitated diffusion also increases, but then it curves/ROR decreases due to the fact that the rate is limited by the amount of carrier proteins as they are working at their max. rate

Question 30

Name two similarities between carrier proteins and channel proteins

Answer 30

both move substances down a concentration gradient
both are specific proteins

Question 31

What do channel proteins do?

Answer 31

they form pores in the cell membrane for charged particles to diffuse through, and they are specific to specific types of charged particles (i.e. Na+)

Question 32

What is active transport?

Answer 32

the movement of molecules or ions into or out of a cell from a region of low to high concentration using carrier protein pumps. it is an active process and therefore requires ATP

Question 33

What molecules are able to diffuse through a membrane using simple diffusion?

Answer 33

small, non-polar molecules like O2 and CO2

Question 34

How does active transport work?

Answer 34

the molecule/ion that is complementary to the carrier protein pump’s binding site binds to the carrier protein, then as it is an active process it needs ATP, so ATP undergoes a hydrolysis reaction which forms ADP and a phosphate group, which then attaches to the protein resulting in it changing shape, allowing the molecule/ion to pass through

the phosphate group is then released so it can join back to the ADP molecule to form ATP again

Question 35

What is osmosis?

Answer 35

the net movement of water molecules from a high water potential to a low water potential through a partially/selectively permeable membrane

Question 36

What is the symbol for water potential?

Answer 36

ψ - psi

Question 37

Why is ψs (solute potential) always negative?

Answer 37

as it affects the water molecules’ ability to move, anything that is not pure water would be below 0

Question 38

Why is ψp (pressure potential) always positive?

Answer 38

as the cell membrane/wall is always pressing against the cytoplasm

Question 39

Where does water always move in terms of ψ?

Answer 39

towards the more negative number (lowest water potential)

Question 40

What is a hypotonic solution?

Answer 40

has more water molecules, and the solute concentration is lower than inside the cell, which causes the water to move into the cell (makes the cell swell/become turgid)

Question 41

What is a hypertonic solution?

Answer 41

has less water molecules, and the solute concentration is higher than inside the cell, which causes the water to move out of the cell (makes the cell to shrivel/become flaccid)

Question 42

How is glucose absorbed from the middle of the lumen of the ileum?

Answer 42

by co-transport

Question 43

Explain the co-transport of glucose with sodium ions

Answer 43

sodium ions are actively transported out of the small intestines’ epithelial cells into the blood by the sodium-potassium pump. this creates a concentration gradient as there is now a higher concentration of sodium ions in the small intestines’ lumen than inside the cell

this causes sodium ions to diffuse from the SI’s lumen into the epithelial cell, down the concentration gradient. this is done via sodium-glucose co-transporter proteins, which carries glucose into the cell along with the sodium.

as a result the concentration of glucose inside the cell increases

glucose then diffuses out of the cell and into the blood through a specific carrier protein by facilitated diffusion

Question 44

Which method of transport across membranes is non-specific?

Answer 44

simple diffusion

Question 45

What are channel proteins for?

Answer 45

transport of ions across cell membranes