PAGS (testings)

Question 1

Test for reducing/nonreducing sugars

Answer 1

Benedict’s test

Question 2

Diff between reducing + non reducing sugars

Answer 2

Reducing can act as reducing agents due to presence of free aldehyde or ketone group + non reducing can’t

Question 3

Example of non reducing sugars

Answer 3

Sucrose

Question 4

Colour of Benedict’s reagent

Answer 4

Blue

Question 5

What does Benedict’s reagent contain

Answer 5

copper (Il) sulphate ions (CuSO4 )

Question 6

What happens to the copper (Il) sulphate ions (CuSO4 ) in Benedict’s solution, when in contact with reducing sugars

Answer 6

Copper (I) oxide forms

Question 7

Why does copper (I) oxide form a precipitate

Answer 7

Insoluble in water

Question 8

Test for reducing sugars method

Answer 8

• Add Benedict’s reagent to the sample in a test tube
  • Heat the test tube in a water bath for 2-3 mins
  Observe colour

Question 9

Positive test - reducing sugar

Answer 9

Coloured precipitate will form

Question 10

Importance of adding excess Benedict’s solution

Answer 10

so that there is more than enough copper (Il) sulfate present to react with any sugar present

Question 11

Colour change for reducing sugars

Answer 11

from blue (no reducing sugar), through green, yellow and orange (low to medium concentration of reducing sugar) to brown/brick-red (a high concentration of reducing sugar)

Question 12

Why is the reducing sugar test described as semi - quantitative

Answer 12

as the degree of the colour change can give an indication of how much (the concentration of) reducing sugar present

Question 13

If there’s more reducing sugar…

Answer 13

Less blue cu 2+ ions left so lighter solution if precipitate is removed

Question 14

Method for test for non reducing sugar

Answer 14

• Carry out reducing sugar test first, if negative boil with dilute hydrochloric acid
• neutralise w/ sodium hydrogen carbonate
• carry out Benedict’s test

Question 15

Why do we add a little more sodium hydrogen carbonate in the non-reducing sugars test

Answer 15

as the conditions need to be slightly alkaline for the Benedict’s test to work

Question 16

Why do we add hydrochloric acid in the non-reducing sugars test

Answer 16

hydrolyse any glycosidic bonds present in any carbohydrate molecules

Question 17

What test is used to identify starch

Answer 17

Iodine from potassium iodide

Question 18

Method to test for starch

Answer 18

• add a few drops of orange/brown iodine in potassium iodide solution to the sample

Question 19

Why do we use potassium iodide when testing for starch

Answer 19

Because iodine by itself is insoluble in water

Question 20

Positive result = iodine starch test

Answer 20

blue-black/purple-black colour

Question 21

What are reagent strips

Answer 21

can be used to test for the presence of reducing sugars, most commonly glucose.

Question 22

What type of molecules are lipids

Answer 22

Non polar

Question 23

Why do we add ethanol when identifying lipids

Answer 23

Cause ethanol is non-polar, so lipids (being non-polar) will dissolve in it

Question 24

What test do we use to identify lipids

Answer 24

Emulsion test

Question 25

Emulsion test method

Answer 25

Add ethanol to the sample to be tested • Shake to mix • Add the mixture to a test tube of water

Question 26

Emulsion test positive result

Answer 26

Milky cloudy emulsion will form

Question 27

Limitations of emulsion test

Answer 27

This test is qualitative - it does not give a quantitative value as to how much lipid may be present in a sample

Question 28

What test is used to identify proteins

Answer 28

Biuret test

Question 29

What does biuret reagent contain

Answer 29

Sodium hydroxide and copper (Il) sulphate which react in the presence of peptide bonds

Question 30

Method for biuret test

Answer 30

Add a few drops of biuret solution to sample. If peptide bonds present then you’ll see it change from blue to a lilac colour

Question 31

Limitations of biuret test

Answer 31

if the sample contains amino acids or dipeptides, the result will be negative • The Biuret test is qualitative - it does not give a quantitative value as to the amount of protein present in a sample

Question 32

Where are inorganic ions found

Answer 32

occur in solution in the cytoplasm and body fluids of organisms

Question 33

What is an inorganic ion

Answer 33

An ion that doesn’t contain carbon

Question 34

What do inorganic ions act as

Answer 34

Co factors

Question 35

What are co factors

Answer 35

non-protein chemical compounds that are required for a protein to function

Question 36

How many bonds does nitrogen form

Answer 36

3

Question 37

What does valency mean

Answer 37

Number of covalent bonds an atom can make.

Question 38

Chemical symbol + function of hydrogen ions

Answer 38

H+ Hydrogen bonding • ATP formation • Control of blood pH • Transport of carbon dioxide

Question 39

Chemical symbol + function of calcium ions

Answer 39

Ca2+ • Cofactor in blood clotting • Synaptic transmission of nerve impulses • Muscle contraction

Question 40

Chemical symbol + function of iron ions

Answer 40

Fe2+/Fe3+ Transport of oxygen via haemoglobin o Transfer of electrons (respiration and photosynthesis)

Question 41

Chemical symbol + function of sodium ions

Answer 41

Na+ Nerve transmission • Reabsorption of water in the kidneys

Question 42

Chemical symbol + function of potassium ions

Answer 42

K+ • Nerve transmission • Reabsorption of water in the kidneys • Opening of the stomata

Question 43

Chemical symbol + function of ammonium ions

Answer 43

NH4+ Deamination of proteins

Question 44

Cations we need to know

Answer 44

Hydrogen ions Calcium ions Iron ions Sodium ions Potassium ions Ammonium ions

Question 45

Anions we need to know

Answer 45

Nitrate ions Hydrogen carbonate ions Chloride ions Phosphate ions Hydroxide ions

Question 46

Chemical symbol + function of nitrate ions

Answer 46

NO3- Source of nitrogen for plants

Question 47

Chemical symbol + function of hydrogen carbonate ions

Answer 47

HCO3- transport of co2 in your blood

Question 48

Chemical symbol + function of chloride ions

Answer 48

Cl- • Maintaining pH balance during carbon dioxide transport

Question 49

Chemical symbol + function of phosphate ions

Answer 49

PO4 3- component of phospholipids, nucleic acid, ATP

Question 50

Chemical symbol c function of hydroxide ions

Answer 50

OH- Bonding between biochemical molecules

Question 51

Colour change for iodine test

Answer 51

Orange/brown to black

Question 52

Answer 52

Question 53

Answer 53

Question 54

Answer 54

Question 55

Answer 55