carbs, proteins and lipids exam Q's

Question 1

describe how you would test a piece of food for the presence of lipid. (2)

Answer 1

• dissolve in alcohol, then add water
• while emulsion shows presence of lipid

Question 2

name the type of bond between glycerol and fatty acids. (1)

Answer 2

ester bond

Question 3

scientists investigated the % of different types of lipid in plasma membranes from different types of cell.
the scientists expressed their results as % of lipid in plasma membrane by mass. Explain how they would find these values. (2)

Answer 3

• divide mass of each lipid by total mass of all lipids
• x100

Question 4

scientists investigated the % of different types of lipid in plasma membranes from different types of cell.
cholesterol increases stability of plasma membranes. Cholesterol does this by making membranes less flexible.
suggest one advantage of the different % of cholesterol in red blood cells compared with cells lining the ileum. (1)

Answer 4

red blood cells free in blood have no support from other cells so need lots of cholesterol to help maintain shape

Question 5

scientists investigated the % of different types of lipid in plasma membranes from different types of cell.
E.coli has no cholesterol in its cell-surface membrane. despite this, the cell maintains a constant shape. explain why. (2)

Answer 5

• it has a rigid cell wall
• unable to change shape

Question 6

name the monomers from which a maltose molecules is made. (1)

Answer 6

glucose and glucose

Question 7

name the type of chemical bond that joins the two monomers to form maltose. (1)

Answer 7

glycosidic

Question 8

describe the difference between the structure of a triglyceride molecule and the structure of a phospholipid molecule. (1)

Answer 8

phospholipid have two fatty acids not three like triglycerides, as one is replaced by a phosphate

Question 9

describe how you would test for the presence of a lipid in a sample of food. (2)

Answer 9

-add ethanol then add water
- white emulsion shows lipid present

Question 10

describe how a saturated fatty acid is different from an unsaturated fatty acid. (1)

Answer 10

saturated have no double bonds between carbons

Question 11

animal fats contain triglycerides with a high proportion of saturated fatty acids. if people have too much fat in their diet, absorption of the products of fat digestion can increase risk of obesity. to help people lose weight, fat substitutes can be used to replace triglycerides in food.
This fat substitute shown ( structure shows 3 propylene glycerol bonded to three fatty acids which is bonded to 2 CH2O and one CHO) cannot be digested in the gut by lipase. suggest why.(2)

Answer 11

• not complementary
• unable to form e-s complexes

Question 12

animal fats contain triglycerides with a high proportion of saturated fatty acids. if people have too much fat in their diet, absorption of the products of fat digestion can increase risk of obesity. to help people lose weight, fat substitutes can be used to replace triglycerides in food.
the fat substitute shown is a lipid. despite being a lipid, it cannot cross the cell-surface membranes of cells lining the gut.
suggest why it cannot cross cell-surface membranes. (1)

Answer 12

it too big/ its hyrophillic polar

Question 13

scientists investigated the hydrolysis of sucrose in growing plant cells by an enzyme called SPS.
name the product of the hydrolysis of sucrose. (2)

Answer 13

• glucose
• fructose

Question 14

describe the structures of starch and cellulose molecules are related to their functions. (5)

Answer 14

STARCH:
- helical shape so compact
- insoluble so osmotically inactive
- branched so glucose is easily released for respiration

CELLULOSE:
- long straight unbranched chains of b-glucose
- joined by hydrogen bonding
- to form fibrils which provides strength

Question 15

Name the molecules that make up a triglyceride. (2)

Answer 15

• glycerol
• fatty acids

Question 16

Describe how you would test a liquid sample for the presence of lipid and how you would recognise a positive result. (2)

Answer 16

-mix a sample with ethanol then water
-white milky emulsion

Question 17

Describe how a peptide bond is formed between two amino acids to form a dipeptide. (2)

Answer 17

• condensation reaction
• between NH2 (amino) and carboxyl

Question 18

The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how. (2)

Answer 18

• hydrogen bonds
• between group of amino acid (NH) and C=O group

Question 19

Two proteins have the same number and type of amino acids but different tertiary structures. Explain why. (2)

Answer 19

• different sequence of amino acids
• forms ionic/hydrogen/disulfide bonds in different places

Question 20

A precipitate is produced in a positive result for reducing sugar in a Benedict’s test. A precipitate is solid matter suspended in solution.
A student carried out the Benedict’s test. Suggest a method other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. (2)

Answer 20

• filter and dry precipitate
• find mass/ weight

Question 21

Use of a colorimeter would improve the repeatability of a students result in an investigation. Give one reason why. (1)

Answer 21

• colour change is subjective
• standardise the method

Question 22

Describe a biochemical test to confirm the presence of protein in a solution. (2)

Answer 22

• add biuret reagent
• positive result= purple

Question 23

A dipeptide consists of two amino acids joined together by a peptide bond. Dipeptides may differ in the type of amino acids they contain.
Describe two other ways in which all dipeptides are similar and one way in which they might differ. (3)

Answer 23

SIMILARITIES:
- both have an amino (NH2) and a carboxyl (COOH) group
- two R groups
- contain nitrogen, hydrogen, oxygen

DIFFERENCE:
- different R groups

Question 24

A solution contained a mixture of 3 different amino acids. A scientist passed an electric current through the solution to separate the amino acids.
She placed a drop of the mixture at one end of the piece of filter paper, attached an electrode to each end of the paper and switched on the current. She switched off the current after 20mins and stained the paper to show spots of the amino acids at new positions.
Her results are in figure 6: ( the drop is placed near the positive electrode on the left and 2 dark spots of amino acids have shown up in the filter paper further up to the right, towards the negative electrode)

Explain what position of the spots in figure 6 show about these amino acids. (3)

Answer 24

• moved to - electrode as positively charged
• spots move different distances because different mass/ charge
• one spot have 2 amino acids because they have the same mass/ charge

Question 25

Draw the structure of of a monosaccharide

Question 26

Draw the structure of an amino acid molecule

Question 27

Draw the structure of a nucleotide molecule

Question 28

Draw the structure of b-glucose

Question 29

Match these molecules found in organisms to the statements: monosaccharide (a-glucose), amino acid, nucleotide, b-glucose. - is a monomer in an enzymes active site - is a monomer in cellulose - is produced during photosynthesis and respiration - forms a polymer that gives a positive biuret test

Answer 29

- AMINO ACID is a monomer in an enzymes active site - B-GLUCOSE is a monomer in cellulose - NUCLEOTIDE is produced during photosynthesis and respiration - AMINO ACID forms a polymer that gives a positive result with a biuret test

Question 31

A biomedical test for reducing sugar produces a negative result with raffinose ( raffinose is a trisaccharide of three monosaccharides: galactose, glucose, fructose) solution. Describe a biomedical test to show that raffinose solution contains a non-reducing sugar. (3)

Answer 31

- heat with acid and neutralise - heat with Benedict’s solution - red precipitate

Question 32

Describe how the structure of a protein depends on the amino acid it contains. (5)

Answer 32

- structure is determined by position of amino acids/ R-group - primary structure is sequence of amino acids - secondary structure formed by hydrogen bonding between amino acids - tertiary structure formed by interactions between R-groups - created active site in enzyme - quaternary structure formed by interactions between polypeptides

Question 33

The general structure of a fatty acid is RCOOH. Name the group represented by COOH. (1)

Answer 33

- carboxylic acid

Question 34

Describe how you would test for the presence of a lipid in a liquid sample of food. (2)

Answer 34

- add ethanol then add water and mix - white emulsion

Question 35

In 1935 scientists suggested a model for the chemical structure of a cell-surface membrane. Figure 2 shows this membrane structure: straight phospholipid bilayer with a line of proteins on either side Give one similarity and two differences between the membrane structure shown in figure 2 and the fluid modaic model of membrane structure. (3)

Answer 35

SIMILARITY: - both have phospholipid bilayer - both have protein DIFFERENCE: - no channel/ carrier proteins whereas fluid mosaic model does - cholesterol not present whereas is present in fluid mosaic model - glycoprotein not present - glycolipid not present

Question 36

A student investigated the activity of the enzyme amylase. He cut 3 identical wells in starch-agar in a pétri dish. He added 0.2cm^3 of : -amylase solution to well D -boiled amylase solution to well E -water to well F After 60mins he covered the starch-agar with iodine solution. Figure 7 shows his result: ( the agar is a blue-black cover apart from a clear circle around well D) Explain the appearance of the agar in the clear area surrounding well D. (2)

Answer 36

- amylase hydrolyses starch to maltose

Question 37

A student investigated the activity of the enzyme amylase. He cut 3 identical wells in starch-agar in a pétri dish. He added 0.2cm^3 of : -amylase solution to well D -boiled amylase solution to well E -water to well F After 60mins he covered the starch-agar with iodine solution. Figure 7 shows his result: ( the agar is a blue-black cover apart from a clear circle around well D) What can you conclude about the activity of amylase from the appearance of the agar surrounding well E and well F in figure 7? (2)

Answer 37

- amylase denatured in E - f: water alone doesn’t cause starch starch hydrolysis

Question 38

A student investigated the activity of the enzyme amylase. He cut 3 identical wells in starch-agar in a pétri dish. He added 0.2cm^3 of : -amylase solution to well D -boiled amylase solution to well E -water to well F After 60mins he covered the starch-agar with iodine solution. Figure 7 shows his result: ( the agar is a blue-black cover apart from a clear circle around well D) The student cut out a piece of agar from the clear area surrounding well D. He obtained a solution of the substances contained in this piece of agar. Describe a different biomedical test the student could use with this solution to confirm that amylase had affected the starch in the clear area surrounding well D. (2)

Answer 38

- heat with Benedict’s solution - red precipitate colour shows maltose

Question 39

A student investigated the activity of the enzyme amylase. He cut 3 identical wells in starch-agar in a pétri dish. He added 0.2cm^3 of : -amylase solution to well D -boiled amylase solution to well E -water to well F After 60mins he covered the starch-agar with iodine solution. Figure 7 shows his result: ( the agar is a blue-black cover apart from a clear circle around well D) The student used a ruler to measure the diameter in mm of the clear area around well D in figure 7. Use this information to explain why the answer to the previous question (calculating the diameter of the clear area that will form around a well containing a specific diluted amylase solution) should be given to the nearest whole number. (1)

Answer 39

- reduces human error - it is the resolution of the ruler - for ruler measurement the uncertainty is +-1mm

Question 40

What is the term used to describe the different structures of a-glucose and b-glucose? (1)

Answer 40

Isomer

Question 41

A student investigated the difference in the reducing sugar content of two fruit juices. He performed a biomedical test on each fruit juice using Benedict’s solution. He then used a colorimeter with each test result. Describe how the results from the colorimeter can identify the fruit juice containing the highest sugar content. (1)

Answer 41

Higher absorbance- has more sugar

Question 42

A student investigated the difference in the reducing sugar content of two fruit juices. He performed a biomedical test on each fruit juice using Benedict’s solution. He then used a colorimeter with each test result. The student controlled variables in the test using Benedict’s solution. Give two variables the student controlled. (2)

Answer 42

- volume of Benedict’s solution - volume of fruit juice

Question 43

Iodine solution stains fresh apple tissue black. When iodine solution is added to apples stored for a week, the stain is less black. The water potential of apple juice decreases when apples are stored. Suggest why the water potential of apple juice decreases when apples are stored. (2)

Answer 43

- starch hydrolysed - maltose is soluble so reduces water potential

Question 44

Describe 2 differences between the structures of the triglyceride shown in figure 3 and a phospholipid. (2)

Answer 44

- phospholipid has 2 fatty acids to one glycerol rather than 3 fatty acids - phospholipids have a phosphate group replacing a fatty acid

Question 45

Explain why phospholipids can form a bilayer but triglycerides cannot. (3)

Answer 45

- both hydrophobic and hydrophilic - triglycerides only hydrophobic - hydrophilic phosphate group in phospholipids attracts water

Question 46

Table 1 shows: time red blood cells of a rat obtained after feeding them added fish oil - 0 months shows mean % of phospholipids containing fatty acids A (saturated) as 19.8, mean % of phospholipids containing fatty acids B (unsaturated) as 1.7, and mean fluidity of the membrane as 31. - 4 months shows mean % of phospholipids containing fatty acid A as 11.7, mean % of phospholipids containing fatty acid B as 9.0, and mean fluidity of the membrane as 97. Suggest why the fluidity of the membrane was higher after 4 months. (3)

Answer 46

- at 4 months less fatty acids A (saturated) and more fatty acid B (unsaturated) - increase in fluidity caused by increased unsaturated fatty acid A - double bonds cause kinks in fatty acid tail

Question 47

Blood donation involves healthy donors giving blood that can be used to treat hospital patients. When doctors arrive, the haemoglobin concentration of their blood is tested. A sample of each donors blood is added to a copper sulphate solution to determine whether the haemoglobin concentration is high enough to donate. Errors occur sometimes with this test. Tom has a concentration of haemoglobin high enough to donate. Lucy has a concentration of haemoglobin too low to donate. Evaluate the consequences of errors occurring when Tom’s and Lucy’s blood samples are tested. (3)

Answer 47

Consequences of measurement error for Tom’s blood: - healthy donor not allowed to donate - less blood collected Consequences of measurement error for Lucy’s blood: - gives blood when it may not safe for her to do so - her blood may not help patients - her missed low haemoglobin goes untreated