Biological structures

Question 1

Tests for reducing sugars

Answer 1

Benedict’s test for reducing sugars

Question 2

Benedict’s test for reducing sugars

Answer 2

A food sample is dissolved in boiling water. Next, a small amount of Benedict’s reagent is added and the solution begins to cool. During the next four to 10 minutes, the solution should begin to change colors. If the color changes to blue, then no glucose is present.

Question 3

Tests for non-reducing sugars

Answer 3

Benedict’s test for non-reducing sugars.

Question 4

Benedict’s solution for non-reducing sugars

Answer 4

If a reducing sugar is present in a solution, adding Benedict’s reagent and heating will form an insoluble red precipitate. Non-reducing sugars do not change the colour of the solution, which is blue, and so we have to break the sugar down to monosaccharides by hydrolysis to prove they’re non-reducing.

Question 5

Test for starch

Answer 5

Iodine-starch test.

Question 6

Iodine-starch test

Answer 6

In the presence of starch, iodine turns a blue/black colour. For example, if iodine is added to a peeled potato then it will turn black. Benedict’s reagent can be used to test for glucose.

Question 7

Test for lipids

Answer 7

Emulsion test.

Question 8

Emulsion test

Answer 8

The procedure is for the sample to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water.

Question 9

Test for proteins

Answer 9

Biuret test.

Question 10

Biuret test

Answer 10

Add an equal volume of potassium hydroxide solution to the tube and stir.
Add two drops of copper sulfate solution and stir for two minutes.
Record the colour of the solution.
If the solution is purple, then it has proteins.

Question 11

What is a monomer?

Answer 11

A single molecule that can be bonded to other identical molecules to form a polymer.

Question 12

What is a polymer?

Answer 12

A polymer is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits.

Question 13

What is a macromolecule?

Answer 13

A molecule containing a very large number of atoms, such as a protein, nucleic acid, or synthetic polymer.

Question 14

What is a monosaccharide?

Answer 14

Any of the class of sugars that cannot be hydrolysed to give a simpler sugar. Eg. glucose.

Question 15

What is a disaccharide?

Answer 15

Any of a class of sugars whose molecules contain two monosaccharide residues.

Question 16

What is a polysaccharide?

Answer 16

A carbohydrate whose molecules consist of a number of sugar molecules bonded together. Eg. starch.

Question 17

Formation of a glycosidic bond by condensation

Answer 17

Condensation occurs wherein hydroxyl groups in the ring structures of the monosaccharides align next to each other, and a water molecule is created (i.e., 2 hydrogens and 1 oxygen are lost from the ring structure).
The oxygen that is left forms a bridge with between the two monosaccharides - also known as a glycosidic bond.

Question 18

Breakage of glycosidic bonds in polysaccharides and disaccharides by hydrolysis

Answer 18

Breakage is when water is added back to the ring structure.
As such, this process is the opposite of condensation, and is called ‘hydrolysis’
Here, disaccharides and polysaccharides breakdown into monosaccharides.
Hydrochloric acid can be used to break disaccharides down into two monosaccharides when testing for the presence of non-reducing sugars (e.g., sucrose).

Question 19

Molecular structure of polysaccharides

Answer 19

These are complex carbohydrates made up of repeating units of monosaccharides that are attached together by Glucosidic linkage. A molecule of a polysaccharide has n number of sugar molecules bound together to form a larger molecule.

Question 20

Function of starch

Answer 20

Store energy for plants.

Question 21

Function of glycogen

Answer 21

Store energy for animals.

Question 22

Function of cellulose

Answer 22

Helps plants to remain stiff and upright.

Question 23

Molecular structure of a triglyceride and function

Answer 23

Triglycerides are the main energy storage molecules of plants and animals. Triglycerides are made of a glycerol molecule bonded to three fatty acid chains.

Question 24

Structure of a phospholipid and functions

Answer 24

Phospholipids consist of a hydrophilic head and a hydrophobic tail. Phospholipids like to line up and arrange themselves into two parallel layers, called a phospholipid bilayer. This layer makes up your cell membranes and is critical to a cell’s ability to function.

Question 25

Structure of an amino acid

Answer 25

A single organic amino acid molecule contains two functional groups – amine and carboxyl – and a unique side chain.

Question 26

The formation of a peptide bond

Answer 26

It occurs when the carboxylic group of one molecule reacts with the amino group of the other molecule, linking the two molecules and releasing a water molecule.

Question 27

Breakage of a peptide bond

Answer 27

They are broken by proteases.

Question 28

Primary structure of proteins

Answer 28

The linear sequence of amino acids within a protein.

Question 29

Secondary structure of proteins

Answer 29

The three dimensional form of local segments of proteins.

Question 30

Tertiary structure of proteins

Answer 30

The three dimensional shape of a protein.

Question 31

Quaternary structure of proteins

Answer 31

The association of several protein chains or subunits into a closely packed arrangement.

Question 32

Type of bonding of primary structure

Answer 32

Peptide bonding.

Question 33

Type of bonding of secondary structure

Answer 33

Hydrogen bonding.

Question 34

Type of bonding of tertiary structure

Answer 34

Covalent bonding.

Question 35

Type of bonding of quaternary structure

Answer 35

Hydrogen bonding.

Question 36

Structure of haemoglobin

Answer 36

Haemoglobin has a quaternary structure. It consists of two pairs of different proteins, designated the α and β chains.

Question 37

Structure of collagen

Answer 37

The collagen protein is composed of a triple helix, which generally consists of two identical chains and an additional chain that differs slightly in its chemical composition.

Question 38

Function of haemoglobin

Answer 38

Essential for transferring oxygen in your blood from the lungs to the tissues.

Question 39

Function of collagen

Answer 39

Provides bone, tendons and ligaments with tensile strength and skin with elasticity.

Question 40

How does hydrogen bonding occur between water molecules?

Answer 40

Hydrogen bonds are attractions of electrostatic force caused by the difference in charge between slightly positive hydrogen ions and other, slightly negative ions. The attraction between individual water molecules creates a bond known as a hydrogen bond.

Question 41

Properties of water to functions in organisms

Answer 41

Water’s extensive capability to dissolve a variety of molecules has earned it the designation of “universal solvent,” and it is this ability that makes water such an invaluable life-sustaining force. On a biological level, water’s role as a solvent helps cells transport and use substances like oxygen or nutrients.