Biological Molecules

Question 1

Chemical Elements in Living Organisms:

Answer 1

Most molecules in living organisms belong to three categories: carbohydrates, proteins, and lipids.
These are considered organic molecules as they all contain carbon.

Question 2

Chemical Elements: Molecule: Carbohydrate

Answer 2

Chemical Elements: Carbon, oxygen, and hydrogen.

Question 3

Chemical Elements: Molecule: Protein

Answer 3

All contain carbon, oxygen, hydrogen, and nitrogen. Some may have small amounts of other elements like sulfur.

Question 4

Chemical Elements: Molecule: Lipid

Answer 4

Chemical Elements: Carbon, oxygen, and hydrogen.

Question 5

Formation of Large Molecules: Carbohydrates

Answer 5

Long chains of simple sugars.
Glucose (a monosaccharide) forms maltose (a disaccharide) when two glucose molecules join. Starch, glycogen, or cellulose (polysaccharides) can form from multiple glucose molecules.

Question 6

Formation of Large Molecules: Fats (Lipids)

Answer 6

Majority are triglycerides, consisting of one glycerol molecule bonded to three fatty acid chains.
Lipids are categorized as fats (solids) or oils (liquids) at room temperature.

Question 7

Formation of Large Molecules: Proteins

Answer 7

Composed of long chains of amino acids (about 20 different types).
Amino acids, when joined together, form proteins with a vast diversity, influenced by the unique ‘R’ group in each amino acid.

Question 8

Protein Structure and Diversity

Answer 8

Proteins can be arranged in any order of amino acids, resulting in hundreds of thousands of different proteins.
Even a slight variation in the amino acid sequence leads to the formation of distinct proteins.

Question 9

Food Tests in Biology: Test for glucose (a reducing sugar)

Answer 9

Add Benedict’s solution into sample solution in test tube
Heat at 60 - 70 °c in water bath for 5 minutes
Take test tube out of water bath and observe the colour
A positive test will show a colour change from blue to orange or brick red

Question 10

Food Tests in Biology: Test for starch

Answer 10

We can use iodine to test for the presence or absence of starch in a food sample. Add drops of iodine solution to the food sample
A positive test will show a colour change from orange-brown to blue-black

Question 11

Food Tests in Biology: Test for protein

Answer 11

Add drops of Biuret solution to the food sample
A positive test will show a colour change from blue to violet / purple

Question 12

Food Tests in Biology: Test for lipids

Answer 12

Food sample is mixed with 2cm^3 of ethanol and shaken
The ethanol is added to an equal volume of cold water
A positive test will show a cloudy emulsion forming

Question 13

Food Tests in Biology: Test for vitamin C

Answer 13

Add 1cm^3 of DCPIP solution to a test tube
Add a small amount of food sample (as a solution)
A positive test will show the blue colour of the dye disappearing

Question 14

Structure of DNA Molecule: What does DNA stand for?

Answer 14

Deoxyribonucleic Acid

Question 15

Structure of DNA Molecule: What is DNA (Deoxyribonucleic Acid)?

Answer 15

Molecule containing instructions for the growth and development of all organisms.
Comprises two strands forming a double helix.

Question 16

Structure of DNA Molecule: What are Nucleotides?

Answer 16

Individual units of DNA.
Consist of a phosphate, deoxyribose sugar, and a base

Question 17

Structure of DNA Molecule: Bases in DNA

Answer 17

Four bases: Adenine (A), Cytosine (C), Thymine (T), and Guanine (G).
All nucleotides share the same phosphate and deoxyribose sugar.

Question 18

Structure of DNA Molecule: Base Pairing

Answer 18

Adenine (A) pairs with Thymine (T) (A-T).
Cytosine (C) pairs with Guanine (G) (C-G).
The bases form the rungs of the DNA ladder, connecting the two strands.

Question 19

Structure of DNA Molecule: DNA Helix

Answer 19

Made of two strands held together by hydrogen bonds.
The phosphate and sugar sections of nucleotides create the ‘backbone’ of the DNA strand.

Question 20

Structure of DNA Molecule: Double Helix Structure

Answer 20

The two strands wind around each other in a double helix formation.

Question 21

Structure of DNA Molecule: Genetic Code

Answer 21

The sequence of bases holds the code for the formation of proteins.
The instructions for the growth and development of organisms are encoded in the DNA sequence.