2.1 – Molecules to metabolism – Sciences for IGCSE & IB

1.Cladograms can be created by comparing DNA or protein sequences. The cladogram on the left is based on DNA sequences and the cladogram on the right is based on comparing protein sequences.

What is the reason that cladograms based on DNA sequences are more reliable predictors of the phylogenetic relationship of species than cladograms based on protein sequences?

Amino acids are not as chemically stable as DNA nucleotides
DNA mutates but amino acids do not
Several different triplets of bases can code for the same amino acid
There are 20 different amino acids but only 4 nucleotides

2. The bacterium Neisseria gonorrhoeae causes infections related to the human reproductive system. The graph shows the percentage of samples in which this bacterium showed resistance to six antibiotics over a period of ten years.

What is a possible explanation for the total percentage resistance being larger than 100% in 2010?

People do not take the antibiotics as prescribed
More people have been sampled in that year
There was an epidemic of Neisseria gonorrhoeae in that year
Some bacteria are resistant to more than one antibiotic

3. Which molecule diagram corresponds to the name?

A
B
C
D

4. The diagram shows a cycle of reactions that occurs in human liver cells.

Which term describes the overall reactions of this cycle?

Oxidation
Catabolism
Condensation
Metabolism

5. The diagram shows the structure of palmitic acid.

What type of fatty acid is palmitic acid?

It is monounsaturated
It is polyunsaturated
It is saturated
It is a trans-fatty acid

6. Glucose is absorbed through protein channels in the plasma membrane of epithelium cells in the small intestine. Which characteristics of glucose prevent its diffusion through the phospholipid bilayer?

It is non-polar and therefore hydrophobic
Its hydrogen bonds link with amino acids in the protein channel
It is polar and therefore hydrophilic.
Its covalent bonds interact with the phospholipids

7. What characteristic shows that this steroid molecule is a lipid?

It is made of carbon rings.
It has a very low proportion of oxygen to carbon
It contains OH groups as do fatty acids
It is made only of nitrogen, oxygen and hydrogen

8.Which molecule can be hydrolyzed?

Glycerol
Maltose
Fructose
Galactose

9. How can the activity of a human amylase enzyme be increased during a laboratory experiment?

Adding sugar to the mixture
Decreasing the pH from 7 to 3
Increasing the temperature from 20 °C to 37 °C
Adding water to the mixture

10. What are the most frequently occurring elements in living organisms?

calcium, phosphorus, iron and sodium
calcium, sodium, nitrogen and phosphorus
carbon, phosphorus, oxygen and nitrogen
nitrogen, carbon, oxygen and hydrogen

11. The image shows the structural formula of a molecule.

What is this molecule?

Amino acid
Ribose
Deoxyribose
Lactose

12. What are the most frequently occurring elements in living organisms?

calcium, phosphorus, iron and sodium
calcium, sodium, nitrogen and phosphorus
carbon, phosphorus, oxygen and nitrogen
nitrogen, carbon, oxygen and hydrogen

13. Which types of molecule are shown in the diagrams?

A
B
C
D

14. Where in the cell do condensation reactions involving amino acids occur?

Nucleus
Golgi apparatus
Ribosomes
Lysosome

15. Which carbon compound produced by living organisms is inorganic?

DNA
Cellulose
Glucose
Carbon dioxide

16. What is involved during oxidation?

The loss of electrons
The gain of electrons
The gain of hydrogen
The loss of oxygen

17. What is phosphorus used for in plant cells?

Structure of hemoglobin
Composition of long-term energy storage
Positive charge of membranes
Composition of nucleic acids

18. Which of the following chemical elements are part of biochemical molecules in living organisms?

nitrogen, sulfur, phosphorus and iron
lead, oxygen, carbon and phosphorus
helium, carbon, sulfur and nitrogen
silicon, helium, oxygen and iron

19. Which of the following is an organic compound made by all plants?

Carbon dioxide
DNA
Lactose
Oxygen

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