IB Docs (2) Team MC test: Biological pigments
Multiple choice test on B.9 Biological pigments
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. As this relates to a sub-topic on the options you may need access to the IB data booklet.
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
Lycopene is found in tomatoes.
Which class of compounds does it belong to?
The long hydrocarbon chain of alternate double and single carbon bonds is a characteristic of carotenoids.
Pelargonidin is found in plants (e.g. geraniums) and berries (e.g. strawberries).
Which class of compounds does it belong to?
Pelargonidin is an anthocyanin - it contains the flavonoid C6C3C6 backbone with extensive conjugation.
Which compounds absorb light in the visible region of the electromagnetic spectrum?
I. 
II.
III. 
Only retinol (II) and cyanidin in alkali solution (III) show extensive conjugation.
The absorption spectra of chlorophyll and carotenoids is shown below.
Which explains why the leaves of trees in spring are green?
The green colour is due to chlorophyll which absorbs blue and red light but transmits/reflects green light.
The graph shows the dissociation curves for haemoglobin for two different concentrations of carbon dioxide.
What may be concluded from the graph?
Y will be at a lower pH and at a higher pressure of carbon dioxide than X as oxygen is released from haemoglobin. At the same partial pressure X is more saturated with oxygen than Y so Y has a lower affinity for oxygen than X.
The diagram shows dissociation curves for myoglobin and two different types of haemoglobin. Myoglobin only releases oxygen when the partial pressure of oxygen is very low.
Which row identifies A, B and C?
| Row | Foetal haemoglobin | Myoglobin | Adult haemoglobin |
| 1 | A | B | C |
| 2 | B | A | C |
| 3 | C | A | B |
| 4 | A | C | B |
Myoglobin only releases oxygen when the partial pressure of oxygen is very low so is represented by A. Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin so that the placenta can take up oxygen from the mother's blood.
Which best describes a molecule of haemoglobin?
Haemoglobin is a protein molecule consisting of two α− and two β− polypeptide chains grouped together around four haem groups.
Which are true statements about porphyrins?
I. All the carbon atoms are sp2 hybridized.
II. They are highly conjugated.
III. They contain four nitrogen atoms that can form coordinate bonds with metal ions.
All the carbon atoms in the porphyrin ring are sp2 hybridised but porphyrins can also contain side chains, e.g. chlorophyll, in which not all the carbon atoms are sp2 hybridized
Which does not contain iron?
Chlorophyll contains Mg2+. All the others contain iron although cytochrome c also contains other metal ions.
What is meant by chelation?
Chelation specifically refers to the formation of two or more coordinate bonds to a metal atom or ion by a polydentate ligand. (In medicine chelation therapy involves using polydentate ligands to remove toxic metals from the body).
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