Outline the difference in absorption of red, blue and green light by chlorophyll.

Explain how the process of photosynthesis affects carbon dioxide concentrations in the atmosphere during a typical year and the likely consequences on Earth of the yearly rises in carbon dioxide concentrations.

a. blue and red light absorbed (the most);
b. greatest absorption in blue light;
c. red light absorbed in high amounts;
d. least/no absorption of green light / green light is reflected/transmitted;
Allow answers shown in an annotated diagram/graph.

Relationship between photosynthesis and carbon dioxide concentration: [4 max]
a. photosynthesis uses carbon dioxide;
b. CO₂ fixed/made into organic molecules/compounds by photosynthesis;
c. lowering carbon dioxide level in atmosphere;
d. annual/seasonal fluctuations of carbon dioxide levels could be related to photosynthesis;
e. caused by increased photosynthesis during spring/summer;

Consequences: [5 max]
f. enhanced greenhouse effect caused by raised levels of carbon dioxide;
g. causing global warming;
h. rising of ocean levels / melting of polar ice caps/glaciers;
i. changes in weather (patterns);
j. ocean acidification;
k. alter food webs;
l. changes/loss of habitat;
m. changes in distribution of plants and animals;
n. may lead to extinction;

Question 6 appeared to be the most difficult question for candidates.

Most candidates knew that chlorophyll absorbs blue and red light and virtually no green light which is consequently reflected. Very few candidates knew that blue light is absorbed most and that red light is absorbed in high amounts.

Question 6 appeared to be the most difficult question for candidates.

Candidates frequently began with the idea that plants take in CO₂ through photosynthesis and that levels of atmospheric CO₂ can be lowered as a result. After that changes in atmospheric levels as a result of seasonal fluctuation was left undeveloped or confused with human production of CO₂ through deforestation etc. Candidates did know about global warming resulting from rising levels of CO₂. They knew a variety of consequences related to global warming which reflected awareness of similar IB questions on past exams. Some candidates still think that CO₂ weakens the ozone layer. It seems that no candidate knew about the enhanced greenhouse effect.