O-LevelBiologyPlant Nutrition5090/21 · May/June 2017 · Q110 Marks

Spirulina is classified in the group bacteria. Spirulina is green in colour and is able to synthesise its own food.

(a)List three characteristics of bacteria.[3]
(b)(i)Suggest the name of the chemical that gives Spirulina its green colour.[1]
(b)(ii)Write, in words or symbols, the equation for the process by which Spirulina synthesises its own food.[2]
(c)Spirulina can be eaten by humans. The United Nations World Health Organization (WHO) made the following statement about Spirulina: 'For WHO Spirulina represents an interesting food for multiple reasons. Rich in iron and protein, it can be given to children without any risk. We at WHO consider it to be a very suitable food.' Use your knowledge of animal nutrition to suggest and explain why WHO considers Spirulina to be a 'very suitable food'.[4]

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[3] 1(a) single-celled; no nucleus / nucleus not membrane bound; no organelles ; cell wall; (cell wall) not cellulose ; cell membrane / cytoplasm; flagella / flagellum ; DNA circular/ loop OR plasmid / single chromosome ; smaller than animal / plant cells OR 1–2 µm ;
[1] 1(b)(i) chlorophyll;
[2] 1(b)(ii) carbon dioxide / 6CO2 + water / 6H2O; glucose / C6H12O6 + oxygen / 602 ;
[4] 1(c) iron + haemoglobin / red blood cells ; prevent anaemia; protein + growth / repair ; protein + (production of) enzymes / antibodies ; carbohydrates / glucose / starch / vitamins / ions; reference to a component of balanced diet / dietary supplement OR to alleviate malnutrition / famine;

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