| Date | May 2015 | Marks available | 1 | Reference code | 15M.3.SL.TZ2.7 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Discuss | Question number | 7 | Adapted from | N/A |
Question
Oxygen consumption by a tissue or organism arises from mitochondrial respiration and non-mitochondrial oxygen consumption. High oxygen levels in the cell can damage DNA, proteins and lipids. In early embryo development, elevated non-mitochondrial oxygen consumption acts as an essential mechanism for protection. The bar chart shows the oxygen consumption rates per embryo (OCR) measured in Zebrafish (Danio rerio) during embryo development in the hours after fertilization.
State the OCR in mitochondrial respiration 24 hours after fertilization.
Compare OCR due to non-mitochondrial oxygen consumption and mitochondrial respiration after fertilization.
Suggest reasons for the rise in mitochondrial respiration in the 48 hours after fertilization.
Non-mitochondrial oxygen consumption does not produce ATP and decreases in relation to mitochondrial respiration 48 hours after fertilization. Discuss the importance of non-mitochondrial oxygen consumption in a developing embryo.
Markscheme
50 (pmol O2 min–1) (allow answers in the range of 49 to 51)
a. both increase with time after fertilization;
b. mitochondrial OCR increases (a lot) more than non-mitochondrial;
c. after 48 hours there is approximately three times more mitochondrial than non-mitochondrial OCR;
d. at 3 hours non mitochondrial OCR is higher than mitochondrial;
a. mitosis requires a large amount of energy;
b. more cells implies higher metabolic rate/DNA synthesis/other cell processes;
c. more mitochondria present with time;
d. mitochondria work more efficiently/faster;
protect DNA/protein/lipids/embryo (until mitochondrial respiration removes oxygen efficiently)
Examiners report
The data for Option C was a bar chart showing oxygen consumption in zebrafish embryos in the first 48 hours after fertilization. The data was fairly well answered with part (c) where the candidates were asked to suggest reasons for the changes in the graph causing most difficulty
The data for Option C was a bar chart showing oxygen consumption in zebrafish embryos in the first 48 hours after fertilization. The data was fairly well answered with part (c) where the candidates were asked to suggest reasons for the changes in the graph causing most difficulty.
The data for Option C was a bar chart showing oxygen consumption in zebrafish embryos in the first 48 hours after fertilization. The data was fairly well answered with part (c) where the candidates were asked to suggest reasons for the changes in the graph causing most difficulty.
The data for Option C was a bar chart showing oxygen consumption in zebrafish embryos in the first 48 hours after fertilization. The data was fairly well answered with part (c) where the candidates were asked to suggest reasons for the changes in the graph causing most difficulty.
