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Answers to Week #2 Lab Team Challenge Questions
Posted By: Jesse_Wolfstadt, Dr. Hawke on Sunday, October 29, 2006
Hey everyone!
I hope you have had enough time to give the Week 2 challenge questions a try. Here are the answers to all three questions. Thanks to everyone who participated and gave some insightful answers.
Question #1: Why does water expand as it freezes?
Answer #1: Good work students of the Alberta Rockies, although I must remind you that Wikipedia is not always the greatest source of information on the internet. Water is a very unique compound because it expands as it freezes, unlike most substances which become more closely packed and dense as they freeze. Water is most dense at 4°C, and becomes less dense as the temperature rises above or cools below 4°C. This is why ice cubes float near the surface of a glass of water. The nature of hydrogen bonding allows a bond to form between the negatively charged oxygen atom of one water molecule and one of the positively charged hydrogen atoms of another water molecule. At 4°C, the water molecules are not very organized and are closely packed. As the temperature decreases to 0°C and lower, the hydrogen bonding becomes more organized and the water forms an orderly crystalline structure. This causes the water molecules to be less closely packed, leading to the expansion of water as it freezes.
Question #2: Why do slow twitch muscle fibres have a red colour? If you are eating chicken for dinner, and you ask for a piece of dark meat, what kind of muscle fibre are you eating: fast or slow twitch fibres?
Answer #2: Awesome answer Carmen of the Antarctic Grizzlies! Slow
Oxidative fibres contain a high concentration of myoglobin, which has a red pigment that causes these muscle fibres to have a dark red colour. Thus, when you ask for a piece of dark meat, you are eating slow twitch fibres. Fast twitch muscle fibres have very low concentrations of myoglobin, giving this muscle type a white colour.
Question #3: In humans, what type of athlete would have a larger proportion of slow twitch fibres and which would have a greater proportion of fast twitch fibres? What type of athlete would have intermediate fibres?
Answer #3: Most people are born with about 50% slow twitch and 50% fast twitch muscle fibres, however some people may be born with slightly more of one type of fibre. Most research has shown that it is not possible to change the distribution of muscle fibres in your body. Athletes that require a lot of endurance, such as long distance runners or swimmers, have a larger proportion of slow twitch fibres. This allows them to remain active for a long time without experiencing fatigue. Athletes that require quick bursts of energy, such as sprinters or long-jumpers, have a larger amount of fast twitch fibers. Athletes that have a lot of intermediate fibres are hockey players and basketball players, who need to maintain a fairly high tempo but rarely go all out for more than a few seconds at a time. These athletes require a mix of high endurance and quick burst of energy, making intermediate fibres the ideal muscle fibre type.
Good work answering the questions!
Jesse Wolfstadt
Dr. Hawke Lab Team, York University
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