BACKGROUND (the questions for this problem are below this background information
ID: 1433334 • Letter: B
Question
BACKGROUND (the questions for this problem are below this background information): A young graduate student at UMass noticed that certain species of bacteria always appeared to swim north on a microscope slide. This motion was not correlated with ambient light, vibrations or other effects. But when he brought a small bar magnet near the slide, the bacteria rapidly swam towards a magnet pole. He had just discovered the first Magnetotactic bacteria. Under a Transmission Electron Microscope (TEM) the bacteria were found to have chains of dark objects, identified as crystals of the mineral magnetite (Fe3O4), which have the proper size and shape to behave as perfect, single magnetic domains. The largest crystals are about 70 nm in length. Originally discovered by Blakemore, these bacteria are now known to leave these crystals of biologically precipitated magnetite in marine and freshwater sediments as 'magnetofossils', and are responsible for much of the magnetization of marine sediments. The bacteria are anaerobic – i.e., oxygen gas is deadly poison to them. For survival, they need to swim downwards, into the mud at the bottom of ponds away from oxygen rich regions. So they need to tell “Up” from “Down”. In this problem, you are asked to think about how such a small bacterium can tell “Up” from “Down” by using the Earth’s magnetic field.
Life on Mars: Crystals morphologially similar to the magnetosomes were found to be present in the carbonate blebs of the ALH84001 Martian Meteorite, and as such were claimed to be bits of evidence for ancient life on Mars.
PROBLEM 1 – 10 points (2 points for each part) The Earth has a magnetic field.
(a) In which hemisphere is the Earth’s magnetic North Pole located (at the moment, at least)?
[ ] southern hemisphere [ ] northern hemisphere
(b) In Massachusetts, the Earth’s magnetic field has a component that points
[ ] vertically downwards [ ] vertically upwards [ ] there is no vertical component.
(c) For the anaerobic bacterium in Massachusetts to swim away from an oxygen rich environment, should it swim in the direction of the magnetic field, or in a direction opposite to the magnetic field?
[ ] in the direction of the field [ ] opposite in direction to the field
(d) If the Massachusetts anaerobic bacteria are taken to a pond in Brazil, what do you suppose will happen to them? [Apart from being fingerprinted on entry at the airport, we mean!]
(e) Closely related species of these bacteria are also found all over the world. If you are given an unmarked vial containing Brazilian bacteria, and another unmarked vial containing Massachusetts bacteria, and you have access only to a microscope and a bar magnet with the poles clearly marked, can you identify which is which? If so, how?
PLEASE HELP!!!! These are actually really easy questions but I don't know how to do it cuz they never taught us! :( PLEASE HELP AND EXPLAIN!!!
Explanation / Answer
a) In Northern hemisphere
b) it lies in Northern hemisphere where magnetic field has vertical downward component
c) since bacteria will move downward in oxygen rich environment and in Northern hemisphere magnetic field is along vertical downward direction so bacteria will move in the direction of magnetic field
d) Brazil lies in southern hemisphere than bacteria will experience a force along upward direction since on Southern hemisphere magnetic field is vertically upward but due to oxygen rich environment it will try to move towards down wards which is not possible so the bacteria will die
e) the Brazilian bacteria bacteria will move towards South Pole and another one will move towards North Pole of bar magnet
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