Hypoxia and Medicine

Biology questions----- please help?

If an ecosystem lost a keystone species, which outcome would you expect? A. A new keystone species would replace the old keystone species. B. The oxygen supply in the ecosystem would be depleted. C. The population numbers of other species would change dramatically. D. The temperature of the ecosystem would increase. The Gulf of Mexico provides 72 percent of the shrimp harvested in U.S. waters. Those populations are at risk because of the dead zone in the Gulf of Mexico. Which statement best describes this dead zone? A. It is a zone of ocean water that has almost no oxygen. B. It is a zone of ocean water that has almost no carbon dioxide. C. It is a zone that formed when it lost its keystone species. D. It is a zone that's been depleted by sea urchins.

Public Comments

1. c a
2. 1 is C nad 2 is C too!
3. 1. c- because of interdependence 2. a. cant survive without oxygen in water and air
4. the answer to the first question is A. and possibly C. as for the 2nd question i have no clue.
5. For the first one, C is correct. Keystone species are vital to the ecosystem and are not easily replaced. However, they usually have nothing to do with oxygen. For example, a keystone species might be sea otters: they regulate the number of urchins, so that other organisms can thrive, since otherwise the urchins would invade other niches. D is just silly. A is correct in the latter. Dead zones are caused by a spiral of events. First, you get an input of nutrients - either by coastal upwelling, pollution, runoff, etc. Then, the number of algae spikes. When the algae die, organic matter falls lower in the ocean, and microorganisms who eat algae start metabolizing and rapidly deplete the oxygen. Thus, you have a layer of anoxic water in the ocean where no organisms can thrive. Loss of CO2 would not cause such massive die-offs, as O2 is the main electron acceptor for many organisms and more important in cellular respiration - in fact, many organisms produce CO2. C is incorrect; when you lose a keystone species, you generally get an explosion of other prey species. D is probably trying to throw you off based on some example they gave in class.
6. 1) C 2) C
7. 1 C 2 A - this is the best answer of these, but it's not great. Oxygen depletion is caused by bacterial decay of algal blooms. The bacteria use the oxygen.
8. well the first bit is c because if you think of it like a cat a bird and an insect then if the bird dies theres nothing for the cat to eat and the insects can breed more because there is nothing trying to eat them. not sure about the other one sorry but its probably c as well seeing as the first bit asked about keystone species x