1.3 - AQUATIC BIOMES Flashcards
Which of communities are characterized by the following?
- Oganisms adapted to extremely high temperatures and pressure
- Chemosynthethic bacteria that convert sulfur compounds to organic molecules.
a) Coral reefs
b) Estuaries
c) Hydrothermal vents
d) Eutrophic lakes
The best way to attack this question is to take the unique characteristics mentioned and think about each ecosystem and if these characteristics are necessary for survival.
A high-temperature situation is going to result from either global location (e.g. equatorial waters) or proximity to geothermal locations (e.g. vents, crustal boundaries). The high-pressure characteristic means that the ecosystem is a deep water as you descend through the water column increases the pressure.
Lastly, the chemosynthetic bacteria indicate an area with low sunlight penetration. Chemosynthetic organisms perform this process due to the lack of sunlight and/or abundance of inorganic chemicals (e.g. sulfur compounds). If sunlight was plentiful, photosynthesis would be the preferred process.
Taking all the above facts into consideration eliminates Choice A coral reefs (sunlight available and no high pressure), Choice B estuaries (sunlight available and no high presssure), and Choice D eutrophic lakes (no high temperature). Choice C hydrothermal vents is the correct answer.
Hydrothermal vent communities occur in the deep ocean where hot-water vents expel sulfur compounds which are then synthesized by chemosynthetic bacteria. These bacteria serve as the primary producers in a food web full of unique organisms adapted to the high heat and pressure around the vents.
The density of water is greatest at which of the following temperatures?
a) 4°F
b) 0°C
c) 32°F
d) 4°C
Under typical conditions, fresh water freezes at 0°C, and ice floats. Choice B and C are not correct since water would be freezing, and floating at that temperature. At this point, two of the remaining choices are fairly close to the same value, and one is very different. If you have ever walked from a shoreline into a natural body of water, such as a lake, until the water is up to your waist or higher, you may have noticed that your feet were in cooler water than the rest of your body.
If water is least dense when it is frozen, yet colder water can also sit at the bottom of a lake prior to freezing, its densest temperature must be close to its freezing point, and it is. Water becomes denser as it cools until it reaches 4°C. It then begins to rise through the water column and ice forms at the surface. Choice D is the best asnwer.
The salinity of freshwater must be
a) 0%
b) Less than 0.1%
c) Within the range from 0% to 3%
d) Within the range from 1% to 3%
Choice B is the correct answer.
Freshwater is typically understood to be water that dos not contain any salt, but that is not the case.
Choice B, less than 0.1%, is the best selection to describe the salinity of freshwater.
Which of the following choices best describes the processes by which Earth’s ocean gained its dissolved compounds?
a) Upwelling and deposition
b) Upwelling and erosion
c) Erosion and deposition
d) Weathering and runoff
The water comprising Earth’s ocean is thought to have originated from outgassing of the crust as the planet cooled after formation, along with water contained in meteorites that impacted the planet shortly thereafter.
Upwelling is a vertical current that brings cold, nutrient-rich water to the surface so while it does contribute to vertical mixing, it does contribute to vertical mixing, it does not alter the salinity at all. This makes Choices A and B incorrect.
Weathering and erosion are related processes, and they work together to release rock so that it can be carried by water. Weathering is breaking the rock into smaller particles, and erosion is the transport of those particles to other places. Erosion can occur through several agents, including wind and gravity, but water is the main way rock is transported and elements often dissolve into the water as it flows toward the ocean.
Choice C does not answer the question correctly, either. This flow of water across Earth’s surface, called runoff, is thought to have originally carried minerals to the ocean. Now the ocean’s salinity is in equilibrium, but salinity can vary locally in areas with greater-than-average evaporation, precipitation, or runoff.
Choice D is the best answer.
The highest salinity surface water would be expected in which climate zone?
a) Subtropical.
b) Tropical.
c) Polar.
d) Temperate.
Temperatures are highest in tropical regions, of course, so you might think they would have the highest salinity due to increased evaporation. Although evaporation plays a role in determinining the salinity of a region, precipitation is also critical and most areas in the tropics receive ample rainfall to compensate for water lost to evaporation. Choice B is incorrect.
Polar regions have variable salinity due to seasonal freezing and thawing of ice, which raises and lowers salinity respectively. You may know that deep water in polar regions is very salty and dense, but this question refers to surface water only. Choice C is invalid.
Temperate regions tend to be in equilibrium for precipitation and evaporation due to seasonal variability as well, so Choice D is not right.
It is the subtropics, Choice A, that has an imbalance. Evaporation exceeds precipitation in those regions, and surface water salinity in the nearby ocean is higher on average than in other climate zones.
