Dissolved Oxygen Is Often Very Low at the Base of the Thermocline

question 8

Multiple Choice

Dissolved oxygen is often very low at the base of the thermocline in the open ocean because

• A) Many fish congregate there
• B) It is low from there, on down to the deep sea bottom, because of poor mixing with surface water
• C) Fine-grained organic matter accumulates there, and microorganisms consume oxygen as they break down this material
• D) This is the depth of the North Atlantic Deep Water, which is very low in dissolved oxygen

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Definitions:

Revolving Nosepiece

Part of a microscope that holds the objectives and can be rotated to change magnification.

Objective Lens

The lens in a microscope closest to the specimen, which magnifies the image of the specimen.

Microscope Head

The microscope head is the upper part of a microscope that contains the ocular lenses or eyepieces through which a specimen is viewed.

Working Distance

The distance between the objective lens of a microscope and the specimen being examined when in focus.