How does the dirty snowball theory explain some of the observed characteristics of comets and how may this description not be correct?
What will be an ideal response?
Comet nuclei have been described as dirty snowballs or icy mudballs, but that seems to be incorrect; their shapes, low densities, and lack of material strength suggest that comets are not solid objects. The evidence leads astronomers to conclude that most comet nuclei must be fluffy mixtures of ices and dust with significant amounts of empty space.
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When macrophages bind antigens, they secrete ____ to attract more phagocytic cells
a. more antigens b. MHC c. cytokines d. antibodies e. complement
Nekton are restricted to particular ocean areas by:
What will be an ideal response?
Defense mechanisms that function to protect the body against many infectious agents are called
a) adaptive b) innate c) barriers to entry d) immunity
Some RNA molecules can function like enzymes. These particular enzymatic RNA molecules are called
A) ribosomes. B) mRNA. C) ribozymes. D) RNase.