The frozen contraction of muscle cells called rigor mortis occurs after death because ____
a. ions are not available in the cytoplasm of muscle cells
b. tropomyosin breaks down quickly
c. crossbriges become very rigid structures
d. ATP production stops
e. muscle cells are flooded with neurotransmitters
ANSWER: d
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Which of the following characteristics, structures, or processes is common to bacteria and viruses?
A) metabolism B) ribosomes C) genetic material composed of nucleic acid D) cell division E) independent existence
The primary role of the two sperm produced in the germ tube of the pollen is to
A. release proteins for germination B. aid the plant's seed production C. ensure that there will be fertilization of the egg and the two central cells D. ensure production of an embryo E. allow the endosperm to become a seed
Answer the following statement(s) true (T) or false (F)
1. The axon of a neuron can only communicate with other neuronal cells. 2. Neurons are the only electrically-active cells. 3. When a neuron is not firing, the sodium-potassium pump is inactive. 4. Humans are unique among animals due to our highly-evolved repertoire of sensory receptors. 5. A single type of receptor is responsible for detecting all tactile pressure in humans.
Based on modern understanding of physiology, DNA sequences, and the fossil record, which of the following types of animals is most closely related to crocodiles?
a. snakes b. birds c. fleshy-finned fishes d. lizards e. mammals