Which essential element is often a limiting factor for plant growth?
a. Calcium
b. Hydrogen
c. Oxygen
d. Phosphorus
e. Carbon
d
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The element to which oxygen (O2) binds in a hemoglobin molecule is ___________
A. nitrogen D. potassium B. carbon E. phosphorous C. iron
Contraction of a skeletal muscle cell is initiated by the
A) release of acetylcholine by a neuron terminating at the neuromuscular junction. B) release of calcium ions by the neuron into the neuromuscular junction. C) electrical current traveling from the neuron directly into the muscle cell. D) hormones delivered by the blood supply to the nearby tissue. E) release of sodium ions by the neuron into the neuromuscular junction.
Which of the following is NOT an example of a human activity that directly threatens the biodiversity of species?
a) the destruction of habitats b) the picking of flowers c) the introduction of invasive species d) the overexploitation of resources e) the burning of fossil fuels
The total number of viable microorganisms remains constant in stationary phase because ________.
A. there is a cessation of cell division even though the cells may remain metabolically active B. there is a balance between cell division and cell death C. either there is a balance between cell division and cell death or there is a cessation of cell division even though the cells may remain metabolically active D. None of the choices are correct.