Rigor mortis sets in after the death of humans and other animals because the supply of ATP decreases to the point at which calcium can no longer be removed from the cell. At this point, the myosin molecules attach to the thin filament
The muscles stiffen, and limbs cannot be moved. Why and for how long does the muscle then remain in this continuously contracted state?
If the myosin molecules cannot disengage from the actin filaments (i.e., the cross-bridges cannot be broken), the muscle cannot rebound back to its starting position, and the muscle will stay locked in that position. Eventually, the actin and myosin proteins themselves will break down, and the muscles will be moveable again.
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Which statement about ecosystems is false?
A) Bacteria and fungi recycle energy within an ecosystem. B) Plants and other photosynthetic organisms are producers in ecosystems. C) Chemical nutrients cycle within an ecosystem. D) In the process of energy conversions within an ecosystem, some energy is converted to heat.
In a growing population, the youngest age classes have
A. the highest number of deaths/year. B. the fewest individuals. C. the most individuals. D. the smallest number of deaths/year. E. the most individuals and the largest number of deaths/year.
Each motor unit is composed of ____
a. both slow and fast aerobic muscle fibers b. both fast aerobic and anaerobic fibers c. all types of muscle fibers mixed together d. only one type muscle fiber e. both slow and fast anaerobic muscle fibers
Digestive wastes of the male Ascaris roundworm exit the body through the
(a) anus. (b) cloaca. (c) mouth. (d) excretory pore.