Which of the following is the correct sequence that describes the excitation and contraction of a skeletal muscle fiber?
1. tropomyosin shifts and unblocks the cross-bridge binding sites.
2. calcium is released and binds to the troponin complex.
3. transverse tubules depolarize the sarcoplasmic reticulum.
4. the thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from atp.
5. an action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane.

Why should the united state be concerned about air pollution in china?

The diagram below represents a marine food web and a process that can harm the human population. each circle represents an organism and the smaller dots inside them represent a toxic substance. what is being represented and how does it harm the population? the diagram represents biological half-life, in which toxins build up in organisms higher up on the food chain, and this can negatively impact humans who consume the organisms and the toxic substance. the diagram represents biomagnification, in which toxins build up in organisms higher up on the food chain, and this can negatively impact humans who consume the organisms and the toxic substance. the diagram represents the process by which different organisms prey upon each other; this can impact the human population by reducing the number of organisms that do not contain the toxin. the diagram represents the way that toxins are metabolized by living organisms, with those at greater trophic levels able to metabolize more efficiently than those at lower levels. this means that those at higher tropic levels are safer for humans to consume compared to the organisms at lower trophic levels.

Which of the following is a difference between active transport and facilitated diffusion? view available hint(s)which of the following is a difference between active transport and facilitated diffusion? facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. active transport involves transport proteins, and facilitated diffusion does not. facilitated diffusion involves transport proteins, and active transport does not. active transport requires the expenditure of cellular energy, and facilitated diffusion does not.