5. When an action potential starts at one end of an axon, can it run out of e ou

Question

5. When an action potential starts at one end of an axon, can it run out of e out of energy and not Pell (a) Yes (b) No 36. The so dium-potassium pump establishes concentration gradients: (a) Of higher sodium concentrations inside the cell and higher (b) Of potassium concentrations outside the cell sodium and potassium but the area of their concentrations (inside or ou outside) depends on the needs of the cell (c) Of higher potassium concentrations inside the cell and high (d) By pumping sodium outside the cell and potassium is cotransported out as wel outside the cell centrations er sodium con 37. ATP is required in the transport of (a) All molecules across a membrane (b) Molecules through a protein channel (c) Molecules to areas of lower concentrations (d) Molecules to areas of higher concentrations 38. The net movement of unc harged, polar molecules across a semipermeable membrane from a low concentration to a high concentration occurs by diffusion (a) True (b) False 39. Fluidity of phospholipid bilayer is increased by (a) Cholesterol at certain temperatures (b) Double bonds between carbon atoms in the fatty acid tails (c) Shorter hydrophobic tails (d) All the above 40. All the following statements concerning transmitter-gated ion channels are (a) Are Ligand-gated channels (b) Are Voltage-gated channels Convert the chemical signal neurotransmitter into an electrical signal (d) Are receptors

Explanation / Answer

35. b. No, when action-potential starts, it does not run out of energy. For the movement of ions at first from higher concentraion to lower concentration, energy is not required, but their transport is facilitated through ion channels, creating a membrane potential. But later during sodium-potassium pump, it requires energy.

36. c. Of higher potassium concentration inside the cell and higher sodium concentration outside the cell.

Sodium -potassium pump requires energy as it transports ions against the concentration gradient (from lower to higher concentration).

37.d. molecules to areas of higher concentration.

38.b. False

Diffusion does not require a semipermeable membrane, but it needs a concentration gradient, that means, diffusion occurs from higher concentraion to lower concentration.

39. d. All the above.

The reason for membrane fluidity, the first being temperature and cholesterol acts as a buffer, increasing fluidity at low temperatures and decreasing fluidity at high temperatures. And unsaturated fatty acids in phospholipid. Increase in the amount of unsaturated fatty acids in cell membrane, increases the fluidity.

40. b. Are voltage-gated channels. (false)

Transmitter-gated ion channels are ligand gated-ion channels. Ligand-gated ion channels, also commonly referred as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl? to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand), such as a neurotransmitter.

When a presynaptic neuron is excited, it releases a neurotransmitter from vesicles into the synaptic cleft. The neurotransmitter then binds to receptors located on the postsynaptic neuron. If these receptors are ligand-gated ion channels, a resulting conformational change opens the ion channels, which leads to a flow of ions across the cell membrane. This, in turn, results in either a depolarization, for an excitatory receptor response, or a hyperpolarization, for an inhibitory response.

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