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

The correct sequence is 5-3-2-1-4.

Explanation:

The signals from the motor neurons are released which helps in releasing the acetylcholine.

The depolarized sarcoplasmic reticulum which releases calcium ions.

The released calcium ions gets attached to the troponin complex. Due to this binding the tropomyosin shifts and unblocks the cross bridge.

The thin filaments are attached to the thick filaments by the help of the head of myosin using the energy generated from ATP.

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.