What is a cross-bridge?
a. a protein found along the groove of the F-actin double helix
b. a T tubule and two adjacent terminal cisternae
c. the combination of myosin heads with active sites on actin molecules
d. the movement of myosin head while attached to actin myofilament
e. after exercise, the oxygen taken in that exceeds the oxygen required for resting metabolism

The correct answer is - option C.

Explanation:

Cross bridge is a structure that is globular made up of the actin filaments and activated myosin attachments. The head of the myosin binds to the binding site that is present on the actin filaments that are exposed to the actin molecules.

Due to this structure, the movement in muscle occurs as they contract while attaching temporarily to the actin filament that is present near and exposed.

Thus, the correct answer is - option C.

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.

that scientist would be robert hooke