When a gecko loses its tail, does it experience any pain?

No, the gecko should not have felt any pain in the loss of its tail. 
When a gecko feels threatened, or is grabbed by the tail, it will drop its tail as a defense mechanism (the tail will wiggle on the ground, and hopefully act as a distraction to the threat while the gecko makes its escape). This process is known as autotomy and is a defense mechanism possessed by several gecko species. The connective tissue of the tail is specially adapted to allow the tail to break off at determined fracture planes, these fracture planes are spaced along the length of the tail. 

When the tail (or part of the tail) is autotomized, the nerves go through a process called vasoconstriction- this process stops the blood flow to the open part of the tail, thereby preventing the wound from bleeding. The tail will grow back in time, however, it is unlikely to resemble the original

22. C

23. C

24. Not clear, maybe 18%

25. Left ventricle, because according to the graph nearly 50% of the organ contains mitochondria, more than the left atrium.

Explanation:

22. Active transport requires cell's energy to move molecules, usually in the form of ATP.

23. This is a trick question, you might think it is diffusion or osmosis, but is is exocytosis. Diffusion and osmosis don't require vesicles for transport. It isn't endocytosis, because that is moving molecules inside the cell. The question asks for moving out the cell.

24. Look at the chart, it is less than 20, but more than 10 and more than halfway. I am not sure exactly the percentage, I would approximate it to be 18%.

25. Most likely left ventricle.

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