The correct sequence is sources emit greenhouse gases; global temperatures rise; snow and ice melt; and sea levels rise. The natural and man made sources emit greenhouse gases that are responsible for the greenhouse effect. The increase in the Earth's temperature due to these gases absorbing more heat from the sun caused climate change like melting of snow and ice which contributes to the rising sea levels.
A membrane bounded organelle whose main function is to undergo protein synthesis would be the ribosomes. These can be embedded in the endoplasmic reticulum or be freely floating in the cytoplasmic region of the cell.
If the stimulus reaches the threshold an action potential will be generated. If the stimulus doesn't reach it no action potential will be generated. If the stimulus will be stronger the action potential will have the same amplitude. The refractory period makes it harder to generate an action potential so they decrease the frequency of action potential production.
