Cells, like humans, cannot generate energy without locating a source in their environment. However, whereas humans search for substances like fossil fuels to power their homes and businesses, cells seek their energy in the form of food molecules or sunlight. In fact, the Sun is the ultimate source of energy for almost all cells, because photosynthetic prokaryotes, algae, and plant cells harness solar energy and use it to make the complex organic food molecules that other cells rely on for the energy required to sustain growth, metabolism, and reproduction.
Cellular nutrients come in many forms, including sugars and fats. In order to provide a cell with energy, these molecules have to pass across the cell membrane, which functions as a barrier — but not an impassable one. Like the exterior walls of a house, the plasma membrane is semi-permeable. In much the same way that doors and windows allow necessities to enter the house, various proteins that span the cell membrane permit specific molecules into the cell, although they may require some energy input to accomplish this task
<h2>Explanation:</h2>
Membranes are semipermeable lipid bilayers. Permeability refers to the ease with which molecules cross biological membranes. Because of the chemical and structural nature of the phospholipid bilayer (hydrophobic core), only lipid-soluble molecules are able to freely pass through the lipid bilayer because it attracts these non polar molecules.
Water soluble or hydrophilic molecules cannot pass through these lipid membranes because hydrophobic bilayer repels hydrophilic molecules. Ions and large polar molecules cannot pass through the lipid bilayer.
But more specifically, whether a molecule can pass through the membrane depends on its size and its electrical nature.
The answer is A. Being a liquid at room temperature, surface tension, and that ice floats.
Above the troposphere lies the stratosphere where jet airplanes fly. Temperatures increase with altitude because of increasing amounts of ozone. The ozone layer within the stratosphere absorbs harmful ultraviolet rays of sunlight. As the mesosphere extends upward above the stratosphere, temperatures decrease.
