1. The plasma membrane is composed of proteins, cholesterol, and phospholipids. This membrane does many things. It can form an impermeable junction around a cell, or prevent cells from separating.
2. Active and passive transport are both mechanisms for transporting molecules across the cell membrane. Passive transport happens along a concentration gradient, and requires no energy input from the organism. Active transport requires energy in the form of ATP and often goes against a concentration gradient.
3. Mitochondria are threadlike membranous organelles. They provide most of the cell’s ATP supply.
4. Diffusion involves the movement of particles from a high concentration to a lower concentration. Osmosis involves only the movement of water across a semipermeable membrane form an area with a low solute concentration to an area with a high solute concentration.
5. Cells placed in an isotonic solution retain their normal shape and neither gain nor lose water. Isotonic solutions have the same concentrations as those found in cells.
When a cell is introduced to a hypertonic solution, it shrinks. This is because hypertonic solutions have a higher concentration of non-penetrating solutions than the cell does.
Because hypotonic solutions contain a lower concentration of non-penetrating solutes than cells, water will soak into the cell until it bursts.
6. Microfilaments are the thinnest element of the cytoskeleton. They are somewhat flexible strands of actin.