Diffusion Across a Cell Membrane. Diffusion is the movement of a substance across a membrane. Substances diffuse across cell membranes in a process known as passive transport. This means that the cell does not expend any energy in transporting substances across the cell membrane. Instead, substances move down their concentration gradient as a result of random thermal motion.
401k and profit sharing plans are both forms of retirement plans. They allow employees to make pre-tax contributions to an account where contributions and earnings are not taxed until distributed. Some 401k plans require an employer to make contributions to a plan.
For purposes of this limit, a SEP is treated as a profit-sharing (defined contribution) plan. However, this percentage limit must be reduced to figure your maximum deduction for contributions you make for yourself. See Deduction Limit for Self-Employed Individuals, earlier. The amount you carry over and deduct may be subject to the excise tax discussed next. Table 4-1 below illustrates the carryover of excess contributions to a profit-sharing plan.