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.
According to CarsDirect, mileage reimbursement up to the federal mileage reimbursement rate is not taxable, but a standard car allowance is considered to be taxable income. If an employee is not reimbursed for mileage, he or she is allowed to list that amount as a deduction on his or her annual tax return.