The rate of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins. The four main kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis.
DEFINITION of 'Privately Owned'. A company that is not publicly traded on a securities exchange. The majority of companies are privately owned, usually by either one individual or by a small group of individuals. Although offering securities for sale to the public can be a good way to obtain large amounts of financing, public ownership requires considerable effort to ensure compliance with securities regulations.
DEFINITION of 'Private Sector'. The part of the economy that is not state controlled, and is run by individuals and companies for profit. The private sector encompasses all for-profit businesses that are not owned or operated by the government. Companies and corporations that are government run are part of what is known as the public sector, while charities and other nonprofit organizations are part of the voluntary sector. Next Up.