part ii: material transport in cell

• For the cells to remain alive, it must maintain a relatively constant internal environment despite changing external conditions, referred to as homeostasis
• For a living cell to function at its optimum, it must allow certain substances to pass through its membrane to regulate its metabolic activities. The property of membranes that permits movement of materials across their surface is called permeability.
• The cell membrane is known to be selectively permeable to carefully maintain the internal environment of the cell. Cell membrane acts as selective barriers in determining what is to enter a cell and what is not.
• Passive transport is the kind of movement of materials that does not require any metabolic energy from the cell but rely solely on the physical properties of the substances themselves.
• Active transport on the other hand, is the movement of molecules that requires cellular energy.
• Molecules of all matter are in constant motion due to their kinetic energy. The naturally occurring Brownian motion drives passive transport processes.
• Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration.
• Osmosis is when some particles move through such a concentration gradient when they are allowed to cross the membrane in case that the particle is water molecules.
• Osmosis is a special type of diffusion, which does not require any cell energy
• Isotonic environment is the condition wherein the external and internal environment of the cell has the same concentration.
• hypertonic environment is the condition where there is more solute outside than inside the cell.
• hypotonic environment is the condition where there is less solute outside than inside the cell.
• hypertonic condition refers to an external environment with a higher concentration compared to the internal environment
• e hypotonic condition has lower concentration on outside environment of the cell compared to its inner environment.
• In animal cells, an increase in osmotic pressure eventually causes the plasma membrane to burst.
• in plant cells, increased osmotic pressure is counteracted by the rigid cell walls that make them turgid
• Some materials probably pass across the membrane through special channels or pores.
• Channels or pores considerably help in maintaining the solute concentration inside the cells but very specific to a particular molecule or ion.
• components within the membrane function as carriers
• In facilitated transport systems, the carriers combine with the molecules in high concentration found at one surface to form complex.
• In active transport systems, the carrier system may be an enzyme that undergoes conformational change when it combines with its passenger molecule.
• If the molecule is too large to cross the membrane, these particles may get into the cell in a bulk transport phenomenon called endocytosis
• pinocytosis is a form of endocytosis wherein the particles are relatively small
• In exocytosis, materials enclosed in a membrane vesicle are brought to the surface membrane.