selectively permeable
Size. Actually very few substances are able to diffuse across the menbrane, most must be transported ie facilitated diffusion, active transport, or receptor-mediated endocytosis. Carbon dioxide, oxygen, water, and some lipid substances are able to diffuse across the membrane
osmosis
Facilitated diffusion is a type of passive transport in which a substance moves across the cell membrane from high to low concentration. In this situation, the substance moves with the concentration gradient, and with the help of carrier molecules, it is able to make it's way across the membrane smoothly and without the expense of energy. Active transport, on the other hand, is the movement of a substance across the cell membrane from low to high concentration, making the transport a bit more difficult and calling for the use of energy. Transport proteins recognize the substance and allow it to cross through the membrane.
Diffusion is the process by which something dissolved in a fluid will move from higher concentrations to lower concentrations. A drop of food coloring in a glass of water will gradually diffuse throughout the entire glass until it is a uniform color. In biology, diffusion is commonly across a membrane (like a cell membrane). If the concentration of sodium is higher on one side of a membrane, and it can pass through the membrane, it will move from the higher concentration to the lower until the two sides have the equal concentration.
Water cannot diffuse a plasma membrane because of the fact that the phosphate heads of the phospholipids are hydrophilic, the hydrocarbon tails of the phospholipids are hydrophobic, meaning they repel water. The bilayer phospholipid model of the plasma membrane shows that the phophates face outward on either side of the membrane and the lipid tails are in the middle of the bilayer.
selectively permeable
Size. Actually very few substances are able to diffuse across the menbrane, most must be transported ie facilitated diffusion, active transport, or receptor-mediated endocytosis. Carbon dioxide, oxygen, water, and some lipid substances are able to diffuse across the membrane
Carbon dioxide, oxygen and some nonpolar molecules diffuse easily.
osmosis
Its going against their gradient
Facilitated diffusion is a type of passive transport in which a substance moves across the cell membrane from high to low concentration. In this situation, the substance moves with the concentration gradient, and with the help of carrier molecules, it is able to make it's way across the membrane smoothly and without the expense of energy. Active transport, on the other hand, is the movement of a substance across the cell membrane from low to high concentration, making the transport a bit more difficult and calling for the use of energy. Transport proteins recognize the substance and allow it to cross through the membrane.
Facilitated diffusion is a type of passive transport in which a substance moves across the cell membrane from high to low concentration. In this situation, the substance moves with the concentration gradient, and with the help of carrier molecules, it is able to make it's way across the membrane smoothly and without the expense of energy. Active transport, on the other hand, is the movement of a substance across the cell membrane from low to high concentration, making the transport a bit more difficult and calling for the use of energy. Transport proteins recognize the substance and allow it to cross through the membrane.
Facilitated diffusion is a type of passive transport in which a substance moves across the cell membrane from high to low concentration. In this situation, the substance moves with the concentration gradient, and with the help of carrier molecules, it is able to make it's way across the membrane smoothly and without the expense of energy. Active transport, on the other hand, is the movement of a substance across the cell membrane from low to high concentration, making the transport a bit more difficult and calling for the use of energy. Transport proteins recognize the substance and allow it to cross through the membrane.
Facilitated diffusion is a type of passive transport in which a substance moves across the cell membrane from high to low concentration. In this situation, the substance moves with the concentration gradient, and with the help of carrier molecules, it is able to make it's way across the membrane smoothly and without the expense of energy. Active transport, on the other hand, is the movement of a substance across the cell membrane from low to high concentration, making the transport a bit more difficult and calling for the use of energy. Transport proteins recognize the substance and allow it to cross through the membrane.
Diffusion is the process by which something dissolved in a fluid will move from higher concentrations to lower concentrations. A drop of food coloring in a glass of water will gradually diffuse throughout the entire glass until it is a uniform color. In biology, diffusion is commonly across a membrane (like a cell membrane). If the concentration of sodium is higher on one side of a membrane, and it can pass through the membrane, it will move from the higher concentration to the lower until the two sides have the equal concentration.
Ions cannot diffuse through a phospholipid bilayer because they are not able to dissolve in lipids, hence the phosphoLIPID bilayer . Also, since they have an electrical charge, they are repelled by the membrane.
Steroid hormones are lipids so are able to diffuse through the membrane without receptors.