Molecules that can pass through cell membranes, among others, are hydrophobic molecules (CO2, O2), and a very small polar molecules (water, ethanol). Meanwhile, other molecules such as polar molecules with large size (glucose), ions and hydrophilic substances require special mechanisms for entry into the cell.
A. Passive transport
Passive transport is movement of molecules down a concentration gradient. This passive transport spontaneous.
Diffusion, osmosis, facilitated diffusion and is an example of passive transport.
Diffusion occurs due to thermal motion which increases the entropy or disorder resulting in a more andom mix. Diffusion will continue for respiration, which consumes O 2 entry. Osmosis is the diffusion of solvent across the membrane selective displacement direction is determined by the total solute concentration difference (from hipotonis to hipertonis). Facilitated diffusion is also still considered to be due to the passive transport of solutes move according to their concentration gradients.
Osmosis
Is the movement of water through a selectively permeable membrane from the more dilute to the more dense. Semipermeable membrane must be penetrated by solvent, but not by the solute, which causes the pressure gradient along the membrane. Osmosis is a natural phenomenon, but can be inhibited artificially by increasing the pressure on the parts with dense concentration exceeds its concentration becomes more dilute. Force per unit area required to prevent the flow of solvent through a selectively permeable membrane and enter the solution with a more intense concentration is proportional to the turgor pressure.
Is the movement of water through a selectively permeable membrane from the more dilute to the more dense. Semipermeable membrane must be penetrated by solvent, but not by the solute, which causes the pressure gradient along the membrane. Osmosis is a natural phenomenon, but can be inhibited artificially by increasing the pressure on the parts with dense concentration exceeds its concentration becomes more dilute. Force per unit area required to prevent the flow of solvent through a selectively permeable membrane and enter the solution with a more intense concentration is proportional to the turgor pressure.
If a plant cell is placed in concentrated salt solution (hypertonic), plant cells lose water and turgor pressure, resulting in weak plant cells. Plants with cells in this condition wilt. Lose more water will cause plasmolysis: keep the pressure decreases until at a point where the protoplasm of cells scraped from the cell wall, causing the distance between cell walls and membranes. Finally cytorrhysis - the collapse of the entire cell wall - can occur. There is no mechanism in plant cells to prevent excessive water loss, also get water in excess, but plasmolysis can be reversed if the cell is placed in hypotonic solution.
Crenation
Crenation occurs because hypertonic environment, (the cell has a solution with a lower concentration than the solution around the outside of cells), osmosis (diffusion of water) causing movement of water out of cells, causing reduced cytoplasmic volume. As a result, the cells shrink.
Same process that occurs in plants is a plant cell plasmolysis which is also shrinking due to put in a hypertonic solution
Same process that occurs in plants is a plant cell plasmolysis which is also shrinking due to put in a hypertonic solution
B. Active transport
Is the opposite of passive transport and is not spontaneous. The direction of this transport movement against a concentration gradient. Active transport requires the help of several proteins. Examples of proteins involved in active transport is the channel proteins and carrier proteins, as well as ionophore
Active transport is divided into primary and secondary active transport. Secondary active transport is also composed of co-transport and counter transport (exchange).
Primary active transport directly uses energy from ATP, such as the Na-K pump and Ca pump. In the Na-K pump, 3 Na is pumped out of the cell was 2 K will be pumped into the cell. In the Ca pump, ca will be pumped out of cells to low concentrations of Ca in the cell.
Primary active transport directly uses energy from ATP, such as the Na-K pump and Ca pump. In the Na-K pump, 3 Na is pumped out of the cell was 2 K will be pumped into the cell. In the Ca pump, ca will be pumped out of cells to low concentrations of Ca in the cell.
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