2. Cell membranes
Cell membranes are barriers around the cell. The job of the cell membrane is to
protect and support cells, which lets them interact with their surroundings. Cell
membranes contain phospholipid molecules, embedded proteins, lipid bilayers,
and cholesterol.
3. Phospholipids
Phospholipids are molecules composed of hydrophobic and hydrophilic
properties. The hydrophobic lipid tails are made of fatty acids connected to the
glycerol. The hydrophilic phosphate groups are placed toward the aqueous
cytosol.
4. Embedded proteins
Embedded proteins also contain hydrophobic and hydrophilic properties as well.
The hydrophobic proteins are nonpolar side groups. Nonpolar molecules can
simply move across the membrane. The hydrophilic proteins are polar side
groups. Polar molecules move across the membrane through transport proteins.
5. Cell membranes and cell walls
Animals, plants, fungi, and protists mainly have cell membranes and walls.
However, an animal cell does not contain a cell wall. Overall, the cell membrane’s
purpose is to protect the cells and interact with their surroundings.
6. Selective permeability
Selective permeability is when a cell membrane lets molecules or ions go
through it by the process of active or passive transport. Active transport requires
the cell to waste energy to move materials. Passive transport does not require
cellular energy.
7. Selective permeability
Facilitated diffusion is a passive transport. Facilitated diffusion allows
compounds like sugars and amino acids in. The K+/NA+ pump is active
transport. The pump moves K and NA against gradients. The process requires
energy. When the energy is being used, ATP falls off and is converted into ADP.
