The cell membrane's main trait is its selective permeability, which means that it allows some substances to cross it easily, but not others. Small molecules that are nonpolar (have no charge) can cross the membrane easily through diffusion, but ions (charged molecules) and larger molecules typically cannot.
Charged Ions
An ion is a molecule that is charged because it has lost or gained an electron. The cell membrane is made of a bilayer of phospholipids, with an inner and outer layer of charged,hydrophilic "heads" and a middle layer of fatty acid chains, which are hydrophobic, or uncharged. Charged ions cannot permeate the cell membrane for the same reason that oil and water don't mix: uncharged molecules repel charged molecules. Even the smallest of ions -- hydrogen ions -- are unable to permeate through the fatty acids that make up the membrane. If ions "want" to enter the cell due to a high concentration of that type of ion on one side of the cell, they can do so by entering through the protein channels that are embedded between the lipids.
Large Polar Molecules
Large uncharged molecules, such as glucose, also cannot easily permeate the cell membrane. Although they do sometimes manage to slip across the membrane through diffusion, the process is extremely slow due to the size of the molecules. In order for these molecules to cross the membrane at a normal rate of speed, they need to resort to ion channels and specific transporters, which require energy output from the cell.
Answer:Bones are composed of a type of connective tissue called _____osseous_____ tissue, immature bone cells that produce bony tissue are called ________osteoblast____, large bone cells that digest bone tissue to shape the bone and smooth it out are called _______osteoclast_______, and mature bone cells are called _______osteocytes_______.
Explanation:bones are made up of 15% water,30% collagen fibres and 55 % mineral salts.
The collagen makes the bone soft and flexible.the mineral salt makes the bone fragile and strong.
The osseous tissue contains the osteogenic cells which are stem cells.they are differentiated into osteoblasts.osteoblasts build bones and are important in the external matrix of the bone.osteoclast forms osteocytes,which are the main bone cells.
Osteoclast breaks down older tissues in order to keep the bone strong.
Answer:
D. more variety in population
