1. Small, uncharged molecules: These include:
* Oxygen (O2): Essential for cellular respiration.
* Carbon dioxide (CO2): Waste product of cellular respiration.
* Water (H2O): Essential for many cellular processes.
* Lipids: Important for cell structure and energy storage.
2. Some larger molecules: These can be absorbed through specific mechanisms, like:
* Glucose: A primary source of energy for cells.
* Amino acids: Building blocks for proteins.
* Ions: Charged particles like sodium (Na+), potassium (K+), and chloride (Cl-) that are important for maintaining cell function.
3. Substances with the help of transport proteins:
* Specific proteins embedded in the membrane: These proteins can help move larger molecules or ions across the membrane that would otherwise not be able to pass through.
However, the cell membrane generally does not absorb:
* Large, polar molecules: These molecules have difficulty crossing the hydrophobic (water-repelling) core of the membrane.
* Charged molecules: These molecules are also repelled by the hydrophobic core.
* Harmful substances: The membrane often has mechanisms to prevent harmful substances from entering the cell.
Important Note: The absorption of substances through the cell membrane is a complex process that depends on many factors, including:
* The size and charge of the molecule
* The concentration gradient across the membrane
* The presence of specific transport proteins
* The type of cell
I hope this helps!
