What are some examples of substances that cross the cell membrane?

Water, oxygen, carbon dioxide, glucose, ions (such as sodium, potassium, and calcium), amino acids, and lipid-soluble compounds like steroid hormones are a few examples of substances that can pass through the cell membrane.

Some examples of substances that can cross the cell membrane include:

1. Water (H2O): Water molecules can cross the cell membrane through a process called osmosis, which involves the movement of water from an area of low solute concentration to an area of high solute concentration.

2. Oxygen (O2): Oxygen molecules can diffuse across the cell membrane, moving from an area of high oxygen concentration (such as the lungs) to an area of low oxygen concentration (such as cells in the body).

3. Carbon Dioxide (CO2): Carbon dioxide molecules, produced during cellular respiration, can diffuse out of cells and cross the cell membrane, moving from an area of high concentration within the cell to an area of lower concentration outside the cell.

4. Glucose: Glucose, a sugar molecule and a vital energy source for cells, can cross the cell membrane using specialized transport proteins called glucose transporters.

5. Ions (e.g., Sodium, Potassium, Calcium): Ions can cross the cell membrane through various mechanisms, including ion channels and active transport processes. For example, sodium ions (Na+) can enter the cell through sodium channels, while potassium ions (K+) can exit the cell through potassium channels.

6. Amino Acids: Amino acids, the building blocks of proteins, can cross the cell membrane through facilitated diffusion or active transport, depending on their size and charge.

These examples illustrate the diverse ways in which substances can cross the cell membrane, including simple diffusion, facilitated diffusion, osmosis, and active transport.