Answer:
Water and gases are essential for proper cell function for several reasons:
Water:
Cellular metabolism: Water is a vital component of all cellular reactions. It serves as a solvent for biochemical reactions, transports nutrients and waste products within the cell, and helps maintain the shape and structure of the cell.
Osmosis: Water movement across the cell membrane via osmosis regulates cell volume and helps maintain homeostasis.
Cellular processes: Water is involved in many key cellular processes such as photosynthesis, cellular respiration, and protein folding.
Gases:
Cellular respiration: Oxygen gas is essential for cellular respiration, the process by which cells convert glucose into energy. Cells take in oxygen and release carbon dioxide as a waste product.
Signaling: Some gases, like nitric oxide, act as important signaling molecules within the cell and between cells.
Regulation: Gases like carbon dioxide can act as regulators of various cellular processes such as blood flow and pH balance.
The cell membrane's selective permeability allows water and gases to cross the membrane while restricting the movement of other molecules. This controlled movement is crucial for maintaining the cell's internal environment and allowing for proper cellular function. Here are some specific mechanisms that facilitate this movement:
Water:
Diffusion: Water molecules can directly pass through the phospholipid bilayer of the cell membrane due to their small size and polarity.
Aquaporins: These are specialized protein channels in the cell membrane that facilitate the rapid movement of water molecules across the membrane.
Gases:
Diffusion: Small, nonpolar gas molecules like oxygen and carbon dioxide can directly diffuse through the phospholipid bilayer.
Transporters: Some gases like carbon dioxide require specific transporter proteins to facilitate their movement across the membrane.
Without the ability of water and gases to freely cross the cell membrane, several critical cellular processes would be disrupted, leading to cell dysfunction and ultimately cell death.