Biology – Movement into and out of cells | e-Consult
Movement into and out of cells (1 questions)
Simple Diffusion: This is the movement of a substance across a semi-permeable membrane from an area of high concentration to an area of low concentration. It occurs without the need for any cellular energy (ATP). The rate of simple diffusion is influenced by several factors:
- Concentration Gradient: A steeper concentration gradient results in a faster rate of diffusion.
- Temperature: Higher temperatures increase the kinetic energy of molecules, leading to faster diffusion.
- Surface Area: A larger surface area allows for more molecules to diffuse across the membrane, increasing the rate.
- Thickness of the Membrane: A thinner membrane reduces the diffusion distance, increasing the rate.
- Molecular Size: Smaller molecules diffuse faster than larger molecules.
Facilitated Diffusion: This is also passive transport, but it requires the assistance of membrane proteins (channel proteins or carrier proteins). These proteins bind to the substance being transported and help it cross the membrane down its concentration gradient. Unlike simple diffusion, facilitated diffusion has a limited capacity and can become saturated. The rate is influenced by the same factors as simple diffusion, but also by:
- Number of Transport Proteins: More transport proteins mean a higher rate of facilitated diffusion.
- Specificity of Transport Proteins: The type of protein determines which substance it can transport.
Osmosis: This is the specific case of diffusion involving water. It's the movement of water across a semi-permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration). Water potential is influenced by solute concentration, pressure, and temperature. The rate of osmosis is influenced by:
- Solute Concentration: Higher solute concentration lowers water potential, driving water movement.
- Temperature: Higher temperatures increase the rate of osmosis.
- Surface Area: Larger surface area increases the rate.
- Thickness of the Membrane: A thinner membrane allows for faster osmosis.