3. Movement into and out of cells (Cambridge IGCSE Biology 0610 for exams in 2026,2027 and 2028)

Movement Across Cell Membranes
📌 Substances move into and out of cells primarily via diffusion, osmosis, and active transport.
💧 Diffusion is the net movement of particles from an area of higher to lower concentration (down a concentration gradient) due to random molecular movement.
🌡️ Factors affecting diffusion rate include surface area, temperature, concentration gradient, and distance.

Diffusion Factors and Principles
🚀 A larger surface area leads to a higher rate of diffusion because more molecules can diffuse simultaneously.
💨 Higher temperature increases the rate of diffusion because molecules have more kinetic energy and move faster.
📈 A greater concentration gradient (larger difference in concentration) results in a faster diffusion rate.

Osmosis and Water Potential
🌊 Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution).
🧪 For osmosis, the term water potential is used instead of concentration; very dilute solutions have high water potential.
🧪 Dialysis tubing acts as a non-living partially permeable membrane in experiments, blocking large molecules like sucrose while allowing water passage.

Effects of Osmosis on Plant Cells
🌱 When plant cells are placed in pure water (high external water potential), water moves in, making cells turgid or swollen; the cell wall prevents bursting.
🌵 When placed in concentrated solutions (low external water potential), water moves out, causing cells to become flaccid or shrink, potentially leading to plasmolysis (cytoplasm pulling away from the cell wall).
💧 Plants absorb water through roots via osmosis, driven by the water potential difference between the soil and the root cells, which is vital for transport and support.

Active Transport
🛑 Active transport moves particles against a concentration gradient (from lower to higher concentration), which diffusion/osmosis cannot achieve.
⚡ This process requires energy from respiration to function.
⚙️ It involves specific embedded protein carrier molecules in the cell membrane that change shape to shuttle molecules across the membrane.

Key Points & Insights
➡️ Diffusion relies on kinetic energy and moves substances *down* the concentration gradient.
➡️ Osmosis is specific to water movement across a partially permeable membrane, governed by water potential.
➡️ Active transport moves substances *against* the concentration gradient and is energy-dependent.
➡️ Plant cell support (non-wilting) is maintained by cell turgidity resulting from water uptake via osmosis.

📸 Video summarized with SummaryTube.com on Feb 03, 2026, 11:51 UTC