Cell Boundaries

1. Cell Boundaries Cell membrane Cell Wall Nucleus Cytoplasm Nucleus Cytoplasm Cell membrane

2. Objectives • Identify the main functions of the cell membrane and the cell wall . • Investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules (TEKS 4B) • Discuss and investigate passive and active transport.

3. Cell Boundaries • All cells are surrounded by a thin, flexible barrier known as the cell membrane. • Many cells also produce a strong supporting layer around the membrane known as a cell wall.

4. Cell Walls • The main function of the cell wall is to provide support and protection for the cell. • Cell walls are found in plants, algae, fungi, and many prokaryotes. Cell Wall

5. Cell Membrane • Cell Membrane – thin, flexible membrane that surrounds all cells. • The main function of the cell membrane is to regulate what enters and leaves the cell. It also provides protection and support. • Most biological membranes are selectively permeable, meaning that some substances can pass across them and others cannot. • Cell membranes are an essential means for homeostasis in our bodies.

6. Passive Transport • Passive transport is the movement of substances across membranes without the need of energy. Substances move from an area of high concentration to an area of low concentration. • Types of Passive Transport: • Diffusion • Osmosis • Facilitated diffusion

7. Passive Transport-Diffusion • Diffusionis the process when particles in a solution move from an area where they are more concentrated to an area where they are less concentrated. • Because diffusion depends upon random particle movements, substances diffuse across membranes without requiring the cell to use energy. • When the concentration of the solute is the same throughout a system, the system has reached equilibrium.

8. Passive Transport-Osmosis • Osmosis is the diffusionof water through a selectively permeable membrane. • Since osmosis is diffusion, it also goes from an area of high concentration (where there’s less solutes) to an area of low concentration (where there’s more solutes). • Water moves to dilute the solute.

9. Passive Transport-Osmotic Pressure Types of Osmotic solutions: Isotonic–equal concentration of solute in the solution (balanced) Hypertonic– solution has greater concentration of solutethan the cell (Water moves out of the cell) Hypotonic– solution has lesser concentration of solute than the cell (Water moves into the cell)

10. Passive Transport-Facilitated Diffusion • Facilitateddiffusionis the movement of specific molecules across cell membranes from areas of high concentration to areas of low concentration through protein channels. • Most molecules because of their size and charge can not move freely across the cell membrane. • Facilitated diffusion can help such molecules across the membrane High concentration of glucose molecules Low concentration of glucose molecules

11. Active Transport • Active Transport is the movement of molecules that requires energy. • Molecular Transport/pumps – moving molecules from low to high concentration • -Small molecules and ions are carried across the membrane by proteins that act as pumps. • -Sodium, calcium, potassium ions, and protons are carried by pumps

12. Concentration Gradient Passive Transport Active Transport ATP

13. Active Transport • Types of active transport: • Endocytosis – process of taking materials into the cell by forming vesicles. Large molecules, clumps of food, liquids and even whole cells can be taken in this way. • -Phagocytosis – “cell eating” Cell engulfs food in vesicle • - Pinocytosis- “cell drinking” Cell engulfs liquids • Exocytosis – Process by which a cell releases a large amount of material