1. 7-3 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.

2. Cell Membrane The cell membrane regulates what enters and leaves the cell and also provides protection and support. The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer. Protein molecules are embedded in the lipid bilayer. Some form channels and pumps that help to move material across the cell membrane.

3. Cell Wall The main function of the cell wall is to provide support and protection for the cell. Made from fibers of carbohydrate and protein. Plant cell walls are composed mostly of cellulose, a tough carbohydrate fiber. Present in many organisms, including plants, algae, fungi, and many prokaryotes.

4. Diffusion Through Cell Boundaries *One of the most important functions of the cell membrane is to regulate the movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side. Solution = mixture of two or more substances. The substances dissolved in the solution are called solutes. The concentration of a solution is the mass of solute in a given volume of solution, or mass/volume.

5. Solution concentration The first solution is twice as concentrated as the second solution.

6. Diffusion In a solution, particles move constantly. They collide with one another and tend to spread out randomly. As a result, the particles tend to move from an area where they are more concentrated to an area where they are less concentrated, a process known as diffusion. When the concentration of the solute is the same throughout a system, the system has reached equilibrium.

7. Suppose a substance is present in unequal concentrations on either side of a cell membrane. The particles will tend to move toward the area where it is less concentrated until substance on both sides of the cell membrane will be the same.

8. Diffusion Because diffusion depends upon random particle movements, substances diffuse across membranes without requiring the cell to use energy. NO ENERGY NEEDED!!!

9. Osmosis – The diffusion of water through a selectively permeable membrane. If a substance is able to diffuse across a membrane, the membrane is said to be permeable to it. Most biological membranes are selectively permeable, meaning that some substances can pass across them and others A membrane is impermeable to substances that cannot pass across it. Most biological membranes are selectively permeable, meaning that some substances can pass across them and others cannot.

10. Selective Permeability

11. There are more sugar molecules on the left side of the membrane than on the right side. That means that the concentration of water is lower on the left than it is on the right. The membrane is permeable to water but not to sugar. This means that water can cross the membrane in both directions, but sugar cannot. As a result, there is a net movement of water from the area of high concentration to the area of low concentration.

12. The Effects of Osmosis on Cells Isotonic – “same strength” Hypertonic – “above strength” Hypotonic – “below strength

13. Facilitated Diffusion Cell membranes have protein channels that act as carriers, making it easy for certain molecules to cross. These cell membrane channels facilitate, or help, the diffusion of glucose across the membrane. (For example in red blood cells) The molecules will move from high concentration to low concentration. No energy needed.

14. Active Transport Cells sometimes must move materials in the opposite direction – against a concentration difference. (low concentration -> high concentration) This requires energy!!!

15. Active Transport Endocytosis – the process of taking material into the cell by means of infoldings, or pockets, of the cell membrane. Phagocytosis – “cell eating” Extensions of cytoplasm surround a particle and package it within a food vacuole. The cell then engulfs it. Pinocytosis – Tiny pockets form along the cell membrane, fill with liquid, and pinch off to form vacuoles within the cell.

16. Active Transport Many cells also release large amounts of material from the cell through a process known as exocytosis. The membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.

17. 7-4 The Diversity of Cellular Life All living things are composed of cells They use the same basic chemistry. The follow the same genetic code, and even contain the same kinds of organelles. BUT….. There’s such great diversity of life!!! Their differences arise from the ways in which cells are specialized to perform certain tasks and the ways in which cells associate with one another to form multicellular organisms.

18. Unicelluar Organisms – single-celled organism Sometimes, a cell is the organism. They grow, respond to the environment, transform energy, and reproduce. They are found everywhere!!! Volvox amoeba Yeast

19. Multicellular Organisms – Organisms made up of may cells. Cell Specialization – The process in which cells develop in different ways to perform different tasks. Red blood cells are specialized to transport oxygen. Muscle cells contract and relax to move part of the body. Pancreatic cells produce compounds such as insulin that the body needs

20. Multicellular Organisms Specialized plant cells, known as guard cells, regulate exchanges of carbon dioxide, oxygen, water vapor, and other gases. Guard cells monitor the plant’s internal conditions, changing their shape according to those conditions.

21. Levels of Organization The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ systems. A tissue is a group of similar cells that perform a particular function Many groups of tissues work together as an organ. A group of organs that work together to perform a specific function is called an organ system.

22. The organization of the body’s cells into tissues, organs, and organ systems creates a division of labor among those cells that makes multicellular life possible.