Grade 8 – Chapter 5 Cells in Their Environment

KEY QUESTION How do substances enter and leave a cell?

Looking Ahead… The cell membrane is a selectively permeable membrane. It regulates the movement of substances into and out of the cell. Diffusion is one of the basic ways that substances move into and out of cells. Osmosis moves water into and out of cells. The skills of scientific inquiry can be used to conduct controlled experiments on diffusion and osmosis. Cells use special processes to move non-dissolved particles, or large amounts of material, into and out of the cytoplasm

Key Terms Selectively permeable membrane Diffusion Concentration gradient osmosis Tugor pressure Endocytosis Phagocytosis Exocytosis

5.1 The Cell Membrane Review… What are the characteristics of living things? Grow in size, reproduce, and are able to repair themselves Require energy Respond to changes in their environment Have a lifespan Produce waste

Where do living things get their energy? Food What happens to the wastes living things produce? They eliminate them from their bodies

The Cell What are the different parts to a cell? Organelles: small structures found within a cell; has a specific function Cytoplasm: watery substance found in a cell which protects and holds the organelles Cell Membrane: the outer layer of the cell which holds the cell together Nucleus: control center of the cell (the Big Boss) Vacuole: storage compartments in the cell that hold fluid Cell Wall: firm structure surrounding the plant cells which provides support and protection Chloroplast: photosynthesis happens here – turns the sun’s energy into food Cilia: tiny hairs surrounding the cell Flagella: tail on the cell to help it move

Parts of a Cell - Continued Mitochondria – produce energy for the cell Ribosome – tiny organelles that produce proteins needed for cell growth, repair and reproduction Endoplasmic Reticulum – folded membranes that transport materials through the cytoplasm Golgi Apparatus – stores and packages proteins produced by the ribosome Lysosome – cleans the cytoplasm by releasing digestive proteins that break down large particles

What parts of a cell are only found in plant cells? Cell wall Chloroplast Everything else is the same

The Cell Membrane What types of materials need to get through the cell membrane in order for the cell to survive? Food, nutrients, waste must be able to move out, etc. Selectively Permeable Membrane: the membrane chooses what should pass through

Selective Permeable Membrane Permeable – allowing passage Impermeable – not allowing passage

Homework Questions What is the function of the cell membrane? Why are cell membranes said to be selectively permeable? In your own words, describe the structure of a cell membrane. Explain how the cell membrane is important to the health of a cell.

5.2 Fluid Movement in Cells: Diffusion Perfume demonstration Raise your hand when you can smell the perfume What did you notice about this demonstration? This is an example of diffusion

Diffusion The movement of particles from an area of high concentration to an area of low concentration

Concentration Gradient The difference in concentration of a substance between two areas Particles move from where there is less room to where there is more room

What is an example of diffusion on our bodies? Oxygen rich blood cells diffuses into our muscles by spreading out from an area of high concentration to an area of low concentration (they go to the muscles that need it) It is then used to make energy

Try This Activity Page 122 Materials needed: 2 beakers, pencil, paper, room-temperature water, hot water, 2 tea bags Answer questions A-D Use terminology from the unit and the previous unit we have talked about Apply the concepts

Homework Questions How have the concepts in this reading added to your understanding of cells? Describe the process of diffusion in your own words. Use the particle theory in your explanation. What does the term “concentration gradient” mean? How is the movement of particles in diffusion determined? Give 2 examples in your everyday experience where diffusion occurs. Can you think of a situation where this might be harmful?

5.3 Osmosis: An Important Type of Diffusion Water particles are small enough to cross the cell membrane by diffusion Osmosis: the diffusion of water across a selective permeable membrane from an area of high concentration to an area of low concentration Osmosis is a type of diffusion

Osmosis

Cells in a Solution Sugars, salts and proteins are common solutes in a cell and water is the solvent Cells need to have a certain amount of solute un order to stay alive When there is a lower concentration of water INSIDE the cell, the water moves in by osmosis (too much will make the cell burst) When there is a lower concentration of water OUTSIDE the cell, the water moves out

Turgor Pressure: Osmosis in Action In a plant, water is stored in the vacuole When a plant needs water, it is released from the vacuole and goes where it is needed

Turgor pressure: outward pressure put on a plant cell wall by the contents inside the cell when water is taken in Think of when you fill a balloon with water What happens to the balloon when you keep putting water in?

Homework Questions Describe an idea in the reading that you found to be particularly important. Why do you think this idea is important? Explain the process of diffusion in your own words. Use a diagram. Explain the process of osmosis in your own words. Use a diagram. Explain how osmosis creates turgor pressure in plants. What cell organelle makes turgor pressure in a plant cell possible? Describe the role of this organelle in this process.

5.6 Endocytosis and Exocytosis

Endocytosis The cell moves large amounts of materials from the outside environment into the cytoplasm (inside the cell) Phagocytosis

Exocytosis Large amounts of material are moved from a cell’s cytoplasm to the outside environment

Homework Questions Give two examples of situations where a cell might use phagocytosis and exocytosis. A cell encounters a large piece of food. Use a simple diagram to show how it might move the food particles into the cell cytoplasm. Include labels in your diagram. What is exocytosis? Explain using a diagram.

Chapter 5 Review Page 134 and 135 Questions on page 136 and 137 #1-15