1. Grade 8 – Chapter 5 Cells in Their Environment

2. KEY QUESTION
How do substances enter and leave a cell?

3. 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

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

5. 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

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

7. 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

8. 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

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

10. 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

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

12. 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.

14. 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

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

16. 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

17. 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

18. 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

19. 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?

21. 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

22. Osmosis

23. 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

24. 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

25. 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?

26. 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.

28. 5.6 Endocytosis and Exocytosis

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

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

31. 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.

33. Chapter 5 Review
Page 134 and 135
Questions on page 136 and 137
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