Movement of Substances

1. Movement of Substances

2. What you need to know • What is diffusion? • What is osmosis? • How is active transport different from diffusion? • What causes the movement of substances? • How does the permeability of the membranes affect the movement of substances? • How does the movement of substances affect cells?

3. Diffusion • Net (overall)movement of substances from a region of higher concentration to a region of lower concentration (down a concentration gradient) • Passive– no cellular energy required • Osmosis – a special type of diffusion

4. Equilibrium

5. Molecules are equally spaced apart/equally distributed throughout the solution

7. Factors affecting the rate of diffusion • Size of the particle: At a given temperature, a smaller particle (molecule) moves/diffuses faster than a larger one. • Temperature: As the temperature increases, particles gain energy and move faster, thus the rate of diffusion is increased. • Concentration Difference: The greater the concentration difference between the two regions, the faster the substance will diffuse • Diffusion Distance: At a given temperature, it takes longer for the particle to diffuse a farther distance, thus the slower the rate of diffusion. • Surface Area: The greater the surface area, the greater the rate of diffusion. • Permeability: The more permeable the separating surface is, the faster a substance can diffuse through it.

8. Life example: Absorption of nutrients by the intestine • Diffusion of digested nutrients (food molecules) into fingerlike structures called villi in the small intestine

9. Life example 2: Exchange of gases in the lungs • Movement of O2 and CO2 between the air sacs (alveoli) and the blood capillaries surrounding them during gaseous exchange in the lungs

10. Active transport • Movement of substances from a region of lower concentration to a region of higher concentration (against a concentration gradient) • Require cellular energy • Involve transport proteins found on the cell surface membrane

11. Life example: Absorption of nutrients from the soil • Some essential nutrients are present in low concentration in the soil • They are taken up by the root hair cells via active transport

12. Osmosis • Net (overall) movement of water molecules from a region of higher water potential (lower concentration) to a region of lower water potential (higher concentration) • Occurs across a partially/semi- permeable membrane • Passive – no cellular energy required

14. Comparison between the 3

15. What causes substances to move passively? • No energy involved • A concentration gradient drives the movement of substances • i.e. a DIFFERENCE in concentration between two regions • E.g., between inside the cell and the cell’s external environment

16. Permeability Membranes can be Permeable – let everything in and out e.g., cell wall Semi Permeable - let some things in and out e.g., cell surface membrane Impermeable – let nothing in and out e.g.,

17. Osmosis and its effects on cells • Depending on the concentration of the environment, cells can undergo physical changes • These changes differ slightly in animal and plant cells because of their structural differences

18. A cell’s external environment can be • Dilute (hypotonic): water molecules > solute molecules • concentrationE < concentrationi • Similar to the cell’s internal environment (isotonic): • concentrationE= concentrationi • Concentrated (hypertonic): water molecules < solute molecules • concentrationE> concentrationi

19. Osmosis and animal cells • Recap: Animal cells do not have a cell wall • Hypotonic: water enters the cell as water potential outside the cell is > water potential inside the cell • Isotonic: no net movement of water molecules since water potential inside and outside the cell is similar • Hypertonic : Water leaves the cell as water potential is inside the cell is > water potential outside the cell

20. What happens to animal cells in different environments?

21. Many animals that live in the sea have cytoplasm with a similar concentration to sea water • It is the function of our kidneys to make sure the fluid in our bodies that surrounds our cells (plasma) has a stable concentration

22. Life example: Amoeba

23. Osmosis and plant cells • Recap: Plant cells have a cell wall • A cell wall keeps the cell in shape despite changes in movement of water

24. Hypotonic: water molecules enter the cells • cells become turgid due to pressure (turgor pressure) exerted on cell wall • Isotonic: no net movement of water molecules • Hypertonic: water molecules leave the cells • Cells become flaccid/plasmolysed • Cytoplasm shrinks away from the cell wall • But cell retains its shape due to presence of a cell wall

26. Plasmolysed red onion cells

27. Importance of turgor pressure • Turgor pressure gives plants their strength • If plants did not have this they would be wilted • Plants that don’t have wood such as lettuce and house plants rely on turgor pressure for strength

28. Osmosis and Food Preservation • Bacteria and Fungi are the most common causes of food spoilage • Both these cells are enclosed by a membrane • If a food is placed in a sugary or salty solution then any bacteria or fungi present will lose the water in their cells to the more concentrated solution outside • When this happens the cells will shrivel and die and the food will not become contaminated with loads of bacteria nad fungi

29. Examples • Fish and Meat (bacon) may be stored in a salty solution • Jams, marmalades and tinned fruits are stored in a sugary solution

30. Life example 1: Absorption of water by roots • Water moves from the soil into the roots and finally into the xylem via osmosis

31. Life example 2: Ultrafiltration by the kidneys

32. Life example 3: Freshwater and marine fishes/animals Saltwater fishes Freshwater fishes

35. Experimental point of view