1 Movement Across Membranes

2 1. Diffusion

3 DiffusionDiffusion Particles in liquids and gases move in random directions with a certain amount of kinetic energy

4 DiffusionDiffusion The overall effect of this is that particles become evenly distributed (equilibrium)

5 DiffusionDiffusion Kinetic Energy can be increased by increasing the temperature

6 Examples from syllabus: Diffusion of CO 2 into stomata of leaves during photosynthesis. Diffusion of CO 2 into stomata of leaves during photosynthesis. Diffusion of O 2 into the alveoli of the lungs Diffusion of O 2 into the alveoli of the lungs Diffusion of O 2 to respiring cells Diffusion of O 2 to respiring cells Diffusion of glucose, amino acids etc. into the villi during digestion. Diffusion of glucose, amino acids etc. into the villi during digestion.

7 2. Osmosis The cell membrane is partially permeable permeable – it allows small, particles to pass through by simple diffusion

8 The cell membrane is partially permeable – it allows small, uncharged or high energy particles to pass through by simple diffusion

9 Osmosis is simply a special case of diffusion… Osmosis is simply a special case of diffusion… …that applies to WATER only. …that applies to WATER only.

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13 Water Potential ‘Water potential’ is a measure of the amount of kinetic (movement) energy water molecules have

14 Water Potential Water potential (  ) is a measure of the amount of kinetic energy water molecules have

15 Water Potential In pure water, water potential is at its highest…

16 “Osmosis is the diffusion of water molecules from areas of high water potential to areas of lower water potential through a partially permeable membrane” Osmosis definition:

17 Osmosis is the diffusion of water molecules from areas of high water potential to areas of lower water potential through a partially permeable membrane. OsmosisOsmosis

18 Exam errors: Forgetting to use the term ‘water potential’ Forgetting to use the term ‘water potential’ Saying water ‘osmoses’ (it doesn’t; it diffuses) Saying water ‘osmoses’ (it doesn’t; it diffuses) Not mentioning ‘selectively permeable membrane’ Not mentioning ‘selectively permeable membrane’ Saying water moves ‘from high to low concentration’ ( you can’t concentrate water! It should be high to low water potential) Saying water moves ‘from high to low concentration’ ( you can’t concentrate water! It should be high to low water potential)

19 Osmosis and Animal Cells Cells placed in a solution of higher water potential

20 Osmosis and Animal Cells Cells placed in a solution of higher water potential Water enters by osmosis Cell bursts (lysis)

21 Osmosis and Animal Cells Cells placed in a solution of lower water potential

22 Osmosis and Animal Cells Cells placed in a solution of lower water potential Water leaves by osmosis Cell shrivels (crenation)

23 This is the reason why animals need kidneys… This is the reason why animals need kidneys… …to keep the blood water levels precisely right. …to keep the blood water levels precisely right. This is called OSMOREGULATION. This is called OSMOREGULATION.

24 Osmosis and Plant Cells Cells placed in a solution of higher water potential

25 Osmosis and Plant Cells Cells placed in a solution of higher water potential Water enters by osmosis Cell becomes TURGID

26 Turgid cells keep a plant supported upright.

27 Osmosis and Plant Cells Cells placed in a solution of lower water potential

28 Osmosis and Plant Cells Cells placed in a solution of lower water potential Water leaves by osmosis Cell shrivels (PLASMOLYSED)

29 When plant cells lose water and plasmolyse… When plant cells lose water and plasmolyse… …the plant is unable to support itself and starts to WILT. …the plant is unable to support itself and starts to WILT.

30 Osmosis and Plant Cells And when turgid turgid the cell contents exert outward pressure on the cell wall This helps to support support plants and keep them upright.

31 Osmosis and Plant Cells

32 This plant is supported by turgid cells, as well as wood.

33 Examples of osmosis: Absorbing water in root hair cells of plants. Absorbing water in root hair cells of plants. Absorbing water in the large intestine (colon). Absorbing water in the large intestine (colon). Pallisade cells absorbing water for photosynthesis. Pallisade cells absorbing water for photosynthesis. Seeds absorbing water prior to germination. Seeds absorbing water prior to germination.

34 Explain why: Placing limp lettuce leaves in water for 20 minutes makes them ‘firm’ again. Placing limp lettuce leaves in water for 20 minutes makes them ‘firm’ again. Pouring salt on slugs effectively kills them. Pouring salt on slugs effectively kills them.

35 Active Transport Active transport moves substances against against a concentration gradient.

36 Active Transport Movement involves the use of ATP from aerobic respiration to supply energy

37 Active Transport Structural changes in the carrier proteins result in the movement of material through the membrane.

38 Examples of active transport: Uptake of minerals by roots Uptake of minerals by roots Concentrating molecules in the vacuoles of plants eg beetroot, rhubarb, mint etc. Concentrating molecules in the vacuoles of plants eg beetroot, rhubarb, mint etc. Impulses firing in nerves of animals. Impulses firing in nerves of animals. Exporting enzymes from cells into the gut. Exporting enzymes from cells into the gut.