Chapter 11 Movement of Substances

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Chapter 11 Movement of Substances
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Syllabus

1. Explain the role of selectively permeable
   membranes.
2. Define the terms osmosis diffusion
3. Give examples of diffusion and osmosis.
4. Define the term turgor.
5. Explain turgidity in plant cells.
6. Describe the application of high salt or sugar
   concentration in food preservation.

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The Cell
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Cell membrane is the boundary between inside
outsideseparates cell from its environment
Can it be an impenetrable boundary?
NO!
IN food carbohydrates sugars, proteins amino
acids lipids salts, O2, H2O
OUT waste ammonia salts CO2 H2O products
OUT
IN
cell needs materials in products or waste out
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Permeability

• Membranes can be
• Permeable let everything in and out
• Semi Permeable - let some things in and out
• Impermeable let nothing in and out

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Homeostasis Maintaining a Balance

• Cells must keep the proper concentration of
  nutrients and water and eliminate wastes.
• The plasma membrane is selectively permeable it
  will allow some things to pass through, while
  blocking other things.

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Diffusion and Osmosis Animations View movement
in the cell membrane, diffusion, osmosis Video
on Osmosos Diffusion
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Structure of the CELL Membrane

• Lipid bilayer two sheets of lipids
  (phospholipids).
• Found around the cell, the nucleus, vacuoles,
  mitochondria, and chloroplasts.
• Embedded with proteins that determine what
  particles can pass through the membrane.

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Diffusion

• movement of molecules from an area of high
  concentration to an area of low concentration.
• Passive transport / no external energy needed.

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Diffusion
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Diffusion in everyday life

• CO2 diffusing into a leaf
• O2 diffusing out of a leaf
• O2 diffusing into an animal cell
• CO2 diffusing out of an animal cell

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Learning check

1. Name 3 different types of membranes.
2. Explain the term Homeostasis.
3. How does the membranes play a role in maintaining
   Homeostasis?
4. Explain the role of selectively permeable
   membranes.
5. Define Diffusion

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Osmosis

• is the movement of water from a region of high
  water concentration to a region of low water
  concentration across a semi-permeable membrane
• Passive transport / no external energy needed.

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osmosis
movement of water
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Learning Check

• What is osmosis?
• Does osmosis require energy?

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Animal cells

• Animal cells in a solution that is the
• same concentration as their Cytoplasm - stay the
  same size
• less concentrated solution - gain water, swell
  and may burst
• more concentrated solution - lose water, shrivel
  and may die

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Osmosis in animal cells
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Shrivelled Animal Cells

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Learning check

1. What surrounds an animal cell?
2. How does water move in and out of an animal cell?
3. What will happen to animal cells in a very dilute
   (watery) solution?
4. What will happen to animal cells in a very
   concentrated solution?

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PLANT cells
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Plant cells in a

• less concentrated solution than their cytoplasm -
  gain water and become turgid (swells) and strong.

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Turgor pressure

• This turgor pressure gives plants their strength
• If plants did not have this they would wilt
• Plants that dont have wood such as lettuce and
  house plants rely on turgor pressure for strength

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Plant cells in a

1. more concentrated solution - lose water and
   become plasmolysed (wilts).

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Learning Check

1. What surrounds the membrane of a plant cell?
2. Can this structure control what moves in and out
   of cells?
3. How does water enter roots of a plant?
4. What is meant by a turgid cell?
5. How could you identify a turgid cell?

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Overcoming Osmosis

• Amoeba survives in a less concentrated
  (freshwater) environment due to its contractile
  vacuole, which eliminates water.

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Food Preservation

• Bacteria and Fungi are the most common causes of
  food spoilage
• If a food is placed in a high sugary or salty
  solution then any bacteria or fungi present, will
  lose the water in their cells by osmosis, shrivel
  and die.
• E.g. Salting fish or high sugar concentration in
  jam.

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Learning Check

1. What is meant by plasmolysis?
2. What kind of a solution would you put plant cells
   in to cause them to palsmolyse?
3. How is plasmolysis used to preserve food?
4. Give an example of some types of food preserved
   in this way?

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• Annimation showing molecules moving in osmosis

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• How Osmosis work animation audio lesson
• Animation How Osmosis Works
• Check out this Shockwave video of simple
  diffusion, facilitated diffusion, and osmosis.
  This is a great overview of these terms
• Animation Membrane

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To show osmosis

• Place bags of visking tubing half-filled with
• (a) distilled water,
• (b) 80 sucrose solution,
• in distilled water.
• Bag (a) stays the same mass and size.
• Bag (b) increases in mass and swells
• as water enters
• due to osmosis.

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