Cell%20Membranes%20Osmosis%20and%20Diffusion

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Cell MembranesOsmosis and Diffusion
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Functions of Membranes

• 1. Protect cell
• 2. Control incoming and outgoing substances
• 3. Maintain ion concentrations of various
  substances
• 4. Selectively permeable - allows some molecules
  in, others are kept out

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Solutions

• Solutions are made of solute and a solvent
• Solvent - the liquid into which the solute is
  poured and dissolved. We will use water as our
  solvent today.
• Solute - substance that is dissolved or put into
  the solvent. Salt and sucrose are examples of
  solutes.

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Methods of Transport Across Membranes

• 1. Diffusion
• 2. Osmosis
• 3. Active Transport
• 4. Facilitated Diffusion

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Methods of Transport Across Membranes

• 1. Diffusion -passive transport - no energy
  expended
• 2. Osmosis - Passive transport of water
  across membrane
• 3. Active Transport- requires energy to
  transport molecules against a concentration gra
  dient energy is in the form of ATP
• 4. Facilitated Diffusion - Use of proteins to
  carry polar molecules or ions across

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Diffusion

• Movement of molecules from an area of high
  concentration to an area of low concentration
  till equilibrium is attained.
• Diffusion can take place anywhere , in living and
  non living organisms
• It is a passive process
• Eg in plants Movement of gases like oxygen and
  CO2 during respiration
• In animals Diffusion of oxygen into the blood
  stream in the lungs.

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Factors affecting diffusion

• 1. Shorter the distance (or thinner the membrane)
  faster the diffusion
• 2. high concentration gradient is essential
• 3. The larger the surface area, faster the
  diffusion ( example Small intestine folded,
  placenta villi folded )

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Diffusion
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Osmosis
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Osmosis

• Movement of water molecules from a region of its
  higher concentration to a region of its lower
  concentration across a semi permeable membrane.
• ? Can take place only in living organisms.
• ? It is a passive process.

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Tonicity is a relative term

• Hypotonic Solution - One solution has a lower
  concentration of solute than another.
• Hypertonic Solution - one solution has a higher
  concentration of solute than another.
• Isotonic Solution - both solutions have same
  concentrations of solute.

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When an animal cell (RBC) is placed in

• Hypertonic solution
• Since salt concentration is more, water from the
  RBC moves out of the cell into the surrounding,
  exosmosis occurs
• RBC shrinks as more and more water leaves the
  cell
• Appearance of the cell changes completely. Edges
  become wavy or crinkled and the cell becomes
  Flaccid.
• Cell becomes crenated (star shaped with edges
  sticking to each other

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When an animal cell (RBC) is placed in

• Hypotonic solution
• . When RBC is put into a hypotonic solution,
  since water potential is higher outside the cell,
  water moves into the RBC by endosmosis.
• The cell becomes turgid gaining water.
• Appearance Cell becomes rounded, swollen and
  edges of the cell are smooth.
• RBC swells up and bursts ultimately as there is
  no cell wall .

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When an animal cell (RBC) is placed in

• Isotonic
• Water potential inside and outside the cell are
  the same.
• There is no net movement of water molecules into
  or outside the cell.
• There is not much difference seen in the RBC as
  the concentration is the same inside and outside
  the cell.

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When a Plant cell is placed in

• Hypertonic solution
• When a plant cell is put in a concentrated
  solution, exosmosis occurs and water leaves the
  cell.
• Water potential is lower in the cell so water
  moves out.
• The plant cell becomes flaccid after losing
  water.
• Appearance cell shrinks and becomes smaller with
  wavy margins
• Further loss of water makes the cell contents
  shrink to the centre, cell membrane tears away
  from the cell wall. The cell is said to be
  plasmolysed and the process is called
  plasmolysis.

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When a Plant cell is placed in

• Hypotonic solution
• Water potential is higher outside the cell, so
  endosmosis occurs.
• Water moves into the cell, cell becomes turgid.
• Gains water and swells up.
• Size increases and edges of the cell smoothen out
  
• The cell doesnt burst because of the elastic
  cell wall present.

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When a Plant cell is placed in

• Isotonic solution There is no net movement of
  water molecules into or outside the cell. Cell
  doesnt gain or lose water, appearance remains
  the same.
• osmosis is reversible in plants cells but not in
  animal cells.
• in some cases where the particles are too large
  to cross a membrane by diffusion or active
  transport, phagocytosis is used, where the WBCs
  engulf the particles and help transport.

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Plant and Animal Cells put into various
solutions
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Active transport

• substances like minerals move from a region of
  lower concentration to a region of higher
  concentration against the concentration gradient
  using energy.
• It is an active process since it requires energy.
  ATP provides the energy
• Carrier proteins in the membranes play a very
  important role in transporting the substances
  across the membrane.
• Example in plants uptake of minerals from soil
• In animals In humans absorption of glucose at
  the villi of the small intestine.

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Types of Transport A Birds View