Biological Science Second Edition

1
HOW SWEET IS A SWEET POTATO?
2
IS A SWEET POTATO SWEETER THAN A BAKING POTATO?
3
WHAT MAKES A SWEET POTATO SWEET?
4
Transport Across Membranes

• Nutrients must pass from the bloodstream into the
  animal cells and the xylem in vascular tissue of
  plants into plant cells
• The plasma membrane, the outer layer of cells in
  the body, is made of a double layer of
  phospholipids called the lipid bilayer

5
Transport Across Membranes

• The nature of the lipid bilayer
• The interior of the bilayer where the fatty
  acid tails of the phospholipids are is
  hydrophobic
• The hydrophilic heads of the phospholipids point
  outward, toward the water

6
Transport Across Membranes

• The bilayer controls what enters and leaves the
  cell semipermeable
• Hydrophobic material can pass directly through
  the membrane
• Hydrophilic material is more difficult to move
  across

7
Diffusion

• Diffusion movement of molecules from where they
  are highly concentrated to where they are less
  concentrated
• Requires no energy spontaneous

8
Diffusion

• Diffusion across a membrane passive transport
• This is how small hydrophobic molecules cross the
  membrane
• Gas molecules, such as carbon dioxide and oxygen,
  cross this way
• Water freely diffuses across plasma membranes

9
(No Transcript)
10
Facilitated Diffusion

• Hydrophilic and charged molecules cannot pass
  directly through the membrane
• There are proteins in the membrane for this
• Proteins in the membrane allow molecules to cross
  the membrane passively in this facilitated
  diffusion
• The membranes facilitate the diffusion

11
(No Transcript)
12
Osmosis

• Osmosis is the passive transport of water across
  a membrane
• Water can leave the cell cell shrivels
• Water can enter the cell cell swells

13
ISOTONIC

• If the concentration of solute (sugar, salt, etc)
  and solvent (water) are identical on both sides
  of a semi-permeable membrane, water will not flow
  in either direction
• If you place a cell that has the same sugar or
  salt concentration inside the cell as found in
  the surrounding environment the cell will neither
  swell nor shrink

14
HYPERTONIC

• If a cell is placed in an hypertonic solution
  (the environment has more salt or sugar than is
  found inside the cell), water will flow out of
  the cell and into the environment where water
  concentration is lower.
• The cell will shrink (and lose weight)

15
(No Transcript)
16
(No Transcript)
17
HYPOTONIC

• If a cell is placed in an hyportonic solution
  (the environment has less salt or sugar than is
  found inside the cell), water will flow out of
  the environment and into the cell where water
  concentration is lower.
• The cell will swell (and gain weight) and may
  burst.

18
Active Transport

• Sometimes cells need to maintain high levels of
  material and still transport more inside
• This requires energy output in a process type
  called active transport

19
(No Transcript)
20
Movement of Large Molecules

• Sometimes molecules are too large to pass through
  a membrane
• They need vesicles to carry them
• Vesicles are made of membrane, so they can fuse
  with the plasma membrane
• This requires energy output

21
Exocytosis

• In exocytosis, a vesicle inside a cell fuses with
  the plasma membrane
• The contents are emptied outside the cell

22
Endocytosis

• In endocytosis, the membrane folds in and
  captures something on the outside
• The vesicle is formed around the particle and
  brings it inside

23
(No Transcript)
24
How much solute is there inside a potato cell?

• You can estimate the concentration of solute
  (sugar, salt, etc) inside a potato cell by
  placing pieces of potato in hypotonic, isotonic
  and hypertonic solutions and monitoring water
  flowing in and out of the cells by weighing the
  pieces of potato before and after treatment
• The solute concentration that results in the
  smallest weight change is the solute
  concentration closes to that on the inside of the
  cell.

25
Comparing solute concentration in the cells of
baking and sweet potatoes

• Prepare 8 cores of both potatoes. Each core
  should be 4 centimeters long.
• Weigh each core and record weight on your data
  sheet

26
Place each core in 100ml of each of the following
solutions

• 2M NaCl
• 1.5M NaCl
• 1M NaCl
• 0.8M NaCl
• 0.6 M NaCl
• 0.4 M NaCl
• 0.2M NaCl
• Water

27

• Soak for at least 30 minutes
• Blot each core dry
• Weigh each core and record post treatment weight
  on your data sheet
• Calculate weight change in each core
• Observe any changes in characteristics of each
  core

28
HOW SWEET IS A SWEET POTATO?

• What is your estimate of intracellular solute
  concentration inside the baking potato and the
  sweet potato?
• Which potato has a higher intracellular solute
  concentration?
• Do sweet potatoes have higher intracellular
  concentrations of sugar than baking potatoes?