Download How Cells Maintain Homeostasis

How Cells Maintain Homeostasis
Objective 2.03: Importance of Water,
How cells maintain homeostasis,
Movement of materials into and out of
cells
? Homeostasis ?
• Maintaining a stable, BALANCED, internal environment
• Example:
Water
Water
Water
Cell
Water
Water
Water
Water
Water
Homeostasis!
• Maintaining a stable, BALANCED, internal environment
• Example:
Water
Water
Water
Cell
Water
Water
Water
Water
Water
Water FYI
• Universal solvent = ability to dissolve many things
• Transports materials in organisms = blood is mostly water
• Makes up 70-95% of most organisms
Water is Polar
Polar Molecule
- Has a positive and negative end
- Attracts other water molecules = surface tension
- Allows water to move up through thin tubes inside of plants =
capillary action
Plasma Membrane:
Structure & Function
Plasma/Cell Membrane
• In an Animal Cell, it is the boundary between the inside and
outside of the cell.
• In a Plant Cell, it is between the cell wall and the inside of the
cell
• It is crucial in maintaining the cell’s homeostasis!!
• It is selectively permeable
(or semi-permeable)
• It is choosy about what enters and leaves the
cell.
• It keeps nutrients in, and harmful substances
out
• The Cell Membrane is referred to as the Fluid Mosaic Model
• Fluid: because the parts inside the cell membrane are always
moving around.
• Mosaic: because it is made of many different parts and
molecules (lipids, cholesterol, proteins, carbohydrates, etc.)
Structure of the Plasma Membrane
• The plasma membrane is a
Phospholipid Bilayer
Phosphate + Fat
2 Layers
• Other Components: Proteins,
Cholesterol, Carbohydrates
Phospholipids
• The “heads”:
– Hydrophilic
– Polar
– Attracted to H2O inside and outside cell
• The “tails”:
– Hydrophobic
– Non-polar
– do NOT like water
– Point to the middle of the plasma
membrane.
Can things move through the cell membrane?
• Of course!
• If they are small, they can go
through without energy needed
–Ex: Water, Oxygen
• If they are large, they have to go
through a protein and it uses
energy
–Ex: Sugar
What do you think…
• A cell in your body does not maintain homeostasis, and too
much water is allowed in.
• What might happen!?
The Movement of Materials into and out
of Cells
Two Types of Cell Transport
Passive Transport
• No energy required
• Movement of materials is
from high to low
• Materials move DOWN a
concentration gradient
• Examples are diffusion,
osmosis, and facilitated
diffusion
Active Transport
• Energy is required
• Movement of materials is
from low to high
• Materials move UP a
concentration gradient
• Requires the use of proteins
Concentration Gradient!?
• When the concentrations of solutions are different
Outside a Cell
HIGH
concentration of
solute (ex: salt)
Inside a Cell
LOW
concentration
of solute
(ex: salt)
Diffusion
• Movement of particles from an area of high concentration to
an area of low concentration
• Goal is to reach dynamic equilibrium = inside and outside the
cell are at equal concentrations
Facilitated Diffusion
• Same as diffusion BUT uses a protein in cell membrane
• Used when particles are too big to squeeze through cell
membrane
Transport Proteins for Facilitated Diffusion
• Channel Protein = does not change shape (a)
• Carrier Protein = can change shape (b)
Osmosis
• Osmosis: The diffusion of water across a semi permeable
membrane.
Hypertonic
(Cell Shrinks)
90% H2O
In cell
10% Water
In beaker
Isotonic
( Dynamic Equilibrium)
50% H2O
In cell
50% Water
In beaker
Hypotonic
(Cell Swells)
10% H2O
In cell
90% Water
In beaker
Cells in Solutions
Bursts
Turgor Pressure –
cell membrane “pushes”
on cell wall
Shrivels
Plasmolysiscell membrane pulling
away from cell wall
Where will the water go?
• 40% water outside cell, 60% water inside cell
• 40% sugar outside cell, 60% sugar inside cell
Passive Transport
Active Transport
• No energy required
• Movement of materials is
from high to low
• Materials move DOWN a
concentration gradient
• Examples are diffusion,
osmosis, and facilitated
diffusion
• Energy is required
• Movement of materials is
from low to high
• Materials move UP a
concentration gradient
Active Transport
• Requires ENERGY!
• Movement is from LOW to HIGH
• Uses transport proteins (carrier or channel)
• Ex: muscle contractions + electrolytes
Energy!!!