Download Cells & Cell Organelles

Hyper – high
Hypo – low
Iso - same
Lesson 9: Homeostasis
and Transport
2006-
Demo: Limp Salad
Homeostasis
Maintaining a balance of conditions within the cell
(or organism).
• maintaining pH (cells need pH of 6.8-7.2)
pH Scale
Acid
Neutral
Base
1 2 3 4 5 6 7 8 9 10 11 12 13 14
most cells
QuickLab: pH paper
Homeostasis
Maintaining a balance of conditions within the cell
(or organism).
• maintaining temperatures
(humans 98.6oF) – shiver/sweat
• metabolism = sum total of the
body’s chemical activities
High metabolism
uses energy
FAST
Low metabolism
uses energy
SLOWLY
Homeostasis
Maintaining a balance of conditions within the cell
(or organism).
• maintaining temperatures
(humans 98.6oF)
shiver/sweat
Temperature
increases
Exercising
Temperature
decreases
Triggers
sweating
Evaporative
cooling
Homeostasis
Maintaining other balances:
Nutrients
coming in
Incoming:
Nutrients
Water
Oxygen
Salts (Na+)
Energy
used up
Outgoing:
Energy
Water
Carbon Dioxide
Products (proteins)
Cell Homeostasis (getting stuff in and out)
 Cells need an inside & an outside…

separate cell from its environment

cell membrane is the boundary
IN
OUT
food
- sugars
- proteins
- fats
salts
O2
H2O
waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
Cell needs materials in & products or waste out
SuperQuick Activity: Colored water into colored water.
Building a membrane
 How do you build a barrier that keeps
the watery contents of the cell separate
from the watery environment?
 FATS 
 LIPIDS 
Remember:
oil & water
don’t mix!!
What substance
do you know
that doesn’t mix
with water?
Lipids of cell membrane
 Membrane is made of special kind of lipid


phospholipids
“split personality”
“attracted to water”

phospholipid bilayer
phosphate
inside cell
lipid
outside cell
QuickLab:
Phospholipid people
 Membrane is a double layer
“repelled by water”
Semi-permeable membrane
 Cell membrane controls what gets in or out
 Need to allow some materials — but not all
— to pass through the membrane

semi-permeable (semi – partly)
 only some materials can get in or out
So what needs to get across the membrane?
sugar lipids
aa
O2
H 2O
salt
waste
Crossing the cell membrane
 What molecules can get through the cell
membrane without doors or help?

fats and oils can pass directly through
inside cell
waste
outside cell
lipid
salt
sugar aa
H 2O
but…
what about
other stuff?
Cell membrane channels
 Need to make “doors” through membrane

protein channels allow substances in & out
 specific channels allow specific material in & out
 H2O channel, salt channel, sugar channel, etc.
inside cell
waste
salt
H 2O
aa
sugar
outside cell
How do you build a semi-permeable
cell membrane?
 Channels are made of proteins

proteins both “like” water & “like” lipids
bi-lipid
membrane
protein channels
in bi-lipid membrane
Protein channels
 Proteins act as doors in the membrane
channels to move specific molecules
through cell membrane
Concentration gradient

HIGH
LOW
Movement through the channel
 Why do molecules move through the
membrane if you give them a channel?
HIGH
?
LOW
?
Molecules move from high to low
 Diffusion (substances move)

move from HIGH to LOW concentration
across the concentration gradient.
Concentration
gradient
Membrane
High
Low
Diffusion
 Move from HIGH to LOW concentration
passive transport
 no energy needed

QuickActivity: Diffusion of food
coloring across a dish.
diffusion
Simple Diffusion
 Move from HIGH to LOW
fat
inside cell
LOW
fat
fat
fat
fat
fat
Which way
will fat move?
HIGH
outside cell
fat
fat
fat
fat
fat
fat
fat
fat
Facilitated Diffusion
 Move from HIGH to LOW through a channel
sugar sugar
sugar
sugar
inside cell sugar
sugar
LOW
Which way will
sugar move?
HIGH
outside cell
sugar
sugar sugar
sugar
sugar
sugar
sugar
Diffusion
 Move from HIGH to LOW concentration

directly through membrane
 simple diffusion
 no energy needed

moves through a protein channel
 facilitated diffusion (with help)
 no energy needed
HIGH
LOW
Simple vs. facilitated diffusion
simple diffusion
inside cell
lipid
facilitated diffusion
LOW
inside cell
H 2O
protein channel
outside cell
outside cell
HIGH
H 2O
Active transport
 Cells may need to move molecules
against concentration gradient

need to pump “uphill”
 from LOW to HIGH using energy
protein pump
 Requires ATP

Notice the direction
of
movement and
the concentrations!
Low
ATP
High
Let’s Review…
simple
diffusion
facilitated
diffusion
active
transport
ATP
Osmosis
Movement of Water
Across Cell Membrane
Osmosis
 Water is so important that we discuss it
separately
 Osmosis

diffusion of water from high concentration
of WATER to low concentration of water
 across a semi-permeable membrane
 Osmosis

diffusion of water from high concentration
of WATER to low concentration of water
 across a semi-permeable membrane
High
Low
Virtual Lab 4:
Osmosis through a Selectively Permeable Membrane
Keeping water balance (Homeostasis)
 Cell survival depends on balancing
water uptake & water loss
freshwater
balanced
saltwater
Virtual Lab 5: Onion Cell Plasmolysis
Keeping right amount of water in cell
 Freshwater
a cell in fresh water
 high concentration of water
around cell

 cell gains water
 example: Paramecium
 problem: cells gain water,
swell & can burst
 water continually enters
Paramecium cell
 solution: contractile vacuole
 pumps water out of cell
Hypotonic
Controlling water
 Contractile vacuole in Paramecium
Keeping right amount of water in cell
 Saltwater
a cell in salt water
 low concentration of water
around cell

 cell loses water
example: shellfish
 problem: cell loses water

 plasmolysis in plants
 shrinking cell

solution: take up water
Hypertonic
Keeping right amount of water in cell
 Balanced conditions

no difference in
concentration of water
between cell & environment
 cell in equilibrium
 example: blood
 problem: none
 water flows across
membrane equally,
in both directions
 volume of cell doesn’t
change
Isotonic
BLOOD!
Take your time to answer each
question. Make sure you know what
the question is asking.
TEST TIPS!
Learning through Osmosis?