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HOMEOSTASIS
HOMEOSTASIS
Keeping an organism’s internal
environment stable
Blood pressure
 Examples

Water balance
60%
H2O
60%
H2O
Temperature
pH
FEEDBACK MECHANISMS

Help the organism respond to stimuli
and maintain homeostasis on a large
scale (whole body)
1.
2.
Negative Feedback
Positive Feedback
NEGATIVE FEEDBACK


When a situation causes a response that
reverses the first condition
Most common in the body
skin cells
detect cold
brain gets
message
normal body
temp
response
shiver, blood vessels
constrict and lower
blood flow to the skin
Soon
after a
meal
Too
High
Pancreas
secretes
insulin
Liver
coverts
glucose to
glycogen
normal blood
glucose level
Long
after a
meal
Too
Low
Blood glucose
level falls
normal blood
glucose level
Pancreas
secretes less
insulin
Liver
converts
glycogen to
glucose
Blood glucose
level rises
POSITIVE FEEDBACK
When a situation causes a response
that amplifies (increases) the initial (1st)
condition
 Ex. Labor pains, milk production,
digestive enzymes

enzymes
enzymes
enzymes
enzymes
enzymes
On a small scale, individual cells
maintain homeostasis by controlling
what gets into and out of a cell.
CELL TRANSPORT

Cells move molecules in and out 2 ways:
1. PASSIVE TRANSPORT: does not use energy, moves
from high to low concentration.
2. ACTIVE TRANSPORT: uses energy, moves from
low to high concentration.
PASSIVE TRANSPORT
***Molecules move with
the flow, from high to
low concentrations.
***No Energy Required!
***3 Types:
Diffusion
Facilitated Diffusion
Osmosis
PASSIVE TRANSPORT

Diffusion: movement
of anything from high to
low concentration.
PASSIVE TRANSPORT

Facilitated Diffusion:
Movement of molecules
from high to low
concentration.

A protein in the
membrane helps make
bigger spaces in the
membrane.
Facilitated Diffusion
Movement of larger molecules (ex. glucose)
from high concentration to low concentration
with the help of a carrier protein
outside cell
inside cell
PASSIVE TRANSPORT

Osmosis: movement of
water from high to low
concentration across a
membrane.
Osmosis
Movement of WATER from high concentration to
low concentration
diffusion with WATER
* When the cell is at equilibrium with
its environment, equal amounts of
water move into and out of the cell
ISOTONIC SOLUTION
60%
H2O
60%
H2O
* When there is more water in a cell than
outside of a cell, water will leave the cell
HYPERTONIC SOLUTION
this can cause a cell to shrink
75%
H2O
2%
H2O
* When there is more water outside a cell
than inside of a cell, water will enter the
cell
HYPOTONIC SOLUTION
this can be bad, if too much water
enters then the cell may lyse (burst)
60%
H2O
80%
H2O
CYTOLYSIS
Plant cells respond differently to osmosis
because of their cell wall
* When water leaves a plant cell, the cell wall’s
shape does not change, but the cell membrane
pulls away and creates an air pocket between
the two. This causes the plant to WILT.
5% H2O
85% H2O
This is called PLASMOLYSIS
* When water enters a plant cell, the cell
membrane pushes against the cell wall and
creates pressure.
98% H2O
85% H2O
This is called TURGOR
PRESSURE
ACTIVE TRANSPORT

Move molecules against
the flow, from low to
high concentration.

Uses ENERGY!
ACTIVE TRANSPORT

For Multicellular
Organisms:

Uses a carrier
protein, to carry them
across the membrane
Active Transport
For Unicellular Organisms
VESICLE --> organelle that transports materials
through, into, or out of a cell
* ENDOCYTOSIS --> into the cell
Pinocytosis --> fluids
Phagocytosis --> foods
vesicle
* EXOCYTOSIS --> out of the cell
CELLS REVIEW!!!
THE CELL
Smallest
unit of life that can carry on all
processes of life
Unicellular
or multicellular
Multicellular
organization
cells  tissues  organs  organ systems
tissue
cell
organ
organism
A group of similar cells is called a tissue.
A group of similar tissues is called an organ.
A group of organs working together form an
organ system or organism
•The scientist Schwann, Schleiden, and
Virchow contributed to what we call today
the …
CELL THEORY



All living things are made of one or
more cells
Cells are an organisms’ basic unit of
structure and function
Cells only come from preexisting cells
(mitosis)
THERE ARE TWO TYPES OF CELLS:
1.
2.

Prokaryotic
Eukaryotic
YOU ARE EUKARYOTIC!
Prokaryotic
DOES NOT have
membrane bound
nucleus
– DOES NOT have
organelles with a
membrane
–Smaller cells
–ALWAYS unicellular

A prokaryotic cell
2. DNA
1. Ribosomes
3. Plasma membrane
4. Cell wall
Eukaryotic
– HAS a membrane
bound nucleus
–HAS organelles with a membrane
–LARGER cells
–Unicellular or multicellular
A eukaryotic cell
1. Nucleus
2. Nucleolus
3. Chromosomes
4. Plasma membrane
5. Organelles