CELLULAR ORGANIZATION
Cells, Tissues, Organs, & Organ
Systems of Animals
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Some animals are single-celled (unicellular)
Some are made of many cells (multicellular)
Everything that an animal does is ultimately
happening at the cellular level.
I. Levels of Specialization
Cells
Tissues
Organs
Organ Systems
Organism
A. Cells – the smallest functional unit
of life
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1. Eukaryote – organism
with a nucleus, membranebound organelles, and more
than one chromosome. Ex. –
anything BUT bacteria
2. Prokaryote –
independent, unicellular
organism with NO nucleus,
NO membrane-bound
organelles, and circularstranded DNA. Ex. –
bacteria
3. Origin of Eukaryotes
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The Endosymbiont Hypothesis:
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i. the first cells on Earth were most likely very simple prokaryotes.
ii. The eukaryotic cell might have evolved when a large
ANAEROBIC prokaryote ingested smaller bacteria and stabilized
them instead of digesting them. This AEROBIC bacteria
developed into mitochondria. Flagella may have arisen through the
ingestion of spiral-shaped bacteria called spirochetes.
Chloroplasts most likely evolved from the ingestion of prokaryotes
that resembled present-day photosynthetic cyanobacteria.
Video
Why are most cells so small?
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As the radius of a cell increases, the volume
of the cell increases faster than the surface
area. If the volume becomes too large, the
intake of nutrients and output of wastes can’t
keep up.
Video
The yolk of an ostrich egg is the largest cell
in existence today!
B. Tissues
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A group of similar cells
specialized for the
performance of a
common function.
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1. Epithelial
2. Connective and Blood
3. Muscle
4. Nervous
C. Organs
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Several different types
of tissue working
together to perform a
common function.
Ex. – heart, lungs, liver,
kidneys, brain, skin
D. Organ System
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A group of organs working
together to perform a specific
function
Skeletal System – provides
protection for internal organs;
serves as an attachment site for
muscles, tendons, and
ligaments.
Circulatory System – brings
oxygen to all cells of the body
and delivers waste to the
kidneys.
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Integumentary System provides protection against
water and heat loss; acts as a
barrier between the body and
the outside world.
Excretory System – gets rid of
excess water, waste, and toxins
accumulated in the body.
Endocrine System – regulates
the production of hormones in
the body.
Digestive System – breaks
down food and delivers
nutrients to the bloodstream.
E. Organism
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All the organ systems
working together to
maintain a complete
living thing.
II. Cell Membranes
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A. Structure: Fluid-Mosaic
Model – portrays the cell
membrane as a thick liquid or
gel in which specific proteins
float like ice burgs.
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1. Phospholipid Bilayer – has
one polar end and one
nonpolar end. The nonpolar,
hydrophobic, tails of each
molecule face each other to
form the “filling of the
sandwich”. The polar,
hydrophilic, heads form the
“bread”. The heads are
phosphate, the tails are lipid.
Hence, phospholipid bilayer.
Coloring Page
Structure Continued
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2. Cholesterol molecules
embedded in the bilayer give it
more of a rigid structure.
3. Carbohydrates attach to the
bilayer itself, forming
glycolipids, or to the floating
proteins, forming glycoproteins.
The combination of glycolipids
and glycoproteins is called the
glycocalyx. Every cell has its
own unique glycocalyx, thus it
is termed the cell’s “fingerprint”.
This fingerprint allows for
coordinating cell behavior and
communication between cells.
Coloring Page
B. Functions
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1. Regulates material moving in or out of the
cell.
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i. selective permeability – lets some things in but
keeps others out; essential for maintaining
homeostasis.
Functions Continued
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2. Provides surface area for chemical
reactions to occur.
3. Serve as receptor sites (glycocalyx).
Movement of H2O Across the Cell
Membrane - Osmosis
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Osmosis – movement of water,
from a high concentration to a low
concentration; requires no energy
input
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1. isotonic – the solute (salt, sugar,
etc) concentration is the same both
inside and outside the cell.
2. hypertonic (more H2O) – higher
concentration of water inside the
cell, so it moves to a lower
concentration OUT of the cell
3. hypotonic (less H2O) – low
concentration of water inside the
cell, so water moves INTO the cell
to even it out.
III. Movement Across Membranes
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A. Simple Diffusion – molecules
randomly move from areas of
high concentration to low
concentration. Requires no
energy input. Ex. – spraying air
freshener through the fence of
a tennis court.
B. Facilitated Diffusion – a
molecule diffuses through a
protein channel. Still moving
from a high to low concentration
gradient requiring no energy
input. Ex. Walking through the
gate onto a tennis court.
Movement Across Membranes Cont’d
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D. Filtration – uses water
pressure or blood pressure
to force small molecules
across a membrane;
requires no energy input.
E. Active Transport – moves
molecules AGAINST the
concentration gradient for
LOW to HIGH; requires ATP
(energy). Ex. – forcing
yourself through the gate of
an extremely crowded tennis
court.
Movement Across Membranes Cont’d
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F. Endocytosis – involves the movement of large or multiple
substances into the cell.
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1. pinocytosis – the intake of fluid, “cell drinking”; arms of the cell surround the liquid
and pull it in.
2. phagocytosis – the intake of solids, “cell eating”; arms of the cell surround the
material and bring it in.
3. receptor-mediated endocytosis – involves a specific receptor protein on the cell
membrane (glycocalyx) that recognizes the molecule and binds with it, allowing it
access into the cell. Then, the arms of the cell surround the material and bring it in.
Movement Across Membranes Cont’d
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Exocytosis – the movement of materials out of the
cell