Unit 1 – Levels of Organization
Chapter 3 - Cells
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75 million cells in your body
Vary in shape. Shape is related to its
function.
Vary in size. i.e. nerve cells have
long thread like extensions to
transport nerves
Cells are basic units of life.
3 Major Parts
 Cytoplasm - all the organelles located in
cytoplasm
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Shape – varies; clear jelly like; also called cytosol
Function – hold organelles in place and site of
metabolic reactions
Nucleus – centrally located
 Nuclear envelope
 Nucleolus
 Chromatin
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Cell Membrane – encloses cytoplasm and
all the organelles.
 Shape – varies in shape; very thin; very
flexible
 Function – controls the movement of
substances in and out of the cell.
 Selectively permeable – allows certain
things in and certain things out; also
called semipermeable or differentially
permeable.
 Phospholipid bilayer – structure is made
of lipids and proteins in two layers
Citation:
http://library.thi
nkquest.org/C0
04535/cell_mem
branes.html
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Membrane Protein – extend through the lipid
bilayer
Peripheral Protein – only one side of bilayer
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Cell Membrane – see earlier notes
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Endoplasmic Reticulum (ER)–
Shape - flattened sacs with canals filled with fluid &
surrounded by a membrane
 Function – communication system in which molecules
can be transported from one part of a cell to another
part
2 Types of ER:
Smooth ER – makes lipids, absorbs fat, breaks
down drugs & alcohol
Rough ER – makes proteins

Citation:
imcurious.wikispaces.com
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Ribosomes –
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Golgi Apparatus –
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Shape – round organelles attached to ER or free in
cytoplasm
Function – make protein (recall protein synthesis)
Shape – stack of about six flat sacs
Function – packaging the proteins after made by the
ribosome
Mitochondria –
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Shape – bean shaped, fluid filled sac with cristae
Function – energy is made and transformed into a
chemical form the cell can use;
Mitochondria
Golgi
Apparatus
Citation: cartage.org.lb
Citation: library.thinkquest.org
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Lysosomes –
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Shape – tiny, membranous sacs
Function – contain powerful enzymes that break
down molecules of nutrients or foreign particles in
cell or old cell parts
Peroxisomes –
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Shape – membranous sacs
Function – hold enzymes inside sac which help with
biochemcial reactions
Lysosome
Citation: micro.magnet.fsu.edu
Citation: mrelderteaching.ca
Peroxisome
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Microfilaments & Microtubules –
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Microfilaments
Shape –tiny rods of actin protein
Function – form internal skeleton of cell to
give cell it’s shape
Microtubules
Shape – long, slender tubes and fatter than
microfilaments
Function - form internal skeleton of cell to
give cell it’s shape
Centrosomes –
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Shape – nonmembranous, two hollow cylinders that
lie at right angles of each other; located near Golgi
Function – aid in moving chromosomes
Citation: teachernotes.paramus.k12.nj.us
Microfilaments & Microtubules
Citation: protopage.com
Centrosome
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Vesicles –
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Shape – membranous sac (bulb shaped)
Function – cell membrane surrounds a substance
(liquid or solid) outside cells to bring it into cell
Cilia & Flagella – (external)
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Cilia –
Shape – many tiny hair like projections on the surface
of epithelial cells
Function – moves fluids; aids in movement
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Flagella Shape – one strand of hair like projection
Function – moves fluid; aids in movement
Citation:
williamsclass.com
Cilia
Citation: microscope-microscope.org
Flagella
Citation: kconline.kaskaskia.edu
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Nucleus –
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Shape – round structure found neat the center of the cell
Function – controls all activity
3 Parts:
Nuclear Envelope –
Shape – inner and outer membrane that is porous
Function – allows substances in and out through pores
Nucleolus Shape - no membrane, small dense area in nucleus
Function - help produce ribosomes; composed on RNA &
protein
Chromatin –
Shape – loosely coiled fibers made of protein and DNA
Function – contains all the genetic information
Citation:
micro.magnet.f
su.edu
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Substances can enter and leave cells in 2
ways:
 Passively:
4 types: diffusion, facilitated diffusion,
osmosis, filtration
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Actively:
3 types: active transport, endocyotsis,
exocytosis
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Diffusion – movement of particles from an
area of greater concentration to an area of
lower concentration
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No energy used
Facilitated Diffusion
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Occurs when molecules are too large to pass through
a membrane by themselves so a protein carrier
molecules moves the particle (i.e. glucose and a.a.)
No energy is used
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Osmosis – movement of water molecules to
make an area of greater concentration of a
substance to a lesser concentration of a
substance through a membrane
 Hypertonic – water leaves a cell that has a greater
concentration of substances on outside
 Hypotonic – water enters a cell that has a greater
concentration of substances inside the cell
 Isotonic – same concentration on the outside of the cell
as the inside
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Filtration - molecules being forced through
membranes
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Common in separating solids from liquids
No energy used
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Active Transport – process that moves
particles through membranes from a region of
low concentration to a region of high
concentration
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Uses energy
Exocytosis – movement of molecules out of a
cell that are too large to leave the cell through
diffusion or active transport.
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Endocytosis – movement of molecules into a
cell that are too large to enter cells through
diffusion or active transport.
3 Types:
1. Pinocytosis – cells take in liquid from outside to
inside of cell
2. Phagocytosis – cells take in solids from outside to
inside of cell
3. Receptor-mediated endocytosis – moves very
specific kinds of particles into cell by binding to
them first (i.e. cholesterol gets into body this way)
Citation:cellbiology.med.unsw.edu.au
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Interphase – cell grows and duplicates much of
its contents
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3 steps in Interphase:
 G1 Phase – cell growth & organelles duplicate
 S Phase – genetic material replicates
 G2 Phase – cell growth & organelles duplicate
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Mitosis – dividing of a cell into two portions;
division of nuclear parts and division of
cytoplasm
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4 Steps in Mitosis:
 Prophase – two set of chromosomes appear
throughout the nucleus ; nuclear envelope breaks
down; spindle fibers start to form out of centrioles.
 Metaphase – chromosomes line up in the middle of
the cell; spindle fibers attach to chromosomes
 Anaphase – chromosomes separate and the
chromatids move to separate ends of the cell
 Telophase – chromosomes begin to elongate and
change back into chromatid form, nuclear envelope
reappears, spindle disappear
Citation: biologycorner.com
Citation: qwickstep.com
Citation: microscopy-uk.org.uk
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Cytokinesis – total division of the cytoplasm to
form two new cells
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Pinching in of the cell membrane causes a division
between the two new nuclei to form two new cells
They are identical cells that contain the identical
DNA in the nucleus
Citation:
biology.iupui.edu
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Cell division that occurs only in sex cells (sex
cells are sperm and eggs)
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Same process as mitosis BUT the steps occur twice to
get ½ as much DNA in the cell
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Specialization – cells develop special
structures or begin to function in different
ways
Differentiation – cells develop different
characteristics in structure and function; all due
to what the DNA says
Throughout life certain cells – stem cells – remain
unspecialized in order to retain the potential to
produce new differentiated cells.
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Cell death is called apoptosis.
A normal part of development.
Example: webbing between the fingers and toes of a
fetus go through apoptosis to disappear
 Example: apoptosis occurs following a sunburn so
the damaged cells peel away and don’t turn
cancerous
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