Basic Structure of a Cell
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Introduction to Cells
Cells are the basic units of organisms
Cells can only be observed under
microscope
Basic types of cells:
Animal Cell
Plant Cell
Bacterial Cell
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Number of Cells
Organisms may be:
• Unicellular –
composed of one cell
• Multicellularcomposed of many
cells that may
organize
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Cells May be Prokaryotic or
Eukaryotic
 Prokaryotes include bacteria &
lack a nucleus or membrane-bound
structures called organelles
Eukaryotes include most other cells
& have a nucleus and membranebound organelles (plants, fungi, &
animals)
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Prokaryotes
Nucleoid region
contains the DNA
•Cell membrane &
cell wall
• Contain ribosomes
(no membrane) to
make proteins in
their cytoplasm
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Eukaryotic Cell
Contain 3 basic cell
structures:
• Nucleus
• Cell Membrane
• Cytoplasm with
organelles
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Two Main Types of
Eukaryotic Cells
Plant Cell
Animal Cell
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Organelles
Very small size
Can only be observed under a
microscope
Have specific functions
Found throughout cytoplasm
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Organelles Found in Cells
Examples of Organelles include:
Endoplasmic reticulum (rough & smooth) –
canals for movement
Golgi Bodies – wrap & export proteins
Nucleolus – makes ribosomes
Lysosomes – digests & gets rid of wastes
Ribosomes – makes proteins
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Golgi Bodies
• Stacks of flattened
sacs—cisternae
• A cell may have many,
even hundreds
• Have a shipping side &
a receiving side
• Receive & modify
proteins made by ER
• Transport vesicles
with modified proteins
pinch off the ends
Transport
vesicle
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Golgi bodies
• Vesicles concentrated in the vicinity of the
golgi apparatus are engaged in the transfer of
material between parts of the golgi and other
structures
• A golgi stack has a distinct structural polarity,
with the membranes of cisternae on opposite
sides of the stack differing in thickness and
molecular composition. The two poles of a
golgi stack are referred to as the cis face and
the trans face; these act as the receiving and
shipping department of the golgi apparatus
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Lysosome
• Contain digestive enzymes
called hydrolytic enzymes
that an animal cell uses to
digest macromolecules.
They work best in an
acidic environment
• Break down food and worn
out cell parts for cells
• Programmed for cell death
(lyse & release enzymes to
break down & recycle cell
parts)
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lysosomes
• Lysosomes carry out intracellular digestion in
a variety of circumstances. Amoebas and
many other protists eat by engulfing smaller
organisms or other food particles, a process
called phagocytosis.
• The food vacuole formed in this way then fuses
with a lysosome, whose enzymes digest the
food.
• Some human cells also carry out phagocytosis.
Among them are macrophages, a type of white
blood cell that helps defend the body by
engulfing and destroying bacteria and other
invaders
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lysosomes
• We just mentioned that they use hydrolytic
enzymes to recycle the cell’s own organic
material, a process called autophagy.
• A human liver cell, for example, recycles half of
its macromolecules each weak.
• The cells of people with inherited lysosomal
storage diseases lack a functioning hydrolytic
enzyme.
• Tay-Sachs disease, for example, a lipiddigesting enzyme is missing or inactive, and
the brain becomes impaired by an
accumulation of lipids in the cells.
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Nucleolus
•
Cell may have 1 to 3
nucleoli
• Inside nucleus
• Disappears when cell
divides
• Makes ribosomes that
make proteins
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Smooth & Rough Endoplasmic
Reticulum
Smooth ER lacks
ribosomes &
makes proteins
USED In the cell
Rough ER has
ribosomes on its
surface & makes
proteins to
EXPORT
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Cell Powerhouse
Mitochondrion
( mitochondria )
Rod shape
Site of Cellular
respiration
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In Animal Cells:
Mitochondria
Active cells like
muscles have more
mitochondria
Burn sugars to
produce energy ATP
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Surrounding the Cell
Cell membrane
Lies immediately
against the cell wall
in plant cells
Made of protein and
phospholipids
Selectively permeable
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Cell or Plasma Membrane
Cell membrane
Living layer
Controls the
movement of
materials into and
out of the cell
Selectively
permeable
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Cytoplasm of a Cell
Cytoplasm
Jelly-like substance
enclosed by cell
membrane
Provides a medium
for chemical
reactions to take
place
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More on Cytoplasm
Cytoplasm
Contains organelles
to carry out
specific jobs
Examples:
chloroplast &
mitochondrion
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Control Organelle
Nucleus
Controls the normal
activities of the cell
Bounded by a
nuclear membrane
Contains chromosomes
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More on the Nucleus
Nucleus
Each cell has fixed
number of
chromosomes that
carry genes
Genes control cell
characteristics
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Plant Cell Organelles
Chloroplast
Contain the green
pigment chlorophyll
Traps sunlight to
make to make
sugars (food)
Process called
photosynthesis
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Plant Cell
Cell wall
Dead layer
Large empty spaces
present between
cellulose fibers
Freely permeable
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Plant Cell
Cell wall
Made of cellulose
which forms very
thin fibers
Strong and rigid
Found in plant cells
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Plant Cell
Cell wall
Protect and support
the enclosed
substances
(protoplasm)
Resist entry of
excess water into
the cell
Give shape to the cell
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Plant Cell Organelles
Vacuole
Have a large central
vacuole
Surrounded by tonoplast
Contains cell sap
Sugars, proteins,
minerals, wastes, &
pigments
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Different kinds of plant
cells
Onion Epidermal Cells
Guard Cells
root hair
Root Hair Cell
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vacuole
cytoplasm
nucleus
mitochondrion
glycogen
granule
Animal cell
No cell wall or
chloroplast
Stores glycogen
in the
cytoplasm for
food energy
cell
membrane
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Animal Cell Organelles
• Near the nucleus
• Paired structures
• Help cell divide
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Different kinds of animal
cells
white blood cell
Amoeba
red blood cell
muscle cell
cheek cells
sperm
nerve cell
Paramecium
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Similarities between plant
cells and animal cells
Both have a cell membrane
surrounding the cytoplasm
Both have a nucleus
Both contain mitochondria
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Differences between plant
cells and animal cells
Animal cells
Plant cells
Relatively
smaller in size
Relatively
larger in size
Irregular shape
Regular shape
No cell wall
Cell wall present
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Differences between Plant
Cells and Animal Cells
Animal cells
Plant cells
Vacuole small or
absent
Large central
vacuole
Glycogen as food
storage
Starch as food
storage
Nucleus at the
center
Nucleus near cell
wall
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Compound Microscope
• Instrument for
observing small
objects
• Magnify images
up to 2000X
their size
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Different parts of
a microscope
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Revolving
nosepiece
Eyepiece
Clip
Body tube
Coarse
adjustment
Fine adjustment
Condenser
Arm
Iris diaphragm
Stage
Objective
Mirror
Condenser
control knob
Base
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The cell is the Basic Unit
of Life
• Cell is the smallest unit of living organisms
• Unicellular organisms are made of one cell
only
• The cells of multicellular organisms are
specialized to perform different functions
– e.g. mesophyll cells for photosynthesis
and root hair cells for water absorption
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Levels of organization
• Cells are
grouped
together and
work as a
whole to
perform special
functions
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Tissue
• A group of similar cells to
perform a particular function
– Animals : epithelial tissue,
muscular tissue
– Plants : vascular tissue,
mesophyll
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Organ
• Different tissues group together
to carry out specialized functions
– Heart : consists of muscles,
nervous tissue and blood
vessels
– Leaf : consists of epidermis,
mesophyll and vascular tissue
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The Structures of a Leaf
(Plant Organ)
Chloroplast
Palisade
Mesophyll Cell
Spongy Mesophyll
Cell
Air Space
Stoma
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The Structures of a Heart
(Animal Organ)
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System
• Several organs and tissues work together
to carry out a particular set of functions in a
co-ordinated way
– Human : digestive, respiratory, excretory,
circulatory and reproductive systems
– Plant : root and shoot systems
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Human Body Systems
Examples of systems :
 Digestive System
 Respiratory System
 Circulatory System
 Nervous System
 Reproductive System
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Examples of a Human Body System
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Examples of a Human Body System
The Respiratory System
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Examples of a Human Body System
Circulatory System
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Examples of a Human Body System
Nervous System
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Levels of Organization
CELLS
(muscle cells,nerve cells)
TISSUES (muscle, epithelium)
ORGANS (heart, lungs,
stomach)
SYSTEMS (circulatory system)
ORGANISM (human)
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It’s You!
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