Cell Facts and Tissues
(rev 3-10)
Cells are the smallest structural and functional unit of life
• All cells are surrounded by a thin, outer membrane called
the plasma membrane (PM).
– This separates the cell from interstitial fluid which
bathes the outside of the cell.
• On the inside of the cell is a gel-like fluid called
cytoplasm. This contains specialized structures called
organelles and the nucleus, a small circular body.
The Plasma Membrane
• Forms the outer boundary of the cell
– Composed of 2 layers of fat molecules called
phospholipids and another kind of fat molecule
called cholesterol
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• The plasma membrane (PM) keeps the cell whole and
intact
– It serves as a gateway (entrance) between the fluid
inside and outside the cell
– It identifies a cell as belonging to one particular
person; the cell’s surface proteins act as identification
tags (each person has different surface proteins)
Cytoplasm: composed of a gel-like fluid called cytosol
– Lies between the PM and the nucleus
– Contains Organelles: structures with specialized
functions which are located in the cytoplasm.
• Also contains a nucleus.
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Nucleus:
• Controls every organelle in the cytoplasm and the cell
reproduction process because it contains the genetic
code—instructions for making proteins, which in turn
determine cell structure and function
• directs all functions of the cell.
Structural features:
• Outer surface is a double-layered nuclear membrane,
also called nuclear envelope.
• Contains 46 chromosomes which contain DNA,
the genetic code
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Figure 3.19a
Organelles
Ribosomes: tiny particles found throughout the cell;
responsible for making enzymes and other protein
compounds
– Made up of 2 tiny subunits mostly made up of a
special kind of RNA— called ribosomal RNA
– Ribosomes may be attached to the Endoplasmic
Reticulum
– Free floating ribosomes produce proteins for use
by the cell
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Endoplasmic reticulum (ER) is a system of membranes
forming a network of connecting sacs and canals that
wind back and forth through a cell’s cytoplasm.
– manufactures proteins and chemical compounds
produced by the cell.
– The sacs and canals carry proteins and other
substances through the cytoplasm of the cell from
one area to another.
Types: rough and smooth
• Rough ER: areas where the surface is dotted with
ribosomes
– Rough ER receives, from the ribosomes, and
transports newly made proteins
• Smooth ER: Areas without ribosomes
– These areas synthesize chemicals and make new cell
membrane
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Golgi Apparatus
• Group of flattened sacs
• Called the chemical processing and packaging
center because it collects chemicals from the
smooth ER in vesicles
Mitochondria:
• Provide most of the power for cellular work;
nicknamed the cell’s “power plant”
• Enzymes found in the mitochondria use oxygen
to breakdown glucose to release energy
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Lysosomes
• contain digestive enzymes that digest food compounds
as well as other substances.
– Can destroy microbes
Centrioles: used in cell division
Cilia: fine, hairlike extensions on the free surface of some
cells; are capable of movement
Flagella: is a single projection from the cell surface; is
larger than cilia; “tails” of sperm cells are the only
example of flagella in humans
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Movement of Substances through Cell Membranes
• Occurs through passive or active transport
• Energy is required only for active transport and
is obtained from adenosine triphosphate or
ATP
– ATP is produced in the mitochondria
• Passive transport processes do not require
added energy and result in movement “down a
concentration gradient”
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• Solution terms
– Solute is a substance that dissolves into another
substance
– Solvent is a substance in which other substances are
dissolved
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Passive Transport
• Transports a molecule without requiring the cell to use
any energy; requires that there be a difference in
concentration between 2 areas, called a concentration
gradient.
• Movement is from area of high to area of low
concentration or “down” the concentration
gradient
• Primary passive transport processes are diffusion and
osmosis
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• Diffusion : movement of molecules from one
region to another as a result of random
movement;
– Molecules move from the area of higher
concentration to the area of lower
concentration
• molecules scatter themselves evenly throughout
a solution
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Diffusion
(Passive transport: no
energy required)
• Diffusion:
movement from
area of high
concentration to
low
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Osmosis is the diffusion of water across a selectively
permeable membrane (the solutes cannot cross the
membrane) from the region of lower concentration to the
area of higher concentration
• Selectively permeable means a membrane will permit
some substances to pass through it but not others
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Active transport
• Movement of substances is “up the concentration
gradient”— movement from an area of lower to higher
concentration
• Requires energy from ATP
• Ion pumps
– An ion pump is a protein structure in the cell
membrane
• Is called a “carrier”
– Ion pumps use energy from ATP to move substances
across cell membranes against their concentration
gradients
– Examples: sodium-potassium pump, calcium pump
– Some ion pumps work with other carriers so that
glucose or amino acids are transported along with
ions
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Na+-K+ Pump
3 sodium ions are
pumped out of the cell
and 2 potassium ions
are pumped in during
a pumping cycle of the
carrier molecule. ATP
is broken down and
used for energy to
pump the ions
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• Why are passive and active transport important
in the human body?
– Hint: how do substances move across the plasma
membrane?
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Body Tissues
• Tissue: group of similar cells that perform a
common function
• 4 main kinds of tissues
– Epithelial
– Connective
– Muscle
– Nervous
• Tissues differ from each other in their
– Size and shape of cells
– Amount and kind of material between the cells
– Special functions they perform
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Epithelial Tissue covers the body and lines
body cavities
– Cells packed closely together
• Can be categorized according to shape:
– Squamous (flat)
– Cuboidal (cube)
– Columnar (tall)
• Can be categorized according to
arrangement-layers of cells:
– Simple
– Stratified
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EPITHELIAL TISSUE
• Absorbs
– substances can easily pass through it for example
absorption of oxygen into the blood
• Secretes
– cells function in clusters and form glands which
make and release substances to help the body work
i.e. saliva, digestive juices, and hormones
– cells forms the urine-producing tubules of the
kidneys
• Protects tissues
– when there are several layers of closely packed
cells, microorganisms can’t get through them
– cilia move mucus and protect against entry of
foreign particles into the lung
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Connective tissue
• Most abundant tissue in body
 Most widely distributed tissue in body
 Multiple types, appearances, and functions
- Connects tissues to each other
- Forms a supportive framework for the body
and the organs
- Transports substances throughout the body
(blood is a type of connective tissue)
- Defends us against microorganisms
 Relatively few cells in an intercellular matrix
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Types of Connective Tissue
• Blood— fluid “tissue”;
– function is transportation and protection
– cells are suspended in a fluid matrix called plasma.
(Considered a connective tissue because all blood
cells derive from earlier stem cells located within
bone.)
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Areolar: glue that holds organs together
Most widely distributed type of connective tissue
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Adipose
(fat)
• specialized
to store lipids
•Oil filled
cells
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Dense
Fibrous
•Has
bundles of
collagen
fibers
arranged in
parallel
rows
•Provides
strength
and
flexibility;
does not
stretch
•example is
tendons and
ligaments
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Bone
• functions
in support
and
protection
•Stores
the
mineral
calcium
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Cartilage
•bone will
be formed
from this
type
tissue
•Matrix is
the
consistency
of firm
plastic or
a gel
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Muscle tissue:
 movement “specialist”;
 can contract
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Skeletal
Muscle
•also called
striated or
voluntary;
•attaches to
bones;
•Has striations
• is
multinucleated
• has long
cells
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Cardiac
Muscle
• also
called
striated or
involuntary
• forms
the walls
of the
heart
•has
intercalated
disks;
fibers
branch
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Smooth
•also called
nonstriated,
visceral, or
involuntary
• found in blood
vessel walls and
hollow organs
• push food and
fluids through
body
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Nervous tissue
provides rapid communication between body structures
and control of body functions
 Consists of 2 types of cells:
 Neurons—conducting cells
 Neuroglia—supportive and connecting cells
 Neurons
 Cell components
o Cell body
o Axon (one or more) carries nerve impulses
away from cell body
o Dendrites carry nerve impulses toward the
cell body
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