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Chapter 2
Cells
Comparing Cells
• Cells differ in size and shape
depending on their function
– Ex: nerve cell needs to
communicate between places,
so it is a long cell
– Ex: a muscle cell can contract
and change it’s shape
• Two cell types:
• Prokaryotic – lack
membrane-bound internal
structures
• Eukayrotic – contain
membrane-bound internal
structures
Cell Organization
Cell wall
– Tough, rigid outer coverings
that protect the cell and give it
shape
– Made of cellulose
– Only in plants, algae, fungi and
most bacteria
– “frame of a house”
• Cell Membrane
– A protective layer around all
cells
– Inside the cell wall, if it is
present
– Allows food and gasses into
the cell and waste products out
of the cell
– “the bouncer”
Cell Structures
• Cytoplasm
– A gelatin-like substance
inside the cell membrane
– Medium for things to move
about in the cell
• Cytoskeleton
– Scaffolding-like structure in
cytoplasm which helps cell
keep its shape
• Organelles
– Membrane bound
structures inside eukaryotic
cells that helps the cell
perform life processes
Cell Structures
• Nucleus
– Organelle that directs
all cell activities
– Contains instructions
for everything a cell
does (within the DNA)
– “foreperson”
Cell Structures
• Chloroplasts
– Organelles in plants and a
few bacteria that help the
organism make food
– Photosynthesis occurs
here
• Mitochondria
– Organelles in all
eukaryotes that release
the energy from food and
turn it into something the
organism can use
– “powerhouse”
Cell Structures
• Ribosomes
– Organelles that make proteins
– Produced in the nucleus
• Endoplasmic Reticulum (ER)
– Series of folded membranes from
the nucleus to the cell membrane
– Moves materials around in a cell
• Two types of ER
– Rough – ribosomes are attached
– Smooth – no ribosomes attached
• Material movement and lipid
processing
Cell Structures
• Golgi Bodies
– Sort proteins and other cellular
substances and package them
into membrane-bound structures
called vesicles
– “post office”
• Vacuoles
– Organelles that serve as
temporary storage for materials
• Can be water, waste products,
food, etc.
– Vacuoles make up most of the
volume of plant cells
Cell Structures
• Lysosomes
– Organelles that
contain digestive
chemicals that help
break down food
molecules, cell
wastes, and worn-out
cell parts
– “recycler”
From Cell to Organism
• Cell
• Tissues
– Groups of similar cells
working together on one
job
• Ex: muscle tissue, nervous
tissue
• Organ
– Different types of tissues
working together
• Ex: muscle, brain
From Cell to Organism
• Organ System
– A group of organs working
together on a particular function
• Ex: muscular system, nervous
system
• Organism
– All of organ systems working
together to create a particular
organism
Review Questions
1.
2.
3.
4.
5.
6.
7.
Explain the important role of the nucleus in the life of a
cell.
Compare and contrast the energy processing
organelles.
Why are digestive enzymes in a cell enclosed in a
membrane-bound organelle?
How are cells, tissues, organs and organ systems
related?
How is the cell of a one-celled organism different from
the cells in many-celled organisms?
What are some differences between plant and animal
cell?
List 3 organelles and give their functions.
Early Microscopes
• Dutch reading glass
maker put two lenses at
ends of a tube (1500s)
– Larger image
• Antonie van
Leeuwenhoek (Dutch
fabric merchant)
– First simple microscope (p.
50 in book)
– Could magnify up to 270
times
Modern Microscopes
• Use lenses to bend light
• A simple microscope has one lens
while a compound microscope
(what we have here) has mulitple
lenses
– Ex: one lens at 10x – 10 times bigger
• Two lenses at 10x – 100 times bigger
• Stereomicroscopes have two
eyepieces, which create a threedimensional image
Electron Microscopes
• Use a magnetic field inside a
vacuum to bend electronic
beams
– Scanning Electron
Microscope (SEM) bounce
electrons off the sample to
create a 3-D image
– Transmission Electron
Microscope (TEM) send
electrons through a sample
to see internally
• Either way, electons then end
up on a screen to produce an
image (kind of like older TVs)
Cell Theory
• 1665, Robert Hooke
looked at cork under
a microscope
– Made of little boxes he
named cells
• 1830s, Matthias
Schleiden studied
plant parts
– Concluded all plants
are made of cells
Cell Theory
• Theodor Schwann looked at
animal cells
– Concluded all animals are
made up of cells
• Rudolf Virchow
– Said that cells come from other
cells that already exist
Cell Theory
• All organisms are
made up of one or
more cells
• The cell is the basic
unit of organization in
organisms
• All cells come from
pre-existing cells
Review Questions
1. Explain why the invention of the microscope
was important in the study of cells.
2. What is stated in the cell theory?
3. What is the difference between a simple
microscope and a compound microscope?
4. What was Virchow’s contribution to the cell
theory?
5. How do electron microscopes work?
6. Why would it be better to look at living cells
rather than dead cells?
Cell Processes
• Passive Transport – the movement of substances
through a cell membrane without the use of energy
– Diffusion or Osmosis
• Active Transport – the movement of substances
through the cell membrane using energy
• Endocytosis & Exocytosis – vesicles transport large
materials into (endocytosis) and out of (exocytosis) the
cell
Cell Processes
• Photosynthesis
– The process plants and other
organisms use to convert
sunlight energy into chemical
energy or sugars to be used as
food
• Respiration
– The process in which chemical
reactions break down food
molecules into simpler
substances and release stored
energy
• Fermentation
– Cells that do not have enough
oxygen for respiration use this
process to release some of the
stored energy in glucose
molecules
Cell Processes
• Cell Division – process where one cell splits into two
cells
• Mitosis – process in which the nucleus divides to form
two identical nuclei
– Four stages: Prophase, Metaphase, Anaphase, Telophase
– Happens during growth of organism or during asexual
reproduction
• Meiosis – process in which the nucleus divides to form
cells with half the genetic material of the original
– Eight Stages: Prophase I, Metaphase I, Anaphase I, Telophase I,
Prophase II, Metaphase II, Anaphase II, Telophase II
– Happens when an organism produces gametes (sex cells) for
sexual reproduction
Review Questions
1. What is active transport?
2. What are the two main types of passive
transport?
3. How do cells get large materials out?
4. What is photosynthesis?
5. What is respiration?
6. What is mitosis and when does it happen?
7. What is meiosis and when does it happen?