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History of cells
Variety in cells
Cell structure
Cell processes
Cell reproduction
• Cells are the units of structure and function
of living things on earth.
• Cytology – study of cells
• Late 16th century – the
compound microscope
was invented (debate
over who really invented
it)
• Robert Hooke (1665)
was observing cork
through a microscope
and saw empty “cells”.
Many other scientists
found similar structure in
other plant and animal
tissue.
• Matthias Schleiden
(1838) proposed the cell
principle after many
observations with plants.
• Theodore Schwann
(1839) expanded the
cell principle to include
animals (all living things).
• Rudolf Virchow (1855)
added the idea that all
cells must come from
preexisting cells.
• All living things are composed of living
units called cells and of cell products and
all cells come only from preexisting cells.
• Are made of cells
• Respond to stimuli
• Grow
• Reproduce
• Maintain homeostasis
Variety in Size
• The size of an organism does not
determine the size of its cells.
• The size of an organism is determined by
the number of cells, not the size of cells.
• Most cells are microscopic, but some (like
the human egg cell) can be viewed with
the naked eye
Variety in Number
• Some cells are independent and can
carry on all life functions with only one
cell
• Most organisms will increase in number
as they age
• Humans are born with about 2 trillion
cells. An adult has 75-100 trillion cells.
Variety in Shape
• Usually cells are thought of as being
round. Most cells are not round.
• For example, some are long and round
(muscle cells), some are square (cuboidal
cells), some change shape (amoeba), some
look like alien creatures (nerve cells).
1. Nucleus – master control center of the
cell
2. Cytoplasm – fluid medium for organelles
and other molecules
3. Cell membrane – separates a cell from
its environment
• Cells are either prokaryotes or
eukaryotes
• Prokaryotes lack a nucleus and
membrane-bound organelles (ex:
bacteria)
• Eukaryotes have a nucleus, cytoskeleton,
and membrane-bound organelles (ex:
animal cell)
• We will focus on eukaryotes
• Contain the master program of the
organism in the form of DNA
(deoxyribonucleic acid)
• The nucleus is surrounded by a membrane
called the nuclear envelope.
• The nuclear envelope contains nuclear
pores which allow small proteins to pass
through
• The nucleolus is found in the nucleus and
manufactures ribosomes.
• The fluid medium of a cell
• Contains organelles and dissolved
chemicals
• Contains raw materials for cell processes,
materials to be exported, and enzymes
• Most cell processes take place in either
organelles or the cytoplasm
• Separates a cell from its external
environment.
• Regulates the flow of materials in and out
of the cell.
• The membrane is constructed of a
phospholipid bilayer. It also contains some
cholesterol that gives it flexibility.
• The membrane is made of hydrophobic
(water-fearing) tails and hydrophilic
(water-loving) heads
• Since they are arranged this way, the
membrane is self-sealing and selfrepairing
• The cell membrane has many proteins in it
that have different jobs. Some jobs are:
• Identification tags – tells the body that the
cell belongs to it
• Carriers – carry larger molecules across the
membrane
• Pumps – pump molecules back and forth
across the membrane to maintain homeostasis
• Sensors – detect hormones and relay
information to the cell about the outside
environment
• Composition/Design - Microtubules and
microfilaments made of protein
• Function - Forms the inner framework of a
cell; helps a cell maintain its shape; gives
a cell rigidity; holds organelles in place
• Composition/Design - Double membrane
with inner folds
• Function - “Power plant” of the cell;
contains enzymes that break down food
molecules and produce ATP; the energy
production process is aerobic (requires
oxygen)
• Composition/Design - RNA and protein
• Function - Fixed ribosomes are bound to
ER; free ribosomes are scattered in the
cytoplasm
• Manufacture proteins from amino acids;
proteins made by free ribosomes are
scattered in the cytoplasm; fixed
ribosomes make proteins that are
exported; found in all cells
• Composition/Design - Network of
membranous channels extending
through the cytoplasm
•RER (rough ER) – has attached ribosomes
•SER (smooth ER) – lacks ribosomes
• Function - Synthesizes proteins, carbs,
and lipids; stores synthesized
material; transports material through
the cell
•SER – makes lipids and carbs and
carbohydrates
•RER – makes proteins
• Composition/Design – Stacks of flattened
membranes containing chambers
• Function – Package proteins and other
molecules for shipment to their intended
destinations
• Composition/Design - Vesicles containing
powerful digestive enzymes; produced by
the Golgi apparatus
• Function - Cleanup and recycle in the cell;
help to fight against disease; can destroy
entire cells
• Known as “suicide packets”
• Composition/Design - containing
degradative enzymes; produced by
existing peroxisomes
• Function - Break down fatty acids and
other organic compounds; during reactions
they generate hydrogen peroxide (H2O2);
other enzymes break apart the hydrogen
peroxide into water and oxygen so it
doesn’t damage the cell
• Composition/Design – Membrane
extensions
• Function – Increase the surface area of the
membrane; found on cells that absorb
materials from the extracellular fluid
• Composition/Design - Composed of
microtubules; 2 centrioles at right angles
to each other
• Function - Create spindle fibers used
during cell division; only found in cells that
divide
• Composition/Design - Membrane
extensions containing microfilaments
• Function - Moves fluids or secretions across
a cell’s surface; ex: respiratory tract
• Composition/Design - Similar to a cilia,
but longer
• Function - Moves a cell through the
surrounding fluid; sperm the only human
cell with a flagellum
• Cell wall – only in plants; give structure to
plants
• Vacuole – found in plant and animal cells;
much larger in plant cells; storage area
• Chloroplast – only in plant cells; contain
chlorophyll; absorb energy from the sun
Homeostasis is maintaining a stable internal
environment.
Cells maintain homeostasis in a variety of
ways:
• Osmotic pressure – the right amount of
water must be inside and outside of the
cell or cells can explode or shrink
• Proper pH – pH is a measure of acid and base
concentration; a deviation of pH can disrupt cell
and tissue function
• Food and wastes – intakes nutrients and gets rid
of waste materials
• Maintenance and repair – replaces old
proteins with new ones; old proteins are
recycled by being broken down into amino
acids; preventative maintenance occurs about
every 7-10 days
In order to maintain homeostasis, cells need
energy. Energy is obtained through
photosynthesis and used through cellular
respiration.
Photosynthesis and cellular respiration are
opposite processes.
• Photosynthesis splits water molecules,
releases oxygen, and uses hydrogen and
electrons to form ATP
• In cellular respiration electrons and
hydrogen are released when glucose is
broken down and water and ATP are
formed. The rest of the sugar molecule is
carbon dioxide, which is released by the
organism.
Active transport is the movement of
molecules across the cell membrane with
the expenditure of energy.
Some methods of active transport:
• Sodium pumps – sodium ions move across
a cell membrane
• Endocytosis – taking materials into a
cell
•Phagocytosis – “cell eating”;
surrounds solid particles with the cell
membrane and engulfs them
•Pinocytosis – “cell drinking”; surrounds
liquid particles with the cell
membrane and engulfs them
• Exocytosis – taking large materials
out of a cell; some are vesicles with
waste products; some are materials
exported by the Golgi bodies
• Cilia – hair-like projections that move
some cells like paramecia through fluid
and moves fluid and air past some other
cells
• Flagella – whip-like tail that moves
euglenas, dinoflagellates, and sperm cells
• Cells will die after a certain time period.
• Lysosomes will release enzymes causing
the cell to die.
• In many organisms when one cell dies
another will take its place through the
process of mitosis.
WORKSHEET
Interphase
1. all of a cell’s normal activities
2. phase between cell division
3. they contain the same information, just
in different forms; chromosomes have the
genetic material tightly coiled up as it
waits to divide
4. they must replicate
5. each cell needs to have the same
information in it
Prophase
6. the DNA is packaged into
chromosomes
7. nucleolus and nuclear membrane
8. chromatids
9. centromere
10. centrioles
Metaphase
11. opposite ends of the cell (poles)
12. centrioles produce spindle fibers
which attach to the chromosomes
13. they line up along the equator of the
cell
14. the chromatids begin to move apart
Anaphase
15. a. chromatids are dragged to
opposite ends of the cell
b. the cell starts to constrict in the
middle
Telophase
16. a. a new nucleolus forms in each cell
b. chromosomes uncoil; turn back into
chromatin
c. two new nuclei form, one on each
end