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Unit 4 Cell Structure, Cell Processes,
Cell Reproduction, and Homeostasis
Mrs. Stahl
AP Biology
How cells first came about!
• http://ed.ted.com/lessons/the-wacky-history-of-cell-theory
Robert Hooke • 1665
• First to identify cells by observing cork from the bark of an oak tree.
Anton Van Leewenhoek
• 1674
• Described living things and observed them in greater detail
• Discovered bacteria (we didn’t call them that yet) and called them “animalcules” because they resembles little animals moving about.
Matthias Schleiden
• 1838
• Found that plants are made of cells
Theodore Schwann
• 1839 • All living things are made of cells
Rudolf Virchow
• 1855
• Proposed that cells come from pre-existing cells
Three Major Principles of the Cell Theory
• 1. All organisms are made of one or more cells, and the life processes of metabolism and heredity occur within these cells.
• 2.All existing cells come from pre-existing cells
• 3. Cells are the basic unit of life
Cell Size
• Cells are small so that they can diffuse (go from areas high concentration to low concentration until equilibrium is met) easily throughout the body = MAINTAIN HOMEOSTASIS
• Rate of diffusion is determined by:
– 1. Amount of surface area available
– 2. Temperature
– 3. Concentration Gradient
– 4. Distance
• As the cell increases in size, the rate of diffusion will also increase. Therefore, smaller cells will move in and out of the cell quicker.
• The larger the cell the more it requires- takes longer for diffusion to occur due to it having to synthesize all of the macromolecules inside of it, transport energy, and regulate metabolic waste.
Why are they so small? Surface Area to Volume Ratio
• Small so that they can maximize surface area on the outside so that nutrients (oxygen) can enter and waste (carbon dioxide) can leave.
• If they are too small the organelles won’t fit. For this reason they could never be infinitely small.
• Surface area-to volume ratio: As a cell’s size increases, its volume increases more rapidly than its surface area.
Further Explanation
Cell where chemical reactions take place
(Volume) Substances going in Waste products being released
Draw into your
notes!
• When a cell increases in size the chemical reactions increase, which means more substances need to be taken in so that the reactions can be fueled and more waste products will be released.
• Each cell can only take in so much due to its surface area.
• When a cell increases in size the surface area doesn’t increase the same as its volume.
• When a cell increases in size the ratio of the cells surface : volume ratio decrease.
Example
• Cube 1= 1 cm.
• Cube 2= 3 cm.
• What is the surface area to volume ratio of each?
– Formulas: SA= 6a2 Volume= a3
• For cube 1: SA= 6 X 12 = 6 cm2 , V=13 = 1cm2
– Ratio= 6:1
• Cube 2: SA= 6 X 32 = 54 cm2 , V= 33 = 27 cm2
– Ratio = 2:1
What happened in Cube 2 that the ratio decreased?
What happens when SA : V ratio gets too small?
1. Substances can’t enter fast enough
2. Waste products leave slowly and can accumulate in the cell
3. Cell can’t maintain homeostasis because it is not able to lose heat fast enough
Extra Resources
• http://www.youtube.com/watch?v=wuXSEOKNxN8
• http://www.bozemanscience.com/014-environmental-matter-exchange/
How do we see cells?
• Assignment- You are to write a minimum of three, maximum of five, page paper (MLA format), with a minimum of three citations about microscopes and the different kinds. You should include:
– Why we can’t see cells
– Light, Compound, and Electron: Scanning and Transmission
– The uses of stains and why they are beneficial
– Due December 8th and 9th
Four features that ALL cells have
• 1. A nucleus or nucleoid- where DNA is stored
• 2. Cytoplasm- jellylike substance that cushions and protects all of the organelles. Also aids in transporting nutrients such as amino acids, sugars, and proteins. – Cytosol- solution in the cytoplasm that is full of organic
compounds and ions
• 3. Ribosomes- synthesize (make) proteins
• 4. Plasma or Cell Membrane- selectively permeable membrane made up of a phospholipid bilayer which picks and chooses what is allowed into the cell.
Nerve Cells
http://www.pinterest.com/pin/32088216071181270/
http://www.nature.com/naturejobs/2013/130815/images/nj7462-367a-i1.0.jpg
White blood cell engulfing a
bacteria cell and spewing
out the remnants
http://io9.com/photos-of-the-amazing-and-gruesome-world-under-a-micros-1291328130
Inside the chloroplast of a
plant cell
Eyelashes!
http://www.ebaumsworld.com/pictures/view/83877873/
http://www.ebaumsworld.com/pictures/view/83877873/
Bacteria on the tongue
Artery and blood cells
http://www.ebaumsworld.com/pictures/view/83877873/
http://www.ebaumsworld.com/pictures/view/83877873/
Clump of sperm tails in the
testes
http://www.sciencephoto.com/media/12812/enlarge
Staphylococcus bacteria in the
trachea
Liver cell
http://www.sciencephoto.com/media/310232/enlarge
Lung Cells
http://images.sciencesource.com/preview/14917208/SQ7335.html
Prokaryotic VS. Eukaryotic
Prokaryotic Cells – No nucleus or membrane bound organelles
– DNA is suspended in the cytoplasm and circular
– Single celled and chemical reactions aren’t compartmentalized, instead they operate as a single unit
– Cell Wall and cell membrane
– MreB protein which is a homologue of actin= these fibers run perpendicular, giving the bacteria cell a rod shape. When MreB is removed , the cells are spherical
– Evolved 3.5 bya
– Two main domains: Bacteria or Archaea • Divided into groups based on their need for oxygen:
– Obligate anaerobes- cannot survive in the presence of oxygen.
– Obligate aerobe- needs oxygen to survive
– Facultative aerobe- can survive whether or not oxygen is present.
Roles of Prokaryotic Cells
• Harvest light via photosynthesis
• Decomposers- break down dead organisms and recycle the nutrients back into the ecosystem
• Some do cause diseases
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Cell wall
Capsule
Flagella A typical
rod-shaped
bacterium
(a)
Bacterial chromosome
0.5 µm
A thin section through
the bacterium Bacillus
coagulans (TEM)
(b)
Structure of a Prokaryote
www.biologyjunction.com Flagella Ribosomes
Pili
DNA
Cell Wall
Cytoplasm
Cell membrane
Draw in
notes!
Functions
• Pili- help prokaryotes stick to the surfaces • Flagellum- tail like structure used for movement. • Plasmid- small piece of DNA that replicates separately
from the main chromosome. • DNA- shaped in a loop or circle and is located in the
cytoplasm. • Cytoplasm- jellylike substance that surrounds
molecules and organelles in a cell • Cell wall- structural support, protection, prevent
excessive uptake or loss of water • Cell membrane- controls the movement of substances
in and out of the cell.
Peptidoglycan
• Cell wall is composed of it
• Peptidoglycan is a carbohydrate matrix that is cross linked by short polypeptide units
• Antibiotics such as penicillin and vancomycin, interfere with the cross link and cause the entire structure to fall apart by allowing water to rush in resulting in cell rupture.
• Some disease causing bacteria secrete a jelly-like protective capsule around them which allows them to stick to surfaces (teeth, skin, nails, food) and invade.
Eukaryotic Cells
