CELL NOTES
Cell Discovery
-(1665) Robert Hooke used a microscope to examine cork and described
the many tiny boxes he saw as cells. His was viewing the remains of
dead plant cells.
-(1673) Anton van Leeuwenhoek was the first to view living cells
through his microscope. This opened a whole new world, the world of
microscopic organisms.
Cell Theory
-All living things are composed of cells
- Cells are the basic unit of structure and function in all living things.
-Cells come from the reproduction of existing cells
Cell Diversity
Size- Cells vary in shape and size. A few are visible with the naked eye
such as a chicken or frog egg. Most are microscopic. Cells are limited in
size by the ratio between their outer surface and their volume. The
surface area must be large enough to allow the materials the cell needs to
enter through the surface.
Shape- Cells differ in shape due to their function.
Ex. Nerve cells have long extensions to transmit nerve impulses.
Skin cells are flat in order to cover the body’s surface.
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Prokaryotes
A unicellular organism that lacks a membrane bound nucleus and
other organelles. These organisms are placed in two kingdoms,
separate from Eukaryotes.
Ex. Bacterium
Eukaryotes
Organisms whose cells contain a membrane-bound nucleus and other
organelles are called eukaryotes.
Ex. Plants, animals, fungi
Cell Membrane
The cell membrane is selectively permeable which means it allows
some substances to cross the membrane while others cannot. The
membrane’s structure depends upon the cell’s job.
Membrane Structure:
1. Lipids
Made up of phospholipids with a polar head and two nonpolar
tails. The head will orient towards water and the tail away from
water. Both sides of the cell membrane are surrounded by water
molecules. This results in the lipid bilayer. Steroids are located in
between the tails.
2. Proteins
Peripheral proteins are located on the interior and exterior of the
membrane. Integral proteins are imbedded in the bilayer . Some
extend through the membrane and are exposed to the inside of
the cell and the outer environment.
3. Fluid Mosaic Model
The lipid bilayer behaves like a fluid. The lipids and proteins
can move laterally in the bilayer.
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Passive Transport
Equilibrium- when the concentration of molecules of a
substance is the same throughout a space.
Direction of Osmosis- depends on the concentration on both
sides of the membrane.
a. Hypotonic-a solution with a concentration of solute lower
than the concentration inside the cell
b. Hypertonic- Solution with a higher concentration of solute
than the concentration in the cell.
c. Isotonic- a solution with a concentration equal to the
inside of the cell.
If the solution outside the cell is hypertonic to the cytosol, then the
cytosol is hypotonic to the solution and the reverse is true.
Contractile vacuole- an organelle in unicellular, fresh water organisms
that is used to remove water from the cell . Water constantly diffuses
into these organisms.
Organelles
nucleus-
cell wall-
chloroplast-
golgi body-
vacuole-
lysosomes-
mitochondria-
ribosomes-
chromatin-
cytoplasm-
centrioles-
endoplasmic reticulum
rough-
smooth-
microtubule-
Plant Cells/Osmosis
Turgor pressure- pressure water molecules exert of the cell wall. Makes
a plant erect.
Plasmolysis- in a hypertonic environment, water leaves the cell through
osmosis and the turgor pressure is lost. This is the reason plants wilt.
Active Transport
Endocytosis- process by which cells ingest external fluid,
macromolecules, large particles and other cells. A portion of the cell
folds around the material and forms a pouch. The pouch pinches off and
becomes a membrane bound organelle called a vesicle.
a. Pinocytosis- endocytosis involving solutes or fluids.
b. Phagocytosis- endocytosis of large particles or whole cells.
Ex. Cells ingest bacteria and viruses by phagocytosis.
Exocytosis- the reverse of endocytosis. Vesicles in the
cytoplasm fuse with the cell membrane and release their
contents from the cell. This process is used to deliver proteins
produced by the ribosomes to the outside of the cell.
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