Download NOTES CH. 7 The Cell

CELL STRUCTURE AND FUNCTION (Ch. 7)
Cell – basic structural and functional unit of all living organisms.
The Cell Theory
 Anton van Leeuwenhoek (1600s) – used a simple light
microscope. He saw living organisms in pond water, milk, etc.
 Robert Hooke (English – 1600s) – studied cork and oak bark.
First to use the word – CELL.
 Schleiden and Schwann formulated Cell Theory:
CELL THEORY:
 All organisms are composed of one or more cells.
 The cell is the basic unit of structure and organization of
organisms
 All cells come from preexisting cells.
Microscopes:
 Light microscopes – uses light (1000x actual size)
 Electron microscopes – uses a beam of electrons instead of
light (500,000x actual size). Specimens must be in a
vacuum.
1. Scanning Electron Microscope (SEM) – 3-D shape
2. Transmission Electron Microscope (TEM) – study
structures within a cell.
TWO types of CELLS:
1. Prokaryotes
 do not have membrane-bound organelles
 most are unicellular
 ex. bacteria
 primitive, small
 no nucleus
2. Eukaryotes
 contain membrane-bound organelles
 most make up multi-cellular organisms
 contains a nucleus – central organelle that manages all
cellular functions
 larger
Cell wall  rigid structure located outside the plasma membrane
 used for additional support and protection
 ex. plants, fungi and bacteria
 Composed of cellulose which is porous. It does not select
which molecules enter or leave
Organelles – small, specialized structures contained within
the cell. Each organelle has a specific function.
Structure
Cell membrane
Function
Selective permeability
Cell Type
All
Cell wall
Support, protection, cellulose, Prokaryotes and
thick tough mesh fibers, very Eukaryotes
porous
(except animal
cells)
Nucleus
Directs activities of other
organelles, two membranes
Eukaryotes
Ribosomes
Site of protein synthesis
All
Cytoplasm
Clear gelatinous fluid
All
Endoplasmic Reticulum
Cellular chemical reactions,
site of protein synthesis,
rough due to ribosomes
Eukaryotes
Golgi Apparatus
Packages proteins in vesicles Eukaryotes
(membrane bound structures)
Vacuole
Storage of food, water,
enzymes, waste
Large in plant
cells,
Small or not
present in animal
cells
Lysosome
Digests excess or worn out
organelles, digests bacteria
and viruses
Can fuse with vacuoles and
digest contents
Can digest cells (tadpole’s
tail)
Converts light energy to
chemical energy
Eukaryotes
Transforms energy
Folded membrane – increases
surface area and maximizes space
for energy production
Eukaryotes
Chloroplasts
Mitochondria
Plant cells, some
algae, some
protists
Cytoskeleton
Supports and anchors organelles,
provides highway system through
which materials move
All
Centrioles
Microtubules used for cell division
Animal cells and
protists
Cilia
Short hairs on outside of cell used
for Locomotion or feeding,
Like oars in a rowboat
Unicellular
Flagella
Whip-like tail for locomotion
Unicellular
The Plasma Membrane –
 flexible boundary between the cell and its environment. It
allows nutrients to enter and waste to leave. Acts to maintain
homeostasis (maintaining balance).
 Selective Permeability – process in which a membrane allows
some molecules to pass through while keeping others out.
(screen door).
 Composition of the Plasma Membrane
 composed of a phospholipid bi-layer – has two layers of
phospholipids
 “tails” of the phospholipid molecule are nonpolar (avoid
water) fatty acids
 “heads” of the phospholipid molecule are polar (attract
water) phosphates
 this creates a barrier that is water-soluble at the outer
surface and water in-soluble in the middle so water-soluble
molecules will not easily move through the membrane
because they are stopped by the water in-soluble layer
 called “fluid-mosaic model” – proteins move along the
membrane
 transport proteins move needed substances or waste
materials through the plasma membrane.
 cholesterol – prevents the fatty acid “tails” from sticking
together
 proteins and carbohydrates stick out from the surface to
identify chemical signals
Fluid Mosaic Model:
CELLULAR TRANSPORT
 Diffusion – net movement of particles from an area of
higher concentration to an area of lower concentration.
This occurs because of brownian motion – the
random movement of atoms and molecules. Diffusion
occurs until dynamic equilibrium is reached. Diffusion
is affected by:
 temperature (↑ temperature, ↑ diffusion)
 concentration (↑ concentration, ↑ diffusion)
 pressure (↑ pressure, ↑ diffusion)
 Concentration gradient – the difference in
concentration across a space. Diffusion occurs until
there is no longer a concentration gradient.
Osmosis – diffusion of water across a selectively permeable
membrane.
1. Isotonic solution – dissolved substances are the same outside
the cell as inside the cell. Experiences osmosis but retains
shape.
2. Hypotonic solution – concentration of dissolved substances is
lower in the solution outside the cell so there is more water
outside the cell than inside. Water flows into the cell causing
the cell to swell.
3. Hypertonic solution – concentration of dissolved substances is
higher in the solution outside the cell so there is less water
outside. Water flows out of the cell causing it to shrivel. ex.
wilting plants.
Passive Transport – requires no energy because movement is
within the concentration gradient. Passive transport can occur
by:
 simple diffusion
 facilitated diffusion – requires transport proteins (channel
proteins) to form channels
Active Transport – movement of materials through a membrane
against the concentration gradient. Requires energy from the
cells.
 carrier protein combines with a specific molecule or ion thus
allowing chemical energy to be used to change the shape of
the carrier protein
 Endocytosis - cell surrounds and takes in large molecules.
Engulfed and enclosed by a portion of the cell membrane.
 Exocytosis – reverse of endocytosis. Explulsion of materials
from a cell. Uses this method to expel wastes.