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Notes – Cells
I. Evolution of the current cell theory
A. Anton von Leeuwenhoek invented the first Microscope in the 17th century. He used it to become
the first person to observe and describe microscopic organisms and living cells.
B. Robert Hooke used the microscope to describe the empty chambers of cork as “Cells”. Hooke was
the first person to use this term.
C. In the mid 1800’s Scientists used different observations to come up with the modern cell theory.
Matthais Schleiden - concluded that all plants are made of cells
Theodor Schwann - concluded that animals are made of cells
Rudolf Virchow - studied cell reproduction
II. The Traditional Cell Theory
A. living things are composed of one or more cells
and cells come from existing cells by the process of cell reproduction
B. cells are the basic units of structure and function of all living things
C. cells contain specialized structures to perform functions necessary for life
The Modern Cell Theory
(in addition to the tenants of the traditional cell theory), it states
A. Energy flow (metabolism and biochemistry) occurs within cells
B. Cells contain hereditary information (DNA) that is passed from cell to cell during cell
division
C. All cells are basically the same in chemical composition in organisms of similar species
III. 2 Basic Types of cells
A. Prokaryotic cells
Simple structure. Cells that DO NOT contain membrane bound organelle.
Most of the unicellular organisms are prokaryotes such as Bacteria.
Metabolism takes place in cytoplasm.
B.
Eukaryotic Cells
Complex structure. Cells that contain membrane bound organelle.
Most of the multicellular organisms are made up of Eukaryotic cells.
e.g. – higher plants and animals.
Exception is Amoeba, Yeast which are unicellular Eukaryotes.
Different parts of the cells perform different functions.
Eukaryotic cells are larger, 100 times bigger than prokaryotic cell.
IV. Cell Structure
The number and kind of organelles differ according to cell function.
(Refer to the Cell Organelle Chart for Organelles’ description and function)
V. Cell Differences
A. Plant cells have cell wall which contains cellulose. Animal cells do not have a cell wall.
B. Plant cells have plastids, which make or store food. An example is a chloroplast.
C. Plant cells have larger, more numerous vacuoles, which are membrane-bound sacs that serve as a
storage area of proteins, wastes, ions, etc.
D. Cell shape is determined by function. Blood cells are round so they can squeeze through tiny blood
vessels.
E. Most cells are small because a small cell has more surface area than a large cell for a given volume
of cytoplasm and it is easier for a cell’s nucleus to control a smaller amount of cytoplasm.
VI. Crossing the Cell Membrane
A. Cell takes in food, water and eliminates waste through cell membrane.
Cell membrane is semi-permeable. It regulates what enters and leaves the cell. It lets some
molecules pass through and keeps out other molecules.
B. Cell membrane also provides protection and support.
C. Fluid Mosaic Model - Cell membrane is composed of phospholipids bilayer, with embedded
protein channels and carbohydrate molecules attached to proteins and hence called as mosaic of
molecules.
D. Cellular Transport – Every living cell contains a liquid interior and is surrounded by liquid.
Cell membrane regulates movement of molecules from one side to the other. Molecules pass
through the cell membrane different ways.
1. Diffusion
a. In a solution, molecules move constantly and spread out randomly. Molecules move
from area of high concentration to areas of lower concentration until equilibrium is
reached
No energy is required; passive transport
Passive
b. Osmosis is the diffusion of water.
transport
Isotonic - same strength, Hypertonic - above strength,
Hypotonic - below strength.
c. Oxygen, carbon dioxide and water pass freely across the cell membrane.
2. Facilitated Diffusion
a. uses protein tunnels or carrier proteins to move molecules through the membrane
b. no energy is required
Active
transport
3. Active transport
a. requires energy to move molecules across membrane
b. moves from an area of lower concentration to an area of higher concentration
4. Bulk Transport
a. Phagocytosis - large molecules are packaged in membrane-bound sacs and moved
in and out of cell
b. Removal of material from cell is exocytosis and taking material into the cell by
means of infoldings is endocytosis
VII. Levels of organization
The levels of organization in a multicellular organism are individual cells, tissues, organs, organ
systems