The Discovery of the
Cell
¨ The invention of the microscope was key to the discovery of the
cell.
Early Microscopes
¨ In the mid-1600’s scientists began to use microscopes to observe
living things.
¨ In 1665, Robert Hooke used an early compound microscope to look
at a thin slice of cork.
¨ The cork seemed to be made of thousands of tiny, empty chambers.
¨ Hooke called these chambers “cells” because they reminded
him of a monastery’s tiny rooms, which were called cells.
¨ But, today we know that cells are not empty chambers but contain
living matter.
¨ In Holland, Anton van Leeuwenhoek used a single-lens microscope
to observe pond water and other things.
¨ He observed a world of tiny living organisms that seemed to be everywhere.
The Cell Theory
¨ Cells are the basic unit of life.
¨ In 1838, German botanist Matthias Schleiden concluded that all plants
were made of cells.
¨ The next year, German biologist Theodor Schwann stated that all
animals were made of cells.
¨ In 1855, German physician Rudolf Virchow concluded that new cells
could be produced only from the division of existing cells.
¨ This lead to the cell theory:
1. All living things are composed of cells.
2. Cells are the basic units of structure and function in living things.
3. New cells are produced from existing cells.
Processes of the Cell
1. Nutrition – Food
molecules needed to supply energy
and building materials in cells. Some make their own,
others get it from their environment.
2. Digestion – Food is broken down
into simpler forms so
cells
can use them.
3. Absorption – Intake of water,
food, ions and other
needed
materials from the environment.
4. Biosynthesis
– Cells make organic substances like
carbohydrates,
fats and proteins. It is necessary for growth and the production of enzymes to
control cell activity.
5. Respiration - The step wise release of energy
from
food. The
energy for cell activity is released from
food burning O2 and used CO2
is given off.
6. Excretion –
When waste materials are given off from
the
cells activities and released into its environment.
7. Secretion – Vitamins and hormones
are molecules
synthesized
by special cells. These are secreted to affect the activities of other cells.
8. Response – Cell activity may
change due to stimuli such
as
heat, light, pressure or chemicals.
9. Reproduction – Cell division
occurs regularly and
orderly. In complex organisms, division results in a larger number of cells in the organism. In unicellular organisms, it leads to more organisms.
Prokaryotes
and Eukaryotes
¨ Cells come in a great variety of shapes and an amazing range of sizes.
¨ Typical cells range from 5 to 50 micrometers in diameter with the smallest being
mycoplasma bacteria at 0.2 micrometers across.
¨ All cells have two characteristics in common:
Ø
They are surrounded by a barrier called a cell membrane.
Ø
They contain the molecule that carries biological information
– DNA.
¨ Cells fall into two categories depending on whether they contain a nucleus.
¨ The nucleus is a large membrane-enclosed
structure that contains the cell’s genetic material in the form of DNA.
¨ The nucleus control the cells activities. (The Brain)
¨
Eukaryotes are cells that contain nuclei.
¨
Prokaryotes are cells that do not contain nuclei.
Prokaryotes
¨ Characteristics of prokaryotes
v
smaller
and simpler than eukaryotes
v
genetic
material is not contained in a nucleus
v
carry
out every activity associated with
living
things (grow, reproduce, respond, move)
v
all bacteria
are prokaryotes
Eukaryotes
¨ Characteristics of eukaryotes
v
larger and more complex than prokaryotes
v
contain dozens of structures and internal membranes
v
highly specialized
v
genetic material is contained within a nucleus and
is separated from the rest of the cell
v
some live solitary lives as single-celled organisms,
protists
v
others form large, multicellular organisms such as
plants, animals, fungi
