Download Cell Reading 2 with lysosomes, golgi and vacuoles.rtf

Cells
The Cell Theory
You learned that all living things do five life processes. Living things have
something else in common. Each living thing is made up of at least one cell.
The cell is the basic structure of all living things. All bacteria, protists, fungi,
plants and animals are made of living cells.
In 1661 Robert Hooke examined the bark from a cork tree underneath the
microscope. What he saw were the cell walls of the cells, but no living material.
Over the years, more powerful microscopes let scientists observe cells in greater
detail. It was nearly 200 years after Hooke saw the cell walls that scientists
realized that these empty boxes once contained the basic materials of life.
After billions of observations over hundreds of years, scientists concluded
that all living things are made of cells. They also observed that single cells
divided to produce two identical cells. These facts were tied together to form the
CELL THEORY.
a. All living things are made of cells.
b. All cells come from other cells.
The cell theory is one of the most important theories in life science since it
is a summary of everything that we know about cells. It ties together
observations from many areas of science. But, like any theory, it could change
with new evidence. Maybe we will find living things with no cells. Maybe we will
find nonliving things with cells. Maybe we will be able to make a cell in a lab.
Science is always being revised and the best theory chosen to fit all the
evidence.
CELL STRUCTURE
Imagine that you could shrink down to enter and explore an animal cell.
You would find three main areas: the cell membrane, the cytoplasm and the
organelles.
First, you would pass through the cell membrane, a thin, two-layered
structure covering the surface of the cell. Materials needed in the cell enter the
cell and wastes leave the cell through the cell membrane.
Next, you would move into the cytoplasm, It is a jellylike substance that
fills most of the cell. Many of the cell's building materials are made and stored in
the cytoplasm.
Cytoplasm
Vacuole
(Dots-Can also be on
the ER)
Organelles are tiny organs that have special jobs. They are found
floating in the cytoplasm. We will look at six different organelles. The nucleus is
the "control center" of the cell. It contains the coded instructions for all of the
cell's activities. Mitochondria are bean-shaped organelles where food and
oxygen react to release energy. They are the "powerhouses" of the cell. The
more active a cell is, the more mitochondria it has.
Mitochondrion (cut open so you can see the inside)
Running through the cell is a network of flat channels called the endoplasmic
reticulum (ER). This organelle manufactures, stores, and transports materials.
ER with ribosomes (dot) on it
Ribosomes are dots attached to some ER. Their job is to put together proteins
which are made of long chains of amino acids. Proteins control just about
everything that goes on in a living thing.
Lysosomes contain digestive enzymes and are used by the cell to digest or
breakdown many molecules.
Golgi Apparatus package materials to be taken out of the cell. It is often called
the “shipping department” of the cell. They are made of stacks of sacs.
Vacuoles have a single membrane surrounding solid or liquid contents including
water and food.
There are two cell parts that are in plant cells, but not animal cells. The
cell wall is stiff and nonliving. It surrounds the plant cell and gives it strength,
support and shape. Cell walls are also found in bacteria, fungi and some
protists. Choloroplasts are dark green organelles that are scattered in the
cytoplasm. They help the plant trap the sun's energy to make sugars. We will
study these more when we learn about photosynthesis. They are also found in
some protists.