TEKS 7.12F Recognize that according to cell theory all organisms are composed of cells and cells
carry on similar functions such as extracting energy from food to sustain life.
Used to see CELLS!
What is cell theory?
Until the 1600s, no one knew cells existed because there was no way to see them. Around 1590, the
invention of the first microscope allowed people to look at very small objects. A microscope is an
instrument that makes small objects look larger. Over the next 200 years, this new technology revealed
that cells came in many shapes and sizes, depending on their function in an organism. Also, depending on
what organism was under study, cells had different organelles. But despite these differences, scientists
determined that cells had many things in common. These studies led to the development of cell theory.
Cell Theory The cell theory is a widely accepted explanation of the relationship between cells and
living things. The cell theory states the following:
• All living things are composed of cells. (1 or more cells) unicellular or multicellular
• Cells are the basic units of structure and function in living things.
• All cells are produced from other cells.
Living things differ greatly from one another, but all are made of cells. The cell theory holds true for all
living things, no matter how big or how small. Because cells are common to all living things, cells can
provide clues about the functions that living things perform. And because all cells come from other cells,
scientists can study cells to learn about growth and reproduction.
1.Recognize According to the cell theory, what are all organisms composed of? cells
________________________________________________________________________________________________________ All cells can…
Cells and Function An organism’s functions are the processes that enable it to live, grow, and
reproduce. Those functions include obtaining oxygen, food, and water and getting rid of wastes. Cells are
involved in all these functions. For example, cells in your digestive system absorb food. The food provides
your body with energy and materials needed for growth. Cells in your lungs help you get oxygen. Your
body’s cells work together, keeping you alive.
How do cells carry out their functions?
In order for each cell to stay alive, it must carry out many of the same functions as the entire organism.
Recall that the organelles carry out functions inside a cell. Each organelle is specialized for processes such
as consuming water and food, changing food into energy for the cell, eliminating wastes, and exchanging
gases.
Function
of substances
Water The cell membrane controls movement of water into and out of a cell. Water moves from areas
of higher concentration to those of lower concentration. Ideally, a cell stays in a state of equilibrium with
the same number of water molecules entering and leaving the cell at any given time.
aka: Homeostasis –
Obtaining Food Organisms that have chloroplasts in their cells make their own food through
maintain balance
photosynthesis. Sugar molecules produced
Example: your body
regulates
by this process are then processed
temperature by
by mitochondria in the cell to provide
Function
sweat/shiver
energy. Organisms that do not have
chloroplasts cannot perform
photosynthesis. Instead, small food
particles pass through their cell
membranes into the cell. Some food
particles are too large to cross the cell
membrane.
Enter
In a process called endocytosis (ehn doh sigh TOH sihs), the cell membrane changes shape and engulfs
the particle. The image shows an amoeba consuming food by endocytosis.
2.Define What is endocytosis? How cell membrane surrounds and consumes food
________________________________________________________________________________________________________
Using Food Some form of sugar is the basic food for all cells, whether it comes from photosynthesis or
from food particles. In animals, lysosomes (LY suh sohmz) break down large food particles into simple
Function
sugars and other nutrients. Mitochondria release the energy stored in sugar through a process called
cellular respiration. Cellular respiration uses oxygen and releases carbon dioxide.
Breathing
3.Recognize Which organelles extract energy from sugar to sustain the life of a cell? …
Function
Mitochondria ________________________________________________________________________________________
Function in animal cells. They also break down
Handling Wastes Lysosomes digest more than just food particles
old cell parts into substances that can be used again. Vacuoles store wastes that the cell cannot use. These
waste-filled vacuoles fuse with the cell membrane and release wastes from the cell through exocytosis
(ehk soh sigh TOH sihs), which is the reverse of endocytosis. Small waste products can leave a cell by
Exit
passing directly out through the cell membrane. Plant cells produce few wastes. The wastes they do
produce are stored in their vacuoles, released as a gas into the air, or leach out of roots or leaves.
Gas Exchange Plant cells must obtain carbon dioxide to perform photosynthesis, and they must
eliminate the excess oxygen that photosynthesis produces. The cell membrane allows passage of carbon
dioxide into and oxygen out of the plant’s cell. Animal cells have opposite needs for exchanging gases.
Animal cells must obtain oxygen for cellular respiration and must rid themselves of the carbon dioxide
they produce. As in plants, the cell membrane allows these gases to pass into and out of the cell.
4.Recognize What cell part controls the movement of life-sustaining gases into and out of a cell?
Cell membrane ______________________________________________________________________________________
Lesson Check
1.Recognize According to cell theory, which organisms are composed of cells?
All living organisms _____________________________________________________________________________
2.Identify Name three basic needs that organisms and cells share.
Oxygen, water, energy, and to get rid of wastes (any 3) ______________________________________
____________________________________________________________________________________________________
3.Infer Complete the analogy.
An organelle is to a cell_________ as an organ is to an organism.
4.Compare Complete the Venn diagram to compare and contrast the cell functions of exocytosis and
endocytosis.
Exocytosis
How
substances
exit
Both
Moving
substances
Endocytosis
How
substances
enter
5.Recognize According to cell theory, what do all cells have in common?
A They are the same size.
B They have the same organelles.
C They carry on similar functions to live.
D They have about the same shape.
6.Recognize All cells must have a way of extracting energy from food to sustain life.
a. How do plant cells obtain the energy they need to live?
Photosynthesis/sun/chloroplast (any option) ________________________________________________
____________________________________________________________________________________________________
b. How do animal cells obtain the energy they need to live?
Eat food/ mitochondria release energy from food ____________________________________________
____________________________________________________________________________________________________
c. Which organelle present in both plants and animals is responsible for transforming simple sugars
into the energy cells need to sustain life?
mitochondria _____________________________________________________________________________________
Lesson Review 7.12F: Cell Theory
TEKS Check
1.Recognize What are the three components of cell theory?
 All living things are composed of cells.
• Cells are the basic units of structure and function in living things.
• All cells are produced from other cells.
2.Recognize Like organisms, cells must exchange gases with the environment.
a. Identify the gases that both plant and animal cells use for life processes.
Oxygen (animals) and carbon dioxide (plants)________________________________________________
b. Describe the movement and use of these gases in a plant cell. Include the terms cell membrane,
photosynthesis, and cellular respiration in your description.
Plant cells must obtain carbon dioxide to perform photosynthesis, and they must eliminate the
excess oxygen that photosynthesis produces. The cell membrane allows passage of carbon dioxide
into and oxygen out of the plant’s cell. Mitochondria perform cellular respiration to release the
energy from the sugar made during photosynthesis.
c. Describe the movement and use of these gases in an animal cell. Include the terms cell membrane
and cellular respiration in your description.
Animal cells must obtain oxygen for cellular respiration and must rid themselves of the carbon
dioxide they produce. The cell membrane allows these gases to pass into and out of the cell.
3.Identify Mitochondria are present in all plant and animal cells. In which cell process are
mitochondria important?
A gas exchange
B production release of energy
C getting food
D waste elimination
4.Recognize Recognize that cells carry on similar functions to sustain life.
a. Identify the role of lysosomes in two different functions within an animal cell.
Lysosomes digest food particles in animal cells. They also break down old cell parts into substances
that can be used again.
b. Which function of lysosomes is carried out by vacuoles in plant cells?
Vacuoles store wastes that the cell cannot use. These waste-filled vacuoles fuse with
the cell membrane and release wastes from the cell.
TEKS in Context
5.Compare You have read that cells and organisms have similar functions that meet similar needs. For
each life function listed below, make a checkmark in the correct column to indicate whether it is a
need of cells or organisms or both.
Meeting Needs
Need
a. Gas exchange
b. Getting food and water
c. Changing food into
energy
d. Eliminating wastes
In Cells?
In Organisms?
In Both?
X
X
X
X
Cell Theory
The discovery of the cell was made possible by the invention of the microscope, which was
made possible by improved lens-grinding techniques. Antoni van Leeuwenhoek (16321723), a Dutch tradesman, learned to grind lenses and
Invented
modern,
1668microscopes. His contemporary
assemble
them
into simple
Robert Hooke (1635-1703) used such an instrument to
observe spaces in cork, sketches of which appeared in his
1665 publication "Micrographia.” Hooke is responsible for
naming these spaces in the cork “cells” – Latin for “little rooms.” Inspired by
Hooke's work, Leeuwenhoek began making microscopic examinations of his
own. In 1678, he reported to the Royal Society that he had discovered "little
animals" -- bacteria and protozoa -- in various samples of pond scum. The
society asked Hooke to confirm Leeuwenhoek's findings, and he did.
This paved the way for wide acceptance that a hidden world existed just
beyond the limits of human vision and encouraged many scientists to take up
the microscope in their investigations. One such scientist was German botanist
Matthias Jakob Schleiden (1804-1881), who looked at numerous plant 1838
samples. Schleiden was the first to recognize that all plants, and all the
different parts of plants, are composed of
cells. While having dinner with zoologist
Theodor Schwann (1810-1882), Schleiden
mentioned his idea. Schwann, who came to
similar conclusions while studying animal tissues, quickly saw the
implications of their work. In 1839, he published "Microscopic Investigations
on the Accordance in the Structure and Growth of Plants and Animals,"
which included the first statement of the cell theory: All living things are
made up of cells.
Then, in 1858, Rudolf Virchow (1821-1902)
extended the work of Schleiden and Schwann by
proposing that all living cells must rise from preexisting cells. This was a radical idea at the time
because most people, scientists included, believed
that nonliving matter could spontaneously
generate living tissue.
List the parts of the Cell Theory, and name the scientists who are credited.
1. All living things are composed of cells. Scientists: Schleiden & Schwann
2. Cells are the basic units of structure and function for living things. Scientists: Schleiden & Schwann
3. New cells are produced from existing cells. Scientist: Virchow
Create a Cell Theory Timeline.
1668
Anton van Leeuwenhoek
Invented the modern
microscope
1665
Robert Hooke
Discovered and named
CELLS while looking
at cork
1839
Theodor Schwann
Discovered all animals
are made of cells
(credited with 1st two
parts of cell theory)
1858
1838
Rudolf Virchow
Matthias Schleiden
Discovered all cells
Discovered all plants
come from existing
are made of cells
st
cells. (3rd pert of cell
(credited with 1 two
theory)
parts of cell theory)