to gain more knowledge

1. LESSON 5
Theory: Cell Theory
1: All living things are made of at least one
cell.
2: Cells are the basic unit of life. Postulate
3: All cells come from preexisting cells.
Scientists once thought that life spontaneously arose from
nonliving things. Thanks to experimentation and the invention of
the microscope, it is now known that life comes from preexisting
life and that cells come from preexisting cells.

2. First proposed by German
scientists Theodor Schwann and
Matthias Jakob Schleiden in 1838,
the theory that all plants and
animals are made up of cells
marked a great conceptual
advance in biology and resulted in
renewed attention to the living
processes that go on in cells.
Who created the cell theory?

3. Cell Parts and Functions
All cells contain specialized, subcellular structures that are adapted to keep the cell alive.
Some of these structures release energy, while others produce proteins, transport
substances, and control cellular activities. Collectively, these structures are
called organelles.
Plant and animal cells both contain organelles, many of which are found in both types of
cells. However, there are some organelles (such as chloroplasts, the cell wall, and large
vacuoles) that are only found in plant cells.

4. Animal Cell Parts And Their Functions
The Nucleus
The nucleus is the control center of the cell and
houses all of the cell’s genetic information. Usually, a
cell has a single nucleus that contains all of its DNA
molecules, but some (such as skeletal muscle cells)
have more than one nucleus.
The nucleus protects the cell’s DNA while controlling
all other cellular activities, such as cell division,
growth, protein production, and cell death.

5. Ribosomes
The DNA molecules housed in the nucleus
also contain blueprints for all of the
proteins produced by a cell. These
blueprints are ‘read’ and interpreted by
ribosomes, which are the site of protein
production in plant and animal cells.

6. Mitochondria
Cells need energy to power their biochemical
reactions, and most of that energy is released by
mitochondria. Mitochondria are the site of
respiration and the ‘powerhouses’ of cells, pumping
out energy which is then stored in ATP (adenosine
triphosphate). ATP molecules are the energy
currency of cells and are used to fuel all the other
activities of the cell.

7. Endoplasmic Reticulum (ER)
The endoplasmic reticulum is a network of
membranes inside a cell, and its main functions are
to process and transport new materials. There are
two types of endoplasmic reticulum; the rough ER,
and the smooth ER.
The rough ER is studded with ribosomes, giving it a
bumpy or ‘rough’ appearance. It folds and tags
newly-synthesized proteins before transporting them
to wherever they are needed in the body. The
smooth ER does not have ribosomes attached to it
and is instead involved in hormone and lipid
synthesis.

8. Golgi Apparatus
Once newly-synthesized substances have left the
ER, they are sent to the Golgi apparatus. This is
a series of flatted, membrane-bound sacs that
packages and distributes substances to the outer
cell membrane, where they either become part
of the lipid bilayer or leave the cell.

9. Cytoplasm
The cytoplasm is a jelly-like substance that fills the
interior space of cells. It is mainly composed of
water, but also contains salts, enzymes, and other
organic molecules. The cytoplasm surrounds and
protects the organelles of the cell and is where
many cellular processes (such as protein synthesis
and glycolysis) take place.

10. The Cell Membrane (AKA The Plasma Membrane)
All cells are surrounded by a cell membrane, which consists of a
semipermeable phospholipid bilayer. The cell membrane controls which
substances enter and leave the cell, and also separates the interior of the
cell from its external environment.

11. Plant Cell Parts And Their Functions
Chloroplasts
Chloroplasts are one of the most important types
of plant cell organelle, as they are the site
of photosynthesis. Photosynthesis is a process
by which light energy from the sun is used to
convert carbon dioxide and water molecules into
glucose, and is how plants produce food.
Chloroplasts are filled with chlorophyll, the green
pigment that gives plants their color. Chlorophyll
harvests light energy, which the chloroplast then
uses to produce glucose. Once glucose has been
synthesized, it is broken down to release energy
during cellular respiration in the mitochondria.

12. The Cell Wall
Plant cells are surrounded by a tough structure
called the cell wall, which is found outside of the cell
membrane and is mainly made of cellulose. The cell
wall supports and protects plant cells, giving them
their characteristic rectangular or box-like shape.

13. The Vacuole
The vacuole is a very large organelle that can
occupy up to 90% of the interior space of plant
cells. One of its key functions is storage. The
vacuole is filled with cell sap, which consists mainly
of water but also contains proteins, sugars, and
other molecules. Another function of the vacuole is
to maintain turgor pressure, which helps the plant
cell to keep its shape and prevents wilting and
bursting.