1. A review by Hubert Asamoah-Boadu
Cell Functions
A review by Hubert Asamoah-Boadu

2. What are cell functions?
Cell functions are activities performed by a cell in order for it to survive, thrive and reproduce.
In this lesson, we will be focusing on the functions of eukaryotic cells (animal and plant cells).
Eukaryotic cells contain organelles, which allow them to perform a variety of specialized activities, compared to their prokaryotic counter-part.

3. Where did these organelles come from?
A widely accepted scientific explanation for the origin of eukaryotic organelles, is the endosymbiotic theory.
This theory suggests that all the organelles that exist in eukaryotes now, are the result of previous symbiotic relationships between ancient single celled organisms.
Essentially: All cells started out as prokaryotes, with some smaller prokaryotes being engulfed (but not digested) by bigger prokaryotes. The two prokaryotes would then enter a symbiotic relationship with each other; each one of them providing mutual benefits for the other.
After millions of years of evolution, this symbiotic relationship would result in full bodied eukaryotic cells being formed.

4. The Cell Wall
The cell wall is the tough, rigid outer structure of the cell. It only exist in bacteria, fungi and plant cells.
This wall serves to provide support to the cell and over it protection from the external environment.
For plant cells in particular it assists in the diffusion in H2O, O2 and CO2 in and out of the cell.
In plant cells, the cell wall is made out of a substance called cellulose, which is built from polysaccharides.

5. The Cell membrane
The cell membrane is composed of a phospholipid bi-layer. This membrane is the outer lining of the cell, which separates it from the outside environment.
The membrane controls what enters and leaves the cell at al times. This membrane exists in all cells (plant, animal, protest, etc.) and has what is referred to as selective permeability.
Selective permeability, means that the membrane can become permeable to the external environment on command.

6. The Nucleus
The Nucleus is the “brain” of the cell, as it coordinates cell activities. The nucleus also holds all of the genetic information for the cell; this DNA is accessed during protein transcription.
The Nucleus has a large-oval shape and is often considered the most important part of the cell.
The Nucleus is also surrounded by the nuclear membrane, which has nuclear pores. This membrane, surrounds and protects the nucleus, as a well as controls what enters and leaves it.
The nuclear pores are what allow things such as mRNA to leave the nucleus and enter the cytoplasm.

7. The Cytoplasm
The cytoplasm is the thick, clear, jelly-like material that fills up the cell. All the organelles, proteins, etc., that are in the cell reside in the cytoplasm
The cytoplasm supports and protects the all of the organelles of the cell. The cytoplasm also contains cytoskeleton fibers, which assist in giving the cell shape and support.
The main function of the cytoplasm is to provide support and protection for the organelles of the cell.

8. Endoplasmic Reticulum (ER)
The Endoplasmic Reticulum Is a network of membrane and tubes that is connected to nucleus. The endoplasmic reticulum can be broken down into two categories: Rough ER and Smooth ER
Rough ER: This portion of the ER is studded with membrane bound ribosomes, giving it its “rough” appearance. The primary function of the rough ER is to produce and transport proteins
Smooth ER: This portion of the ER lacks the membrane bound ribosomes, but is still a very important part of the ER. The smooth ER focuses much more on lipid production and transport.

9. The Golgi Apparatus
This very complex organelle, is involved in the packaging and transportation of proteins and other molecules. This Golgi Apparatus works very closely with the ER; packing the proteins and lipid products that the ER makes.
The Golgi Apparatus also creates lysosomes, the “clean up crew” of the cell. The lysosomes are filled with digestive enzymes, which have the ability to digest about anything (even the cell itself.)

10. Special Showcase: The Lysosomes
The lysosomes are pretty incredible structures, their digestive enzymes are what allow for the cell to break down materials, invading pathogens and other foreign bodies.
The lysosomes should not be underestimated as just a “clean up crew”, they also have the potential to destroy the cell from the inside out.
If the cell has to destroy itself for any reason:; its becoming cancerous, its infected by a pathogen and needs to perish, or it is simply scheduled to die, it will commit apoptosis.
Apoptosis is when a cell purposely kills itself, by the use of lysosomes.

11. Vacuoles
Vacuoles are membrane bound sacs in the cell that serve as storage units. The vacuole can store food, waste or any other materials in the cell.
In plants the vacuole is very important; not only does it provide large amounts of storage it also provides structural support for the plant cell.
Plant cells will often have one central vacuole, which takes up a large portion of space within the cell. This vacuole will provide structural support, water disposal and controlling turgor pressure.
Turgor pressure, dictates how rigid the plant cell will be. High turgor pressure produces a stiff and rigid plant cell, while low turgor pressure results in a weak plant cell and results in a wilting plant.

12. The Ribosomes
The Ribosomes are the little protein factories of the cell and are responsible for creating all of the proteins that exist in the cell.
When mRNA is sent to the ribosomes, it is read in a process called translation In this process the mRNA is decoded by the ribosomes in order to produce a polypeptide chain, which then folds to create a protein.
The ribosomes brings tRNA that has complementary anticodons that meet up with the codons from the mRNA.

13. The Mitochondria
The famous “powerhouse of the cell” that is responsible for producing all of the ATP that the cell uses.
The mitochondria is able to utilize glucose and oxygen in order to create ATP in a process called aerobic respiration.
The mitochondria has a large amounts of folds in its inner membrane, known as the cristae. This cristae, dramatically increases the surface area of the mitochondria creating more room for reactions and allow for more ATP to be created.

14. The Chloroplast
The chloroplast is a special organelle only found in animal cells ,that Is able to convert the light energy from the sun into glucose (sugars).
This process is known as photosynthesis and creates oxygen as a byproduct of the reaction.
The chloroplasts are also green in color as a result of the green chlorophyll molecules

15. The Centrioles
The centrioles are small sets of microtubules that are arranged in groups of nine. The centrioles are only be found in animal cells and assist in cell division. When it is time for the cell to divide, the centrioles will pair up and move towards the poles of the cells.
The centrioles are not necessary for plant cells, as the rigid cell wall, makes it easy for the plant cell to divide.

16. Citations
Cell Functions. (n.d.). Retrieved May 30, 2016, from
Cell Functions. (n.d.). Retrieved June 01, 2016, from
Endoplasmic Reticulum (Rough and Smooth). (2015, November 19). Retrieved May 30, 2016, from and-smooth/
Golgi Apparatus - Packing Things Up. (n.d.). Retrieved May 31, 2016, from
Ribosomes. (n.d.). Retrieved May 31, 2016, from astr.gsu.edu/hbase/biology/ribosome.html
Chloroplast. (n.d.). Retrieved June 01, 2016, from
What is a cell? (May/June). Retrieved June 01, 2016, from