Cells and Organelles

                Everything you need To know about Cells!

Basic cell structure

“Cells are the Basic unit of structure and Function”

The Levels of Organization

1. Organism

2. Organ Systems

3. Organs

4. Tissue

5. Cell

6. Organelle (which is made up of molecules)

The Cell Theory

1. all living things are composed of one or more cells.

2. The cell is the basic unit of life.

3. All cells come from pre-existing cells.

Stem Cells and Differentiation

An average Human has 46 Chromosomes

Stem Cell

  • All multicellular organisms begin as a single cell
  • The original stem cell has the potential to become any type of cell

Note: Although all resulting cells in the body have the same ancestor and same DNA, they have different functions, eg. Neuron vs. Bone cell vs. muscle cell

Cellular differentiation

  • the process by which a cell becomes specialized to perform a specific function.

The Cell Cycle and Mitosis

Cell cycle

The repeating cycle of events in the life of a cell is called the cell cycle.

Cell division involves packaging the genetic information in the nucleus into two equal portions, called Mitosis. In every cell, there contains chromosomes. Each chromosome is an individual long piece of coiled DNA and proteins. 


A cell spends almost all of its life in interphase. During this elongated time period, the cell is constantly Growing. Specifically, during interphase, the cell takes in nutrients, grows and conducts other normal cell functions. There are three stages of Interphase (below)





There are 4 phases of Mitosis: Prophase, Metaphase, anaphase, and telophase.


During this phase, the chromatin (which is basically DNA and proteins) condenses. Furthermore, the chromosome is two identical copies named sister chromatids, which are both attached together at the centromere. To allow the movement of these sister chromatids, the nuclear structures and the nuclear envelope disintegrate. Also, a framework that helps the chromatids to move around the cell freely called the mitotic spindle forms. Specifically, in animal cells, a pair of organelles called the centrioles move to the end of the cell, forming the poles of the mitotic spindle.


in this stage, the chromosome becomes completely condensed and move toward the centre of the cell and line up at the middle of it. the mitotic spindle (framework) is completely formed and extend from the middle of the cell to both poles of the cell. This framework connects the centromere of each chromosome to the two poles.


In this phase, the sister chromatids separate at the centromere. Then the separated chromosomes are pulled to the  opposite ends of the cell.

Telophase & Cytokenesis

During this last phase of mitosis, (telophase) the cell divides the cytoplasm into two equal portions. this process of splitting the very cytoplasm is called cytokenesis. There are different scenarios that occur in plant cells and animal cells during this phase. In animal cells the cell membrane pinches inwards, in plant cells the cell plate forms the cell wall and the inner membrane in each of the new cells. since the cells repeat this infinite cycle, the two new cells enter the G1 phase of interphase.

Here is a picture of Mitosis at work!

Are Cells immortal?

Cells have a limited lifespan depending on how their cell cycle was completed. For example, some cells die earlier than others because they suffered an injury during mitosis. The cells also die a regulated death (just as humans die naturally from old age), which is called apoptosis. 

Cancer Cells

A cancer cell is a cell that divides uncontrollably. A cancer cell is generally forms when a cell mutation occurs, which occurs when a cell’s DNA is altered or it can be caused from cigarette smoking. A cancer cell is called an “immortal cell” because it does not stop dividing, which contrasts a normal cell that only divides 50-60 times.  Cancer cells are also dangerous because they can move to other parts of the body through blood vessels. An example would be that a cancer may occur in someone’s thigh, and travel up to their abdomen, where the cancer cells start reproducing again. 

What is Diffusion?

Diffusion is the natural process where particles move from a region of higher concentration to a region of lower concentration.

Organisms are limited to a specific size. the Cell membrane acts as a barrier from the surrounding environment and as a gateway for movement of nutrients and waste. As a cells gets bigger, ratio of surface to the volume increases.

The three rules of cell size and cell properties:

Gloger’s Rule: Darker pigmented forms of an organism tend to be found in more humid climates, such as equatorial environments.

Allen’s Rule: Organisms from colder climates have shorter limbs than similar animals from warmer climates.

Berman’s Rule: Body mass increases with latitude for a specific species. 



Transgenics allow scientists to develop organisms that express a novel trait not normally found in the specified species. 

-Possible transgenic combinations can be broken down generally into three categories (here “animal” refers to non-humans) 

1)plant-animal-human combinations

2)animal-animal combinations

3)animal-human combinations



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