Human Biology Enabling Course – Module 2 Cellular Level of Organisation This document is the property of Endeavour College of Natural Health and contains confidential information of Endeavour College of Natural Health. Copyright in the whole and every part of this document belongs to Endeavour College of Natural Health and may not be used, sold, transferred, adapted or modified or reproduced in whole or in part in any manner or form or in any media, to any persons other than in agreement with Endeavour College of Natural Health. This document remains the confidential information of Endeavour College of Natural Health and should not be used for any other purpose other than that expressly approved by Endeavour College of Natural Health at the time the document was provided by Endeavour College of Natural Health. May 2011
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Human Biology Enabling Course –
Module 2
Cellular Level of Organisation
This document is the property of Endeavour College of Natural Health and contains confidential information of Endeavour
College of Natural Health.
Copyright in the whole and every part of this document belongs to Endeavour College of Natural Health and may not be
used, sold, transferred, adapted or modified or reproduced in whole or in part in any manner or form or in any media, to
any persons other than in agreement with Endeavour College of Natural Health.
This document remains the confidential information of Endeavour College of Natural Health and should not be used for any
other purpose other than that expressly approved by Endeavour College of Natural Health at the time the document was
provided by Endeavour College of Natural Health.
May 2011
Endeavour College of Natural Health Page 2 Enabling Course: Human Biology Module 2
Contents
Module 2 – Cellular Level of Organisation
1 Introduction
1.1 Background
2 Anatomy and physiology of the human cell
2.1 The plasma membrane
2.2 Plasma membrane proteins
2.3 Diffusion
2.4 Cytoplasm
2.5 Cytoskeleton
2.6 Endoplasmic reticulum (ER)
2.7 Ribosomes
2.8 The Golgi complex
2.9 Lysosomes
2.10 Mitochondria
2.11 Nucleus
2.12 Cell Division
2.13 Mitosis
2.14 Prophase
2.15 Metaphase
2.16 Anaphase
2.17 Telophase and Cytokinesis
2.18 Meiosis
2.19 Activity
3 References
Endeavour College of Natural Health Page 3 Enabling Course: Human Biology Module 2
Module 2 – Cellular Level of Organisation
1 Introduction
1.1 Background
As briefly mentioned in module 1, there are various levels of organisation that make up a
human body. The first level is the chemical level and contains the smallest units known as
atoms. Over millennia atoms formed molecules through a multitude of chemical reactions
and eventually gave rise to the living cell.
The human body is made up of trillions of cells. There are many different types of cells, for
example, liver cells, brain cells and muscle cells. Every cell is programmed by human DNA
to carry out a specific function (physiology) such as the liver cell’s role in detoxifying
substances taken into the body in the form of liquids, food or airborne pollutants. When
viewed under the microscope cells vary in shape and size (anatomy) but they all essentially
share common features and it is these similarities that this module will focus on using a
generic model/picture of a cell as a reference point such as Figure 1.
Figure 1. Human cell
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2 Anatomy and physiology of the human cell
2.1 The plasma membrane
Figure 2. Plasma Membrane
As mentioned in Module 1 (cellular level) each cell is a complex factory of important parts
that work integrally to maintain the life and function of the cell. To contain and protect the
inner components of the cell a protective membrane formed known as the plasma
membrane Figure 2. The term plasma refers to the contents of the cell.
The plasma membrane is made up of a phospholipid (phospho = containing phosphorus;
lipid = fat) double layer known as a bilayer. Facing the extracellular (outside) and
intracellular (inside) environments are phosphorous polar (charged) heads (see Figures 2 &
3.) that attract water and known to be hydrophilic (hydro = water; philic = attract).
Between the layers of polar heads are the lipid tails (non-polar) that repel water making them
hydrophobic (phobic = repel). Together this arrangement makes up the cell (plasma)
membrane (Figure 3). It is important to note that plasma membrane and cell membrane are
terms used interchangeably.
Figure 3. (from http://www.prism.gatech.edu)
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The plasma membrane separates the contents of the cell (intracellular) from the outside
(extracellular) environment. It functions like a gatekeeper allowing some substances such as
nutrients like glucose to pass into the cell for metabolism while keeping other harmful
substances out. This protective role can break down in the face of some viruses and bacteria
that have developed ways to trick the cell into allowing them to pass.
Figure 4. Cell membrane proteins
2.2 Plasma membrane proteins
The plasma membrane is littered with various shaped bodies some of which penetrate
through the double layer to the inside of the cell (Figures 2 & 4). These structures are protein
molecules that may function as locks and gatekeepers.
This arrangement of surface proteins provide the mechanism of entry for life giving
substances into the cell needed for metabolism and the exit points for waste products that
are produced as a result of metabolism. It’s essentially the same as when you eat food and
your digestive system extracts the nutrients required for health and expels the waste in the
form of urine or faeces.
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2.3 Diffusion
Some substances such as oxygen and carbon dioxide enter and exit the cell membrane with
ease a process referred to as simple diffusion (see Figure 5). Diffusion occurs when a
substance moves from an area of high concentration to an area of lower concentration
known as the concentration gradient.
In the example of oxygen and carbon dioxide, the concentration of oxygen is greater on the
outside of the cell as fresh oxygen arrives from the lungs, while on the inside of the cell the
process of metabolism has created a higher concentration of carbon dioxide (waste product).
Therefore according to simple diffusion laws oxygen will naturally flow into the cell where it’s
concentration is lower and carbon dioxide will flow toward the outside of the cell where it’s
concentration is lower. This process ensures that body cells always have a fresh supply of
life giving oxygen and also ensures that waste products are removed from the cell to
maintain homeostasis.
Figure 5. Simple Diffusion
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Figure 6 shows that larger substances such as glucose require a protein receptor to facilitate
passage into the cell through a process called facilitated diffusion.
Figure 6. Facilitated Diffusion
Visit the links below to view an animation of receptor proteins at work.