Cells are the basic units of life that can carry out all life processes. The reason why we learn about cells is because it is our smallest building block of life – all living together and coexisting in harmony to make up our human biology.
Read on to see how you can learn about the structures and functions of cells, as well as some common examples for cell specialisation, using analogies and diagrams!
Table of Contents:
- Two main organism types
- Structure & Function of Plant & Animal Cells
- Levels of Cell Organisation
- Division of Labour (Multicellular Organisms)
- Cell Specialisations/Adaptations
Two Main Types of Organisms
Before we zoom in to analyse cells in detail, we first must understand that cells are the building blocks of life that make up the organisms that exist in our world today. There are many, many different types of organisms that exist on planet Earth, from our human species, to the different species of animals – insects, fish, etc. Furthermore, there are even smaller organisms that we cannot see with our naked eyes – called microorganisms as they are only visible under a microscope.
Organisms can be classified into two types – unicellular and multicellular organisms.
Unicellular organisms
These are organisms which only consist of a single cell. Because of that, these are microorganisms that are extremely small in size, but are able to function pretty well on its own without needing to have more than one cell type to perform different functions.
Some examples of this would be bacteria or amoeba.
Diagram of a bacteria cell
Multicellular organisms
On the other hand, multicellular organisms that are made up of two or more (multiple cells). This can be further divided into two types that we will be learning about – plant & animal cells.
Structure & Function of Plant & Animal Cells
Using an analogy, let’s run through the basic components of the cell. We can compare a cell to the layout of this minimalistic kitchen here 😀
Here is the annotated picture for the parts of a cell:
Found in Animal Cells:
- Cell Membrane – Door (controls movement of substances in and out of the cell)
- Nucleus – The Person In The Room (controls all activities in the cell + contains the genetic material)
- Cytoplasm – Space in Kitchen Room (the medium in which most chemical reactions take place)
- Vacuole – Fridge (store dissolved nutrients and mineral salts → note: this is called cell sap in the large central vacuole of a plant cell)
Components found only in Plant Cells:
- Cell Wall – The walls surrounding your house (Gives cell a regular shape + Maintains the turgidity of the cell)
- Chloroplast🍀 – The windows allowing sunlight to enter – Contains chlorophyll which absorb sunlight/light energy to make food (Photosynthesis)
For a more in-depth explanation on how you can use analogies to aid your learning, check out the article here!
Levels of Cell Organisation
Table Illustrating Levels of Cell Structure:
| Level | Plants | Animals |
| Cells | Leaf Cells, root hair cells | Skin Cells Muscle Cells |
| Tissues | Root Hairs, | Muscle Tissue |
| Organs | Xylem, Phloem, Leaves | Heart Lungs Stomach Liver Kidneys Muscles Skin |
| Organ Systems | Root System – Food & Water Transport System Shoot System | Circulatory Digestive System Respiratory Skeletal Muscular Nervous Endocrine |
| Organism | Plant | Human |
- Our foundational level would be cellular level. This is where we have all the trillions of tiny cells in our body – from skin cells, muscle cells, bone cells, you name it
- As these cells come together and work in harmony, they form tissues. Not the tissue paper that we use, but tissues that are made out of a group of cells (identical) – for example: muscle tissue
- Moving on to the next level, these tissues then make up what we call organs – these include your heart, lungs, skin, liver, just to name a few.
- Organs – which performs their specific function(s), will then be classified under organ systems. For example, the stomach, small intestine, large intestine/colon, etc. will make up the digestive/gastrointestinal system.
- Organ Systems, which include many of the body systems that we name – such as circulatory, respiratory, muscular, skeletal, gastrointestinal/digestive – will make up the organism that we are.
FlowChart for Cellular Organisation
How I like to group them together is to remember a specific pathway that sticks to my head well. For example, we can construct and draw a quick flowchart for this –
- Cells – Red Blood Cells – carry oxygen throughout the body
- Tissues – Red Blood Cells are carried in blood vessels throughout the body – which comprises of several layers of blood vessel tissues (tunica intima/interna ,tunica media – smooth muscle layer, tunica adventitia/externa, internal and external elastic lamina)
- Organs – These blood vessel tissues then make up the organs we know – Arteries, Veins, Capillaries
- Organ System – These organs combine to make up what we know as our circulatory system – Heart (organ) pumping blood through the vessels to the lungs + all parts of the body and vice versa
- Organism – Together with other systems in our body which carry out different functions, it give rise to what we are today
Now after learning the various levels of cell organisation, let’s discuss the benefits of cell structure and organisation.
Division of Labour (Multicellular Organism)
As a multicellular organism, we are able to perform many specialised tasks, and that is because cells of different types are adapted to specifically perform their particular functions.
Two main benefits:
Cells can work together simultaneously
Having multiple cells that perform different functions (heart/cardiac muscle cells, skeletal muscle cells of your body), allows you to carry out different life processes at the same time!
While you are going about your day – walking, running, talking, etc – your organs are each performing their individual functions.
Ensures that our body/organisms function as a whole.
Your lungs continues to facilitate gaseous exchange and take in oxygen ~
Your brain could be constantly churning out new ideas, thinking about something, while your heart and lungs move automatically, helping to sustain life.
To illustrate this concept, let’s use running as an example. (Note that this is not exclusive, there are other systems in our body which are also active in this process but are not mentioned here)
🫁Respiratory system
As your body requires more oxygen to facilitate effective functioning of muscles, your respiratory system will work extra hard to take in more oxygen through your nose/mouth to your lungs. It also gives out more carbon dioxide in expired air (exhaled) through your nose/mouth – where the main function is to facilitate gaseous exchange. This is also supported by the various muscles and structures surrounding the chest/thoracic cavity. (Intercostal muscles between the ribs, diaphragm, abdominal and neck muscles, etc.)
🫀Circulatory System
Your heart never stops pumping or takes a break when you are doing something else, and when you are running, your heart beats faster to transport oxygen at a higher rate to your muscles – to transport/circulate blood throughout the body.
💪🏻Muscular System
When you are running, your leg muscles have to contract with more power, and at a higher rate – to support our movement, and your body will use up more oxygen during respiration to produce energy in the form of ATP (adenosine triphosphate)
This all happens at the same time (simultaneously) and also showcases how different organ systems work together to ensure that we expend energy efficiently to support our physical exercises.
Cell Specialisation/Adaptations
Tip: Always consider and link the structure to the function
Red Blood Cell🩸
Function: Is to transport oxygen efficiently to our muscles for aerobic respiration to produce energy💪
Source:Database Center for Life Science (DBCLS), CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
- Distinctive biconcave shape → Can contain more haemoglobin which binds to oxygen at high affinity
- Contains haemoglobin (Binds to oxygen to carry it to all parts of the body)
- No Nucleus → Increase surface area for diffusion of oxygen
Think of a red blood cell as a boat, which allows you to scoop up more fish (oxygen – a useful substance for our body) – by having a biconcave shape and also does not have excess stuff on board (no nucleus) to store more fish.
Root Hair Cell🪴
Function of Roots: To absorb water & mineral salts from the soil/surroundings into the plant & anchor the plant firmly to the ground.
Having these fine hair-like projections (root hairs), enables roots to branch out and reach further and deeper into the soil. As trees grow larger in size, they will also need more water and mineral salts to support the growth and life processes of more cells and organs (leaves, flowers, fruits, etc.). Thus, root hairs are just extensions of the main root branches, and they are made up of root hair cells.
- Elongated Structure which increases surface area to volume ratio
Xylem
On the inner side of your xylem, it has a hollow lumen (empty vessel) with lignin on the walls to support the flow of water and mineral salts from the roots to the leaves. The lignin on the walls provide structural support, withstanding high pressure and preventing the xylem from collapsing.
Concluding Remarks
All in all, these are just some of the key facts on a foundational level regarding cells. Do not hesitate to leave a comment if you would like additional information added, or if you spot any discrepancies.
Happy reading & share it with someone you know if it could be of use to them!