Levels of Organization: Study with Video Lessons, Practice Problems & Examples

This course explores biological organization from the atomic and molecular levels to the organismal level, emphasizing the structure-function relationship at each stage. Key concepts include macromolecules like proteins and enzymes, cellular functions, and tissue types studied through histology. Understanding organ systems and their interconnections is crucial, as changes at one level can impact others. The study of gross anatomy involves visible structures, while physiological processes like action potentials and enzyme interactions are foundational for grasping complex biological functions.

The Levels of Organization

As we go through this course, you're likely to realize that you're learning things at all sorts of different levels from the molecular all the way up to the whole organism. We're going to go through those levels now, and we're going to use this diagram to do so. Now I realize this may look a little convoluted. Don't worry, we're going to take it step by step. At the smallest level, we have the atomic and the molecular level.

This is really the chemistry of the body. Don't worry, you do not need to be an expert chemist to do well in this class, but you do need to know the basics. To understand how the nervous system works, for example, you need to understand the properties of ions. Early on in this course, you're going to be responsible for knowing some of that material, but there's a review chapter to get you up to speed if you need it. As we move up, we're going to reach the macromolecule level.

The macromolecule level is the biochemistry of life, the large biomolecules, things like proteins and enzymes, lipids, DNA and RNA. Again, you do not need to be an expert biochemist to do well in this class, but you need to know the basics. A lot of physiology is based on how enzymes work or how molecules interact with lipid bilayers. Again, you are going to be responsible for some of this material in this class, but early on, there's going to be a chapter that reviews it to get you up to speed if you need it. As we move up a level, we reach the cellular level.

The cellular level with all the organelles and all the cell parts, we usually call the basic unit of life. And we say that because we usually say that nothing smaller than a cell is alive, and you are alive because you're made of trillions of cells. The cell is the smallest thing that performs all of life's functions. Again, you're going to be responsible for understanding the basics of cellular function and cell parts, but early on in the course, we'll review that material and get you up to speed if you need it. If you study anatomy and physiology at the cellular level, we say that you are doing cytology.

And being a cytologist is a career that you could pursue. Now as we move up, we're going to reach the tissue level. And this is probably the first level that you're going to study in a way that you've never seen before. The tissue level is when you take groups of cells that are all doing the same thing, put them together, and they're performing a common function. Now when you study anatomy and physiology at the tissue level, we say that you are doing histology.

There are only a few types of tissues in the body, and the different little tweaks that you make to them in the different ways that you put them together, you can create different organs. The organ level we're going to define as groups of tissues that are bound together, working together to perform a common function. Now you have lots of organs in your body, but of course, they don't work on their own. Organs work in organ systems. We're going to say that an organ system is a group of organs that are working together to perform one common function.

Now the organ system level, that's how we're going to break up a lot of this course. Chapter by chapter will be one organ system and then often the next chapter will be a different organ system. Of course, no organ system works completely on its own. When you put a bunch of organ systems together, you're going to reach the organismal level. That's going to be you and people like you.

Now you'll notice that I have this bracket around these largest levels here. This bracket represents the study of gross anatomy. Gross anatomy is the study of anatomy that you don't need a microscope for, things that you can just see and dissect. If you're taking an anatomy lab where you're doing dissections, that's probably a gross anatomy lab. Now gross here means this larger scale, but you can remember it because if you're taking a gross anatomy lab, you're doing dissections.

Things may squirt on you. Some people think that's gross. Be careful. An important thing to remember, we've been talking about the structure-function relationship. This structure-function relationship is going to exist at all levels of organization.

Why do enzymes function the way they do? They function the way they do because of the way they're structured. Why do organ systems function the way they do? They function the way they do because of how they're structured. And also, it's important to remember that all levels of organization are connected.

A change at the macromolecule level is going to have ripple effects all the way up to how organ systems function. If you change the anatomy of an organ system, that's going to change a lot of things in the body, and it will ripple down and could even have effects down to the molecular level. So as you're learning this material, remember the structure-function relationship works at all levels. All things are connected. The more you integrate this stuff together, remember that all these levels, all these connections exist, the more you'll understand this material in a rich and important way.

With that, we have another example below, practice problems to follow, and I'll see you in the next video.

Levels of Organization Example 1

This example tells us that statins are some of the most prescribed medications in older adults, and that tells us that the following statements explain how statins work. So there's going to be 1, 2, 3, 4 statements, and then we have 2 questions. A, at what level of organization do statins work most directly? And B, what other levels of organization do statins affect physiologically? So keep those questions in mind as we go through these statements.

First off, we have statins share a chemical similarity to the molecule HMG Coenzyme A, leading them to inhibit the enzyme HMG Coenzyme A reductase. Alright. Inhibiting an enzyme sharing a chemical similarity, that seems like it's happening at the molecular level or maybe you could say macromolecule level. Well, I'll write molecular for now. The next statement says inhibiting HMG Coenzyme A reductase lowers overall cholesterol production in the liver.

Alright. Now we're talking about how an organ is functioning. That's another level. Next, it says lowering cholesterol production in the liver leads to lower blood cholesterol levels and less plaque formation on artery walls. Alright.

Now we're talking about whole different parts of an organ system: blood and artery walls, and how plaque formation comes about. And then finally, we have reducing plaque formation reduces the risk of death from heart attack, stroke, and other causes. Alright. I can't think of anything that affects the whole organism more than death, so I think I'm gonna say at the end, it affects the whole organism. So at what level does it seem to work most, directly?

I'm gonna say molecular. Right? It's inhibiting an enzyme. But what other levels does it affect? I'm going to say all of them.

Right? We talked about the liver. We talked about a whole organ system, blood and blood vessels and artery walls. And then we're talking about death, something that definitely affects a whole organism. So this relationship between different levels is really important to remember as you go on.

Yes. You can focus on studying a specific level. Some people are molecular physiologists. Some people do more gross anatomy. But all of these levels affect each other and are intertwined and are really impossible to completely separate.

So with that, we have a few more problems below, and I'll see you in the next video.

Given the following 5 levels of organization, which represents the correct hierarchy from smallest to largest?

A) Tissue B) Organ C) Molecule D) Cell E) Organism

• A. A, D, C, E, B.
• B. B, E, D, A, C.
• C. C, D, A, B, E.
• D. C, A, B, D, E.

Which statement about the levels of organization in anatomy and physiology is most correct.

• A. To understand any other level, you must be an expert in atoms & molecules because they are the most basic. 
• B. The molecular and organ system levels are most closely related.
• C. Changes to anatomy or physiology at one level are likely to affect function at many other levels.
• D. People who study whole organ systems are unlikely to need to understand the behavior of atoms.

During a cancer screening a doctor may choose to screen using histological or cytological methods. Cytological methods are often less invasive than histological methods. Why do you think this may be?

• A. Histology usually requires intact tissue gathered from a biopsy or dissection, while cytology usually looks at individual cells which can be collected without greatly disturbing the entire tissue.
• B. Histology often requires imaging of the whole body, while cytology requires an external exam of the body without any imaging tools.
• C. Histology involves surgery so that whole organs can be examined, while cytology can be performed using genetic or molecular analysis of bodily fluids such as saliva or urine.
• D. Histology requires removing and analyzing single cells from an intact tissue, while cytology can be performed using imaging techniques such as MRI and therefore does not require removing cells or tissue from the body.

Here’s what students ask on this topic:

What are the levels of biological organization from smallest to largest?

The levels of biological organization from smallest to largest are: atomic, molecular, macromolecular, cellular, tissue, organ, organ system, and organismal. At the atomic and molecular levels, we deal with the chemistry of the body, including ions and small molecules. The macromolecular level involves large biomolecules like proteins and DNA. The cellular level includes cells and their organelles, the basic units of life. Tissues are groups of similar cells performing a common function. Organs are made up of different tissues working together. Organ systems consist of multiple organs that perform a collective function. Finally, the organismal level encompasses the entire living being.

What is the structure-function relationship in biological systems?

The structure-function relationship in biological systems refers to the idea that the way something is structured determines how it functions. This concept applies at all levels of biological organization. For example, the specific shape of an enzyme allows it to catalyze a reaction efficiently. Similarly, the structure of tissues and organs determines their roles in the body. Understanding this relationship helps explain why changes in structure, such as mutations in DNA or damage to tissues, can affect function. This principle is crucial for understanding how biological systems operate and interact.

What is the difference between cytology and histology?

Cytology is the study of cells, including their structure, function, and chemistry. It focuses on the cellular level of organization and involves examining cell parts and processes. Histology, on the other hand, is the study of tissues. It involves analyzing groups of similar cells that work together to perform specific functions. While cytology looks at individual cells, histology examines how cells are organized into tissues and how these tissues contribute to the function of organs and organ systems. Both fields are essential for understanding the complexities of biological organization.

Why is it important to understand the interconnections between different levels of biological organization?

Understanding the interconnections between different levels of biological organization is crucial because changes at one level can impact others. For example, a mutation at the molecular level can alter the structure of a protein, affecting cellular functions and potentially leading to tissue and organ dysfunction. Similarly, damage to an organ can have ripple effects on the entire organ system and the organism as a whole. Recognizing these interconnections helps in diagnosing and treating diseases, as well as in understanding how complex biological systems maintain homeostasis and respond to changes.

What is gross anatomy and how does it differ from microscopic anatomy?

Gross anatomy is the study of anatomical structures that can be seen with the naked eye, such as organs and organ systems. It often involves dissection and examination of larger body parts. Microscopic anatomy, on the other hand, involves studying structures that require a microscope to be seen, such as cells and tissues. While gross anatomy provides a broad overview of the body's structure, microscopic anatomy offers detailed insights into the cellular and tissue levels, helping to understand how these smaller components contribute to the function of larger systems.