There are several stereotypical characteristics of life. These characteristics are essential to the maintenance of life and in many ways are each interdependent on the other.







Characteristics of Life
Growth and Development



Like salt and pepper, growth and development travel as a pair. If they did not, you would be a really big baby right now. Instead, over time, not only do organisms grow, they also mature resulting in functional changes.

At some point in their development skin cells start to produce more protein, sex cells more hormones, nerve cells make more connections, etc. Also as time progresses there may be a lessening of function, not because of disease, but as a normal consequence of the development process.

This process may be demonstrated on an organismal level as humans develop from infant to toddler, child, adolescent, and so forth.



Characteristics of Life
Irritability and Responsiveness



Heart beats quicken with anxiety. Sweat pours from our bodies with exercise. Water is retained when a cool drink is not immediately available. These are examples of the characteristic of life known as irritability and responsiveness.


Irritability and responsiveness is the ability of body structures to detect changes in the internal and external environment and fashion intentional responses to them.



Characteristics of Life
Maintenance of Boundaries



Imagine if you had no skin. There would be no way to separate your internal environment from the external environment. On an organismal level, there would be no internal environment.

Indeed people with severe burns on large percentages of their bodies are at great risk to succumbing to infection and dehydration as the absent skin no longer keeps microbes out or water in.

Whether skin on an organismal level or the plasma membrane on the cellular level the maintenance of boundaries is crucial.




Characteristics of Life
Reproduction



Obviously reproduction is an essential characteristic of life.


The majority of cells in the human body reproduce by a process known as mitosis when one cell ultimately splits into two identical cells. This is known as asexual reproduction.

On an organismal level human reproduction is known as sexual reproduction. Sexual reproduction is characterized by the combination of genetic material from a male and female resulting in a genetically diverse offspring.



Characteristics of Life
Digestion



The food pictured to the left has little nutritional value until it is ingested and digestion commences.

The digestion process makes available to the body the building blocks of essential chemicals that sustain life.



Characteristics of Life
Excretion



Most physiological reactions yield unintentional substances characterized as waste.

The most common waste products of physiology are water and carbon dioxide.

If waste products build up they may become toxic.

The process of excretion involves the removal of waste products.

As an example, water and carbon dioxide are easily excreted each time you breathe out.



Characteristics of Life
Metabolism



Metabolism is the sum total of the body’s catabolic and anabolic reactions.

Anabolism is the opposite of catabolism. Anabolic reactions are characterized by the chemically combining simpler substances to synthesize more complex ones.



Characteristics of Life
Movement



Movement is another characteristic of life. Movement can be viewed on the organismal level, as in walking or running. It can also be viewed as internal movement, such as blood being pumped around the body.



Characteristics of Life
Cellular Basis



As previously stated, all organisms are composed of cells or cell products. Therefore all living things have a cellular basis.


In fact, as the modern cell theory states, an organism's structure and function are due to the structure and function of the cells it is composed of.


Therefore, if the cells cannot do it then the organism cannot do it.




—CHECKPOINT—



This is a good time to pause and assess your knowledge of key concepts.

Below are links to a few learning activities that might assist your mastery of the material. Completing some of the tasks may also earn you class participation credit! However, most importantly it will assist in your learning.


You should attempt to complete the assignments without using your text, notes, etc., as they are designed to test your knowledge—just like taking a test in class—but without the grade consequences.


Tasks include mock exams, games, clinical scenarios, and more. Click/tap on the activities and see how much you know!


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