1.8.1: Basic Life Processes and Functions

Master this section and you'll be able to:

• Explain the importance of organization and boundaries in maintaining internal stability and function in the human body.
• Describe how anabolic and catabolic reactions contribute to metabolism. Include the production and use of ATP.
• Identify the characteristics of life. Focussing on responsiveness and movement, give at least two examples of how organ systems support these functions.
• Compare and contrast growth, differentiation, and reproduction.

 

The human body is composed of multiple organ systems, each with specialized functions and distinct roles in maintaining physiological balance. Together, these systems work to support overall health and survival. For example, the respiratory system is responsible for gas exchange, while the circulatory system transports blood throughout the body. These individual functions contribute to broader life-sustaining processes that are considered defining characteristics of living organisms.

Let's take a look at six such functions:

1) Organization and Maintaining Boundaries

Maintaining boundaries is fundamental for the organization and survival of all living things, especially at the cellular level. Without a stable boundary, cells could not control their internal environment, making life-sustaining processes impossible. To stay alive, the human body must keep its internal environment separate from the outside world — and even separate different parts inside the body. This is called maintaining boundaries, and it is a key part of the body's overall organization.

A human body consists of trillions of cells organized in a way that maintains distinct internal compartments. The plasma membrane plays a vital role in maintaining the life of a cell by acting as a physical barrier that separates the internal environment from the outside world. It is selectively permeable, meaning it carefully controls what enters and leaves the cell — helping maintain homeostasis even when external conditions change. In addition to protection, the membrane also allows for communication and exchange, enabling the movement of nutrients, waste, and chemical signals. This balance of separation and interaction helps the cell regulate its internal conditions, such as pH, ion levels, and metabolic activity, and protects it from harmful substances and pathogens.

In your body, every cell maintains its own boundary, and together, these boundaries allow tissues, organs, and organ systems to function in an organized, coordinated way.

The body’s largest organ system is the integumentary system, which includes the skin and its associated structures, such as hair and nails. The surface tissue of skin is a barrier that protects internal structures and fluids from potentially harmful microorganisms and other toxins. Stay tuned for the integumentary system, as that will be the first body system we will be studying.

 

2) Metabolism: Your Body’s Energy Game Plan

According to the first law of thermodynamics, energy cannot be created or destroyed, it can only change forms. That means your body’s job is not to make energy out of thin air, but to take in energy from food, convert it into usable fuel, and then use that fuel to power everything from muscle movement to cell repair.

Your body handles this through a pair of constantly running chemical reactions: anabolism and catabolism.

• Anabolism is like building with Legos: your body takes smaller, simpler molecules (like amino acids from food) and uses energy to build larger, more complex structures (like proteins).

• Catabolism is the opposite: it breaks down big molecules (like glucose or fat) into smaller ones (ultimately carbon dioxide and water), thereby releasing energy your body can use.

Together, these two processes make up your metabolism — the total of all the chemical reactions happening in your body, all the time, to keep you alive and functioning. Whether you are sleeping, eating, or running late to class, metabolism is working behind the scenes to keep your body in business.

 

Figure \(\PageIndex{1}\): Anabolism & Catabolism. Both anabolism and catabolism occur simultaneously and continuously to keep you alive.

Your body is made up of trillions of cells, and each one depends on a special molecule called adenosine triphosphate (ATP) to get its work done. Often described as the cell’s “energy currency,” ATP stores and delivers energy where and when it is needed. As food is broken down through catabolic reactions, cells use the released energy to produce ATP. This ATP can then be stored — like saving money for later — or spent right away to power essential tasks such as muscle contraction, nerve signaling, or building new molecules during anabolic reactions.

 

3) Responsiveness

Responsiveness is the ability of an organism to adjust to changes in its internal and external environments. An example of responsiveness to external stimuli could include moving toward sources of food and water and away from perceived dangers. Changes in an organism’s internal environment, such as increased body temperature, can cause the responses of sweating and the dilation of blood vessels in the skin in order to decrease body temperature, as shown by the runners in Figure 1.8.1.2
 

4) Movement

Human movement includes not only actions at the joints of the body, but also the motion of individual organs and even individual cells. As you read these words, red and white blood cells are moving throughout your body, muscle cells are contracting and relaxing to maintain your posture and to focus your vision, and glands are secreting chemicals to regulate body functions. Your body is coordinating the action of entire muscle groups to enable you to move air into and out of your lungs, to push blood throughout your body, and to propel the food you have eaten through your digestive tract. Consciously, of course, you contract your skeletal muscles to move the bones of your skeleton to get from one place to another (as the runners are doing in Figure 1.8.1.2), and to carry out all of the activities of your daily life.

Figure \(\PageIndex{2}\): Marathon Runners. Runners demonstrate two characteristics of living humans—responsiveness and movement. Anatomic structures and physiological processes allow runners to coordinate the action of muscle groups and sweat in response to rising internal body temperature. (credit: Phil Roeder/flickr)

 

5) Development, Growth and Reproduction

Development includes the process of cell differentiation, where unspecialized cells become specialized in both structure and function to carry out specific roles in the body. Differentiation is essential not only during early development but also throughout life, as it supports the body’s ability to grow, heal, and adapt.

Development also encompasses growth and repair. Both depend on cell division and differentiation. Growth refers to an increase in body size and occurs in several ways: by increasing the number of cells, expanding the extracellular (non-cellular) materials such as the mineral content of bones, and, to a limited extent, enlarging individual cells.

Reproduction, finally, is the biological process by which new organisms are produced from parent organisms. In humans, this function is carried out by the male and female reproductive systems. Since all complex organisms eventually die, reproduction i essential to ensure the continuation of the species.