Life

Life Functions

All life forms require certain core elements as well as physical and chemical factors from the ecosystem
for biochemical functioning.

Learning Objectives

Categorize living organisms and non-living things

Key Takeaways

Key Points

  • Living organisms are systems made from cells and are capable of life functions such as reproduction, metabolism, response to stimuli, and homeostasis.
  • Nonliving things are either living things that have died or inanimate objects that were never alive.
  • The nonliving (abiotic) components of an ecosystem include energy, oxygen, water, nutrients, and temperature.
  • Living organisms have ranges of ecosystem conditions where they can perform all physiological functions of life. Organisms cannot perform these functions as well or at all outside of these conditions, but some organisms have developed ways to adapt to environmental changes. Migration and hibernation are two examples of these adaptations.
  • Organisms called extremophiles can assume forms enabling them to withstand freezing, dehydration, starvation, high levels of radiation, and other physical or chemical challenges. Extremophiles can survive exposure to such conditions for weeks, months, years, or even centuries.
  • All life forms require certain core chemical elements for biochemical structure and function. These include carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—the elemental macronutrients for all organisms—often represented by the acronym CHNOPS.

Key Terms

  • extremophile: A microorganism that can survive in extreme environmental conditions.
  • organism: A contiguous living system that can metabolize, grow, respond to stimuli, reproduce, and adapt to its environment.
  • life: A status given to any entity with the properties of reproduction and metabolism, including
    animals, plants, fungi, bacteria, and archaea (single-celled microorganisms).

Living Organisms

An organism is a living system capable of growth, reproduction,metabolism, response to stimuli, adaptation and homeostasis.
Cells are the basic unit of life that can be found in every living organism. Organisms can be unicellular or multicellular and include plants, animals, bacteria, archaea, and fungi. Multicellular organisms are typically made up of organ systems, organs, tissues, and cells. More complex organisms are capable of communication.

The world is made up of both living (biotic) and nonliving things. Nonliving things are living things that have died or inanimate (abiotic) objects that were never alive to begin with. Living and nonliving things can be distinguished by function. Nonliving things are not capable of growth, reproduction, response to stimuli, adaptation, or homeostasis.

It is unknown whether viruses are actually alive. They are capable of reproduction (within a host) and adaptation, but they are not capable of homeostasis or metabolic functions. Because viruses exhibit some but not all characteristics of organisms, they cannot be fully considered living things.

Ecosystems Are Important for Life

The abiotic components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or chemical energy), water, temperature, oxygen, and nutrients. In most ecosystems, the environmental conditions vary throughout the day or over the course of seasons. Organisms who live in an ecosystem must be able to survive its range of conditions, called the “range of tolerance.” Outside the range of tolerance are the “zones of physiological stress,” where survival and reproduction are possible but not optimal. Beyond these zones are the “zones of intolerance,” where life for that organism is impossible. Many organisms can adapt to intolerance in their environment through seasonal migration, hibernation, or other adaptations.

Many microorganisms have evolved adaptations that allow them to survive in zones that are intolerant for most other organisms, such as extreme heat or cold, dehydration, starvation, or high levels of radiation. These microorganisms are called extremophiles, and they thrive outside the ranges where life is commonly found. They excel at exploiting uncontested sources of energy. While all organisms are composed of nearly identical types of molecules, evolution has enabled extremophile microbes to cope with this wide range of physical and chemical conditions.

This image shows plant growth in the Hoh rainforest, specifically trees and foliage that are able to adapt to conditions in this environment.

Rainforest Trees: Plant growth in the Hoh Rainforest

Chemical Requirements for Life

All life forms require certain core chemical elements for biochemical functioning. These include carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—the elemental macronutrients for all organisms. Together these make up carbohydrates, nucleic acids, proteins, and lipids, the four categories of molecules that make up the structure and function of organic life. The most widespread and important of these elements is carbon, which holds molecules together through multiple, stable covalent bonds. Organic molecules generally contain carbon, and inorganic molecules generally do not contain carbon (with the key exception of carbon dioxide). Organic molecules and their properties form the basic structure of cells and allow physiological processes to occur.

Survival Needs

To sustain human life, certain physiological needs include air, water, food, shelter, sanitation, touch, sleep and personal space.

Learning Objectives

Identify the eight minimal physiological requirements for survival

Key Takeaways

Key Points

  • While the development of tools, plumbing systems and food preservation have enabled modern man to live life with many creature comforts, the truth remains that the requirements for human survival are quite basic.
  • Physiological needs include air, water, food, shelter, sanitation, touch, sleep, and personal space.
  • As humans have evolved to interact in community settings, both hunting and gathering in groups, touch—as in a caring caress—is often considered a basic human survival need. In fact, empirical evidence has shown touch to be essential to the early growth and development of healthy humans.

Key Terms

  • survival: The fact or act of surviving; continued existence or life.

From the times of our first primate ancestors, innovation has progressed at a rapid clip. While the development of tools, plumbing systems and food preservation have enabled modern man to live life with many creature comforts, the truth remains that the requirements for human survival are quite basic. There are eight minimal physiological requirements for survival. These are: air, water, food, shelter, sanitation, sleep, space, and touch.

Survival Needs

  1. Air: Consisting of oxygen within a particular range of pressure, concentration, and purity is vital to survival.
  2. Water: Access to a safe, clean and adequate water supply is necessary for human survival.
  3. Food: Our food must be adequate in calorie and nutritional standards in order to sustain life.
  4. Shelter: Since exposure to cold and heat can lead to hypothermia or hyperthermia, shelter which offers protection from extremes of heat, cold, intense sun, and prolonged precipitation is a human survival need.
  5. Sanitation: Proper means for the removal of human waste helps protect from deadly toxins and pathogens and is critical in promoting human survival.
  6. Sleep: Seven to eight hours of uninterrupted sleep each night is optimal for human survival.
  7. Space: As humans, we require personal space. In addition to the requirement for shelter, or suitable indoor living space, humans need outdoor space, to avoid overcrowding and chaos.
  8. Touch: As humans have evolved to interact in community settings, both hunting and gathering in groups, touch—as in a caress—is often considered a basic human survival need. In fact, empirical evidence has shown that touch is essential for the early growth and development of healthy humans.
image

A Child Sleeping: Adequate sleep is necessary to sustain life.

Levels of Organization

Living organisms are made up of four levels of organization: cells, tissues, organs, and organ systems.

Learning Objectives

Order the levels of organization for living organisms

Key Takeaways

Key Points

  • Cells are the most basic unit of life at the smallest level of organization.
  • Cells can be prokaryotic (without nucleus) or eukaroyotic (with nucleus).
  • The four categories of tissues are connective, muscles, epithelial, and nervous tissues.
  • Organs are made of different types of tissues and perform complex functions. They can be hollow or solid.
  • Organ systems are groups of organs that perform similar functions or perform functions together.
  • Many physiological functions are carried out by multiple organ systems working in tandem.

Key Terms

  • cell: The smallest unit of life capable of independent reproduction. Generally contains nucleic acid, cytoplasm, a cell membrane, and many other proteins and structures.
  • organ: A structure made of different tissues that work together to perform physiological functions.
  • organ system: A group of organs and tissues that work together to perform specific functions.
  • Tissues: A group of similar cells with the same origin that work together to perform the same function.

Examples

Using the circulatory system as an example, a cell in this system is a red blood cell, the heart’s cardiac muscle is a tissue, an organ is the heart itself, and the organ system is the circulatory system.

An organism is made up of four levels of organization: cells, tissues, organs, and organ systems. These levels reduce complex anatomical structures into groups; this organization makes the components easier to understand.

Level 1: Cells

The first and most basic level of organization is the cellular level. A cell is the basic unit of life and the smallest unit capable of reproduction. While cells vary greatly in their structure and function based on the type of organism, all cells have a few things in common. Cells are made up of organic molecules, contain nucleic acids (such as DNA and RNA), are filled with fluid called cytoplasm, and have a membrane made out of lipids. Cells also contain many structures within the cytoplasm called organelles, which perform various cellular functions.

Cells may be prokaryotic (without a nucleus) in bacteria and archaea (single-celled organisms), or eukaryotic (with nucleus-enclosing DNA) in plants, animals, protists, and fungi. In humans, most cells combine to form tissues, but some cells are found independent of solid tissues and have their own functions. A red blood cell found circulating in the bloodstream carrying oxygen throughout the human body is an example of an independent cell.

Level 2: Tissues

Tissues are a group of similar cells of the same origin that carry out a specific function together. Humans have four different types of basic tissues. Connective tissues such as bone tissue are made up of fibrous cells and give shape and structure to organs. Muscle tissue is made up of cells that can contract together and allow animals to move. Epithelial tissues make up the outer layers of organs, such as the skin or the outer layer of the stomach. Nervous tissue is made of specialized cells that transmit information through electrochemical impulses, such as the tissue of nerves, the spinal cord, and the brain.

Level 3: Organs

An organ is a structure made up of different tissues that perform specific bodily functions. Most organs contain tissues such as parenchyma (used to perform the organ functions),  stroma (connective tissue specific to organs) and epithelial. Organs may be solid or hollow, and vary considerably in size and complexity. The heart, lungs, and brain are all examples of organs.

Level 4: Organ Systems

An organ system is a collection of organs that that work together to perform a similar function. There are eleven different organ systems in the human body, each with its own specific functions. One example is digestive system, which is made up of many organs that work together to digest and absorb nutrients from food. While most organ systems control a few specific physiological processes, some processes are more complex and require multiple organ systems to work together. For example, blood pressure is controlled by a combination of the renal system (kidneys), the circulatory system, and the nervous system.

This image provides an example of the levels of organization in a living organism, with illustrations of a cell, of tissue, of the stomach (organ), and of the full digestive system.

Levels of Organization in Animals: An organism contains organ systems made up of organs that consist of tissues, which are in turn made up of cells.