Organism: Living Systems, Reproduction, and Biological Diversity

Examples include:

• a human;
• a dog;
• a tree;
• a mushroom;
• an insect;
• a bacterium;
• a whale;
• a single-celled amoeba.

Organisms differ greatly in size and structure. A bacterium may consist of one cell, while a human body contains many specialized cells working together.

Common expressions include:

• living organism;
• single-celled organism;
• multicellular organism;
• sexually reproducing organism;
• disease-causing organism;
• genetically modified organism;
• marine organism;
• host organism.

Examples include:

• Every organism requires energy to survive.
• A bacterium is a single-celled organism.
• The study examined how the organism reproduced.

The adjective organismal refers to the level of the whole organism:

• organismal biology;
• organismal development;
• organismal reproduction.

These may include:

• cellular organization;
• metabolism;
• growth and development;
• response to stimuli;
• regulation of internal conditions;
• reproduction;
• heredity;
• adaptation across generations.

Not every individual organism reproduces. Infertile organisms, children, older adults, and nonreproductive individuals are still fully living organisms.

Examples include:

• many bacteria;
• some fungi;
• protozoa;
• certain algae.

A multicellular organism consists of many cells with specialized roles.

Examples include:

• humans;
• animals;
• most plants;
• many fungi.

In multicellular organisms, cells may form tissues, organs, and organ systems that cooperate to maintain life.

A species is a broader biological group whose members share important inherited characteristics and, under common definitions, may reproduce with one another.

For example:

• one human is an organism;
• humans collectively belong to the species Homo sapiens.

An organism belongs to a species, but the two terms are not interchangeable.

Some organisms are made of one cell, so the cell and the organism are effectively the same individual. Multicellular organisms contain many cells that depend on one another.

Human sperm and egg cells are living cells, but they are not normally described as independent human organisms. After fertilization, biological development proceeds through stages whose scientific, legal, ethical, and philosophical interpretations may differ.

Sexual reproduction

Sexual reproduction generally involves genetic material from two reproductive cells, often called gametes. It usually creates offspring with a mixture of inherited traits.

Asexual reproduction

Asexual reproduction involves one parent organism and does not require the fusion of gametes.

Examples include:

• binary fission;
• budding;
• fragmentation;
• vegetative reproduction;
• parthenogenesis in certain species.

Some organisms can reproduce through both sexual and asexual methods.

However, biological systems vary greatly. Species may include:

• separate male and female organisms;
• hermaphroditic organisms;
• organisms that change sex;
• organisms with environmental sex determination;
• species with several mating types;
• organisms reproducing without sex.

Human concepts of gender identity and social gender roles should not be applied automatically to nonhuman organisms.

These can include:

• reproduction;
• mate selection;
• pair bonding;
• social communication;
• competition;
• pleasure or stimulation;
• tension reduction.

Animal sexual behavior is diverse, but observations of nonhuman organisms do not automatically establish what is ethical, healthy, or socially acceptable for humans.

Human sexual conduct also involves language, culture, law, personalvalues, consent, and moral responsibility.

Microorganisms include many:

• bacteria;
• protozoa;
• microscopic fungi;
• microscopic algae.

Some microorganisms live harmlessly or beneficially in the human body. Others can cause disease, including certain sexually transmitted infections.

Viruses are often discussed alongside microorganisms, but whether viruses should be considered living organisms remains scientifically debated because they cannot reproduce or maintain metabolism independently.

Every organism has many cells.
Numerous organisms consist of only one cell.

Every organism must reproduce personally.
An individual remains an organism even if it never reproduces.

Sexual reproduction always requires male and female organisms.
Reproductive systems vary widely across species.

A species and an organism are the same thing.
An organism is an individual; a species is a biological group.

Animal sexual behavior determines human ethics.
Human conduct also depends on consent, responsibility, culture, and law.

1. Organism is the scientific term for an individual living entity.
2. Organism may consist of one cell or many specialized cells.
3. Organism requires energy and maintains biological processes necessary for life.
4. Organism belongs to a species but is not the same as the species itself.
5. Organism may reproduce sexually, asexually, or through both methods.
6. Organism does not need to reproduce personally to be considered alive.
7. Organism may interact with other organisms through competition, cooperation, mating, or symbiosis.
8. Organism should be studied according to its biology rather than through unsupported human assumptions.

Comparing organisms helps scientists understand the evolution and diversity of reproduction. However, nonhuman mating behavior should not be used as a simple model for human relationships or ethics.

Accurate sexuality education combines biological knowledge with recognition that human sexuality also involves identity, communication, social meaning, bodily autonomy, and voluntary consent.