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- All life on earth, no matter its size, is composed of basic units called cells. Unicellular organisms are made up of a single cell, while multicellular organisms such as humans are composed of several billion cells. What is the Basic Unit of Life? A cell is the most basic unit of life.
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2 days ago · Life is the vaporware of chemistry: a property so obvious in our day-to-day experience—that we are living—is nonexistent when you look at our parts. If life is not a property of matter, and ...
- Overview
- Introduction
- Properties of life
- 1. Organization
- 2. Metabolism
- 3. Homeostasis
- 4. Growth
- 5. Reproduction
- 6. Response
- 7. Evolution
Learn about the basic properties of life as well as ongoing debates about the definition of life.
Introduction
In the intro to biology video, we defined biology as the branch of science concerned with the study of living things, or organisms. That definition is pretty straightforward. However, it opens the door to more difficult—and more interesting—questions: What is life? What does it mean to be alive?
You are alive, and so am I. The dog I can hear barking is alive, and so is the tree outside my window. However, snow falling from the clouds is not alive. The computer you’re using to read this article is not alive, and neither is a chair or table. The parts of a chair that are made of wood were once alive, but they aren’t any longer. If you were to burn the wood in a fire, the fire would not be alive either.
What is it that defines life? How can we tell that one thing is alive and another is not? Most people have an intuitive understanding of what it means for something to be alive. However, it’s surprisingly hard to come up with a precise definition of life. Because of this, many definitions of life are operational definitions—they allow us to separate living things from nonliving ones, but they don’t actually pin down what life is. To make this separation, we must come up with a list of properties that are, as a group, uniquely characteristic of living organisms.
Properties of life
In the intro to biology video, we defined biology as the branch of science concerned with the study of living things, or organisms. That definition is pretty straightforward. However, it opens the door to more difficult—and more interesting—questions: What is life? What does it mean to be alive?
You are alive, and so am I. The dog I can hear barking is alive, and so is the tree outside my window. However, snow falling from the clouds is not alive. The computer you’re using to read this article is not alive, and neither is a chair or table. The parts of a chair that are made of wood were once alive, but they aren’t any longer. If you were to burn the wood in a fire, the fire would not be alive either.
Biologists have identified various traits common to all the living organisms we know of. Although nonliving things may show some of these characteristic traits, only living things show all of them.
Living things are highly organized, meaning they contain specialized, coordinated parts. All living organisms are made up of one or more cells, which are considered the fundamental units of life.
Even unicellular organisms are complex! Inside each cell, atoms make up molecules, which make up cell organelles and structures. In multicellular organisms, similar cells form tissues. Tissues, in turn, collaborate to create organs (body structures with a distinct function). Organs work together to form organ systems.
Life depends on an enormous number of interlocking chemical reactions. These reactions make it possible for organisms to do work—such as moving around or catching prey—as well as growing, reproducing, and maintaining the structure of their bodies. Living things must use energy and consume nutrients to carry out the chemical reactions that sustain life. The sum total of the biochemical reactions occurring in an organism is called its metabolism.
Metabolism can be subdivided into anabolism and catabolism. In anabolism, organisms make complex molecules from simpler ones, while in catabolism, they do the reverse. Anabolic processes typically consume energy, whereas catabolic processes can make stored energy available.
Living organisms regulate their internal environment to maintain the relatively narrow range of conditions needed for cell function. For instance, your body temperature needs to be kept relatively close to 98.6∘ F (37∘ C). This maintenance of a stable internal environment, even in the face of a changing external environment, is known as homeostasis.
[Show example of how homeostasis is maintained.]
Living organisms undergo regulated growth. Individual cells become larger in size, and multicellular organisms accumulate many cells through cell division. You yourself started out as a single cell and now have tens of trillions of cells in your body1 ! Growth depends on anabolic pathways that build large, complex molecules such as proteins and DN...
Living organisms can reproduce themselves to create new organisms. Reproduction can be either asexual, involving a single parent organism, or sexual, requiring two parents. Single-celled organisms, like the dividing bacterium shown in the left panel of the image at right, can reproduce themselves simply by splitting in two!
In sexual reproduction, two parent organisms produce sperm and egg cells containing half of their genetic information, and these cells fuse to form a new individual with a full genetic set. This process, called fertilization, is illustrated in the image at far right.
Living organisms show “irritability,” meaning that they respond to stimuli or changes in their environment. For instance, people pull their hand away—fast!—from a flame; many plants turn toward the sun; and unicellular organisms may migrate toward a source of nutrients or away from a noxious chemical.
[See a plant respond to touch.]
Populations of living organisms can undergo evolution, meaning that the genetic makeup of a population may change over time. In some cases, evolution involves natural selection, in which a heritable trait, such as darker fur color or narrower beak shape, lets organisms survive and reproduce better in a particular environment. Over generations, a he...
All life on earth, no matter its size, is composed of basic units called cells. Unicellular organisms are made up of a single cell, while multicellular organisms such as humans are composed of several billion cells.
What is biology? In simple terms, biology is the study of living organisms and their interactions with one another and their environment. This is a very broad definition because the scope of biology is vast. Biologists may study anything from the microscopic or submicroscopic view of a cell to ecosystems and the whole living planet ( Figure 1.1 ).
- Katherine Mattaini
- 2020
Cells are the basic unit of life. The smallest organism consists of one cell. Within that cell is the cellular equivalent of organs, called organelles. Organelles are made of molecules or macromolecules such as carbohydrates, lipids, proteins, and nucleic acids.
Oct 31, 2023 · cell: The basic unit of a living organism, consisting of a quantity of protoplasm surrounded by a cell membrane, which is able to synthesize proteins and replicate itself.
Jan 12, 2021 · The cell is the basic structural and functional unit of life. Cells are independent, single-celled organisms that take in nutrients, excrete wastes, detect and respond to their environment, move, breathe, grow, and reproduce.
