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By the end of this section, you will be able to:
  • Identify and describe the properties of life
  • Describe the levels of organization among living things
  • Recognize and interpret a phylogenetic tree

Biology is the science that studies life, but what exactly is life? This may sound like a silly question with an obvious response, but it is not always easy to define life. For example, a branch of biology called virology studies viruses, which exhibit some of the characteristics of living entities but lack others. It turns out that although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life. Consequently, virologists are not biologists, strictly speaking. Similarly, some biologists study the early molecular evolution that gave rise to life; since the events that preceded life are not biological events, these scientists are also excluded from biology in the strict sense of the term.

From its earliest beginnings, biology has wrestled with three questions: What are the shared properties that make something “alive”? And once we know something is alive, how do we find meaningful levels of organization in its structure? And, finally, when faced with the remarkable diversity of life, how do we organize the different kinds of organisms so that we can better understand them? As new organisms are discovered every day, biologists continue to seek answers to these and other questions.

Properties of life

All living organisms share several key characteristics or functions: order, sensitivity or response to the environment, reproduction, adaptation, growth and development, regulation, homeostasis, energy processing, and evolution. When viewed together, these nine characteristics serve to define life.

Order

A photo shows a light-colored toad covered in bright green spots.
A toad represents a highly organized structure consisting of cells, tissues, organs, and organ systems. (credit: “Ivengo”/Wikimedia Commons)

Organisms are highly organized, coordinated structures that consist of one or more cells. Even very simple, single-celled organisms are remarkably complex: inside each cell, atoms make up molecules; these in turn make up cell organelles and other cellular inclusions. In multicellular organisms ( [link] ), similar cells form tissues. Tissues, in turn, collaborate to create organs (body structures with a distinct function). Organs work together to form organ systems.

Sensitivity or response to stimuli

A photograph of the Mimosa pudica shows a plant with many tiny leaves connected to a central stem. Four of these stems connect together.
The leaves of this sensitive plant ( Mimosa pudica ) will instantly droop and fold when touched. After a few minutes, the plant returns to normal. (credit: Alex Lomas)

Organisms respond to diverse stimuli. For example, plants can bend toward a source of light, climb on fences and walls, or respond to touch ( [link] ). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis ) or light ( phototaxis ). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response.

Questions & Answers

what is demand and supply
Lansana Reply
what is liquidity
VICTOR Reply
the ability to easily turn asset or investment to cash
Johnson
liquidity is refers to the ease with which an asset or security, can be converted into ready cash without affecting it's market price. example is milk and checking a account in the bank.
Gyamfua
the meaning PPP is public _private partnership and PPP in economic is purchasing power_parity.
Gyamfua
what is economy production
Miracle Reply
what is Monopoly
Miracle
what is monopoly
Aina Reply
what is the full meaning of gpa?
Eedris Reply
why the firm will be happy to make normal profit?
Anold Reply
1.to make further increase 2.to established the firm 3. to draw and attract more customers 4. to foresee the future of the firm. 5. to get goods in galore
Castino
when marginal utility is zero? what is the total utility?
Scott Reply
definition of choice?
Anick Reply
it refers to the act of selecting one alternative from the other
Donfack
State and explain three advantages and two disadvantages of capitalist economic system
Ghislain Reply
What is cross elasticity of demand
Justice Reply
Is a demand in which the of goods change over time.
Shadrick
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Shadrick
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Castino
it measure the extend in which the quantity demanded of a good respond to change in price of other good.
Donfack
refers to sensitivity of quantity demanded in change of price of commodity
Daniel
meaning of PPP
OBANYI
What is balance of payments
Bah Reply
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Maillot Reply
how do you determine price change
Matri Reply
what is economics?
Yaya Reply
what is economic
Nana Reply
Economics is the study of how Individual consumer, institution and society as a whole uses its available finite resources to satisfy infinite needs and wants
Richard
Explain the following concepts using suitable exemple. 1) National budget. 2) National debt
Rosalie
While the American heart association suggests that meditation might be used in conjunction with more traditional treatments as a way to manage hypertension
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Source:  OpenStax, Introduction to bis2a: modules 0.0 to 1.2. OpenStax CNX. Jun 15, 2015 Download for free at https://legacy.cnx.org/content/col11825/1.1
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