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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 economic integration
Mohamed Reply
why does it makes sense to let the sewage disposal company in your town have a monopoly?
Janice Reply
how might a monopoly affect price?
Janice
how might a monopoly affect prices?
Janice
The principle of Economic is one to be involved in any economic buying substance
Anastassiya Reply
reason of corporation
Mohamed
What is economic integration
Mohamed
what are the principle of economics?
oche Reply
What is (Qs)
Bigi Reply
What is (Qs) and (Qd)
Bigi
Quantity of supply and Quantity of demand
Dilshoda
Qs: Is quantity of supply and Qd: quantity of demand
Cabdikariim
give as me quantitys
ahmed
among all the definition of economics which of the definition is generally acceptable?
oche
i science that studies human behavior as a relationship between ends and scarcity that have alternative uses
ousman
okay......
oche
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oche
what Make things scarce
Soudani Reply
why do we studied economic
Soudani
for the stability and growth of any reign.
Fayaz
what is macro economics.?
Fayaz
which part of economics is interesting..
Fayaz
what is economic integration
Mohamed
how does economics define me
clement Reply
what are the factors that determines the demand and supply
sillah
what are the importance of Economics
Betty Reply
tell me something very important about economics..
Fayaz Reply
how may I solve arithmetic mean ,,,all example
Cee Reply
what is agriculture
Itoe Reply
simple method of understanding cost concept
Oludare Reply
what is inflation
Christiana Reply
Inflation is a general increase in price levels
Zuko
is the action of inflating something
Abdifatah
inflation is the persistent increase in general price level of goods and services in an economy over a considerable period of time .
Tetteh
inflation is the general increase of a commodity in a particular period of time.
Turay
inflation is a general increase in price levels of commodities
shehu
what are the types of inflation?
Ebrima
inflation is the period of persistent rise in the general level of the price of goods services over time
Emmanuel
we have creeping inflation, demand pull inflation ,cost push inflation, and galloping inflation .
Emmanuel
I s Nigeria in any kind of in inflation? If yes which kind?
Martins
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Jonathan
and u
ahmed
no discassion just question
Aliraza
what is science and art economic
Sadanu
how can a location of a firm create difference between producers
joy Reply
what is monetary policy
joy
hello
Abdifatah
is a monetary from policy that's authorized of country encharces
Abdifatah
What would you say about the the mobility of enterprise as a factor of production?
Cathryn Reply
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
Leah Reply
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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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