CHAPTER 1 THE CHARACTERISTICs OF LIVING THINGS Eas HOSE IN iving things include many kinds of organisms from the plants ani mals fungi and algae that can be readily seen in nature to the multitude of tiny creatures known as protozoa bacte ria and archaea that can be seen only with a microscope Living things can be found in every type of habitat on Earth on land and in lakes rivers and oceans Although all these organisms are very different from one another they all have two things in common They are descended from a single ancient ancestor and they are alive Most scientists believe that the first living organism on Earth probably evolved within a billion years of Earth s formation which occurred roughly 4 5 billion years ago This belief is based on evidence from the fossil record Fossil remains of microorganisms resembling cyanobacteria a group of micro organisms formerly known as blue green algae were discovered embedded in rocks that were roughly 3 5 billion years old A A IO
THE CHARACTERISTICS OF LIVING THINGs The colors of Morning Glory Pool a hot spring in Yellowstone National Park are the result of different types ofcyanobacteria which are micro organisms that thrive in harsh environments Shutterstock com The early Earth was very different from the Earth of today The atmosphere was rich in hydrogen which was critical to the chemi cal events that later took place According to one scientific hypothesis soupy mixtures of elements important to life such as carbon II
A CLOSER LOOK AT LIVING THINGS nitrogen oxygen and hydrogen were concen trated in warm pools bathed in the ultraviolet rays of the Sun Out of this mix chemical elements combined in reactions that grew increasingly complex forming organic mol ecules such as proteins and nucleic acids As they combined and recombined these mole cules eventually formed a highly primitive cell capable of reproducing itself Over millions of years the process of natural selection then aided the evolution of single and multicelled organisms from an ancient common ancestor There are seven key functions or pro cesses necessary for life To be categorized as a living thing an organism must be able to do all of these MoVEMENT Living things have the ability to move in some way without outside help The move ment may consist of the flow of material within the organism or external movement of the organism or parts of the organism SENSITIVITY Living things respond to conditions around them For example green plants grow toward 12
THE CHARACTERISTICS OF LIVING THINGS sunshine certain microorganisms shrink into tiny balls when something touches them and human beings blink when light shines into their eyes RESPIRATION All living organisms must be capable of releasing energy stored in food molecules through achemical process known as cellular respiration In aerobic respiration oxygen is taken up and carbon dioxide is given off In single celled organisms the exchange of these gases with the environment occurs across the organism s cellular membrane In multicellular organisms the exchange of the gases with the environment is slightly more complex and usually involves some type of organ specially adapted for this pur pose Large multicellular animals such as birds and mammals must breathe in oxygen IST which travels to the lungs and is transferred to the blood flow of the body s arteries The arterial system carries this fresh oxygen to all the tissues and cells of the body where it is exchanged for carbon dioxide a cell lular waste product that must be carried back to the lungs so that the organism can exhale it 13
