Download The Characteristics of Living Things: Biology Scientists are

The Characteristics of Living Things: Biology
Scientists are discovering new species at an exponential rate. In the Andes a bat the size of a raspberry was recently
discovered and in Singapore a nematode (small flatworm) that lives only inside the lungs of the changeable lizard was found! By
those who find a new species get to name it! So far scientists have named and recorded 1.3 million species that have lived or
are living on earth. A Canadian scientist, Boris Worm, estimates that there are 8.7 million species on the planet. Thus, our
biological picture of our planet is not yet complete.
Bio is from the Greek word bios meaning life, and logy from the Greek word logia meaning the study of. Together, these root
words become “Biology,” the discipline upon which our seventh grade science class is based. Before scientists can study life,
they must define what is alive and what is not. Some non-living things exhibit life-like properties, such as a crystal when it
grows larger, but in order for something to be considered alive, most scientists agree that it must exhibit the following eight
characteristics. 1. All living organisms are made up of one or more cells that contain cytoplasm. Cytoplasm contains the
materials each cell needs to survive (water, carbohydrates, proteins, lipids, and nucleic acids). 2. All living organisms exhibit
growth and development. 3. All living species stay within a limited range of sizes and overall shape. An adult human is between
3 and 8 feet and will never be shaped like an octopus. 4. All living organisms take in energy and release energy. To perform the
cellular functions necessary to stay alive plants must take in sunlight and use this energy to create the food they eat. Animals
evolved to use the excess food plants make for the energy their cells need. 5. Life forms adapt to both external and internal
stimuli in ways that increase their chances for survival. Birds have been seen dropping nuts that they cannot crack onto
streets. When a car rolls over the nut, the bird picks up the pieces. 6. All species inherit traits. These traits change as
generations experience environmental pressures that favor some traits over others. 7. All life forms reproduce and have a
limited lifespan. Cellular division creating two identical cells from one is a form of asexual reproduction. Many life forms use
sexual reproduction to create a unique life form that is a mixture of the two parents. 8. All organisms use nucleic acids in the
form of DNA or RNA to pass traits from one generation to the next.
The Classification of Living Things:
Now that we have defined life, we seek to sort and categorize those organisms. Carolus Linnaeus came up with a system that
although modified by new discoveries, we still use today. As the understanding of organisms improved, it became necessary to
adjust the system of biological classification. Two things in particular have had a large effect on biological classification. One
of these is Charles Darwin's theory of evolution. The other is advances in technology that have enabled scientists to take a
better look at organisms.
Evolution and Classification
Today, most biologists believe that wolves and lions both developed from a meat-eating animal ancestor that existed about 60
million years ago (mya). And lions and house cats both developed from a catlike animal that lived about 15 mya. During the long
history of life on Earth, organisms have changed or evolved. You can think of evolution as the process in which new kinds of
organisms develop from previously existing kinds of organisms.
Evolutionary relationships, such as those between the ancient catlike animal and house cats or between wolves and lions, are
extremely important to modern taxonomists (biologists who classify living organisms). Evolutionary relationships are the basis
for the modern system of biological classification. Modern taxonomists try to classify living things in such as way that each
classification group contains organisms that evolved from the same ancestor.
The knowledge of evolution has changed the nature of biological classification groups.
It has also changed the job of
taxonomists. Because they did not know about evolution, taxonomists of the past felt free to classify organisms in any manner
that made sense to them. They did not classify prehistoric organisms because they did not know about them, and they could
choose any characteristics that they thought were important as their basis for classification, just as you will do in your
Animacules Lab.
Present-day taxonomists, on the other hand, classify organisms in a way that shows evolutionary relationships. They must
consider organisms that existed in the distant past as well as those that exist in the present. And they classify organisms using
characteristics that are proven to be good indicators of evolutionary relationships.
Today, more than 200 years after Linnaeus completed his work, scientists consider many factors when classifying organisms.
Of course, they still examine the large internal and external structures, but they also rely on other observations. The invention
of the microscope has allowed scientists to examine tiny structures hidden within the cells of an organism. It has also allowed
them to examine organisms at their earliest stages of development. Today scientists use a database that contains all the known
genetic sequences of organisms to help determine evolutionary relationships between organisms. By comparing similar genes, or
sequences of DNA, we can tell how similar the two species genetic codes are. Similar sequences between species indicate close
evolutionary relationships. Scientists conclude from various studies that human DNA is about 96% similar to a chimpanzee’s
DNA. This number has changed as scientists learn more about genetics. In fact, chimps have two more chromosomes than
humans, but we still share many similar genes. Many genes show a 99% similarity between us.
There are a few different systems of classifying organisms that are in use today. As information about life on earth improves,
modifications are made to previous systems and new systems are developed. Phylogeny is a classification system that shows
evolutionary relationships and has prompted the tree of life project. Another system of classification is an adaptation of
Carolus Linnaeus’s model. This is the system we will use in class.
Linnaeus’s system gives each organism a unique name that scientists all over the world can use and understand. Also, it groups
organisms according to basic characteristics that reflect their evolutionary relationships. All living things are classified into
seven major groups: kingdom, phylum, class, order, family, genus and species. The largest and most general group is the
kingdom. For example, all animals belong to the Kingdom Animalia. The second largest group is the phylum (pl. phyla). A phylum
includes a large number of very different organisms. However, these organisms share some important characteristics. A
species is the smallest and most specific group in the classification system.
Members of the same species share many
characteristics and are similar to one another in appearance and behavior. In addition, members of the same species can
interbreed and produce viable offspring. Viable means that the offspring are in turn able to produce offspring of their own.
After the discovery of ancient forms of bacteria that live in extreme environments more similar to earth as it was billions of
years ago, scientists created 3 domains. The domains are even larger and more general than the kingdoms. Thus our new
system places the organism’s domain first. The hierarchy now is: domain, kingdom, phylum, class, order, family, genus and
species.
Fig. A phylogenetic tree based on rRNA data, showing the separation of bacteria,
archaea, and eukaryotes
The Domains and the Kingdoms of all Living Things
Domain Archaea > Kingdom Archaebacteria
The Archaea Domain is the first domain. The organisms within Archaea are composed of some of the oldest species on Earth.
All organisms in this domain fall within the Kingdom Archaebacteria and are often referred to as such. This term however is
misleading, as their genetic make-up is no more similar to bacteria than ours is. They are not bacteria, they are uniquely
Arcahea. Most archaens are known as extremophiles, because they live in extreme environments , such as the halophiles which
thrive in salt, or thermophiles which live in temperatures of up to 110 degrees Celcius. Archaens are unicellular (composed of
one cell) and they have a cell membrane and a cell wall that separates their internal environment from their external
environment. They are prokaryotes, thus, they have no membrane bound organelles inside their cell membrane. Organelles are
structures that organize the cell’s internal components, surround and protect the genetic material (nucleus), and generally
increase the productivity and efficiency of the cell. Archaens gather energy in a variety of ways, but they are all autotrophic.
Autotrophs obtain energy by making their own food using sunlight (phototrophs) or chemicals (chemotrophs).
Domain Bacteria > Kingdom Eubacteria
The Domain, Bacteria, consists of the second set of organisms to evolve on earth. There are about 40 million bacteria in a small
pinch of dirt and the collective biomass of all the bacteria on Earth is more than that of all plants and animals combined! All
organisms within this domain are found within the Kingdom Eubacteria. Many structures and biochemical properties of bacteria
are unique to this group and are not found in Archaea or Eukarya. Bacteria are all unicellular prokaryotes. Bacteria have a cell
membrane, and a cell wall around the membrane as further protection from the environment. This cell wall also defines the
shape of bacteria. Bacteria are either coccus (spherical), bacillus (rods), spirillum (spirals) or filamentous. Bacteria are either
heterotrophs, autotrophs, or chemotrophs.
Cynobacteria perform photosynthesis and are considered the first oxygen
producing phototrophs to evolve on Earth. Heterotrophic bacteria gather food from their environment, while chemotrophs use
chemicals to create their own food.
Domain Eukaryota > Kingdom Protista, Kingdom Fungi, Kingdom Plantae, Kingdom Animalia
The third and final domain is Eukarya. All members of Eukarya are eukaryotes. Eukaryotes have a highly organized cellular
structure that includes organelles. Organelles carryout specific tasks and improve the efficiency of the cell. One noticeable
structure found in eukaryotic cells is the nucleus which houses and protects the genetic material in a cell. Domain Eukarya
contains the Kingdoms Protista, Fungi, Plantae, and Amimalia.
Kingdom Protista.
Protists are the only unicellular eukaryotes, although some species live together in large colonies that give
the appearance of being multicellular. A number of protists are capable of animal like movement but also have some distinctly
plant like characteristics. Specifically, they are green in color and can use the energy of light to make their own food from
simple substances. However, they are neither plants nor animals. Protists were the first kind of cells that contained a nucleus.
Protist cells only have a cell membrane. Ancient types of protists that lived millions and millions of years ago are probably the
ancestors of fungi, plants, animals and the modern protists. The protozoa are a group of organisms commonly studied in life
science that includes ameba, paramecium and euglena are classified in this kingdom.
Kingdom Fungi: These are multicellular organisms that lack photosynthetic pigments and absorb nutrients directly from their
surroundings (heterotrophs). The cells of a fungus have a cell wall surrounding each cell membrane. Mushrooms and toadstools
are fungi, as are the molds that sometimes grow on leftover foods that have remained too long in the refrigerator. The mildews
that may appear as small blacks spots in damp basements and bathrooms are also fungi.
Kingdom Plantae: Plants make up this kingdom. These organisms are multicellular autotrophs. Plant cells are surrounded by a
tough cell wall. Cell walls help the plant form and maintain a shape while providing extra protections for the cell. You are
probably quite familiar with members of this kingdom, which includes flowering plants, mosses, ferns and trees.
Kingdom Animalia:
Animals are multicellular organisms with specialized tissues.
All animals are heterotrophs.
Animals
reproduce sexually, must take in oxygen to respire.
DIRECTIONS: Answer using complete sentences on a separate sheet of paper. Restate part of the question in your answer and
do not use the word “it” or “they” in your answer.
1.
What are the characteristics of living things? Briefly state these in one long sentence.
2.
What is evolution, and how does it affect the way organisms are classified?
3.
Explain why knowing the classification of an unfamiliar organism can tell you a lot about that organism.
4.
Make a chart showing the three domains and the six kingdoms of living organisms and list three important characteristics
of each of the five kingdoms.
5.
How is the way an autotroph gets food different from the way a heterotroph gets food?
6.
Suppose that creatures from a distant planet are multicellular heterotrophs whose cells lack cell walls. Which domain and
kingdom of the Earth's organisms do these creatures most closely resemble?