The Characteristics of Living Things

Biology as the study of living things is a vast and fascinating field. To get a starting point in the study of biology, it is perhaps worthwhile to try to define what you mean by "life". Audesirk and Audesirk give a list of basic characteristics of living things. Karp approaches the same ideas in terms of the properties of living cells.

Yockey has a very concise characterization of life: "The existence of a genome and the genetic code divides living organisms from nonliving matter."

Classification of Organisms
Energy cycle in living things
Chemical elements in living things
Index

Reference
Audesirk & Audesirk

Yockey
p3
 
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Classification of Organisms

The word "organism" may be used to describe one individual living system. It can be thought of as the smallest unit of that kind of life that possesses all the characteristics of life. Audesirk & Audesirk supply the following table of characteristics used to classify organisms.

Domain
Kingdom
Cell Type
Cell Number
Major Mode of Nutrition
Bacteria
??
Prokaryotic
Unicellular
Absorption, photosynthesis
Archaea
??
Prokaryotic
Unicellular
Absorption
Eukarya
Protista
Eukaryotic
Unicellular
Absorption, ingestion, or photosynthesis
Eukarya
Fungi
Eukaryotic
Multicellular
Absorption
Eukarya
Plantae
Eukaryotic
Multicellular
Photosynthesis
Eukarya
Animalia
Eukaryotic
Multicellular
Ingestion

Those organisms that make use of photosynthesis manufacture their food by capturing energy from sunlight and constructing energy-rich molecules such as sugars and fats. These organisms are called "autotrophs", meaning "self-feeders". Other organisms must obtain their energy-rich molecules from other organisms and are called "heterotrophs" or "other-feeders".

Index

Reference
Audesirk & Audesirk
Ch 1
 
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