The Living Realm
Where Insects Fit Among Living Things
David J. Shetlar, Ph.D.
The Ohio State University,
OARDC & OSU Extension
© March, 2011, D.J. Shetlar, all rights reserved
Title Slide -
Hi, I’m Dave Shetlar! I go by the professional nickname of the BugDoc. In this lecture, I will cover the living realm, that is, all living things! More specifically, the primary goal of this lecture is to provide you with the biological terms used to describe living organisms and to give you a perspective as to where insects and arthropods fit among all living things!
So, What is a Living
What is Life? Seems like a simple question, but it has confounded biologists for years, especially when theorists talk about other types of life that may occur in extreme environments or on other planets!
Many of you probably state that living things grow, reproduce and respire! 3
On the Earth, living organisms: •
Are made up of cells consisting primarily of organic compounds
(contain: C, H, O & N)
Need an energy source (sun, chemical, foods of organic compounds) in order to survive, grow and reproduce.
Have genetic material which directs internal functions and is passed on to offspring (DNA > RNA > proteins).
On the earth, all living organisms consist of cells, from single-celled bacteria and protozoa to large, multi-celled organisms. All cells need some kind of energy in order to function. They may gather this energy from the sun, through photosynthesis, or get it from food. We also know that some microbes can get their energy from the heat and chemicals generated by the earth!
All living cells have genetic material which is used to direct the cellular processes, especially
DNA making RNA which functions to construct proteins. This genetic material is passed on to offspring and often changes slightly over time, that is, it evolves!
Cells – Two Basic Types!
Prokaryote (=before kernel) – are cells without a defined nucleus; genetic material is not contained within a membrane.
Eukaryote (=with kernel) – are cells that have a defined nucleus where genetic material is kept.
Biologists recognize that organisms use one of two types of cells. It is believed that the most basic of these cell types contain the genetic material loose within the cell wall and this genetic material is not constrained within a membrane. All the bacteria have these types of cells which are called prokaryotes, meaning, before a kernel. Protozoa, fungi, plants and animals have cells in which the
DNA genetic material is kept constrained within a nuclear membrane. These are called eukaryotes which simply means, with a kernel. This kernel or nucleus is easily visualized with stains.
This illustration of a generalized bacterial cell shows that there is considerable complexity even within prokaryote cells. (click) Most importantly, notice that the DNA genetic material is loosely contained within the central part of the cell. There are also distinctive differences in the cell wall makeup, the size of the ribosomes, where RNA makes proteins, and the way that flagella, when present, are constructed.
These are illustrations of plant and animal eukaryote cells. You can immediately see that the
DNA is contained within a defined nucleus and there are numerous other, complicated cellular structures, called organelles. One of the most striking differences between plant and animal cells is the presence of the chloroplasts. Chloroplasts contain chlorophyll and the mechanisms for converting light energy into chemical energy or food. All the organelles types, membranes and flagella are beyond our current discussion.
The Five Kingdom System