The concept of a hierarchy of biological organization
Biological organization is characteristically hierarchical and there is a constant inter play between events at different levels. This interplay extends from the events that happen very slowly at the scale of the ecosystems down to the most rapid events operating at the scale of cells and macromolecules. I will try to explain each organizational level starting from the smallest unit. It is easy for one to understand that the cell is the smallest and ultimate unit of living matter, bounded by membrane.
However before getting to the cell, there are the sub-atomic particles. These include Electrons, Protons and Neutrons. Protons and neutrons are in the atomic nucleus. Protons have a positive electrical charge, neutrons have no charge. Electrons occur in only certain energy levels or shells and only so many electrons can occupy each energy level. It is important to note that electrons can carry and release energy. Another example of another subatomic particle is the photon.
The next level is the Atom. Atoms are the smallest unit of matter that has the chemical properties of a particular element. In other words, they have the same atomic number. Atoms of an element have the same number of protons and electrons but two atoms of the same element may differ in terms of the number of neutrons.
This brings us to the molecules. In this level there are the small molecules and the larger molecules which can be referred to as macro-molecules. The small molecules are the molecules that are the small building blocks from which larger molecules are made. Examples include glucose, glycerol, amino acids, fatty acids, nucleotides, and a cluster of other atoms with unique chemical properties. Macro-molecules are larger molecules consisting of many subunits. Examples include starch molecules which consist of many glucose units and proteins some of which consists of amino acids. In some reference books and literatures, molecular assemblies are mentioned in this are of the biological organization.
Molecular assemblies are large organized sets of molecular units that make up parts of organelles. An example is the microtubule which is important in forming structures in the cell related to maintaining the cell structure. Speaking of organelles, this is the next level in the biological organization. Organelles are specialized structures inside of a cell. They are some times surrounded by a plasma membrane. Examples are the nucleus, mitochondria, endoplasmic reticulum, chloroplast, and cilium. Ok, now we finally get to the main organizational unit that is considered the smallest unit of the biological organization, – the cell. The cell is the ultimate unit of living matter, bounded by plasma membrane. It has the capacity to survive, carry out complex chemical reactions, and is potentially capable of self reproduction. Not all cells have nucleus, but all true cells have genetic material in the form of DNA.
The next level is the tissue. A tissue is a group of distinct and similar cells that carry out a specific set of functions. For example, muscle tissue is for contraction. Connective tissue is tissue consisting of cells surrounded by a large amount of non living material. Nerve tissue is for the conduction of nerve impulses and secretion of specialized chemicals called neurotransmitters.
Organs which is another level, are groups of tissues organized together to carry out a particular set of functions. The stomach has an inner lining of tissue that secretes digestive enzymes. Other examples include brain, spinal cord and nerves.
This leads us to the next level; the Organ system. Multicelluar organisms, especially animals typically are organized into organ systems. This is groups of organs that function together to carry out broad sets of functions. Examples of organ systems in humans are the digestive system, circulatory systems, and nervous systems.
Organism is the next level. The organism is that level of biological organization that has its own distinct existence as a complex, self reproducing unit. Humans are multicellular organisms in that we are made of many highly specialized cells which cannot exist independently of other cells in the organism.
Population is another biological organizational level. A population is actually group of freely interacting and inter- breeding individuals of the same species. For example, all the bull frogs in a pond can be considered a population of bullfrogs. Species is the technical name given for a kind of organism. For example, all people are considered to be one species distinct from other primates based on common appearance and more importantly that all races can interbreed with each other.
Community: This is all the populations of different species living and interacting together in a distinct area. An example is the species in a prairie.
Ecosystem: This is the second to the last level. Ecosystems are distinguishable groups of species and the abiotic (non-living) components of the environment with which the living creatures interact. Examples of ecosystems include ponds, tropical forests, and prairies.
The last level of the biological organization is the Biosphere.
The biosphere is the region on, below and above the earth’s surface where life exists. Living things can be found well into the atmosphere, the deepest parts of the ocean, and at least in some areas, microbes live in rock several kilometers below the surface of the earth.
After reading, taking notes and understanding this chapter, I found it amazing that we are all made out of the same things. I mean, how complex things must be that we can all be made out of the same non-living particles. We are made out of the same types of atoms in a coffee mug or pencil. It is interesting how much easier it is for us to differentiate rather than realize the characteristics that show similarities. It is no wonder some educators and scientists seem to be amazed in contemplating the commonalities of things around us- living and non-living. I think that in order to better understand the differences around us, we first need to observe and recognize the similarities and hopefully appreciate everything and every living creature.
What is meant by the phrase “the whole is greater than the sum of its parts”?
I once read a phrase from a book whose title and Author I have long forgotten. However, the author was writing about emergence. He defined the concept of emergence as “much coming from little”. I understood from that book that emergent phenomena can be seen as the result of small elements working together to produce a unified whole. The nucleotides in DNA are such elements. Each is very simple, yet when combined, they can create something which is truly more than the sum of its parts. The cell, which is the smallest organizational unit that has the ability to survive and reproduce on its own can only do so if given DNA instructions, building blocks, energy inputs, and suitable conditions.
The behavior of living organism as an integrated whole cannot be understood from the study of its parts alone. The whole is more than the sum of its parts. The essential properties of an organism, or living system, are properties of the whole, which none of the parts have. They arise from the interactions and relationships among the parts. These properties are destroyed when the system is dissected, either physically ore theoretically into isolated elements. Although we can discern individual parts in a system, these parts are not isolated, and the nature of the whole is always different from the mere sum of its
The differences between living and nonliving things.
I have to admit that before studying the characteristics of living things, I made a list of my own. In this list I included breathing and movement. Well, was I wrong? Trees do not breathe!! From the chapter in my biology text book and the recommended sites in the lesson, I was able to understand the characteristics of living things and the difference between living things and nonliving things. It is understandable that different authors out lined more characteristics than others. However, for my own understanding, I grouped all the characteristics into six groups.
A. Organization. The first characteristic of living things is that they are organized functional patterns, which are not encountered elsewhere. Even the earliest structural and nonliving things had definite sizes and structures. Therefore, they can be recognized in ancient microfossils. Cells which are the structural and functional units of all living matter are of enormous complex. They have nucleus, and many smaller structures, or organelles each of which has a specific function. Plants and animals are made up of millions of such cells organized into tissues, organs, and systems, each geared to carry out a particular function. Organization is one of the most important properties by which living matter can be identified.
B. Homeostasis. The second characteristic is closely related to the first. Living systems maintain a chemical composition quite different from that of their surroundings. The atoms present in different proportions and arranged in different ways. Although living systems constantly exchange certain materials with their environment, a dynamic process, these systems maintain their characteristic chemical composition. This important property is called homeostasis. It is also defined as dynamic equilibrium. Some examples are body temperature, blood sugar (glucose) concentration, chlorophyll concentration in leaves.
C. Energy Utilization. Living things have the capacity of taking in energy from their environment and to transform and use it to make and remake molecules and to form structures. All organisms carry out reactions that release chemical energy. The organisms use some of this energy immediately and store the rest. Metabolism is the sum of all chemical reactions which occur in an organism. Metabolism can be divided into catabolism and anabolism. Catabolism is a biochemical process where complex molecules are broken down into simpler molecules to release energy. An example of catabolism is cellular respiration. Anabolism is a biochemical process where complex molecules are synthesized from simpler molecules; therefore this process requires energy. An example is photosynthesis.
Living systems can respond to stimuli. Bacteria move toward or away from particular chemicals; green plants bend towards light; worms congregate where it is damp; cats pounce on small moving objects. These phenomena are manifestations of a property generally known as irritability. Although different organisms respond to widely varying stimuli, and the complexity of the response may vary greatly, the capacity to respond is a fundamental and universal characteristic of life.
E. Reproduction. Living things have the capacity to reproduce themselves with astonishing fidelity. Reproduction may be divided in the following manner; Cellular reproduction which is where one cell reproduces another. This is an asexual type of reproduction and it occurs during the growth of an organism, repair of damaged cells of an organism, and formation of a new organism by asexual reduction such as unicellular (amoeba, bacteria) reproduction. Sexual reproduction is where genetic material from two organisms combines and forms an individual with genetic material of both parents. When organisms reproduce, the offspring are not exact copies of themselves. The difference between parents and offspring may be transmitted to the next generation along with more changes. This process of reproducing offspring with changes is responsible for the evolution of living organisms through adaptations.
F. Adaptation. Finally, among living things, some are selected as time passes because they are adapted to cope with their environment. An example is a giraffe with long neck. It did not grow the long neck to reach tall tree branches, or a flower that emit sweet odor. The odor is not to attract bees. These things happen such that in the course of evolution, the activities and the structures that make them possible have proved to be of survival value for the individual species. This process is call natural selection. Adaptation is uniquely a biological phenomena and all living things must be able to adapt to their environment.
Only living things have live cycles. Life cycle is the entire span of life of an organism from fertilization to the time it reproduces in turn. Nonliving things do not have life cycles, although they do have cycles.