miicrobiology-blog

[miicrobiology-blog]

introductory biology properties

I’m madly in love with our biological surroundings and everything in it, from the massive trees to the tiniest of microbes. The sheer diversity of living things boggles my mind but it makes me appreciate everything ten-fold. This post generally introduces the key biological concepts that define life.

Some learning objectives to keep in mind when reading this post: a) List and describe the eight properties of living things. b) Define homeostasis and discuss its importance to living organisms. c) Differentiate reproduction, growth & development, adaptation, and evolution. d) Interpret whether viruses could be classified as a living organism or not.

1. Order

The organization of living things tends to direct what that thing will do and how it lives. Down to the atomic level, the subatomic particles make up elements and compounds that dictate the organism’s structure, its reactive chemistry, and its intrinsic ability to obey the laws of physics. Organisms can be simple unicellular organisms more complex as a multicellular being. The different order of atoms, elements, compounds, cellular organelles, and cells set the scene for the prescribed structure and function of the organism.

2. Response to Stimuli

This is another property of living organisms that classifies them as “living.” They need some way to respond to their immediate environment to let them continue surviving, which can be carried out a plethora of ways. Humans have sense organs like the eyes, ears, nose, skin (embedded with many types of receptors), and the tongue to send sensory information from these organs to the brain for processing, then sending the appropriate signals to the body according to the brain’s interpretation. For example, a bad taste can alert you that the food you just ate is rotten or poisonous, or a hot pan shouldn’t be touched; these situations help promote your survivability in your environment. Probably more exemplary of stimuli response mechanisms are the taxis concepts: aerotaxis (oxygen), gravitaxis (gravity), hydrotaxis (water/moisture), magnetotaxis (magnetism), phototaxis (light), and so on.

3. Reproduction

As we might be well aware of, reproduction continues an organism’s lineage and passes on genetic information either sexually or asexually (and very rarely through parthenogenesis - read this neat article about these “virgin births” in lizard [Harmon, 2010]). These processes should trigger your memory about mitosis and meiosis, along with DNA replication and the principles of genetics, which I will gladly cover in another post!

4. Adaptation

Another concept intertwined with reproduction and evolution is adaptation. The simplest way to explain this is that each organism fits into its environment as it suits their ability to survive and reproduce. Arctic hares thrive in the cold climate of the tundra and are active all year round, while some extremophile archaea are adapted to the extremely high- or low-temperature environments. As a microbiologist, please read over this article “Living at the Extremes: Extremophiles and the Limits in a Planetary Context” to gain an appreciation of living organisms being able to adapt to literally all types of environments, like temperatures, pressures, pH, and salinity (Merino et al., 2019). An important thing to keep in mind is that adaptation is ongoing as environments tend to change.

5. Growth & Development

Because cells undergo cell division, you might expect that multicellular organisms will grow as more cells are produced. This, of course, depends on the instructions contained within the genetic material of each cell, but generally organisms will grow and develop over time. You can see this in humans, obviously, as we develop from the fertilized egg, into a fetus, into a baby, toddler, child, adolescent, adult, and older adult. Plants continue through various stages, starting from a seed to grow into a young seedling and onwards to a mature, reproducing plant (of course there are many variations depends on the type of plant). The general idea here is that living organisms progress through various stages where they advance through cellular growth and development.

6. Homeostasis

From the Greek homoisos/homeo (like/similar) and stasis (stoppage), homeostasis is the carefully maintained normal range of functioning that is critical for the survival of living things, as seen in temperature, pH, chemical and ionic concentrations, etc. I like to think of this concept as a “steady state” where the internal mechanisms of a living thing are kept relatively constant. There is small degree of leeway, as seen in the normal range of body temperature between 97-99 degrees F (36-37.2 degrees C; though there is also the consideration of varying normal levels for each individual where one person’s normal temperature is 97 so their homeostatic range might be between 96 and 98 degrees). Anyway, this maintenance of a normal range is critical for survival as cells contain proteins (i.e., enzymes) that are able to function optimally at a specific temperature, pH, and ion concentrations. Any deviance from the normal range can throw off homeostatic balance and cause the body to go into crisis mode.

7. Energy Processing

All living things require energy to carry out cellular metabolic activities. Plants use the sun’s energy and convert it into chemical energy to integrate it into photosynthesis that ultimately makes useable sugars and other important metabolic intermediates. Humans need to harvest energy from secondary sources (food) because we unfortunately cannot use the sun’s energy for our inner metabolism, except for vitamin D synthesis but that’s a different story. The point here is that all organisms rely on some sort of energy source to power the cellular activities that govern pretty much cellular survival and organismal survival.

8. Evolution

Tying many of these concepts together results in evolution, the theory that all species are related at one point and have deviated through natural selection and adaptation. Random mutations in the genetic material might lead to positive changes that confer a benefit to the organism in its survivability over others, and if it successfully breeds and passes on this beneficial information to its offspring, this new characteristic can contribute to a change in the population of the organism (hence, natural selection). This is such an interesting topic and I will definitely make a few posts about this theory and the arguments for and against it to be completely objective.

Notice how a bunch of these concepts end up relating back to reproduction? This is an interesting and open-ended question to consider, but it mainly refers to the biologically-ingrained need to reproduce and pass on genetic material. Why??? It promotes diversity with the chance that the replication mechanisms make a mistake (mutations) and create new, interesting features of an organism (or, on the flip side, completely devastate the organism to the point of unviability), and still leads to more questions about why life exists and why we have such a desire to answer deep questions. Another question to ponder, as it relates to both this post and in our current world situation: do you think viruses should be classified as living organisms or non-living things? 

References:

Harmon, K. (2010). No sex needed: All-female lizard species cross their chromosomes to make babies. Retrieved from https://www.scientificamerican.com/article/asexual-lizards/

Merino, N., Aronson, H. S., Bojanova, D. P., Feyhl-Buska, J., Wong, M. L., Zhang, S., & Giovannelli, D. (2019). Living at the extremes: Extremophiles and the limits of life in a planetary context. Front. Microbiol., 10(780). https://doi.org/10.3389/fmicb.2019.00780