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Name: Stan
Status: educator
Grade: 9-12
Location: CA
Country: USA
Date: Summer 2012


Question:
I trying to ask in the proper way a very direct, strictly science question, namely what is the proper scientific term one should use to describe the nature of the "energy" in every cell or molecule of a living organism so that that cell or molecule has some form of "awareness" of the external environment and can then send the proper signal to the cell/molecule to respond to the situation, for example to obtain the chemical nutrients it needs to survive. For example, how does a plant "know" it should photosynthesize and knows how to photosynthesize, namely synthesize chemical compounds it "needs" for its continued survival with the aid of radiant energy, especially light. Isn't there something in the plant's DNA structure or platforms that gives the cells/molecules in the plant the ability to "know" what to do, namely it "needs" to photosynthesize, and it "knows" and how to do it. Is there a proper scientific term for that.



Replies:
I think you are trying to apply consciousness to a plant, that is, the plant “knows”, “needs”, “awareness”, etc. This is not a fertile way to attribute the plants chemistry. The plant has no brain. It responds when a whole set of chemical and physical variables take on certain values and/or certain limits. For example, a tree doesn’t “know in the usual sense” that it needs water because it has been dry for a long time. Various processes in the tree slow down, turn off, or otherwise alter their function because the processes require water. When water is deficient certain chemical reactions no longer operate properly, and the plant’s chemistry changes. But the plant isn’t “thinking”, “Oh!, I need water.” It’s just chemical reactions taking place.

Vince Calder


The term is Homeostasis.

Hope this helps, Burr


Stan,

First off, I want to emphasize that to our knowledge cells and molecules do not have 'awareness' or 'knowledge' of their surroundings - the complex behavior we observe in cells arises not from a guiding intelligence but rather through the combination of many simple processes into a more complex system.

There are two basic answers to your query. First, cells can carry out a specific function (say, photosynthesis) entirely due to their DNA. The genetic information contained inside a cell provides an 'instruction' book for the cell to produce a series of proteins that are involved in a given function. Transcription of DNA and expression of proteins is regulated by a complex array of proteins and other molecules. These proteins in turn are switched 'on' or 'off' through environmental factors (for example, the presence or absence of a nutrient, growth factor, or even ion), and are themselves produced by the cell's DNA. So, you can think of the cell as a self-regulating machine that takes in environmental inputs and uses those stimuli to control which genes get expressed at any given time.

On a somewhat more systemic level, one can think of cellular processes as being controlled by a complex series of feedback loops. A common cellular mechanism to control levels of a protein or molecule is 'negative feedback' - if you start to produce a lot of the molecule in question, it directly inhibits further production of itself (often, by binding to a protein or gene and blocking further chemical reactions). Conversely, positive feedback is used to rapidly increase the amount of a molecule, where the product itself causes a signal to the cellular machinery to produce more of the molecule. One can imagine that the complex layering of many different feedback systems together to control the levels of all proteins/molecules in the cell will result in the dynamically regulated 'state' of a cell. This state can be perturbed by environmental factors, which can push the cell into a new 'state' depending on its programming (DNA).

I hope this helps to answer your question! S.Uterman Ph.D.



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