Students of many fields find themselves studying physics in one way or another, because of the basic role it plays in day-to-day physical phenomena. Let us consider the life cycle of a tree as an example.



Seed sown in the ground goes on to develop shoot of the plant as it reaches out for the light. At the same time, roots of the plant will spread deep in the soil, as they search for water and other resources.



Water from the soil passes into the roots, if and only if, the soil has higher concentration of water than the root cells. From the roots, liquid water flows into the woody stem of the tree and then into the green leaves, where food will be made.









The question is, how do these water molecules go upward against the effects of gravity? The answer is pretty simple, to be honest.





In the green leaves, most of the available water is used up for photosynthesis. However, some of it escapes as vapour, water in gaseous form, because from the heat of the sunlight, as shown below.









Since the molecules of water in the root and stem stick to one another due to cohesion, the vapours which escape from the leaves, sort of, drag or pull the remaining water upward behind them. This procedure is called transpiration.

The next question is, where does the structure of the tree come from? It is generally thought that plants grow out of the ground. However, apart from water and vital nutrients, the ground does not contribute in the building up of the tree.



It is important to understand that mass of the tree is primarily carbon, and where does all the carbon come from? The answer is, from the atmosphere, although, not in pure form.









Like we breathe in oxygen, trees soak up carbon dioxide from the air. This is generally why it's recommended to plant more trees. Well, in fact, it is estimated that an acre of mature trees can capture 2.5 tonnes of carbon dioxide per year!





The absorbed carbon dioxide when acted upon by the sunlight, is reduced to carbon only. The trees utilize these carbon molecules to construct their body tissues, for example, as in fruits. The oxygen molecules, on the other hand, are spit back into the air.









Thus, combination of water, air and light, as they come from the ground, atmosphere and sun, respectively, mediate the growth and the flowering of the tree.





Towards the end of life, a tree is cut and its wood used as fuel for combustion. Friction gets it started because of the heat, and the carbon molecules reunite with the oxygen molecules, in a terrible catastrophe, fire, as we call it, producing a bright flame.



This light and heat of the fire is, in actuality, the light and heat of the sun that went in. So, it is kind of a stored sun, that is coming out, when you burn a log. Nature definitely knows how to come back in a full circle!









Summing up: the cohesion or linkage between water molecules, creation of pressure in the stem due to evaporation in the leaves, conversion of sunlight into food, and restoration of the same energy in the chemical process of burning. From our example of tree, it is clear how in biological processes, physics has a role to play.