According to high school students, leaves of plants use carbon dioxide of the atmosphere and water absorbed by the roots to make starch in the presence of sunlight for the cells of plants to use. As a layman, I have certain doubts about what I discussed with senior students and a professor in university. After discussing, instead of clearing my mind, I want to confirm my thesis that every cell in the plant (except dead cells!) re-uses the CO2 and H20, released during respiration, for synthesizing starch. My conclusion is purely a philosophical one as I lost touch with the world of science in March 1957 after B.Sc. Now I will tell you my points.
1) The extremely tender, minute root tips are always growing and require continuous supply of starch.In very tall trees,the distance from top leaves to the root tips may be as much as 300 metres.There is no proper mechanism for transport of starch over such distance,unless we can locate different channels for upward movement of water and downward movement of starch in dissolved form, right from root tip to leaf tip and back.Xylem and phloem tissues are mentioned as responsible for this movement,but in trees like teak, jackwood etc all tissues inside the bark except perhaps a thin layer of cortex, are absolutely dead and impervious to water, being filled with wood oil and compressed by the weight of the trunk. That is why we are able to make furniture,boats,ships etc with wood. Actually, the clever tree is making use of the dead cells as a skeleton-like support for its branches and leaves,the latter being mercilessly dropped after making use of them!
2) In Silent Valley in Kerala, I was shown a very tall tree, hollow inside, with two convenient natural holes, one at the bottom and the other at the top. We can see the sky, looking up from the bottom hole! The tree is alive. How is water and starch transported when xylem and phloem are absent?
3) In Australia, ring cutting was extensively resorted to, for felling trees. The bark and a small part of cortex was removed by making an eight inch deep cutting round the trunk at the bottom. After about six months, the tree falls down dead. This clearly proves that the outermost live cells are responsible for water transport.
4) We plant rose cuttings. The cells on one end develop into a shoot and cells on the other side produce roots.Plant cells are remarkably versatile.Every cell can split and produce all chemicals required for making a duplicate cell.It is impossible to believe that a root cell will wait for starch to come from leaves, when raw materials are available as a result of its own respiration, and it has the necessary technical know-how for making even complicated proteins. Do we not re-use waste in a space station? Are we cleverer than plants?
5) There is no way for a plant cell,except in the leaves,to get rid of CO2produced during respiration.When I, earlier, circulated my doubts in this regard, via email,I got only one response.The botanist had only one word-‘diffusion’ to describe the process. In the humans, is it enough if we just say ‘respiration’? We study all detailed mechanism in human physiology. In the same way, should we not describe the method used by plants to obtain oxygen and get rid of CO2? The professor also said the same thing.As adjoining cells are also producing CO2, how is diffusion possible?The area surrounding the roots will become saturated with CO2.The root will die.The conclusion is inescapable: cells are recycling water and CO2 produced during respiration.
6) When mango fruits are produced in bulk during the season,the number of leaves are actually curtailed! Will farmers curtail production of food grains when it is required in bulk? Laburnum tree becomes almost yellow with flowers in the season, leaves hardly visible.How is starch produced when leaves are reduced?
7) Bamboo,papaya tree etc are hollow,in the case of the former, there are segments,each one a waterproof compartment.Coconut tree mysteriously carries gallons of water to make toddy. If you cut the tree, not a trace of water is found. Are trees using nano technology?
8) In my view,the main function of leaves is to pump water up for which lot of energy is required.Naturally,they make large quantities of starch which attracted the attention of botanists who hastily came to the conclusion that only leaves are concerned in this process.
9) Maximum number of fish thrive in the deep oceans eating planktons which make starch in strata which receive practically no sunlight. In view of the above, I feel more research is needed before we come to a firm conclusion about the mechanism for production of starch and its transportation. Today, institutions like NASA have all the technical capabilities to study this issue which should not be left to the comparatively ill equipped botanists.