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Re: Energy use in plants

> Date: Thu, 6 Nov 1997 02:28:53 -0500 (EST)
> From: JOlson8590 at aol_com
> Subject: Energy use in plants
> A subscriber wrote:
> <<This is where I break down to speculation, and someone else could probably
> give a better answer.  It seems inevitable to me that the plant's task of
> providing oxygen to its roots places an energy burden on the plant.  If
> the roots are kept under aerobic conditions, then the plant doesn't have
> that burden, and the energy can be used for growth or fruiting. >>
> I think this is a common misunderstanding as to "how plants work." Plants are
> not animals - the movement of chemicals, water, sugars, etc., in a plant is
> governed by physics, and the plant does not expend any energy to move these
> things.


The original statement was my own, and I feel obliged to respond.

Plants - in fact all living things - use energy.  My understanding of the
use of energy from plants comes largely from Raven's book "Energetics and
Transport in Aquatic Plants" (not light reading).

Any process that occurs in a plant that wouldn't occur spontaneusly in the
absence of the plant requires an input of energy from the plant.  The
inputs are generally not the kind of mechanical work (pumping) that is
referred to in the letter.  Instead it is mostly chemical energy.

In the case of gas-filled space in plant roots, it takes energy to make
the structure to start with.  It takes an on-going input of energy for the
plant to resist the collapse pressure from the surrounding soil and water
and there is probably also an input of energy by the plants to control the
permeability of various cellular membranes to the passage of oxygen, CO2,
and so on.  Movement of some - if not most - of the essential plant
nutrients actually requires a relatively active input of energy to
maintain concentration gradients in the plant, transport the nutrients
across several membranes and to balance the ionic charge within the cell

Jean is right in that these processes are governed by physics.  However,
the processes aren't free.  Physics requires the plant to expend energy to
make things happen.

Roger Miller

In Albuquerque and feeling combative in preparation for the big Taekwondo
tournament in the Denver area this weekend.