1) Photosynthesis uses sunlight energy to produce
sugar. Sugar goes from one cell to another until it reaches the cells which don’t
have access to sunlight (or they don’t get enough sunlight), so they can’t make
any photosyntesis or they make very little photosyntesis. That’s how the leaves
of a plant feed the roots of the same plant. When that cell receives the sugar,
it makes cell respiration to convert it back to water and CO2 and release energy.
When an animal eats a plant, animal cells also make this respiration process
with the sugar.
The chemical equation is basically the opposite:
Photosyntesis: water + CO2 -> O2 + sugar
Respiration: sugar + O2 -> CO2 + water
2) The DNA duplication is semiconservative, which means each
new double chain contains 1 original molecule and 1 newly synthesized molecule.
When DNA is duplicated, each one of the molecules (chains) acts
as a template for one of the chains that are being synthesized. Wherever there
is an A in the old molecule, the new molecule will have a T. G goes with C, C
goes with G and T goes with A. The way this happens is related to the number of
hydrogen bonds (C and G have 3, whereas A and T have 2) and the molecular size
(A and G have 2 cycles, whereas T and C have 1 cycle – so it is always a big
one with a small one, total = 3 cycles). You can compare it with a chocolate mold:
if you want a chocolate to be heart-shaped, you have to get a mold which has a
heart-shaped hole and put the warm chocolate inside. So the mold and the
chocolate have the opposite shape – complementary shape. But in this case, once
the duplication process ends, mold and new DNA stay together as a brand new
couple, and the mold never goes back with the other mold.
