READING: PHOTOSYNTHESIS
On our planet we find that most living things (plant or animal) are made up of tiny
microscopic structures called cells. It is important to understand that all of the activities
connected with living things occur within these microscopic structures....including life's
biggest business, the transformation of energy. You might think that all the really
important processes happen on the really big scale of you as a person, but in reality, the
absolutely required processes are mainly happening on the scale of a single cell.
Without the transformation of energy at a cellular level, life could not occur on our
planet.
The reason for this is that there must be a method through which living things can
obtain the energy provided by the non-living world. On Earth, they most reliable and
intense source of energy is the SUN. So, the question is how does the radiant energy
from the sun get transformed into a form of energy usable in the living world? This is
what this reading assignment is all about.
If we examine most forms of life on our planet (plants and animals), we find that they all
share something in common. Their cells use as their basic energy source a special type
of carbohydrate, or sugar, called GLUCOSE. The energy found in the chemical
molecules of glucose is the type of energy we earlier referred to as chemical energy.
Think about this for a moment... chemical energy!
Question: If energy is stored in a chemical molecule, what must be true about the
bonds which hold the molecule together? Are they strong bonds or weak bonds? How
do you know?
The next obvious question is... where did the chemical energy that was used to form the
sugar glucose come from in the first place? If sunlight is the most reliable source of
energy, the sun should have something to do with this... in some way, the sun's energy
is continuously being transformed into the chemical energy of glucose that can then be
used as food by the living things.
Don’t assume too much!!
There are special types of living things on our planet that have the tools required to
carry out this transformation, they are the GREEN PLANTS. Notice only green plants
are mentioned. All other organisms [such as fungi (molds, mushrooms etc.) and
animals, none of which are green] lack the tools to make this transformation of energy
occur.
Green plants are important!
They perform the chemical activity (used to transform energy from sunlight into food for
living things) called…
PHOTOSYNTHESIS.
PHOTOSYNTHESIS
Photosynthesis is a chemical activity that can be understood at many levels… from
simple explanations to very, very complex descriptions of the process. ISP takes the
simplified approach.
It is easy to assume that plants absorb sunlight and use its energy to grow directly, after
all sunlight is energy. However, if this were the case, why can’t all living cells do this
trick? Green plants use specialized cells, and the process of photosynthesis, to capture
the energy from sunlight and store it by creating sugar (glucose) molecules.
It is important for you to realize that this alone can not sustain life.
Plants, much less all the animals, can not stay alive if this was all that happened.
Remember, glucose is like a storage house for energy, storing the chemical energy
obtained from the sun.
A second important activity must occur to release this stored energy. This second
reaction is called…
RESPIRATION
How Does Photosynthesis Work?
In a way, the word PHOTOSYNTHESIS defines itself:
Photo = light, or radiant ENERGY which provides the ENERGY to...
Synthesis = to build or construct
But what is constructed by the green plants? They use “simple” chemicals, meaning that
they have a small number of atoms in each molecule, to construct more “complex”
chemicals such as the sugar called glucose.
The simpler chemicals include carbon dioxide and water which must be available to the
green plant. So, using the energy from sunlight, carbon dioxide and water molecules
chemically react, meaning that their atoms are rearranged into the form called glucose.
During this rearrangement, the sun's radiant energy is transformed into chemical energy
which is stored in the glucose molecule.
Here is a simple word equation which summarizes the whole thing:
Carbon Dioxide + Water −−−> Glucose + Oxygen + Water
Question: How does sunlight fit into this equation? Where should it be written in?
To make all this happen a special substance is required. That substance is called...
CHLOROPHYLL — it is the green pigment found in green plants. Chlorophyll is what makes
green plants green.
Chlorophyll has the ability to trap the sun's radiant energy, and use it to rearrange those
carbon dioxide and water molecules into the glucose.
Only chlorophyll can do this.
No chlorophyll would mean no photosynthesis.
Let's summarize our story of photosynthesis:
Carbon Dioxide + Water + Sunlight == Glucose + Oxygen + Water
captured by stored chemical given off as
chlorophyll energy waste products.
RESPIRATION
Some form of respiration occurs in EVERY living thing, every cell of every plant AND
animal.
Respiration releases the chemical energy stored in food.
Respiration releases the chemical energy stored in glucose, which is used by the cells
to carry out their life activities (growing, moving, etc.). The following diagram attempts to
summarize the important relationship between photosynthesis and respiration. (This
reading is concerned with photosynthesis. Your next reading focuses on respiration.)
Sunlight (radiant energy)
is Transformed through the process of
Photosynthesis in Green Plants
Transforming the radiant energy into
GLUCOSE (chemical energy)
which can be
Respired by
Plants & Animals
to Transform chemical energy
Into other forms
Required to continue living.
RESPIRATION -
The chemical activity occurring in all plant and animal cells releasing the energy from
glucose.
Respiration is NOT the same as what we call breathing!
Respiration is a chemical reaction…
Photosynthesis Review
1-In the process of photosynthesis ______________ energy is transformed into
________ energy.
2-The reactants of photosynthesis are _____________, _____________ and
_________.
3-The products of photosynthesis are __________, ___________, and
_____________.
4-One of the waste products of photosynthesis is ______________. The plant does not
need it so it
_____________________________________________________________.
5-Photosynthesis happens in the _________________. The chemical in the chloroplast
is called ________________________.
6- The prefix chloro- means ___________________.
7-The prefix photo- means ___________________.
8-The suffix –synthesis means ___________________.
9-After Oxygen is made it is stored in the ________________ layer and finally released
through the __________________.
10-The __________________ opens at night to release gas and water.
11-The part of the leaf that is NOT a cell, that is made of wax is the
________________.
12-The vein transports materials in the leaf. The phloem transports _______________
and the xylem transports ____________________.
13-Three kinds of carbohydrates are ____________________, ______________ and
___________________.