Cell Membrane |
Prokaryotic and Eukaryotic Cells |
RNA's Role |
The Role of the Endoplasmic Reticulum and the Golgi Apparatus | Energy Capture and Storage |
What Determines the Eukaryotic Cell's Shape?
|Energy Capture and Storage|
|CA GR 9-12 Biology 1.i.|
Everything that lives needs energy.
And since everything that lives is made up of cells, cells need energy too.
But where do they get it?
More specifically, cells break down sugars and turn them into energy. That process is called metabolism. Metabolism is a big word. It is the sum total of all the chemical reactions an organism (like us) goes through to survive.
There are two processes involved in metabolism -- and they make our world go around. Those processes are photosynthesis and cellular respiration.
Photosynthesis is the process by which plants make carbohydrates (sugars).
cellular respiration is the process by which cells convert these sugars into ATP, the basic “fuel” for all living things. You’ll learn more about it in our next Instruction.
But now we’d like to talk about photosynthesis.
Here’s how photosynthesis works:
Let’s look at these diagrams of plant cells and chloroplasts:
Besides sunlight, the raw materials for photosynthesis are carbon dioxide (CO2)
and water (H2O). (A plant gets water through its roots or leaves and gets carbon
dioxide from the atmosphere).
During the first (“light reaction”) stage, the chlorophyll uses this solar energy to split water (H2O) into Oxygen (O2), protons (hydrogen ions, H+) and electrons.
During the second (“dark reaction”) stage, no light is needed.
The chloroplasts can make carbohydrate in the dark if they’re
provided with ATP (fuel), NADH (an enzyme catalyst) and CO2.
This is when the protons and electrons actually convert the carbon
dioxide into carbohydrates (sugar) and oxygen.
During photosynthesis the CO2 is reduced and the water
oxidized. In green plants most of the ATP for protein synthesis comes from
Energy from SUNLIGHT + 6H2O+6CO2 produce C6H12O6+602
If you don’t speak “chemistry,” it goes like this:
Light plus six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.
Here’s another brief description of how photosynthesis works:
Something else you should know is that it’s the chlorophyll in the chloroplast of plant cells that makes plants green. Of course not all plants are green, but most are – and here’s why.
Why Plants Look Green
As you know, light is transmitted at different wavelengths. And it’s those wavelengths that determine the colors we see. Any substance that absorbs light is called a pigment. Chlorophyll absorbs light, so it’s a pigment.
Different pigments absorb different wavelengths of light. What they don’t absorb, they reflect. And it’s the wavelengths they reflect that determine what colors we see. Auxiliary pigments in the chloroplasts of plant cells are responsible for absorbing protons of different wavelengths of light.
Chlorophyll absorbs red and blue wavelengths -- but it doesn’t absorb green. It reflects green. So when we look at most plants, we see green.
Experiments for Home and Classroom
Why do leaves change color in the fall? -- photosynthesis. This web site
explains the process very carefully (ignore the overly simple "I Can Read"
section) and also has three interesting experiments to help students understand
how the process works. Don't be put off by the word chromatography -- it simply
means "separation of colors." Scroll down to "Projects to Do Together." Click:
In order to carry out photosynthesis, plants must pull water from the soil. This
entertaining experiment, called "Celery Stalks at Midnight," shows how this
happens (the process is called capillary action). Materials required include 4
stalks of celery, 4 cups or glasses, food coloring, a measuring cup, paper
towels, a vegetable peeler, a ruler and some old newspapers. Click: