Photosynthesis & Respiration

9.1 - Energy in Living Systems
All living things require energy.  They store this energy in the chemical bonds of biomolecules (carbohydrates, lipids, proteins, and nucleic acids).

Most of the energy used by living things on Earth comes from the sun.

Photosynthesis is the process in which plants, algae, and some prokaryotes convert the energy in sunlight into chemical energy in biomolecules.  The formula for photosynthesis is:

6CO2  +  6H2O  ===>  C6H12O6  +  6O2

An organism that is able to perform photosynthesis is called an autotroph, or a producer.  An organism that cannot make its own food by photosynthesis (and must take in food from its environment) is called a heterotroph, or a consumer.

In photosynthesis, an organism builds an organic molecule (glucose sugar - C6H12O6) to store energy.  When the organism wants to use this energy, it breaks down the organic molecule (glucose) into smaller molecules.  The energy is released and can be used by the organism.  The process of breaking down organic molecules for energy is called cellular respiration.  The formula for this is:
                C6H12O6  +  6O2   ===>  6CO2  +  6H2
Notice that this is just the reverse of the formula for photosynthesis.

In a cell, photosynthesis happens in thechloroplast, while cellular respiration happens in themitochondrion.

The main energy molecule that is used by cells is called ATP (adenosine triphosphate).  In cellular respiration, the energy stored in glucose (or other biomolecules) is converted into ATP, which can then be used to run cell functions.

ATP is made up of an adenine molecule with a chain of three phosphate groups attached to it.  Energy for the cell is stored in the bonds between the phosphate groups.  When one of these bonds is broken, energy is released.  A phosphate comes off of the ATP, making ADP (adenosine diphosphate).

The enzyme, ATP synthetase, is a carrier protein for H+ ions in the membrane of mitochondria.  For each H+ ion that flows through it, ATP synthetase combines an ADP and a P (phosphate group) to make an ATP.  The H+ molecules are transported back across the membrane (against their concentration gradient) by the electron transport chain.

 9.2 - Photosynthesis
Light is a type of radiant energy.  Radiant energy is energy that can travel through space in waves.  Some examples are radio waves, X-rays, visible light, microwaves, and UV (ultraviolet) rays.  Different types of radiant energy have different wavelengths.  We see the different wavelengths of visible light as different colors.  (All of the colors of light combined form white light.)

A pigment is a substance that absorbs certain wavelengths (colors) of light and reflects others.  Think about it like this: the pigment in a blue shirt reflects blue light to your eyes, so the shirt looks blue.  The other colors are absorbed by the blue pigment, so they don't get reflected to your eyes.

Photosynthesis is generally divided into two parts:
1. The Light Reaction              (See the PowerPoint attached below.)
    - Occurs in the thylakoid, inside the plant cell's chloroplasts.
    - Sunlight is absorbed by chlorophyll, and the energy is stored
       in ATP and NADPH.
    - Water is used in this reaction.
2. The Calvin Cycle
    - Carbon Dioxide (CO2) is taken in and combined with other
       carbon compounds.
    - The energy from ATP and NADPH are transferred into these
       compounds, making a 3-carbon sugar.
    - The final 3-carbon sugar can be used to make other organic
       compounds for the plant (glucose, sucrose, starch, etc.)