Photosynthesis

Plants and some other types of organisms are able to use light energy from the sun to produce food.

Plants and organisms that cannot produce their own food are called heterotrophs.

Autotrophs

Energy comes in many forms, including light, heat, and electricity.

ATP and ADP - The activities of the cell are powered by chemical fuels. One of the principal chemical compounds that living things use to store energy is adenosine triphosphate (ATP).

An ATP molecule consists of a nitrogen containing base called adenine, a 5-carbon sugar called ribose, and three phosphate groups.

Energy

ADP has a structure that is similar to ATP but with one important difference: ADP has two phosphate groups instead of three.

Adenosine diphosphate (ADP)

A single ATP molecule provides enough energy to cause the sodium potassium pump to move three sodium ions and two potassium ions in different directions. (Na 11 K 19)

ATP also powers movement within the cell. Cell organelles are moved along microtubules by motor proteins that use the energy of ATP to generate force. When enough ATP is available the organelle moves quickly along the microtubule.

Energy from ATP

Active Transport

Even though ATP is very efficient at transferring energy, it is not very good for storing large amounts of energy over the long term.

A single molecule of the sugar glucose stores more than 90 times the chemical energy of a molecule of ATP.

Cells can regenerate ATP from ADP as needed by using the energy in carbohydrates like glucose.

ATP and Glucose

Plants use the energy of sunlight to convert water and carbon dioxide into oxygen and high energy carbohydrates (sugars and starches).

Photosynthesis

In the 1600’s, a Belgian physician named Jan van Helmont devised an experiment to determine where the mass from a plant comes from.

In the 1700’s, Priestley determined that plants produced oxygen, the substance necessary for burning by placing a live sprig of mint in a sealed jar with a candle. The candle was lit, burning all of the oxygen in the jar. The candle was able to be lit again after the mint produced oxygen after a few days. The jar had to have been completely sealed and airtight for this period of time.

(Priestley didn’t know what oxygen was at the time. He discovered oxygen in 1774)

Joseph Priestley

Finds that aquatic plants produce oxygen bubbles in the light but not in the dark. He concludes that plants need sunlight to produce oxygen.

Jan Ingenhousz

The Photosynthesis Equation

Photosynthesis Equations

Plants gather the sun’s energy with light absorbing molecules called pigments. The plants’ principal pigment is chlorophyll.

There are two main types of chlorophyll: chlorophyll a and chlorophyll b.

Chlorophyll a absorbs light in the blue part of the spectrum.Chlorophyll b absorbs light in the red part of the spectrum.

Plants are green because they do not absorb light in the green part of the spectrum.

Light and Pigments

Chlorophyll a and b

Photosynthesis takes place inside of chloroplasts.

The chloroplasts contain saclike membranes called thylakoids.

Thylakoids are arranged in stacks called grana.

Inside of a Chloroplast

Scientists break photosynthesis into two parts: light dependent reactions and light independent reactions.

Light dependent reactions take place inside of thylakoids.

Light independent reactions (Calvin cycle) take place inside of the stroma.

The stroma is the region outside of the thylakoid membrane.

Photosynthesis