Photosynthesis

The Sun!! Photosynthesis Where does the energy come from that sustains all life? The Sun!! Well most of it anyway……

What is photosynthesis? In the process of photosynthesis, plants convert the energy of sunlight into the energy in the chemical bonds of carbohydrates-sugars and starches.

Discovery of the process: For many years, people wondered how a few seedlings could develop into a large tree. The mass of seedlings are only a few grams, where as the mass of a tree is several tons. Dutch physician Jan Van Helmont devised an experiment to determine where the mass came from. He concluded that the mass grew from the water, because that was the only thing he had added to the pot. Later it was determined that most of the mass comes from the air.

What makes photosynthesis complete? Helmont did not realize that carbon dioxide in the air also plays a major role in the contribution of mass growth. The carbon in carbon dioxide is what is used to make carbohydrates in photosynthesis.

Priestly placed a candle in a jar along with a mint plant. Later on, scientist Joseph Priestly performed an experiment that would give rise to why oxygen is released in photosynthesis, and why sunlight is needed for it to photosynthesize. Priestly placed a candle in a jar along with a mint plant. He then realized that the candle could only stay lit when the mint plan was present. This would mean that the plant was releasing oxygen.

Why is Photosynthesis important? Through experiments, it was realized that in the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen. Plants that are able to use a source of energy, such as sunlight, to provide food directly from simple inorganic molecules are known as autotrophs. *Some bacteria and protists are also autotrophs. Photosynthesis and chemosynthesis are two ways in which organisms can make food.

WHAT IS THE DIFFERENCE BETWEEN A HETEROTROPH & AN AUTOTROPH? Quick Concept Check: WHAT IS THE DIFFERENCE BETWEEN A HETEROTROPH & AN AUTOTROPH?

the equation for photosynthesis is: LIGHT Carbon Dioxide + Glucose Water + Oxygen LIGHT 6 CO2 + 6 H2O C6 H12 O6 + 6O2

The sugars that result from photosynthesis are produced by adding the hydrogen ions and electrons from water to carbon dioxide, NOT by splitting CO2 and adding water! oxidized H+ and e- 6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O reduced

Plant Photosynthesis internal leaf structure chloroplasts Figure: 06-01 Title: An overview of photosynthetic structures. Caption: chloroplasts outer membrane inner membrane thylakoid

Photosystems use some wavelengths of light but reflect others…

Another way in which light energy is trapped in chemical form involves adenosine triphosphate or ATP. During photosynthesis, green plants produce ATP, which is the energy storing compound used by every living cell. The energy is released by means of breaking the phosphate bonds which make up the ATP cycle. The energy is used in almost all cellular activities.

Respiration vs. Photosynthesis

Photosynthesis and respiration are complementary processes in the living world. Photosynthesis uses the energy of sunlight to produce sugars and other organic molecules. These molecules in turn serve as food. Respiration is a process that uses O2 and forms CO2 from the same carbon atoms that had been taken up as CO2 and converted into sugars by photosynthesis. In respiration, organisms obtain the energy that they need to survive. Photosynthesis preceded respiration on the earth for probably billions of years before enough O2 was released to create an atmosphere rich in oxygen. (The earth's atmosphere presently contains 20% O2.)

Self-Evaluation Questions 1. In the process of photosynthesis, plants convert the energy of sunlight into what? 2. When Helmont devised an experiment, he concluded that the mass grew from the_____, which was the only thing he had added to the soil. 3. What scientist gave rise to the explanation of plants giving off oxygen, and the reason sunlight is needed in order for plants to photosynthesize? 4. Fill in the missing part of the equation for photosynthesis--Carbon dioxide + water yields what? (two things) 5. What do you call plants that obtain their nutrients in organic molecules through photosynthesis?