Photosynthesis Notes

Why Study Photosynthesis?

• *All food webs start with photosynthesis!*• Photosynthesis is arguably the most important

biological process on earth because of two key chemical reactions– Liberating oxygen:• Generating oxygen gas from carbon dioxide

– Consuming carbon dioxide• This carbon dioxide comes from the air!

How does photosynthesis affect us?

• Photosynthesis fulfills our food requirements• Photosynthesis fulfills our needs for fiber and

building materials• Energy stored in petroleum, natural gas, and

coal all came from the sun via photosynthesis• Firewood is only made with photosynthesis• Photosynthesis controls the makeup of our

atmosphere (high oxygen, low carbon dioxide)

Photosynthesis and Food

• What biological kingdom serves all of our energy needs directly or through herbivorous animals?– Plant Kingdom

• What is sunlight?– Pure energy

• To be beneficial:– Energy in sunlight must be converted to other forms– The process changes the energy in sunlight to kinds

of energy that can be stored for later use

Where is photosynthesis carried out?

• Photosynthetic reaction centers– Which are found in leaves– Which convert light energy to chemical energy (the form

used by all living organisms)• One of the major energy harvesting processes in plants

involves using the energy of sunlight to convert carbon dioxide from the air into sugars, starches, and other high-energy carbohydrates– What is released in the process? Oxygen– Later, when the plant needs food, it draws upon energy

stored in these carbohydrates

How do we get energy from spaghetti?

• This will be part of our Do-Now question tomorrow. You must do your best to explain this based on the reading and we will review tomorrow!

How did the absence of photosynthesis lead to the extinction of the dinosaurs?

• This will be part of our Do-Now question tomorrow. You must do your best to explain this based on the reading and we will review tomorrow!

Photosynthesis and Energy

• What makes up the bulk of dry wood and other plant material? Cellulose – Which is one of the carbohydrates resulting from

photosynthesis• How does firewood lead to heat?– This will be part of our Do-Now question

tomorrow. You must do your best to explain this based on the reading and we will review tomorrow!

Our current sources of energy

• Coal• Oil• Natural Gas• All three of the above come from ancient plants

and animals. The energy stored within them is chemical energy that originally came from sunlight through the process of photosynthesis– Thus all of the energy we use today was originally

solar energy!

Photosynthesis Fiber and Materials

• Besides being burned for firewood, wood is used for:– Building, making paper, cotton, wool, etc.

• Paper = cellulose produced from photosynthesis• Cotton = a plant

• Petroleum (oil) is needed to make plastics and synthetic (man made) fibers that make up many of the things we use. Because oil comes from once living materials, even plastics depend on energy from the sun!

Photosynthesis and the Environment

• Why are greenhouse gases bad?– Photosynthesis converts carbon dioxide from the

air to carbohydrates and other kinds of “fixed” carbon an releases oxygen to the atmosphere

– Conversely, when we burn firewood, coal, oil, and other fossil fuels, oxygen is consumed, and carbon dioxide is released back to the atmosphere

– So the big problem is that we are releasing carbon dioxide back to the atmosphere faster than plants are able to remove it!

Don’t forget to answer your assigned question!