Lecture 4: Sun Worship ("Thank you, Plants!"), Photosynthesis; Plant Evolution

9/15/25

Why is photosynthesis considered one of the most significant things to learn about in college?

Because it is the main process that captures solar energy to feed nearly all life on Earth and plays a huge role in climate regulation

What percentage of photosynthesis on Earth occurs in the ocean?

Approximately 50%

How does photosynthesis impact climate change?

It removes carbon dioxide from the atmosphere, helping to reduce greenhouse gases

What is the original source of energy in gasoline, coal, and natural gas?

The Sun, via photosynthesis

What is the original source of energy in solar, wind, and hydropower?

The Sun, bypassing photosynthesis

What is the original source of energy in nuclear power?

The strong nuclear force that binds quarks together

What is the original source of energy in food?

Photosynthesis

What is the basic equation for photosynthesis?

CO2 + H2O + sunlight —> Glucose + O2

What is the basic equation for cellular respiration?

Glucose + O2 —> CO2 + H2O + ATP (energy)

Where does photosynthesis occur?

In the chloroplasts of plant cells

Where does cellular respiration occur?

In the mitochondria of cells

What molecule is produced in cellular respiration that powers cellular work?

ATP (Adenosine Triphosphate)

What is NADPH used for in plants?

It’s an energy-rich molecule produced in the light reactions of photosynthesis and used in the Calvin Cycle to help convert CO2 into sugar

What are the two major steps in photosynthesis?

1. Light Reaction - captures sunlight to make ATP and NADPH

2. Calvin Cycle - uses ATP and NADPH to fix CO2 into sugar

What happens during the light reaciton?

• Light excites electrons in photosystems

• Water is split to provide electrons

• Electron transport chain creates a H+ gradient

• H+ flows through ATP synthase, producing ATP

• NADPH is also made

What pigment captures light in photosynthesis?

Chlorophyll

Why do leaves change color in the fall?

Chlorophyll breaks down, revealing other pigments like carotenoids

What is the role of Ribisco?

It’s an enzyme that grabs CO2 from the air and helps convert it into a sugar in the Calvin Cycle

List 3 things sugar made in photosynthesis is used for

1. Cellular respiration (energy)

2. Starch and cellulose (storage and structure)

3. Other organic molecules (like DNA, proteins lipids)

What is C3 photosynthesis?

The normal type of photosynthesis where a three-carbon compound is first formed

What is C4 photosynthesis?

A more efficient version found in plants like corn and sugarcane, where a four-carbon compound is formed first to improve CO2 fixation in hot climates

How do desert plants like pineapples adapt photosynthesis to dry environments?

They can CAM photosynthesis, fixing CO2 at night to save water and releasing it during the day for photosynthesis

What do phytoplankton do?

Perform photosynthesis in the oceans, producing oxygen and absorbing CO2

Where does most oxygen in the air come from?

From water during photosynthesis, when water is split and O2 is released

What does photosynthesis in leaves rely on from the roots?

Water and essential nutrients like nitrogen (N), phosphorus (P), and potassium (K)

Where does most oxygen in the atmosphere come from?

Water via photosynthesis

How do roots support photosynthesis?

By absorbing water and nutrients like N, P, K, from the soil

Which enzyme is responsible for capturing CO2 in the Calvin cycle?

Ribisco

What are ATP and NADPH used for in photosynthesis?

To power the Calvin cycle and fix CO2 into sugar

Why is the sun the original source of energy for most life?

It provides the energy captured by photosynthesis, which fuels food chains and fossil fuels