Energy and Photosynthesis

Why is algae special?

It has the ability to capture sunlight and convert it into energy (fuel in the form of oil)

Why don’t we just use biofuels all the time?

It’s limited and still expensive

Harvested energy is from breaking what? 

Covalent bonds 

Potential Energy

Stored energy in chemical bonds

Kinetic Energy

Energy of motion (if released creates motion)

What is the byproduct of kinetic energy/ random movement of molecules or atoms?

Heat

What’s the important downside to energy transformation?

It’s not very efficient

What is the first law of thermodynamics?

Energy can’t be created or destroyed, just changed

What are the two terms for how organisms capture energy?

• autotrophs

• heterotrophs

Autotrophs 

Capture and transform the energy of sunlight by photosynthesis 

Heterotrophs

Obtain energy by eating other organisms 

Photosynthesis

Process by which plants and other autotrophs capture the energy of sunlight to ake energy-rick molecules (like glucose)

Where does photosynthesis occur?

In chloroplasts 

Where does photosynthesis occur in a prokaryotic cell?

In the cytoplasm

“Photo” Step 

Chloroplasts capture the energy of sunlight. Water is split and oxygen is a byproduct

“Synthesis” Step

The captured energy is used to convert CO2 into energy rich sugar like glucose

What are the most important parts of the chloroplast?

• double membrane

• stroma

• thylakoid

Stroma 

Bunch of enzymes for making sugar 

• “synthesis” happens here 

Thylakoid

Converts light energy into chemical energy

• “photo” happens here

What is the first step of photosynthesis?

Chlorophyll absorbs light → excites electrons → generates energy-carrying molecules (ATP, NADPH), while splitting water to release oxygen

• light dependent reactions

What is the second step of photosynthesis?

ATP and NADH are used in the stroma to fix carbon dioxide into sugars

• light independent reactions

What pigment drives photosynthesis, and how does it interact with light?

Chlorophyll (thylakoid), absorbs light wavelengths except green

What happens when photons are absorbed by chlorophyll?

Electrons become “excited”, leading to ATP production and formation of NADPH

Where does the electron transport chain (ETC) occur in photosynthesis?

Thylakoid Membrane

What starts the electron transport chain?

Chlorophyll absorbs light, exciting electrons in Photosystem 2

How are new electrons supplied to PS2 after it loses it excited electrons?

Water is split, releasing oxygen and releasing H+ ions into the thylakoid space, and replacing electrons for PS2

After leaving PS2, where do electrons go?

They get passed along a chain of proteins

How is the energy from moving electrons used in the ETC?

The proteins use it to pump H+ ions from the stroma into the thylakoid space (makes the gradient)

What happens to electrons when they reach the end of the ETC?

They enter photosystem one, where they ping-pong again to get to a higher energy level

What happens to the high energy electrons from PS1?

They are passed to NADP+ along with H+ to form NADPH

What are the two main energy molecules made by the ETC?

ATP and NADPH (needed for the Calvin Cycle)

What are the main products of the light-dependent reactions?

• oxygen (byproduct)

• NADPH

• ATP

What happens to NADPH after it’s formed?

It moves to the stroma to supply power for the Calvin Cycle

What is the general equation for photosynthesis?

6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂

Light Dependent

Uses light + water → produces ATP, NADPH, O2

• photo

Light Independent

Produces sugars (Calvin Cycle)

• synthesis

How are light dependent and light independent reactions connected?

Light dependent reactions provide ATP and NADPH for the Calvin Cycle which is then used to make sugars

In photosynthesis, when does carbon fixation occur?

After transfer of electrons NADP+, but before synthesis of glucose