Photosynthesis

Topic: Photosynthesis

In this learn assignment you will:

• What photosynthesis is
• The steps of the light dependent reaction
• The steps of the light independent reaction
• Lights role and properties

Associated Course Competencies

CC1. Describe the biological, geological, physical, and chemical features that influence the evolution of life in Earth’s interconnected marine environments. (I) CC10. Describe the flow of energy and cycling of nutrients within and among marine systems. (IV)

Image Details: The open ocean environment is any part of the ocean that isn't near land. Its different ecosystems are characterized by depth.

Review Chemistry

You will notice that as you go through the learn assignments this week they are will be heavier on the chemistry terms than our last several weeks. Don't recall our chemistry overview please review the Intro to Chemistry section in our Physical and Chemical Features Learn Assignment. I have embedded the presentation below for your convienience. If you feel comfortable with chemistry feel free to move onto the next slide.

Photosynthesis

"When life hands you light, make sugar!"

• Photosynthesis is a series of metabolic pathways uses the energy from the light, converts it into ATP (biological energy storage molecule) and NADPH (a different energy molecule that is a temporary transport), and then stores the energy in glucose or other sugar molecules.
• Used by most autotrophs
• Requires:
• Light
• Water
• Carbon Dioxide

Steps of Photosynthesis

• Overall Chemical Formula: 6CO2 + 6H2O → C6H12O6 + 6O2
• Two major steps:
• Light Dependent
• converts light to biological energy
• ATP
• NADPH
• Light Independent (Calvin Cycle)
• converts biological energy to sugar

Properties of Light

The electromagnetic spectrum

• What is light?
• formed when an excited electron "drops down" to a stable orbital giving off it's excess energy
• a packet of energy, called a photon, with a particular wavelength
• Different wavelengths make-up different parts of the electromagnetic spectrum

Properties of Light

How we see

• Color vision
• Our eyes have color-receptive cones that detect when a photon of light impacts it
• Our brain then interprets that as color
• Object color
• Light photons that bounce off of pigment (a type of protein)

Note: Color blindness isn't uncommon. The images to the right might look the same if you have a common type of color blindness.

Properties of Light

The electromagnetic spectrum

• Wavelength
• measured by the distance of cycle
• Spectral Colors (Visible Light)
• Wavelengths between 700nm (red) and 400nm (violet)
• This is range humans can see, but this isnt true for all life:
• Most mammals: 2 of color-receptive cones
• Humans: 3 types of cones
• Birds, Reptiles, many fish: 4 types of cones
• Mantis shrimp: 16 types of cones
• Yellow light is the most abundant visible light (yellow sun)

Properties of Light

The electromagnetic spectrum

• Non-spectral Colors
• Ultraviolet, X-ray, Gamma-rays
• under 400nm
• Infrared (heat), microwaves, radiowaves, TV waves, etc.
• over 700nm

Properties of Light

Light and Photosynthesis

• Photosynthesis uses photoreceptors to capture light energy
• Some wavelegnths of light are used more than others

Chloroplasts

Stroma (fluid inside)

Outer membrane

Inner membrane

Intermembrane space

Thylakoid (single disk) Granum (stack of disks) Lumen (fluid inside the thylakoid)

• Evolutionary history - cyanobacteria symbiote that became an organelle.
• We know this because it has a two layers of membrane and it's own DNA that resembles a bacteria
• Role: produces glucose which is moved to other parts inside and outside the cell

Optional Reading, before we move onto the steps

Photosynthesis is a fun example of discovering things in "odd" ways. Science doesn't always work in the order or expected way (not all discoveries were intentional). The discovery of how photosynthesis works and its pathway is a whole series of right answer found the wrong way or just odd ways of thinking. This quote showcases this well: "The history of science is never written by the scientists involved in making discoveries. That would be too painful, too embarrassing..." - Andy Benson (1977)A couple examples for photosynthesis:

• Realizing that plants used CO2 because the room felt better with plants
• The way the scientists figured out how it works was figured out by algae lollypops and the scientist overheating in his wife's car while she was shopping.

The first article linked below tells the story of how photosynthesis was discovered. It isn't required, but I do highly recommend reading it. It tells more about the examples above.

Optional Reading: Discoveries in oxygenic photosynthesis (1727–2003): a perspective

Steps of Photosynthesis

You Are Here Membrane of the thylkoid

Light Dependent Reaction Steps

Photosystem II

Before we begin the steps, please note:

• I am going to describe the steps and then there will be a video that shows the whole thing through.
• Don't stress is some of the details feel confusing. Just notice that it uses light to move things. That movement works like a current that generates energy.
• Don't memorize protien names. Just notice that CO2 is used, water is used, and O2 is made. Notice that the O2 isn't made from the CO2 (it comes from the water) and that all the CO2 is put into sugar.

H+

H+

Stroma Side

e-

Lumen Side

e-

H20

H+

H+

H+

H+

H20

O2

Steps of Photosynthesis

You Are Here Membrane of the thylkoid

Light Dependent Reaction - Step 1

Photosystem II

• Moves through a chain of proteins called photosystems.

• Starts with photosystem 2
• It was discovered second and so is called photosystem 2 (represented with II)

• Captures light energy and uses it to break water and excite (energize) electrons

H+

H+

Stroma Side

e-

Lumen Side

e-

H20

H+

H+

H+

H+

H20

O2

hydrogen pump proteins

Steps of Photosynthesis

H+

plastoquinone

Stroma Side

Light Dependent Reaction - Step 2

H+

cytochrome

H+

• Electrons used in next two proteins in the sequence to pump hydrogens
• These are literally pumps. They move the hydrogens from one side to the other to build up a concentration gradient (like filling a dam with water)
• A third protein carries it to the next photosystem

e-

e-

e-

PC

e-

H+

H+

H+

H+

Lumen Side

H+

H+

H+

Steps of Photosynthesis

NADP

NADPH

Light Dependent Reaction - Step 3

photosystem I

e-

• Photosystem I Complex
• Photosystem I
• Two additional protiens that sit on top.
• The photosystem uses light to re-excite the electron and make NADPH (a temporary energy storage molecule)

Stroma Side

e-

e-

PC

Lumen Side

H+

H+

H+

H+

H+

H+

H+

H+

ATP Synthase

Steps of Photosynthesis

ATP

ATD

Light Dependent Reaction - Step 4

H+

• ATP Synthase
• Uses the concentration gradient of H+ to make ATP
• H+ ions either:
• used to make NADPH
• re-pumped through by the hydrogen pump proteins

Stroma Side

H+

Lumen Side

H+

H+

H+

H+

H+

H+

H+

Steps of Photosynthesis

H+

Diagram of all the Light Dependent Reaction Parts

ATP

H+

NADPH

H+

Stroma Side

e-

e-

Thylakoid Membrane

e-

H+

e-

Lumen Side

e-

H20

H+

H+

H+

H+

H+

H+

H+

O2

H+

Steps of Photosynthesis

You Are Here The Stroma

Light Independent Reaction (Calvin Cycle)

• This part doesn't require light and can happen at night.
• It is a three-phase cycle.
• Its a cycle because the starting enzyme replenishes in the cycle.

Steps of Photosynthesis

You Are Here The Stroma

Light Independent Reaction (Calvin Cycle)

• Phase 1 : Carbon Fixation
• Uses CO2 and ATP to make temporary molecules
• Phase 2: Reduction
• Uses NADPH and makes one glucose.

• Phase 3: Regeneration of RuBP
• Uses more ATP and the rest of the carbon to resets the Rubisco enzyme to be reused

All Steps of Photosynthesis

Wrap-Up: Discussion Board

To complete this learn assignment please submit the following: A labeled drawing(s) of the light dependent pathway and light independent cycle of photosynthesis. This drawing must be your own, but can be either hand drawn or digitally drawn (not AI).