DNA: What do all of these plants have in common?

Photosynthesis, Part 1

What Is Photosynthesis?• The conversion of

light energy to chemical energy

• Light energy = photons from the sun

• Chemical energy = glucose

What do we start and end with?

EQUATION: 6CO2 + 6H2O + light C6H12O6 + 6O2

• The molecules on the left side are the reactants.

• This is what the plant already has and will use

• The plant uses carbon dioxide, water, and light energy to make…

• The products. These are the molecules on the right side.

• The products are glucose (a simple carbohydrate) and oxygen.

Where does photosynthesis occur?

The Pathway

Why are plants green?

• Pigments are compounds that absorb and reflect specific kinds of light energy

• The pigment most important for photosynthesis is chlorophyll

• Chlorophyll reflects green and absorbs other colors (wavelengths)

• The wavelengths absorbed from the sun provide the energy for photosynthesis

LET’S EXPLORE PIGMENTS!• Set up your lab• You will need:– Filter Paper– Beaker– Penny– Leaf– Tape– Pencil

• Observe the demo from the teacher for instructions

• When you are finished, answer the following questions in your lab notebook:

• 1. What are the products of photosynthesis?

• 2. Where does photosynthesis occur?

• 3. You see a student wearing a red shirt. What wavelengths (colors) is the shirt reflecting? Absorbing?

DNA: Write the equation for photosynthesis. Under the

equation, list the names of the chemicals that are shown in the

equation.

(ex: CO2 is Carbon Dioxide)

Photosynthesis, Part 2

The PathwayThe Light Reactions

• Requires sunlight• Takes light energy and

generates energy that can be used by the cell to synthesize food (glucose)

• Oxygen is a waste product of the light reactions

The Dark Reactions

• Does not require sunlight• Uses the energy from the

light reactions + carbon dioxide to make sugar

• The sugar can then be used by the plant for food

Who Cares?

• How does photosynthesis affect us?

EQUATION: 6CO2 + 6H2O + light C6H12O6 + 6O2

• What are the products?• What do people breathe in?• What do people eat?• What do people breathe out?• Plants and animals are in symbiosis

Answer in your notebook:

1. What is symbiosis?

2. Why are plants and animals in symbiosis?

Photosynthesis, Part 3

The Light Reactions

The Light Reactions - Structure

• Occurs in the thylakoid membrane of the chloroplast

• In the membrane of the thylakoid, there are two very important proteins: Photosystem I and II

• This is where the light reactions will occur

The Light Reactions

The Light Reactions – Process• 1. Light hits a protein called

Photosystem II. The energy from the light “excites” an electron, which passes through a series of proteins to…

• 2. Photosystem I. Light hits this system, exciting the electron again.

• 3. The electron is finally added to make a substance called NADPH.

The Light Reactions – Process, Cont.• Two very important things

happen while the light reactions are going on:– Water is split: The oxygen is

released as a waste product, the electron replaces the one lost in PSII, and the hydrogen is pumped into the thylakoid against the concentration gradient (active transport)

– As the hydrogen flows back out, it produces energy via chemiosmosis

Time to finish your lab!• Answer the following questions in your lab

notebook as your exit ticket. Your notebook must be checked by the teacher BEFORE YOU LEAVE!– What color is the most abundant (is there a lot of)?– What other colors do you see?– What are these colors called?– How do these colors assist in photosynthesis?– What property of water allowed the rubbing alcohol

to travel up the paper strip?

Photosynthesis, Part 4

The Dark Reactions

…a.k.a. The Calvin Cycle

The Calvin Cycle

• Occurs in the stroma (fluid surrounding the thylakoids)

The Steps• Part 1: Carbon Fixation– Carbon Dioxide and a five

carbon compound called RuBP combine to form 12 three carbon compounds called 3-PGA.

• Part 2: Reduction– 3-PGA is turned into a new

three carbon compound called G3P. This requires the energy made during the light reactions (ATP and NADPH)

The Steps• The G3P created will

become glucose, which can be used by the entire plant for food and energy

• Part 3: Regeneration– More energy is used to

make more RuBP to start the cycle over again

• This is a cycle. It will continue to turn again and again unless the plant does not have enough energy or carbon dioxide

Alternate Pathways

• Some plants, such as cacti, have developed other ways to fix carbon

• These pathways are called C3, C4, and CAM

• These pathways are found in plants that live in extreme environments, and help prevent water loss and other dangers

Choose any part of photosynthesis that interests you. Draw an

illustration representing your part. Write at least two key facts under

your illustration.