Chapter 6: Photosynthesis Mrs. Stewart Honors Biology Central Magnet

Standards CLE 3210.3.3 - Investigate the relationship between the processes of photosynthesis and cellular respiration. SPI 3210.3.3 - Compare and contrast photosynthesis and cellular respiration in terms of energy transformation.

Objectives Summarize the reactants and products of photosynthesis. Describe the reactants and products of the light reactions. Describe the reactants and products of the Calvin Cycle (dark reactions). Summarize how the light reactions and Calvin cycle work together to create a continuous cycle of photosynthesis.

Q: Where does the energy come from in each stage of the food chain? Think – Pair - Share Q: Where does the energy come from in each stage of the food chain?

Autotrophs Make their own food

Heterotrophs Cannot make their own food

WHAT is the energy? Much of the energy used by living organisms is in the form of ATP

Chemical Energy and ATP The principal chemical compound that cells use to store and release energy is called ATP (adenosine triphosphate)

Storing Energy ATP stores energy in the bond between the second and third phosphate group ATP is like a fully charged battery Energy

Releasing Energy Think – Pair - Share Q: How is the energy in ATP released? A: Break bond between the second and 3rd phosphates 2 ADP

ATP vs. ADP ATP – has all 3 phosphate groups Fully charged battery Brief energy storage Can remove a phosphate group to release energy and form ADP ADP – has only 2 phosphate groups Partially charged battery Can add a phosphate group to make ATP

ATP Availability Most cells only have enough ATP for a few seconds of activity Why? Not good at storing energy over the long term Glucose stores 90 times the chemical energy of ATP Cells generate ATP from ADP as needed by using the energy in foods (like glucose)

6-1: Photosynthesis

Photosynthesis The process in which plants use the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates – sugars and starches – and oxygen as a waste product

Photosynthesis 6CO2 + 6H2O C6H12O6 + 6O2 LIGHT (Carbon Dioxide) (Water) (Sun) (Glucose) (Oxygen)

Photosynthesis

The Visible Light Spectrum

Pigments Absorb different wavelengths of light (colors) Reflect (transmit) what they do not absorb We see what is reflected back.

Chlorophyll The plant’s principal pigment absorbs light energy blue-violet red

Chlorophyll a and Chlorophyll b Absorption of Light by Chlorophyll a and Chlorophyll b Absorption of Light by Chlorophyll a and Chlorophyll b Chlorophyll b Chlorophyll a V B G Y O R

Think – Pair - Share Q: Why are leaves green? A: because chlorophyll absorbs the blue-violet and red light and reflects the green back.

Because light is a form of energy… Anything that absorbs light also absorbs the energy from that light When chlorophyll absorbs light, much of the energy is transferred to electrons in the chlorophyll molecule, raising the energy level of these electrons These high-energy electrons make photosynthesis work

Photosynthesis Basics Where does photosynthesis take place? In organelles called chloroplasts.

Thylakoids Sac-like photosynthetic membranes arranged in stacks

Grana Stacks of thylakoids Granum – singular Grana - plural

Stroma The region outside the thylakoid The watery region in a chloroplast Similar to the cytoplasm in the cell

Photosynthesis occurs in two parts: Light – dependent reactions (takes place in the thylakoid membranes) Light – independent/Calvin Cycle reactions (takes place in stroma)

ANALYZE THE PICTURE List the reactants and products for The light dependent reactions The Calvin Cycle (light independent) reactions List the location where each reaction occurs

Pg. 123

Light Dependent Reactions “photo” part of photosynthesis Reactants: H2O, energy from light (photons) NADP+, ADP+ and phosphate group Products: Oxygen gas, ATP, NADPH

Think – Pair – Share Q: Where did the Oxygen, produced by the light dependent reactions come from? A: H2O

What you need to know: Where do the light reactions occur? What is needed (reactants)? What is created (products) In the thylakoids. Light (photons) water ATP & NADPH - go on to Calvin cycle Oxygen - that is released

Carrier Molecule Compound that can accept a high energy electron and transfer it along with most of its energy to another molecule Ex.) NADP+ + H  NADPH

The Calvin Cycle The “synthesis” part of photosynthesis These reactions don’t require light, therefore these reactions are called Light – Independent or Dark reactions

The Calvin Cycle Reactants: ATP and NADPH (from light – dependent reactions) and CO2 Products: high energy sugars (C6H12O6) and NADP+ and ADP+ (which will go back to light dependent reaction for reuse)

Carbon Fixation The incorporation of CO2 into organic compounds The Carbon in CO2 is “fixed” into the usable energy form of sugar 6 CO2 molecules will go into the cycle to produce each organic molecule of 6-Carbon sugar. (C6H12O6 )

Factors Affecting Photosynthesis Not enough water Temperature Light intensity CO2 levels

Objectives (Did we…) Summarize the overall reactants and products of photosynthesis. Describe the reactants and products of the light reactions. Describe the reactants and products of the Calvin Cycle (dark reactions). Summarize how the light reactions and Calvin cycle work together to create a continuous cycle of photosynthesis.