Chapter 6: Photosynthesis

Mrs. StewartHonors BiologyCentral 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.

ObjectivesSummarize 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

AutotrophsMake their own food

HeterotrophsCannot 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 ATPThe principal chemical compound that cells use to store and release energy is called ATP (adenosine triphosphate)

Storing EnergyATP stores energy in the bond between the second and third phosphate group

ATP is like a fully charged battery

Energy

Releasing EnergyQ: How is the energy in ATP released?A: Break bond between the second and 3rd

phosphates

ADP

2

Think – Pair - Share

ATP vs. ADPATP – 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

PhotosynthesisThe 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.

ChlorophyllThe plant’s principal pigment

absorbs light energy blue-violet red

Absorption of Light byChlorophyll a and Chlorophyll b

Absorption of Light byChlorophyll a and Chlorophyll b

V B G Y O R

Chlorophyll b

Chlorophyll a

Q: Why are leaves green?

A: because chlorophyll absorbs the blue-violet and red light and reflects the green back.

Think – Pair - Share

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.

ThylakoidsSac-like photosynthetic membranes arranged in stacks

GranaStacks of thylakoids

Granum – singularGrana - plural

StromaThe region outside the thylakoid

The watery region in a chloroplast

Similar to the cytoplasm in the cell

Photosynthesis occurs in two parts:

1. Light – dependent reactions (takes place in the thylakoid membranes)

2. Light – independent/Calvin Cycle reactions (takes place in stroma)

ANALYZE THE PICTURE List the reactants and products for

1. The light dependent reactions2. 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

Q: Where did the Oxygen, produced by the light dependent reactions come from?

A: H2O

Think – Pair – Share

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 MoleculeCompound 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 CycleThe “synthesis” part of photosynthesis

These reactions don’t require light, therefore these reactions are called Light – Independent or Dark reactions

The Calvin CycleReactants: 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 FixationThe incorporation of CO2 into

organic compoundsThe 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 waterTemperature Light intensityCO2 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.