1. Photosynthesis
Why don’t bushes or other trees usually grow underneath large trees?
Not enough sunlight for such plants to grow.
WHY do plants need sunlight to grow?
To make food thru photosynthesis!!!

2. Lesson Objectives Identify the kind of energy that powers life.
State why living things need energy.
Evaluate the importance of autotrophs for providing energy to all life.
Describe how autotrophs and heterotrophs obtain energy.
Define chemosynthesis.
Compare and contrast glucose and ATP.
Outline how living things make and use food.
Outline the stages of photosynthesis.
Describe the chloroplast and its role in photosynthesis.
Identify the steps of the light reactions and the Calvin cycle.

3. Terminology Review What is energy? _________________________________
What is the ultimate source of all energy?
The ability to do work.
Sunlight
Energy, unlike materials, cannot be recycled. The story of life is a story of energy flow – its capture, transformation, use for work, and loss as heat.
Energy, the ability to do work, can take many forms: heat, nuclear, electrical, magnetic, light, and chemical energy. Life runs on chemical energy - the energy stored in covalent bonds between atoms in a molecule. Where do organisms get their chemical energy? That depends…
Most food is made in the process of photosynthesis. This process provides more than 99% of the energy used by living things on Earth. Photosynthesis also supplies Earth’s atmosphere with oxygen.

4. Kinds of energy which power life
What forms can energy come in? __________________________________
Where is energy stored? __________________________________
How is this energy released? __________________________________
Light, heat, chemical, nuclear, magnetic, and electrical
In chemical bonds
By breaking the chemical bonds

5. How Do Organisms Get Energy? Autotrophs vs. Heterotrophs
Living organisms obtain chemical energy in one of two ways.
They make it themselves OR
They consume those who can make it themselves

6. CAN MAKE IT THEMSELVES Autotrophs—Photosynthesize
Plants, algae, and some bacteria
Producers, begin food chains which feed all life
Store chemical energy in carbohydrate food molecules
Organic molecules made through photosynthesis store chemical energy (food)
Food provides both the energy to do work and the carbon to build bodies. Autotrophs make food for their own use, but they make enough to support other life as well. Almost all other organisms depend absolutely on these three groups for the food they produce.

7. Photosynthesis
Provides over 99 percent of the energy supply for life on earth
Uses solar energy to convert water and carbon dioxide into oxygen and glucose

8. CONSUMERSHeterotrophs
Animals, fungi, and many protists and bacteria
Consumers, cannot make their own food
Obtain energy through food consumption
Autrotrophs or other Heterotrophs
Highly diverse organisms
The producers, or autotrophs, begin the food chains which feed all life. They produce food not only for themselves but for all other living things as well (which are known as consumers or heterotrophs). This is why autotrophs form the basis of food chains.
If plants, algae, and autotrophic bacteria vanished from earth, animals, fungi, and other heterotrophs would soon disappear as well. All life requires a constant input of energy. Only autotrophs can transform that ultimate, solar source into the chemical energy in food which powers life.

9. Chemosynthesis
Other autotrophs: mostly bacteria in dark or low-oxygen environments
– produce food using the chemical energy stored in inorganic molecules such as hydrogen sulfide, ammonia, or methane.
Tubeworms deep in the Gulf of Mexico get their energy from chemosynthetic bacteria living within their tissues. No digestive systems needed!

10. Food to Energy Molecules: Glucose and ATP
Two of the most important energy-carrying molecules
Glucose: simple carbohydrate; energy-rich product of photosynthesis; chemical formula C6H12O6
“deliverable” form of energy; carried in blood through capillaries and taken up by trillions of cells
nearly universal food for life.
ATP: store smaller quantities of energy; product of first stage of photosynthesis and used during second stage to make glucose
provides cells with energy for cellular processes
“useable” form of energy for your cells

11. Why Organisms Need Both Glucose and ATP
Glucose more chemical energy in a smaller ‘‘package” than a molecule of ATP
more stable than ATP; better for storing and transporting energy
BUT too powerful for cells to use.
ATP  right amount of energy to power life processes within cells
like a rechargeable battery
energy released when broken down into ADP and phosphate
“worn-out battery” ADP recharged using new energy to attach a new phosphate; rebuilds ATP.
The materials are recyclable, but recall that energy is not!
How much energy does it cost to do your body’s work? A single cell uses about 10 million ATP molecules per second, and recycles all of its ATP molecules about every seconds.

12. ATP and ADP
ATP: adenosine triphosphate; principle chemical compound in which living things store energy.
Adenine: nitrogen-containing
compound
Ribose: a 5-carbon sugar
3 phosphate groups

13. ADP: adenine diphosphate; structural similar to ATP but with one important difference: ADP has only two phosphate groups. ADP is converted to ATP when available energy is used to add a phosphate group to it.
ADP
Adenine: nitrogen-containing
compound
Ribose: a 5-carbon sugar
2 phosphate groups
two phosphates

14. Releasing Energy from ATP
Energy stored in ATP is released when it is converted to ADP and a phosphate group.
Adding or subtracting a
3rd phosphate group allows
the cell to store and release
energy as it is needed
The characteristics of ATP make it an exceptionally useful molecule that is used by all types of cells as their basic energy source. O

15. Using Biochemical Energy
How the cells use ATP:
To conduct active transport; like the sodium-potassium pump
It moves sodium ions (Na+) out of the cell and potassium ions (K+) into the cell
A single ATP molecule provides the energy to move three sodium ions and two potassium ions in different directions
Powers movement within the cell
Moves cell organelles along microtubules by motor proteins that use energy from ATP to generate force
What are active transport methods in the cell that we have already learned about?
Endocytosis, Phagocytosis, Exocytosis, Sodium-Potassium Pump

16. Photosynthesis: The Most Important Chemical Reaction for Life on Earth
Necessary conditions include: 
enzymes - proteins to speed up chemical reactions
chlorophyll - a pigment which absorbs light
chloroplasts – which contain chlorophyll, accessory pigments, and enzymes in patterns which maximize photosynthesis
Remind them of reactant and product locations; co-efficients and subscripts
Within plant cells or algal cells, chloroplasts organize the enzymes, chlorophyll, and accessory pigment molecules necessary for photosynthesis. When the reactants meet inside chloroplasts, or the very similar cells of blue-green bacteria, chemical reactions combine them to form two products: energy-rich glucose molecules and molecules of oxygen gas.
HO: RUBEN-KAMEN & CROSSWORD NOW…

17. Stages of Photosynthesis
Two stages:
light reactions uses water; changes light energy into chemical energy
releases oxygen as a waste product.
Calvin cycle uses chemical energy in ATP and NADPH to make glucose

18. Chloroplasts: Theaters for Photosynthesis
Chloroplast contain:
neat stacks called grana (singular, granum).
consist of sac-like membranes, known as thylakoid membranes
Thylakoid membranes
contain photosystems
groups of molecules that include chlorophyll
light reactions occur in thylakoid membranes.
stroma
space outside the thylakoid membranes
reactions of the Calvin cycle occur here
Chloroplasts closely resemble some types of bacteria and even contain their own circular DNA and ribosomes.
Endosymbiotic theory holds that chloroplasts were once independently living bacteria (prokaryotes).

19. Chloroplasts Function
Work with enzymes and two basic molecules: pigments and electron carriers
Pigment molecules, arranged together within proteins in large, complex photosystems, absorb specific wavelengths of light energy and reflect others; thus they appear colored.
Most common photosynthetic pigment is chlorophyll, which absorbs blue-violet and red wavelengths of light, and reflects green.
Accessory pigments absorb other colors of light and then transfer the energy to chlorophyll.
These include xanthophylls (yellow) and carotenoids (orange).
HO: CHLOROPHYLL WS

20. Electron carrier molecules are usually arranged in electron transport chains (ETCs).
These accept and pass along energy-carrying electrons in small steps; they produce ATP and NADPH, which temporarily store chemical energy.
Electrons in transport chains behave much like a ball bouncing down a set of stairs – a little energy is lost with each bounce.
However, the energy “lost” at each step in an electron transport chain accomplishes a little bit of work, which eventually results in the synthesis of ATP.

21. Photosynthesis Stage I: The Light Reactions Chloroplasts Capture Sunlight’s Energy
Light is the source of energy for photosynthesis, and the first set of reactions which begin the process requires light – thus the nameEvery second, the sun fuses over 600 million tons of hydrogen into 596 tons of helium, converting over 4 tons of helium (4.3 billion kg) into light and heat energy. Countless tiny packets of that light energy travel 93 million miles (150 million km) through space, and about 1% of the light which reaches the Earth’s surface participates in photosynthesis.
Light Reactions  light is absorbed and transformed to chemical energy in the bonds of NADPH and ATP
light strikes chlorophyll (or an accessory pigment in photosystem II) within the chloroplast, it energizes electrons within that molecule. These electrons jump up to higher energy levels; they have absorbed or captured, and now carry, that energy. High-energy electrons are “excited.”
excited electrons leave chlorophyll to participate in further reactions, leaving the chlorophyll “at a loss” for electrons; eventually they must be replaced.
replacement process also requires light, working with an enzyme complex to split water molecules.
process of photolysis (“splitting by light”), H2O molecules are broken into hydrogen ions, electrons, and oxygen atoms.
electrons replace those originally lost from chlorophyll.
Hydrogen ions and the high-energy electrons from chlorophyll will carry on the energy transformation after the Light Reactions are over
oxygen atoms, however, form oxygen gas, which is a waste product of photosynthesis
oxygen gas given off supplies most of the oxygen in our atmosphere

22. Light-Dependent Reactions
Require LIGHT
Use light energy to produce
Oxygen gas
Convert ADP to
energy carrying
ATP
Convert NADP+ to
NADPH

23. Steps of the light-dependent reactions
1st * Pigments in photosystem II absorb light…light makes high-energy electrons…these electrons are passed to the electron transport chain
* Thylakoid membrane continues to provide new electrons to chlorophyll…the new electrons come from water molecules…enzymes on inner surface of
thylakoid membrane break down each water molecule into 2 electrons, 2 H+ ions, and 1 oxygen atom through photolysis (“splitting by light”)…~ 2
electrons replace high-energy electrons chlorophyll has lost to electron transport chain…~ oxygen released into the air as O2…~ 2 H+ ions released
inside thylakoid membrane creating an electrochemical gradient
2nd High-energy electrons move through electron transport chain from photosystem II to photosystem I…energy from electrons is used by molecules as
they move through the electron transport chain to transport H+ ions from the stroma into the inner thylakoid
3rd Pigments in photosystem I use energy from light to reenergize the electrons…NADP+ picks up high-energy electrons from outer surface of thylakoid
plus an H+ ion and becomes NADPH
4th As a result of the H+ ions released during the splitting of water molecules and electron transport, inside the thylakoid membrane is positively charged
and outside is negatively charged (electrochemical gradient). This difference in charge provides the energy to make ATP.
5th H+ ions cannot cross the membrane directly. Thus membrane has a protein called ATP synthase that allows H+ ions to pass through it. ATP
synthase rotates like a turbine when the H+ ions pass through it and binds ADP and a phosphate group together to form ATP.
6th ATP and NADPH go to the light-independent reactions (Calvin Cycle)

24. Photosynthesis Stage II: The Calvin Cycle Making Food “From Thin Air”
Three major steps:
Carbon fixation
Reduction
Regeneration
second stage of photosynthesis takes place in the stroma (a matrix that contains dissolved enzymes)…First carbon dioxide is ”fixed.” …Then ATP and NADPH from the Light Reactions provide chemical energy to combine the fixed carbons to make glucose…The reactions of this stage can occur without light, so they are sometimes called light independent or dark reactions…also known as the Calvin cycle because its reactions were discovered by a scientist named Melvin Calvin.
Steps of the Calvin Cycle
The Calvin cycle has three major steps: carbon fixation, reduction, and regeneration. All three steps take place in the stroma of a chloroplast.
• Step 1: Carbon Fixation. Carbon dioxide from the atmosphere combines with a simple, five-carbon compound called RuBP. This reaction occurs with the
help of an enzyme named RuBisCo and produces molecules known as 3PG (a three-carbon compound, 3-Phosphoglyceric acid).
• Step 2: Reduction. Molecules of 3PG (from Step 1) gain energy from ATP and NADPH (from the light reactions) and re-arrange themselves to form G3P
(glycerate 3-phosphate). This molecule also has three carbon atoms, but it has more energy than 3PG. One of the G3P molecules goes on to form glucose,
while the rest of the G3P molecules go on to Step 3.
• Step 3: Regeneration. The remaining G3P molecules use energy from ATP to form RuBP, the five-carbon molecule that started the Calvin cycle. This allows
the cycle to repeat.
You can also watch an animation of the Calvin cycle at this link:

25. Why is Carbon Dioxide “Fixed”
Life on Earth is carbon-based
needed in building blocks of biological molecules
ultimate source of carbon is carbon dioxide
Animals and most other heterotrophs cannot take in CO2 directly
Only autotrophs can build low energy inorganic CO2 into high-energy organic molecules like glucose

26. Three Pathways for Carbon Fixation—Calvin Cycle
C-3 pathway
Most common
6-C molecule splits into two 3-C molecules
C-4 pathway
a. creates a 4-C molecule
3. CAM (Crassulacean Acid Metabolism)
a. cacti and succulents
b. Fix carbon dioxide at night
Dry air, hot temperatures, bright sunlight lead to below two pathways:
Dry air, hot temperatures, and bright sunlight slow the C-3 pathway for carbon fixation. This is because stomata, tiny openings under the leaf which normally allow CO2 to enter and O2 to leave, must close to prevent loss of water vapor . Closed stomata lead to a shortage of CO2. Two alternative pathways for carbon fixation demonstrate biochemical adaptations to differing environments.
Plants such as corn solve the problem by using a separate compartment to fix CO2. Here CO2 combines with a 3-carbon molecule, resulting in a 4-carbon molecule. Because the first stable organic molecule has four carbons, this adaptation has the name C-4. Shuttled away from the initial fixation site, the 4-carbon molecule is actually broken back down into CO2, and when enough accumulates, RuBisCo fixes it a second time! Compartmentalization allows efficient use of low concentrations of carbon dioxide in these specialized plants.
Cacti and succulents such as the jade plant avoid water loss by fixing CO2 only at night. These plants close their stomata during the day and open them only in the cooler and more humid nighttime hours. Leaf structure differs slightly from that of C-4 plants, but the fixation pathways are similar. The family of plants in which this pathway was discovered gives the pathway its name, Crassulacean Acid Metabolism, or CAM. All three carbon fixation pathways lead to the Calvin Cycle to build sugar.

27. Factors Affecting Photosynthesis
Shortages of water slow process down; can stop it
Plants that live in dry areas have a waxy coating on their leaves that reduces water loss
Temperature also can slow or stop it
Enzymes used by plants for photosynthesis function best between 0°C and 35°C (32°F to 95°F)
Intensity of light
More light = greater rate of photosynthesis until maximum reached
Maximum rate varies from plant to plant
Do SAS Activity!!!!

28. Let’s Review Where does photosynthesis occur? _________________
What are the saclike photosynthetic membranes in the chloroplast called? _________________
The thylakoids are arranged in stacks called __________.
What is found inside the grana? ______________________________________
What are photosystems? ______________________________________
What do photosystems do? ______________________________________
In the chloroplasts
thylakoids
grana
Clusters of chlorophyll and other pigments
Proteins found in the grana
They capture the energy of sunlight

29. How many stages does photosynthesis have? ______
What are they? ____________________________________________________________________
Where do the light-dependent reactions take place? __________________________________
Where do the light-independent reactions take place? __________________________________ 2
Light reactions
Light-independent reactions (Calvin cycle)
Thylakoid membrane
Stroma; region outside of the thylakoid membrane