Sunlight Sunlight – the energy source– the energy source

Sunlight appears white – actually many Sunlight appears white – actually many different wavelengthsdifferent wavelengths Different wavelengths have different Different wavelengths have different

amounts of energyamounts of energy PigmentsPigments – –

Compounds that absorbCompounds that absorblightlight

light they don’t absorb is light they don’t absorb is reflected = color we seereflected = color we see

Photosynthetic PigmentsPhotosynthetic Pigments What is the main photosynthetic pigment?What is the main photosynthetic pigment? Chlorophyll Chlorophyll

Typically green or blue greenTypically green or blue green (Chlorophyll a and Chlorophyll b)(Chlorophyll a and Chlorophyll b)

What are the accessory pigments?What are the accessory pigments? CarotenoidsCarotenoids - pigments that assist the chlorophyll in the - pigments that assist the chlorophyll in the

absorption of lightabsorption of light When do you see carotenoids?When do you see carotenoids?

Fall. These are usually masked by the higher amount of Fall. These are usually masked by the higher amount of chlorophyll pigments (see them in the fall when chlorophyll chlorophyll pigments (see them in the fall when chlorophyll breaks down)breaks down)

Orange / yellow pigmentsOrange / yellow pigments

Light AbsorptionLight Absorption Look at the graph: What colors does a plant Look at the graph: What colors does a plant

primarily use for photosynthesis?primarily use for photosynthesis? Plants primarily use blue and red light for Plants primarily use blue and red light for

photosynthesis (not green)photosynthesis (not green)

This graph shows the light wavelengths This graph shows the light wavelengths that the carotenoids absorbthat the carotenoids absorb Notice they absorb no orange / yellow light Notice they absorb no orange / yellow light

wavelengthswavelengths

Why is the sky blue?Why is the sky blue?

1-4 ATB

In your own words, what is photosynthesis? (write something b/c I will be asking you)

Today: Get your tests back Begin discussing photosynthesis

1-5 ATB

What are the necessary reactants need for photosynthesis to occur?

Today: 15 minutes – finish pages 2 and 3.

Pg 4 is homework (if you’re done with pages 2 and 3, work on it)

Review

Photosynthesis Photosynthesis and Cellular and Cellular RespirationRespirationChapter 6Chapter 6

Review:Review:

Where does all of the energy in an Where does all of the energy in an ecosystem come from?ecosystem come from? The sunThe sun

What is the one exception?What is the one exception? Deep sea vents – chemosynthetic bacteriaDeep sea vents – chemosynthetic bacteria

Which organisms are able to access the Which organisms are able to access the sun’s energy to make food?sun’s energy to make food? PlantsPlants

What is the name of organisms that can What is the name of organisms that can make their own food?make their own food? Autotrophs / producersAutotrophs / producers Organisms that use sunlight OR chemical bonds Organisms that use sunlight OR chemical bonds

to make glucoseto make glucose Examples – Examples –

Plants or Bacteria near hydrothermal Plants or Bacteria near hydrothermal ventsvents

What do we call organisms that must eat What do we call organisms that must eat other organisms for food?other organisms for food? Heterotrophs / consumersHeterotrophs / consumers Organism that obtain organic compounds from Organism that obtain organic compounds from

other living organismother living organism Examples – humans, birds, etcExamples – humans, birds, etc

Photosynthesis OverviewPhotosynthesis Overview What is needed for photosynthesis?What is needed for photosynthesis?

Light, Water and CO2Light, Water and CO2

What happens?What happens? The Light Energy converts Water (HThe Light Energy converts Water (H220) 0)

and Carbon Dioxide (COand Carbon Dioxide (CO22) into Oxygen ) into Oxygen (O(O22) and glucose (C) and glucose (C66HH1212OO66))

ReviewReview: What is the name of the energy storing : What is the name of the energy storing molecule?molecule?

Adenosine Triphosphate - (ATP)Adenosine Triphosphate - (ATP) Composed of 3 parts:Composed of 3 parts:

Nitrogen base (adenine)Nitrogen base (adenine) sugar (ribose)sugar (ribose) 3 phosphate groups.3 phosphate groups.

Review: Building ATP.Review: Building ATP.

• If Adenosine is attached to one If Adenosine is attached to one phosphate it’s called…phosphate it’s called…•Adenosine monophosphate (AMP)Adenosine monophosphate (AMP)

• If an AMP molecule bonds with If an AMP molecule bonds with another phosphate, what is it another phosphate, what is it called?called?•Adenosine diphosphateAdenosine diphosphate

• If ADP bonds with another If ADP bonds with another phosphate, what is it called?phosphate, what is it called?•ATPATP

Review: How is energy released from Review: How is energy released from ATP?ATP?• A phosphate bond is brokenA phosphate bond is broken• What are the products of the What are the products of the

reaction?reaction?• ATP ATP Energy + ADP + 1 phosphate Energy + ADP + 1 phosphate

groupgroup

One phosphate bond has been removed

Energy Release SummaryEnergy Release Summary

1-6 ATB

Where do we get the energy to create ATP? Where is the energy stored in ATP?

Today: Summarize photosynthesis

Where is the ATP used?

What do we know about What do we know about photosynthesis?photosynthesis? What is photosynthesis?What is photosynthesis?

What type of organisms?What type of organisms?

In which organelle?In which organelle?

What reactants are needed?What reactants are needed?

What is produced?What is produced?

1-10 ATB

What is the purpose of having accessory pigments in a plant? (look at your assignment from Thursday)

Today: Use the laptops to find and use the website

to answer the questions on the worksheet.

1-11 ATB

What is our definition of photosynthesis? Turn in your online assignment Discuss light absorption by plants (notes) Complete the rest of the packet using the

book Discuss the reading when your done

PhotosynthesisPhotosynthesis

Class definitionClass definition Process autotrophs use to convert carbon Process autotrophs use to convert carbon

dioxide and water, using light, into dioxide and water, using light, into carbohydratescarbohydrates

TRAPPING ENERGY FROM SUNLIGHT

The process that uses the suns energy to make simple sugars is called: photosynthesis

Simple sugars are converted into __carbohydrates / starch__, which store energy.

Identify the two phases of photosynthesis and what is produced in each: __Light dependant (light rxns)___- NADPH, ATP, Oxygen __Light independent (dark reactions) __- Sugars, NADP+,

ADP

Photosynthesis OverviewPhotosynthesis Overview What is the balanced equation for What is the balanced equation for

Photosynthesis?Photosynthesis? 6 CO6 CO22 + 6 H + 6 H220 0 C C66HH1212OO6 6 + 6 O + 6 O22

Identify the general equation for photosynthesis below:

Think! What does the large 6 in front of the molecules mean? What do the subscripts after certain elements mean?

What organelle is involved in photosynthesis (pictured at the right)? Chloroplast

Inner MembraneOuter membrane

Granum

Thylakoid

Thylakoid Membrane

Stroma

The LeafThe Leaf

What organelle in the leafWhat organelle in the leafis responsible for photosynthesis?is responsible for photosynthesis? ChloroplastChloroplast

Parts of a chloroplastParts of a chloroplast Thylakoids - Thylakoids -

Flattened sacs where photosynthesis occurs – surrounded by Flattened sacs where photosynthesis occurs – surrounded by a membranea membrane

Grana – Grana – Stacks of thylakoidsStacks of thylakoids

Stroma –Stroma – Solution that surrounds the granaSolution that surrounds the grana

ChloroplastChloroplast

Pigments are used to absorb sunlight. They are arranged within the ___tylakoid___________ membranes in clusters known as ____photosystems__________.

The most common pigment is __chlorophyll_________. Chlorophyll ___absorbs_________ most wavelengths of light, except ___green___________.

Because chlorophyll cannot absorb this wavelength, it is _____reflected_____, giving plants and leaves their ___green____ appearance.

In the fall, trees stop producing chlorophyll in their leaves. Other pigments become visible giving leaves the colors that we see in the fall.

THINK! What are the yellow pigments called? What are the orange pigments called? Carotenes – orange Xanthophylls - yellow

1-13 ATB Describe why do plants appear

green? Today:

Review Describe the light

dependant reactions ATB’s due

tomorrow! Quiz Tuesday?

Review: Where does photosynthesis occur?

Occurs in the Occurs in the leaves of leaves of plants in plants in organelles organelles called called chloroplasts.chloroplasts.

ReviewReview::

What are the 3 monomers of a carbohydrate?What are the 3 monomers of a carbohydrate? Glucose, Fructose, GalactoseGlucose, Fructose, Galactose

What was the chemical formula for these What was the chemical formula for these monosaccharide's? monosaccharide's?

CC66HH1212OO66 Many monosaccharide's liked together form what?Many monosaccharide's liked together form what?

Polysaccharides / carbohydratesPolysaccharides / carbohydrates

Photosynthesis and Cell RespirationPhotosynthesis and Cell Respiration What do plants need for photosynthesis? (A and B)What do plants need for photosynthesis? (A and B)

Sunlight, Water and Carbon dioxideSunlight, Water and Carbon dioxide

What do plants /What do plants / animals need animals need for cell for cell respiration? (C) respiration? (C) Oxygen / Carbs.Oxygen / Carbs.

What is theWhat is theproduct of cellproduct of cellrespiration? (D)respiration? (D) ATPATP

Two Stages of Two Stages of PhotosynthesisPhotosynthesis

Light Dependant Reactions and Light Light Dependant Reactions and Light Independent Reactions (Calvin Cycle)Independent Reactions (Calvin Cycle)

Inner MembraneOuter membrane

Granum

Thylakoid

Thylakoid Membrane

Stroma

Light ReactionsLight Reactions Occurs on thylakoid membraneOccurs on thylakoid membrane Chlorophyll absorbs light and electrons get Chlorophyll absorbs light and electrons get

excited – e- flow on electron transport chainexcited – e- flow on electron transport chain Energy in excited electrons is used to create Energy in excited electrons is used to create

NADPH and ATPNADPH and ATP These are temporary energy carrier moleculesThese are temporary energy carrier molecules

Water is needed – electron donorWater is needed – electron donor releases O2 releases O2 Hydrogen ion gradient is used to create Hydrogen ion gradient is used to create

ATPATP

ATP and NADPH are then used to ATP and NADPH are then used to create glucose in the Calvin Cyclecreate glucose in the Calvin Cycle

Overview of Light Rxns

SummarySummary

LIGHT DEPENDANT RXNS

INPUTS OUTPUTS:

1-14 ATB

What is produced from the light reactions that will be used in the Calvin cycle?

Today: Review the light dependant reactions Start discussing the light independent

reactions

LIGHT-DEPENDENT REACTIONS (from your packet)

Just like the name says, this reaction requires ___light___________.

Light from the sun strikes chlorophyll in the thylakoid membranes. The sunlight’s energy is transferred to ___electrons_____.

These highly energized or excited electrons are passed from chlorophyll to an _____electron transport chain_________, which is a series of proteins embedded in the thylakoid membrane.

What happens to electrons as they move along the electron transport chain? They lose energy

There are two photosystems that electrons pass through. As electrons pass through the first photosystem, the energy given off from them is used to create ___ATP________. When electrons arrive at the second photosystem, they are re-energized.

Remember! Which part of a chloroplast are the light-dependent reactions taking place in? Thylakoid membrane

So energy is not wasted, the electrons are transferred to the ___stroma______, the enzyme-rich liquid inside the chloroplast. The electron carrier molecule called ___NADP+____ combines with two excited electrons and a hydrogen ion to become ____NADPH______.

NADPH does not use the energy present in the energized electrons; it simply stores the energy until it can transfer it to the ___stroma_______, where it will play an important role.

SummarySummary

ATP Synthesis (H+ gradient)ATP Synthesis (H+ gradient)

If in the beginning of this process electrons got excited and left one photosystem for another, how are the electrons replaced? What molecule serves as the “donor” to replace these lost electrons? Water

What is the process called where a water molecule is split by light? _____photolysis____________

When water is split, 2 ___electrons_____, 2 ___hydrogen_____ ions, and ½ __oxygen______ molecule is produced.

The oxygen produced by photolysis is released into the ___atmosphere________ and supplies the oxygen we breathe!

Photolysis – Replacing e- Water broken down Where do the parts

go? e- go into e-

transport chain H+ stays inside to

form gradient (for ATP production)

Oxygen is released

The electrons are returned to replace those lost in the first photosystem, the hydrogen ions will be pumped into the thylakoid space, purposely creating an imbalance. The hydrogen ions can only get out one way. By going through a special enzyme, this is how ATP is generated for the cell for photosynthesis. NOTE: you’ll learn a similar method for cellular respiration!

THINK! What were the “inputs” thus far in the light-dependent reactions (what was used)? What were the “outputs” thus far? Try to list them below:

INPUTS: Light, water, NADP+, ADP

OUTPUTS Oxygen, NADPH, ATP

Summary of the Light Summary of the Light Rxns. Rxns. DRAW!DRAW!1.1. LightLight

2.2. Water is split into 2 Water is split into 2 hydrogen's, 2 electrons, hydrogen's, 2 electrons, oxygenoxygen

3.3. ADP ADP converted converted ATPATP

4.4. NADP+ picks up e- and a NADP+ picks up e- and a hydrogenhydrogen

5.5. NADPH and ATP go to NADPH and ATP go to the Calvin cyclethe Calvin cycle

Light dependant reactions

Animation clips…

Calvin Cycle - OverviewCalvin Cycle - Overview Process by which plants use enzymes to Process by which plants use enzymes to

produce sugars produce sugars Occurs in stroma of chloroplastOccurs in stroma of chloroplast Does not need lightDoes not need light

but usually happens during the daybut usually happens during the day

NADPH and ATP from light reactions are used NADPH and ATP from light reactions are used to create carbohydrates (using CO2)to create carbohydrates (using CO2)

The NADP+ and ADP then goes back to the The NADP+ and ADP then goes back to the light reactions to be “recharged”light reactions to be “recharged”

Carbon FixationCarbon Fixation – – process of taking in carbon to make sugarsprocess of taking in carbon to make sugars

DiagramDiagram

LIGHT-INDEPENDENT REACTIONS(Calvin Cycle) As indicated by the name, this phase of

photosynthesis DOES or DOES NOT require sunlight? DOES NOT

Another name for these reactions is called the ___Calvin Cycle_______. It is here that __CO2_______ is used in a series of reactions to form __6 carbon sugars__. This cycle takes place in the ___stroma____.

WHAT YOU NEED TO KNOW ABOUT THE CALVIN CYCLE!

It is a “cycle” because the molecule that you end with is also the molecule that you start with.

Energy from ATP and NADPH (created during the light-dependent reactions) is used to power the Calvin Cycle.

As ATP and NADPH are broken down, they go back to the thylakoid and are recycled.

It is here that carbon dioxide is turned into glucose (a 6 CARBON sugar)

THINK! What were the “inputs” thus far in the Calvin Cycle (what was used)? What were the “outputs” for the Calvin Cycle? Try to list them below:

INPUTS NADPH, ATP, CO2

OUTPUTS NADP+, ADP, sugars

Calvin Cycle (Light independent rxns) What were the inputs

from the Light Dependant rxns? NADPH, ATP

What are the outputs 6 carbon sugars ADP NADP+

THINK! Between inputs and outputs for both the light-dependent and independent reactions, did you account for everything from the general equation of photosynthesis? You should have! If not, ask your instructor!

****You should be able to answer the questions in the "Section Assessment" after completing section 9.2!***

The End Results The two sets of

photosynthetic reactions work together

The light-dependent reactions trap the energy of sunlight in chemical form, and the light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water.

In the process, animals, including humans, get food and an atmosphere filled with oxygen.

Kids rapping http://www.youtube.com/watch?v=q6XrL

9uYJXo&feature=related

LIGHT DEPENDANT RXNS

LIGHT-DEPENDENT REACTIONS Generating ATP and NADPHGenerating ATP and NADPH

The light-dependent reactions encompass the The light-dependent reactions encompass the steps of photosynthesis that directly involve steps of photosynthesis that directly involve sunlight.sunlight.

The light-dependent reactions occur in the The light-dependent reactions occur in the thylakoids of chloroplasts. thylakoids of chloroplasts.

Light is absorbed – excites electrons in Light is absorbed – excites electrons in pigments = start of photosynthesispigments = start of photosynthesis

Thylakoids contain clusters of chlorophyll Thylakoids contain clusters of chlorophyll and proteins known as and proteins known as photosystems.photosystems.

Photosystems absorb sunlight and Photosystems absorb sunlight and generate high-energy electrons that are then generate high-energy electrons that are then passed to a series of electron carriers passed to a series of electron carriers embedded in the thylakoid membrane.embedded in the thylakoid membrane.

Photosynthesis involves two sets of reactionsPhotosynthesis involves two sets of reactions 11stst is light dependant because they involve the is light dependant because they involve the

direct involvement of light and light absorbing direct involvement of light and light absorbing pigmentspigments

The light dependant use energy from the sun The light dependant use energy from the sun to produce ATP and NADPHto produce ATP and NADPH NADP+ (nicotinamide adenine dinucleotide

phosphate) is a carrier molecule. Take place in the thylakoid membraneTake place in the thylakoid membrane Water is required as an electron donor and Water is required as an electron donor and

oxygen is released as a byproductoxygen is released as a byproduct

The Light-Dependent Reactions: Generating ATP and NADPH Thylakoids contain clusters of chlorophyll

and proteins known as photosystems. Photosystems absorb sunlight and

generate high-energy electrons that are then passed to a series of electron carriers embedded in the thylakoid membrane.

Photosystem II Light energy is absorbed by

electrons in the pigments within photosystem II, increasing the electrons’ energy level.

The high-energy electrons are passed to the electron transport chain, a series of electron carriers that shuttle high-energy electrons during ATP-generating reactions.

Photosystem II The thylakoid

membrane provides new electrons to chlorophyll from water molecules.

Enzymes of the inner surface of the thylakoid break up water molecules into 2 electrons, 2 H+ ions, and 1 oxygen atom.

Photosystem II The 2 electrons

replace the high-energy electrons that have been lost to the electron transport chain.

Oxygen is released into the air. This reaction is the source of nearly all of the oxygen in Earth’s atmosphere.

The H+ ions are released inside the thylakoid.

Electron Transport Chain

Energy from the electrons is used by proteins in the electron transport chain to pump H+ ions from the stroma into the thylakoid space.

Electron Transport Chain

At the end of the electron transport chain, the electrons pass to photosystem I.

Photosystem I Because some

energy has been used to pump H+ ions across the thylakoid membrane, electrons do not contain as much energy as they used to when they reach photosystem I.

Pigments in photosystem I use energy from light to reenergize the electrons.

Photosystem I

At the end of a short second electron transport chain, NADP+ molecules in the stroma pick up the high-energy electrons and H+ ions at the outer surface of the thylakoid membrane to become NADPH.

Hydrogen Ion Movement and ATP Formation

H+ ions accumulate within the thylakoid space from the splitting of water and from being pumped in from the stroma.

The buildup of H+ ions makes the stroma negatively charged relative to the space within the thylakoids.

Hydrogen Ion Movement and ATP Formation

This gradient, the difference in both charge and H+ ion concentration across the membrane, provides the energy to make ATP.

Hydrogen Ion Movement and ATP Formation

H+ ions cannot directly cross the thylakoid membane. However, the thylakoid membrane contains a protein called ATP synthase that spans the membrane and allows H+ ions to pass through it.

Hydrogen Ion Movement and ATP Formation

Powered by the gradient, H+ ions pass through ATP synthase and force it to rotate.

As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP.

Hydrogen Ion Movement and ATP Formation

This process, called chemiosmosis, enables light-dependent electron transport to produce not only NADPH (at the end of the electron transport chain), but ATP as well.

Light Reactions (in depth)Light Reactions (in depth)

Diagram of Light Diagram of Light ReactionReaction

LIGHT-INDEPENDENT REACTIONS

Light-Independent Reactions Plants absorb carbon dioxide from the

atmosphere and complete the process of photosynthesis by producing sugars and other carbohydrates.

During light-independent reactions, ATP and NADPH molecules produced in the light-dependent reactions are used to produce high-energy sugars from carbon dioxide.

Light-Independent Reactions

No light is required to power the light-independent reactions.

The light-independent reactions take place outside the thylakoids, in the stroma.

The Light-Independent Reactions: Producing Sugars

What happens during the light-independent reactions?

During the light-independent reactions, ATP and NADPH from the light

dependent reactions are used to produce high-energy sugars.

The Light-Independent Reactions: Producing Sugars

During the light-independent reactions, commonly referred to as the Calvin cycle, plants use the energy that ATP and NADPH contains to build stable high-energy carbohydrate compounds that can be stored for a long time.

Carbon Dioxide Enters the Cycle

Carbon dioxide molecules enter the Calvin cycle from the atmosphere.

An enzyme in the stroma of the chloroplast combines carbon dioxide molecules with 5-carbon compounds that are already present in the organelle, producing 3-carbon compounds that continue into the cycle.

Carbon Dioxide Enters the Cycle For every 6 carbon dioxide molecules

that enter the cycle, a total of twelve 3-carbon compounds are produced.

Carbon Dioxide Enters the Cycle

Other enzymes in the chloroplast then convert the 3-carbon compounds into higher-energy forms in the rest of the cycle, using energy from ATP and high-energy electrons from NADPH.

Sugar Production

At midcycle, two of the twelve 3-carbon molecules are removed from the cycle.

These molecules become the building blocks that the plant cell uses to produce sugars, lipids, amino acids, and other compounds.

Sugar Production

The remaining ten 3-carbon molecules are converted back into six 5-carbon molecules that combine with six new carbon dioxide molecules to begin the next cycle.

Summary of the Calvin Cycle

The Calvin cycle uses 6 molecules of carbon dioxide to produce a single 6-carbon sugar molecule.

Summary of the Calvin Cycle

The energy for the reactions is supplied by compounds produced in the light-dependent reactions.

Summary of the Calvin Cycle

The plant uses the sugars produced by the Calvin cycle to meet its energy needs and to build macromolecules needed for growth and development.

When other organisms eat plants, they can use the energy and raw materials stored in these compounds.

The End Results

The two sets of photosynthetic reactions work together—the light-dependent reactions trap the energy of sunlight in chemical form, and the light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water.

In the process, animals, including humans, get food and an atmosphere filled with oxygen.

Movie Clips…Movie Clips…

Warm Up 1/20Warm Up 1/20

If a plant is left in the dark for a significant If a plant is left in the dark for a significant amount of time, what will happen to glucose amount of time, what will happen to glucose production? What will the plant do to surviveproduction? What will the plant do to survive

Today:Today: Quiz on photosynthesisQuiz on photosynthesis Discuss how plants store extra carbs.Discuss how plants store extra carbs. Discuss effects on photosynthesisDiscuss effects on photosynthesis

Tomorrow: Seat change!Tomorrow: Seat change!

Warm Up 1-21Warm Up 1-21

What are the products of the light-dependant What are the products of the light-dependant reactions? What are they used for? What are the reactions? What are they used for? What are the products of the light-independent reactions (Calvin products of the light-independent reactions (Calvin cycle)?cycle)?

Review for test tomorrow (get review sheets)Review for test tomorrow (get review sheets) Test / Review sheet due MondayTest / Review sheet due Monday Today:Today:

Seat ChangeSeat Change Discuss how plants store extra carbs.Discuss how plants store extra carbs. Discuss effects on photosynthesisDiscuss effects on photosynthesis Complete page 1 and 2 (23 and 24) of worksheet packetComplete page 1 and 2 (23 and 24) of worksheet packet

Summary of PhotosynthesisSummary of Photosynthesis

Some extras?Some extras? Extra FoodExtra Food Plants make extra carbohydrates which Plants make extra carbohydrates which

are stored as starch (like a potatoes)are stored as starch (like a potatoes) These carbohydrates are what These carbohydrates are what

heterotrophs rely on for survivalheterotrophs rely on for survival

Environmental Effects on Environmental Effects on Photosynthesis?Photosynthesis?

What are some possible environmental What are some possible environmental factors that could effect photosynthesis?factors that could effect photosynthesis? WaterWater Light IntensityLight Intensity CO2 LevelsCO2 Levels TemperatureTemperature

Temperature The reactions of

photosynthesis are made possible by enzymes that function best between 0°C and 35°C.

Temperatures above or below this range may affect those enzymes, slowing down the rate of photosynthesis or stopping it entirely.

Light High light intensity

increases the rate of photosynthesis.

After the light intensity reaches a certain level, however, the plant reaches its maximum rate of photosynthesis, as is seen in the graph.

Water Because water is one of the raw

materials in photosynthesis, a shortage of water can slow or even stop photosynthesis.

Water loss can also damage plant tissues.

Plants that live in dry conditions often have waxy coatings on their leaves to reduce water loss. They may also have biochemical adaptations that make photosynthesis more efficient under dry conditions.

Alternative PathwaysAlternative Pathways There are different methods in which plants There are different methods in which plants

create carbohydrates (we discussed the most create carbohydrates (we discussed the most common)common)

Plants in dry climates use the C4 pathway or Plants in dry climates use the C4 pathway or CAM pathwayCAM pathway

Why?Why? Both deal with controlling water lossBoth deal with controlling water loss

Extra stuff: Why do cactus have “ridges”?Extra stuff: Why do cactus have “ridges”?

Photosynthesis Under Extreme Conditions

In order to conserve water, most plants under bright, hot conditions close the small openings in their leaves that normally admit carbon dioxide.

This causes carbon dioxide within the leaves to fall to very low levels, slowing down or even stopping photosynthesis.

C4 and CAM plants have biochemical adaptations that minimize water loss while still allowing photosynthesis to take place in intense sunlight.

C4 Photosynthesis C4 plants have a specialized chemical pathway

that allows them to capture even very low levels of carbon dioxide and pass it to the Calvin cycle.

The name “C4 plant” comes from the fact that the first compound formed in this pathway contains 4 carbon atoms.

The C4 pathway requires extra energy in the form of ATP to function.

C4 organisms include crop plants like corn, sugar cane, and sorghum.

CAM Plants

Members of the Crassulacae family, such as cacti and succulents, incorporate carbon dioxide into organic acids during photosynthesis in a process called Crassulacean Acid Metabolism (CAM).

CAM Plants CAM plants admit air into their

leaves only at night, where carbon dioxide is combined with existing molecules to produce organic acids, “trapping” the carbon within the leaves.

During the daytime, when leaves are tightly sealed to prevent water loss, these compounds release carbon dioxide, enabling carbohydrate production.

CAM plants include pineapple trees, many desert cacti, and “ice plants”.

The EndThe End

!!

Warm Up 1-22Warm Up 1-22 What are four factors that can limit What are four factors that can limit

photosynthesis?photosynthesis? Today:Today:

Get out worksheet packetGet out worksheet packet Get a book: Get a book:

pg 118 – Section Review questions #1-4 and 8pg 118 – Section Review questions #1-4 and 8 Pg 124 – Section Review questions #1, 4 & 5Pg 124 – Section Review questions #1, 4 & 5

Worksheet page to complete: pg 2 (#38)Worksheet page to complete: pg 2 (#38) Review stages of photosynthesisReview stages of photosynthesis Monday: Review gameMonday: Review game Test / Review sheet TuesdayTest / Review sheet Tuesday

Warm Up 1-25Warm Up 1-25

Why do plants use alternative methods of Why do plants use alternative methods of photosynthesis than the one we discussed?photosynthesis than the one we discussed?

Today:Today: Review sheetsReview sheets Review game for testReview game for test

Tomorrow:Tomorrow: TEST! TEST! Review sheets due!Review sheets due!

Warm Up 1-26Warm Up 1-26

Test!Test! Get out a pencilGet out a pencil Questions?Questions?

Turn in review sheetTurn in review sheet Turn in your warm upsTurn in your warm ups #32 = AE#32 = AE

ATB 1-27ATB 1-27

Start a new warm up sheet – draw a Start a new warm up sheet – draw a picture of your favorite animalpicture of your favorite animal

Objectives:Objectives: Get back all your old papers / homework Get back all your old papers / homework

assignmentsassignments Discuss your test – any questions?Discuss your test – any questions? Start next chapter – cell respirationStart next chapter – cell respiration