7-1 chapter 7 lecture outline see powerpoint image slides for all figures and tables pre-inserted...

7-1

Chapter 7

Lecture Outline

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Photosynthesis animation

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Photosynthesis and Life

During photosynthesis– Organisms use the energy of light to build

high-energy organic molecules.– Plants, algae and some bacteria can do

this. Can make their own food using light Called photosynthetic autotrophs

99.9% of all life on earth relies on photosynthesis for their energy.– Heterotrophs eat autotrophs.


An Overview of Photosynthesis

Photosynthesis occurs in– Chloroplasts

Contain the pigment that captures the energy in light– Chlorophyll– Found in membranous sacs called thylakoids– A stack of thylakoid is called a granum (pl. grana).– Grana are suspended in a fluid-filled space called

the stroma. During photosynthesis

– The energy in light is used to make ATP.– The energy in ATP is used to make organic

molecules such as glucose.


Photosynthesis, Chloroplasts, and the Structure of a Leaf



The chemical equation of photosynthesis:Light energy + carbon dioxide + water glucose and oxygen

The three events of photosynthesis Light-capturing events

– The pigment chlorophyll absorbs certain wavelengths of light and some of its electrons become excited.

Light-dependent reactions– These reactions use the energy in the excited electrons to

make ATP and NADPH. Light-independent reactions

– ATP and NADPH from the light reactions is used to reduce carbon dioxide to make glucose.


Light-capturing Events: Fundamental Concepts

Visible light– Combinations of different wavelengths of light– Can be seen as different colors

Pigments are molecules that absorb light.– Each pigment absorbs certain wavelengths of light.– The wavelengths that they do not absorb, they reflect.

This is the color we see.– In photosynthesis, only the wavelengths that are absorbed can be

used to do work. Chlorophyll: The main photosynthetic pigment

– Two forms; a and b– Absorb light in the blue and red portions of the spectrum– Reflect green wavelengths


The Electromagnetic Spectrum, Visible Light and Chlorophyll


Other Types of Pigments

Accessory pigments– Include carotenoids

Absorb blue and green wavelengths Reflect orange and yellow Found in leaves, masked by chlorophyll

– In the autumn, when chlorophyll disintegrates, accessory pigments show through (fall colors).

Chlorophyll + accessory pigments– Organized into photosystems that harvest the energy from

many wavelengths of light– Found in thylakoids of the chloroplasts

When pigments absorb light– Some of their electrons become “excited”


*Light-dependent Reactions: Fundamental Concepts

The excited electrons from chlorophyll– Are passed through an electron transport chain– The energy released is used to pump protons up their

concentration gradient.– When protons diffuse through ATP synthase, ATP is made.

Excited electrons passed to NADP+ to make NADPH Water is split

– Electrons are donated to chlorophyll to replace the donated electrons.

– Oxygen is produced. Occurs in the thylakoid membrane

– ATP and NADPH move to the stroma to be used in the dark reactions.


*Light-independent Reactions: Fundamental Concepts

The ATP and NADPH from the light-dependent reactions

– Provide the energy and electrons needed to build sugar from carbon dioxide

CO2 is captured by an enzyme called RuBisCO– Combines CO2 with ribulose to form a 6-carbon molecule

This is immediately split into two 3-C molecules.

NADPH is used to reduce these molecules. Glyceraldehyde-3-phosphate is formed.

– Can be used to make sugars, proteins or fats


*Photosynthesis: Fundamental Description


Light-capturing Events: The Details

Light– Packaged as photons– Each photon has a distinct wavelength.– The energy in a photon is related to its

wavelength.– When a photon hits a pigment molecule, electrons

are excited. This means that the electrons jump up to a higher

energy level.


Light-capturing Events: The Details Continued

Photosystems– Structures in which the light-capturing events take

place– Found in the thylakoid membranes– Made up of antenna complexes and a reaction center

Networks of chlorophyll and accessory pigments Capture the energy in many different wavelengths of

light and pass it to the reaction center– The reaction center is a special chlorophyll molecule that

passes its excited electrons to an electron acceptor.

– There are two photosystems, I and II.


Light Dependent Reactions: The Details

Photosystem II (PSII)– Occurs first– Donates its excited electrons to the electron transport chain– Splits water to replace the electrons it donated

O2 is released.

Photosystem I (PSI)– Occurs second– Donates its excited electrons to NADP+ to form NADPH

NADPH released into the stroma– Accepts electrons from the electron transport chain to

replace the electrons it donated PS I and II are in the thlyakoid membrane.


The Electron Transport Chain

and ATP Synthesis

Between PSII and PSI– Electrons are passed through an electron

transport chain (ETC). This releases energy. This energy is used to pump protons from the stroma

into the thylakoid space. This creates a proton concentration gradient. Protons diffuse through ATP synthase. ATP synthase makes ATP that is released into the

stroma.


PS II and I: How They Interact


Light Independent Reactions: The Details

Takes place in the stroma of the chloroplast Uses

– CO2 (from the atmosphere)– ATP and NADPH (from the light-independent

reactions) – Ribulose (recycled)

Also called the dark reactions Also called the Calvin cycle


Carbon Fixation and Sugar Formation

Carbon dioxide gas is combined with a 5-carbon sugar called ribulose.

Accomplished with an enzyme called ribulose bisphospate carboxylase (RuBisCO)

Forms a 6-carbon molecule– Immediately broken down into two 3-carbon molecules– These 3-carbon molecules are

Energized by ATP Reduced by NADPH

Glyceraldehyde-3-phosphate is formed.


The Calvin Cycle


Glyceraldehyde-3-phosphate: The Product of Photosynthesis

Glyceraldehyde-3-phosphate can be used for many things.

– Used to make glucose– Used to recycle ribulose for

the Calvin cycle– Used to make the sugars

needed to build ATP, DNA and RNA

– Can be converted into lipids– Can be converted into

amino acids to make proteins

– Can be broken down in glycolysis


Other Aspects of Plant Metabolism

Plant cells can use the organic molecules produced in photosynthesis to make– Fats, proteins and other carbohydrates– Toxins for their protection

Many of these are useful medicines. Some can be used as natural insecticides.

– Vitamins Molecules that we cannot make, but that we need


Interrelationships Between Autotrophs and Heterotrophs

Autotrophs use the energy in light to make food.– Autuotrophs use the food they make in cellular respiration.

Plants use the sugar they make! Plants use the oxygen they make!

Heterotrophs eat the autotrophs.– Then use the food from the autotrophs to fuel cellular respiration– They also use the excess oxygen given off by autotrophs.

All organisms respire! The circle of life:

– Animals get sugar, oxygen, amino acids, fats and vitamins from plants.

– Plants get carbon dioxide, water and nitrogen from animals.


The Relationship between Photosynthesis and Cellular Respiration

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