Chapter 8

I. Energy and Life

• Energy = ability to do work• w/o energy life would cease A. Autotrophs and Heterotrophs

– Originally most all energy comes from ________

• Plants and some other organisms use the sun’s energy to produce____________.

sun

food

– ________________make their own food.– _________________obtain energy from food

they consumer– Some obtain energy as decomposers– There are several forms of energy-

radiant(light),electrical,chemical,mechanical

autotrophs

heterotrophs

B. Chemical Energy and ATP

– When electrons in bonds are shifted from higher to lower energy levels,_______________is released as heat and light

– ___________________is one of the principal chemical compounds used to store and release energy

The extra energy

Adenosine triphosphate

The 3 Phosphate groups are the key to ATP’s ability to store and release energy

1) Storing energy

• _______________________is a compound that looks a lot like ATP,except it has 2 phosphate groups and this difference is the key to storing energy.When a cell has energy available it can store small amounts by adding a phosphate to ADP,making ATP (think of ATP like a fully charged battery)

Adenosine diphosphate (ADP)

2) Releasing Energy

• Energy stored in ATP is released by breaking the bond between the 2nd and 3rd phosphates,releasing energy as needed.This can power such things as _______________across the membrane of the cell,protein synthesis and muscle contraction

Active transport

• ATP is exceptionally useful as the _____________________________.

Basic energy source of all cells

C. Using Biochemical Energy

– For active transport----____________________________that pumps Na+ out of cell and K+ into the cell.ATP keeps the pump working and keep ions balanced

A sodium-potassium pump-a membrane protein

• ATP powers synthesis of proteins,__________________ and responses to _____________________.

Nucleic acids

Chemical signals @ cell surface

• Cells only have a small amount of ATP,to last seconds…..not good for long term storage(1 molecule glucose stores 90 x the chemical energy of ATP ).Cells can regenerate ATP from ADP as needed by the energy in foods like glucose

• autotrophs

D. Heterotrophs and Autotrophs_____________________________gets food from eating or ingesting others-may eat autotrophs or other heterotrophs---includes fungi________________________make their own food/primarily by photosynthesis-which uses light to convert CO2 and H2O into carb’s and O2

heterotrophs

II .Photosynthesis:An Overview

– Plants use the energy of sunlight to convert water and CO2 into sugars and starches,as well as O2

A. Investigating Photosynthesis

– Centuries ago the simple question was did the increase in tree’s mass come from soil,water or air?

• 1) Van Helmont’s Experiment-• 1600’s-Belgian physician did an experiment to

see if the soil caused plants to grow,by trying to grow w/o soil….he concluded most of the gain in mass was from water…..this accounts for ½ the products of photosynthesis.

2) Priestly’s Experiment

– Candle w/jar over it-concluded that air enabled it to burn

– He put a sprig of a plant under the jar and waited a few days,…The candle could burn briefly under the jar…So he concluded the plant ________________________

Produced oxygen

3) Jan Ingenhoutz

• —showed the plant produced oxygen only if exposed to light

» In conclusion to all 3 experiments,it is concluded that plants exposed to CO2 and light and water,produce O2 and carb’s

B. The Photosynthesis Equation

• 6 CO2 + 6 H2O--- C6H12O6 + O2

light

• Plants use the sugars to produce complex carb’s such as _______

starches

C. Light and pigments

• Photosynthesis also requires light and Chlorophyll (found in Chloroplasts)

• White light is a mixture of different wavelengths of light---seen as __________

• Plants gather the sun’s energy with light absorbing molecules called____________.

Color pigments

• The principal plant pigment is__________________.-chlorophyll a and b

• Chlorophyll absorbs light well in the blue-violet and red regions,but not well in the _______________region,which is reflected by leaves

Chlorophyll

green

• Contain red and orange pigments like _________________,that absorb light in other regions

• When chlorophyll absorbs light,much of the energy is transferred directly to electrons in

Chlorophyll ,raising _________________________-which make photosynthesis work!!!

carotenesThe energy levels

• Chloroplasts contain pigments in membranes called ____________________/a stack= 1 granum ;plural are grana

• Fluid portion of chloroplast is called stroma• A large portion of light absorbed by the chloroplast

transfers directly to electrons in the chlorophyll molecule itself .By raising energy levels , light can produce steady supply of high energy electrons---the key to photosynthesis

Thylakoids

• D. High Energy Electrons

• The high energy electrons produced by chlorophyll are highly reactive and need a special carrier(think of “hot potato “ analogy )

• Electron carriers= compounds that accept a pair of high energy electrons and transfer them/along w/ most of energy to another molecule

Absorption of Light byChlorophyll a and Chlorophyll b

V B G YO R

Chlorophyll b

Chlorophyll a

Section 8-2

Figure 8-5 Chlorophyll Light Absorption

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III. The Reactions of Photosynthesis

• A. Inside a Chloroplast– Photosynthesis takes place in the

_____________.– The chloroplasts contain saclike

membranes called _________________ which are arranged in stacks known as ________________

chloroplastsTHYLAKOIDS grana

– Proteins in the Thylakoid membrane organize chlorophyll and other pigments into clusters known as ___________________-These are the light –collecting units of the chloroplast

– Light dependent reaction happens in _____________________.

photosystems

Thylakoid membrane

• Light-independent (Calvin-cycle) reaction happens in _____________-region outside thylakoid membranes

stroma

ChloroplastLight

O2

Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPH

ATP

ADP + PNADP+Chloroplast

Section 8-3

Figure 8-7 Photosynthesis: An Overview

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water

B. Electron Carriers

• When sunlight excites electrons in chlorophyll,the electrons gain a great deal of energy…..They require a carrier---__________________by electron transport chain

– ________nicotinamide adenine dinucleotide phosphate-accepts 2 high energy electrons along w/ a H+,converting it into __________.This is one way some of energy of sunlight is trapped in chemical form

Compound that can accept a pair of high energy electrons and transfer w/ most of the energy to another molecule

NADP+ NADPH

• ______________________-then becomes an electron carrier

NADPH

C. Light –Dependent Reactions

– Require light– Light is used to produce ATP and NADPH

HydrogenIon Movement

Photosystem II

InnerThylakoidSpace

ThylakoidMembrane

Stroma

ATP synthase

Electron Transport Chain Photosystem I ATP Formation

Chloroplast

Section 8-3

Figure 8-10 Light-Dependent Reactions

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– 1-Photosynthesis begins when pigments in photosystem II absorb light.Energy is absorbed by high energy electrons and passed on to electron transport chain.New electrons come from the water (water is required in these reactions to provide source of electrons and H+ ions),and O2 is released into air-as a BYPRODUCT

– 2-High –energy electrons move from electron transport chain from photosystem II to photosystem I(simply discovered before photosystemII).Energy from electrons is used by molecules in electron transport chain to transport H+ ions from stroma into the inner thylakoid space.

– 3--Pigments in ___________________use energy from light to regenerate electrons.NADP+ picks up high energy electrons,along w/ H+ ions,at outer surface of thylakoid membrane…+ H+ ion=NADPH/Photosystems are clusters of chlorophyll and protein and are essential to light dependent reaction.They absorb light and make high energy electrons that are passed onto high energy electron carriers in thylakoid membrane.

Photosystem I

• 4- As electrons pass from chlorophyll to NADP+,more________________are pumped along the membrane….Eventually ,the inside of the membrane fills w/ H+ ions……outside of membrane is _______________________charged…The difference in charges (a gradient)produces energy for ATP….This is why H+ ions are so important.

H+ ions

negatively

• 5--H+ ions cannot cross membrane directly…..But, the membrane contains a protein called __________that goes across the membrane and allows H+ ions to pass through it.(produced by gradient)As H+ passes through ,ATP synthase,the protein rotates,binding w/ ADP and a phosphate group to make_________________ So….. light-dependent part makes high energy electrons and also ATP.

ATP synthaseATP

• Electron transport chain= series of electron carriers proteins that move electrons during reactions fueled by ATP.At end of chain electrons pass to photosystem I

• Pigments in photosystem I use energy from light to reenergize electrons/NADP+ NADPH

D. The Calvin Cycle

– The ATP and NADPH from light-dependent part are not stable enough to store energy for more than a few moments….these are used in _____________to make high energy compounds that can last a long time----it makes ________________.

– Absorb CO2 and use ATP and NADPH to make high energy sugars

– Does not require light so is called ______________________

Calvin Cycle

sugars

Light-independent

ChloropIast

CO2 Enters the Cycle

Energy Input

5-CarbonMoleculesRegenerated

Sugars and other compounds

6-Carbon SugarProduced

Figure 8-11 Calvin Cycle

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• 1) 6 CO2 molecules enter from the atmosphere.They combine w/ 6 ____________________.The result is 12 3-C molecules.

• 2) 12 3-C molecules convert to higher energy forms….The energy for this comes from ATP and ____________________.

5-Carbon atoms

High energy electrons from NADPH

• 3) 2 3-C molecules removed from cycle…these are used to produce_________________________________________________________________________ needed for

plant metabolism and growth

Building blocks of Sugars,lipids,amino acids and other compounds-other macromolecules

• 4) Remaining 10 3-C are converted back into 6 5-C molecules.They combine w/ 6 new CO2 molecules to begin cycle again.

• ***** 2 sets of photosynthetic reactions work together-light-dependent traps energy of sunlight in ____________ and light –independent reactions(Calvin Cycle) use that chemical energy to produce stable,high energy sugars from CO2 and water….also O2 is produced

Chemical form

E.Factors affecting Photosynthesis

• Water supply• Temperature---affects enzymes• Light intensity----it does reach a

maximum-or optimal level of light,depending on plant type---eg.conifers only photosynthesize on __________________________.

Warm.sunny days

• Photosynthesis Under Extreme Conditions

• To conserve water,most plants under bright light close openings in leaves that normally take in CO2-keeps plants from drying out, but CO2 levels fall low and photosynthesis slows down

• However,some plants have adapted to such bright light and hot conditions

• C4 plants-specialized chemical pathway to capture even low amounts of CO2 for Calvin cycle(1st compound made has 4 C’s)/requires extra ATP-include crops like corn,sugarcane,and sorghum

• CAM plants-plants adapted to dry climate get CO2 while minimizing water loss-family CRASSULACEAE- (CRASSULACEAEN ACID METABOLISM)-CO2 becomes part of organic acids-Admit air into leaves only at night-During day leaves sealed tight-release CO2,allowing carb production(pineapple trees, many cacti ,ice plants)