1. plants and other autotrophs are the producers of the ... · 2019-01-09 · benchmark...

• Photosynthesis nourishes almost all of the living

world directly or indirectly.

• All organisms require organic compounds for energy and to make organic molecules from their carbon skeletons.

• Autotrophs produce organic molecules from CO2

and other inorganic raw materials obtained from the

environment. Heterotrophs (like us) can’t do this.

• Autotrophs are the producers of the biosphere.

1. Plants and other autotrophs are the

producers of the biosphere

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Benchmark Clarifications

Students will explain how the products of photosynthesis are used

as reactants for cellular respiration and vice versa.

Students will explain how photosynthesis stores energy and

cellular respiration releases energy.

Students will identify the reactants, products and/or the basic

function of photosynthesis.

Students will identify the reactants, products and/or the basic

functions of aerobic & anaerobic cellular respiration.

Students will connect the role of ATP to energy transfers within

the cell.

Content Limits

Items will not require memorization of the stages,

specific events or intermediate molecules produced

during these processes.

Items do not require the balancing of equations.

Items will not assess plant structures.

Scenarios may include chemical equations.

Scenarios referring to adenosine triphosphate should use

the abbreviation ATP rather than the words adenosine

triphosphate.

• Using glucose as our target product, the equation

describing the net process of photosynthesis is:

• 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2

• How is this similar to the general equation of respiration?

Chloroplasts split water molecules and

produce oxygen in photosynthesis


• Living is work.

• To perform their many

tasks, cells must bring in

energy from outside

sources.

• In most ecosystems, energy enters as sunlight.

• Light energy trapped in organic molecules is available to both photosynthetic organisms and others that eat them.

Introduction


Fig. 9.1

• Any green part of a plant has chloroplasts.

• However, the leaves are the major site of

photosynthesis for most plants.

• There are about half a million chloroplasts per square

millimeter of leaf surface.

• The color of a leaf comes from chlorophyll, the

green pigment in the chloroplasts.

2. Chloroplasts are the sites of

photosynthesis in plants


• Each chloroplast has two membranes around a

central fluid space, the stroma.

• In the stroma are

membranous sacs,

the thylakoids.

• Thylakoids may be stacked into columns called grana.


Fig. 10.2

• The light dependent reactions convert solar energy

to chemical energy.

• The light independent reactions, a.k.a. Calvin

cycle incorporates CO2 from the atmosphere into an

organic molecule and uses energy from the light

reactions to “fix” the new carbon piece into sugars.

This process is therefore called carbon fixation.

• Both processes happen inside the chloroplast.

Photosynthesis consists of two processes



Fig. 10.4

• When light meets matter, it may be reflected,

transmitted, or absorbed.

• Different pigments absorb photons of different

wavelengths.

• A leaf looks green

because chlorophyll,

the dominant pigment,

absorbs red and blue

light, while transmitting

and reflecting green

light.


Fig. 10.6

• The light reaction can perform work only with

those wavelengths of light that are absorbed.

• In the thylakoid are several pigments that differ in

which colors of light they absorb best.

• Chlorophyll a, the

dominant pigment,

absorbs best in the

red and blue

wavelengths, and

least in the green.


Fig. 10.8a

• Collectively, these photosynthetic pigments

determine an overall action spectrum for

photosynthesis. Similar to the last graph?

• An action spectrum measures changes in some measure

of photosynthetic activity (for example, O2 release) as

the wavelength is varied.


Fig. 10.8b

• Only chlorophyll a participates directly

in the light reactions, but antenna

pigments absorb light and transfer

energy to chlorophyll a.

• Chlorophyll b, carotenoids and

xanthophylls can funnel the energy

from other wavelengths to

chlorophyll a



Fig. 10.9

• In the thylakoid membrane, chlorophyll is organized

along with proteins and smaller organic molecules

into photosystems.

• A photosystem acts like a light-gathering “antenna

complex” consisting of a few hundred chlorophyll a,

chlorophyll b,

and other accessory

pigments


Fig. 10.11

• When any antenna molecule absorbs a photon,

it is transmitted from molecule to molecule

until it reaches a particular chlorophyll a, called

the reaction center, right in the middle of the

photsystem.

• The reaction center chlorophyll a becomes so

energized by the light that it loses 2 electrons

to a nearby molecule.

• This starts the light dependent reactions.


• There are two types of photosystems.

• Photosystem I

• Photosystem II

• These two photosystems work together to use light

energy to generate ATP and NADPH.

• The folding of the innermost membrane into

thylakoids allows for many photosystems to exist

here, enhancing the amount of light dependent

reactions that can happen. Does this sound

familiar? What theme is this an example of?


Let’s watch the light dependent reactions

1. When photosystem II absorbs light, an excited electron is captured by the primary electron acceptor, leaving the reaction center chlorophyll awith an electron “gap”.

2. An enzyme extracts electrons from water and passes them to the chlorophyll a to fill the gap.

• This reaction (photolysis) splits water into two hydrogen ions and an oxygen atom, which combines with another to form O2.

• This is where the oxygen that all aerobically respiring organisms (like you and I) depend on comes from.


http://vcell.ndsu.nodak.edu/animations/photosynthesis/index.htm

3. Excited electrons from photosystem

II pass along an electron transport

chain of cytochrome molecules before

ending up at a photosystem I reaction

center.

4. As these electrons pass along the

transport chain, their energy is

harnessed to produce ATP, again by a

chemiosmotic process.



Fig. 10.12

5. At the bottom of this electron transport chain,

the electrons fill an electron “gap” in the PS I

chlorophyll a reaction center.

6. This gap was created when photons excite

electrons on the photosystem I complex.

• The excited electrons are captured by a second primary

electron acceptor which transmits them to a second,

shorter electron transport chain.

• Ultimately, these electrons don’t participate in

chemiosmosis, but instead are passed from the transport

chain to NADP+, creating NADPH.

• NADPH will carry these high-energy electrons to the

Calvin cycle.


• The Calvin cycle regenerates its starting material

after molecules enter and leave the cycle, just like in

the Krebs Cycle. Let’s watch

• CO2 enters the cycle and leaves as sugar.

• The cycle spends the energy of ATP and NADPH to

make the sugar.

• The actual sugar product of the Calvin cycle is not

glucose, but a three-carbon sugar, glyceraldehyde-3-

phosphate (G3P or PGAL)

4. The Calvin cycle uses ATP and NADPH to

convert CO2 to sugar: a closer look


../Animations/Animation 10.3 Calvin Cycle.MOV

• Each turn of the Calvin cycle fixes one carbon.

• For the net synthesis of one G3P molecule, the

cycle must take place three times, fixing three

molecules of CO2.

• To make one glucose molecules would require six

cycles and the fixation of six CO2 molecules.

• Since these reactions do not directly require light,

they are also called the light independent reactions.


• The Calvin cycle has three phases.

• In the carbon fixation phase, each CO2 molecule is

attached to a five-carbon sugar, ribulose

biphosphate (RuBP).

• This is catalyzed by RuBP carboxylase or rubisco, the

most abundant protein in the world.

• The six-carbon intermediate splits in half to form two

molecules of 3-phosphoglycerate (PGA) per CO2.



Fig. 10.17.1


Fig. 10.17.2

• If our goal was to produce one glucose net, we would start

with 6 CO2 (6C) and 6 RuBP (30C).

• After fixation and reduction we would have 12 molecules

of G3P (36C).

• Two of these 12 G3P (6C) combine to make 1 glucose.

(Remember in glycolysis this was reversed?)

• This molecule can exit the cycle to be used by the

plant cell.

• In the last phase, regeneration of the CO2 acceptor (RuBP),

the other 10 G3P molecules (30C) are rearranged to form

the 6 RuBP molecules (30C) we started with. In actuality,

there are millions of CO2 molecules involved.



Fig. 10.17.3

• In photosynthesis, the energy that enters the

chloroplasts as sunlight becomes stored as chemical

energy in

organic

compounds.

6. Photosynthesis is the biosphere’s

metabolic foundation: a review


Fig. 10.20

• Sugar made in the chloroplasts supplies the entire

plant with chemical energy and carbon skeletons to

synthesize all the major organic molecules of cells.

• About 50% of the organic material is consumed as fuel

for cellular respiration in plant mitochondria.

• Carbohydrate in the form of the disaccharide sucrose

travels via the veins to nonphotosynthetic cells.

• There, it provides fuel for respiration and the raw

materials for anabolic pathways including synthesis of

proteins and lipids and building the extracellular

polysaccharide cellulose.


• Plants also store excess sugar by synthesizing

starch.

• Some is stored as starch in chloroplasts or in storage

cells in roots, tubers, seeds, and fruits.

• Heterotrophs, including humans, may completely or

partially consume plants for fuel and raw materials.

• On a global scale, photosynthesis is the most

important process to the welfare of life on Earth.

• Each year photosynthesis synthesizes 160 billion metric

tons of carbohydrate per year.


Without Photosynthesis to grow plants:

• Cows

everywhere

would be

forced to starve

or jump.

Study the equation below. What product is

missing from the equation for photosynthesis?

Name the reactants and the products in the

equation.

sunlight

6CO2 + 6H2O → ____ + 6O2

Autotrophs, such as plants, use light to make

their own food. What happens to light

absorbed by a plant during photosynthesis?

A. It is converted to kinetic energy

B. It powers a reaction that produces carbon

dioxide and water

C. It is converted to chemical energy, which the

plant stores.

D. It powers a reaction that produces oxygen and

carbon dioxide.

Of the following factors, which will not have an

effect on the photosynthetic process?

a. Light intensity

b. Water availability

c. Nitrogen concentration

d. Temperature fluctuation

Gasses are a part of the photosynthesis process,

different phases. Which gas is removed from the

atmosphere during photosynthesis?

a. Hydrogen

b. Oxygen

c. Nitrogen

d. Carbon dioxide

A. Use few plants

B. Reduce the amount of water

C. Use a larger container

D. Move the light closer to the beaker

What are the reactants for photosynthesis and

how do they enter the plant?

There are reactants and products in the

photosynthesis process. What is the one

component in photosynthesis that is NOT

recycled and must be available to the plant?

1. plants and other autotrophs are the producers of the ... · 2019-01-09 · benchmark...

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