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Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs?...

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Page 1: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.
Page 2: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

Chapter Introduction

Autotrophy and Photosynthesis

4.1 What Are Autotrophs?

4.2 Overview of Photosynthesis

4.3 The Light Reactions

4.4 The Calvin Cycle

Photosynthesis and the Environment

4.5 Rate of Photosynthesis

4.6 Photorespiration and Special Adaptations

4.7 Photosynthesis and the Atmosphere

Chemoautotrophy

4.8 Varieties of Chemoautotrophs

4.9 Chemoautotrophs and the Environment

Chapter Highlights

Chapter Animations

ChapterMenu

Page 3: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

A State the importance of photosynthesis and identify the plant structures that are involved in photosynthesis.

Learning Outcomes

By the end of this chapter you will be able to:

B Identify the steps by which light energy is converted to chemical energy during the light reactions.

C Discuss the importance of the Calvin cycle.

D Describe how environmental factors affect the rate of photosynthesis and photorespiration.

E Describe the effects of photosynthesis on the atmosphere.

F Discuss varieties of chemoautotrophs and their distribution in the environment.

Page 4: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

How could animals survive without plants?

Autotrophy: Collecting Energy from the Nonliving Environment

How do organisms obtain energy from their environment?

This photo shows a group of fungi.

Page 5: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Photosynthesis can be compared to a “living bridge”—connecting the Sun with the organisms on Earth by providing the energy needed for life.

• Some bacteria obtain energy from minerals such as iron or sulfur instead of sunlight.

This photo shows a group of fungi.

Autotrophy: Collecting Energy from the Nonliving Environment

Page 7: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Photosynthesis, performed by plants, some bacteria, and other small organisms called algae, uses the energy of sunlight to convert carbon dioxide to sugars.

Autotrophy and Photosynthesis

4.1 What are Autotrophs?

• Autotrophs such as plants that depend on photosynthesis for both energy and carbon compounds are known as photoautotrophs.

• We depend on photosynthesis for agricultural production and the products of ancient photosynthesis—petroleum and coal.

Page 8: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• In environments where photoautotrophs cannot survive, bacteria called chemoautotrophs obtain energy by oxidizing inorganic substances such as iron, sulfur, or other minerals.

4.1 What are Autotrophs? (cont.)

Autotrophy and Photosynthesis

In the upper geyser basin at Yellowstone National Park, note the steam rising from the water. The water is too hot to support photoautotrophs.

Page 9: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

4.1 What are Autotrophs? (cont.)

Autotrophy and Photosynthesis

Page 10: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Photoautotrophs have adapted to take advantage of sunlight.

4.2 Overview of Photosynthesis

• Light consists of a vibrating electric and magnetic field like a wave.

• The length of the waves determines the light’s color and energy; the shorter the wave, the greater its energy.

Autotrophy and Photosynthesis

Page 11: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Energy that radiates from the Sun forms a continuous series of waves called a spectrum. The range of wavelengths that animals can detect with their eyes—visible light—is roughly the same range plants use in photosynthesis. Shorter wavelengths (blue light) have more energy than longer wavelengths (red light).

Page 12: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Photoautotrophic cells contain light-absorbing substances, or pigments, that absorb visible light.

• The light-absorbing pigments are embedded in membranes within cells, called thylakoids, that form closed sacs.

• In the cells of plants and algae, each thylakoid sac is part of an organized structure called a chloroplast.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Page 13: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Electron micrograph of a chloroplast in a leaf of corn, Zea mays, x24,000. The darker areas are stacks of thylakoids called grana; the drawing shows the structure of one enlarged granum. Photosynthetic pigments are embedded in the thylakoid membranes; DNA, RNA, and Calvin-cycle enzymes are in the stroma.

Page 14: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Most photosynthesis depends on the green pigment chlorophyll, found in the thylakoids.

• Plants contain two forms of chlorophyll, a and b.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

The structure of chlorophyll a. Chlorophyll b differs only in having a CHO—group in place of the circled CH3—. The part of the molecule shown in green absorbs light; the hydrophobic tail helps to keep the molecule anchored in the lipid-rich thylakoid membrane.

Page 15: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Chlorophylls a and b absorb light in the violet/blue and orange/red ranges, but not in the green range.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Page 16: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The green light that is not absorbed gives leaves their color.

• Other accessory pigments absorb additional wavelengths of light.

• As the chlorophyll content of leaves declines in the fall, the accessory pigments become more visible.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Page 17: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The process of photosynthesis involves three energy conversions:

1. absorption of light energy

2. conversion of light energy into chemical energy

3. storage of chemical energy in the form of sugars

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Page 18: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• In the light reactions, pigment molecules in the thylakoids absorb light and convert it to chemical energy.

• The energy produced by light reactions is used to make 3-carbon sugars from carbon dioxide in a series of reactions known as the Calvin cycle.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Page 19: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Solar energy is converted to chemical energy in the thylakoid membranes.

Enzymes of the Calvin cycle use this energy to reduce carbon dioxide, forming sugars.

Page 20: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The following equation summarizes the overall reactions of photosynthesis:

4.2 Overview of Photosynthesis (cont.)

Autotrophy and Photosynthesis

Page 21: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• During light reactions, chlorophyll and other pigments in the thylakoid:

– absorb light energy

– water molecules are split into hydrogen and oxygen

– light energy is converted to chemical energy which powers sugar production in the Calvin cycle

4.3 The Light Reactions

Autotrophy and Photosynthesis

Page 22: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

The light reactions of photosynthesis

Click the image to view an animated version.

Page 23: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The light-absorbing pigments form two types of clusters, called photosystems (PS) I and II.

4.3 The Light Reactions (cont.)

• The chlorophyll and other pigments in each photosystem absorb light energy and transfer it from one molecule to the next.

Autotrophy and Photosynthesis

• All this energy is funneled to a specific chlorophyll a molecule called the reaction center.

Page 24: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Some of the electrons from the reaction-center molecules jump to other molecules, known as electron carriers, forming an electron transport system between the two photosystems.

• Electrons from PSII move through the system to replace electrons lost from PSI.

• PSII receives replacements for these electrons from an enzyme near its reaction center that oxidizes water.

4.3 The Light Reactions (cont.)

Autotrophy and Photosynthesis

Page 25: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Some photosynthetic bacteria obtain electrons from hydrogen sulfide gas (H2S) instead of water, resulting in solid sulfur as a by-product.

4.3 The Light Reactions (cont.)

Autotrophy and Photosynthesis

The photosynthetic bacterium Chromatium oxidizes hydrogen sulfide gas instead of water, producing the yellow sulfur globules visible in its cells.

Page 26: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• When electrons from water reach PSI, they receive an energy boost giving them enough energy to reduce a molecule known as NADP+ (nicotinamide adenine dinucleotide phosphate).

• The electrons, along with protons from water, combine with NADP+ to convert it to its reduced form, NADPH, ending the electron flow in the light reactions.

• NADPH provides the protons and electrons needed to reduce carbon dioxide in the Calvin cycle.

4.3 The Light Reactions (cont.)

Autotrophy and Photosynthesis

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• The solar energy that the electrons receive from PSII powers the active transport of protons across the thylakoid membrane.

• The concentrated protons inside the thylakoid then diffuse out, transferring energy to the enzyme complex ATP synthetase.

4.3 The Light Reactions (cont.)

Autotrophy and Photosynthesis

• The enzyme uses this energy to synthesize ATP from ADP and phosphate.

Page 28: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• There are two reasons that photosynthesis does not stop with the synthesis of ATP and NADPH:

1. ATP and NADPH are not particularly stable compounds.

2. The light reactions do not produce any new carbon compounds that the organism can use to grow.

4.3 The Light Reactions (cont.)

Autotrophy and Photosynthesis

Page 29: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The Calvin cycle conserves the chemical energy produced in the light reactions in the form of sugars that the organism can use for growth.

4.4 The Calvin Cycle

Autotrophy and Photosynthesis

– The Calvin cycle occurs in the stroma of a chloroplast.

– The Calvin cycle completes the process of photosynthesis.

Page 30: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

Reduction of carbon dioxide to sugars in the Calvin cycle

Click the image to view an animated version.

Page 31: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The Calvin cycle includes the following steps:

1. A molecule of carbon dioxide combines with the 5-carbon sugar-phosphate, ribulose bisphosphate (RuBP), producing an unstable 6-carbon molecule that immediately splits into two molecules of the 3-carbon acid, phosphoglyceric acid (PGA).

2. Two enzymatic steps reduce each molecule of PGA to the 3-carbon sugar-phosphate, phosphoglyceraldehyde (PGAL), requiring one molecule each of ATP and NADPH.

4.4 The Calvin Cycle (cont.)

Autotrophy and Photosynthesis

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3. A series of enzymatic reactions, combines and rearranges molecules of PGAL, eventually producing a 5-carbon sugar-phosphate.

4. Using an ATP molecule to add a second phosphate group to the 5-carbon sugar-phosphate, a molecule of the starting material, RuBP, is created, completing the cycle.

4.4 The Calvin Cycle (cont.)

Autotrophy and Photosynthesis

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• Three turns of the Calvin cycle, results in the formation of six molecules of PGAL, one of which is available for the organism to use for maintenance and growth.

• Sugar-phosphates such as PGAL are removed from the Calvin cycle for use in other cellular functions.

• Plants that use only the Calvin cycle to fix carbon dioxide are called C3 plants.

4.4 The Calvin Cycle (cont.)

Autotrophy and Photosynthesis

Page 34: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

4.4 The Calvin Cycle (cont.)

Autotrophy and Photosynthesis

Plants use the sugars produced in photosynthesis to supply energy and carbon skeletons for growth and other cell work. Much of this sugar is converted to sucrose or starch.

Page 36: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Environmental conditions such as light intensity, temperature, and the concentrations of carbon dioxide and oxygen all affect the rate of photosynthesis.

Photosynthesis and the Environment

4.5 Rate of Photosynthesis

• Environmental effects on organisms are usually described in terms of how they affect the rate, or activity per unit of time, of a biological process.

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• The rate of photosynthesis levels off before the light reaches the intensity of full sunlight.

4.5 Rate of Photosynthesis (cont.)

Photosynthesis and the Environment

As light intensity increases, the rate of photosynthesis increases and then reaches a maximum rate. Data are generalized to show trends in C3 plants.

Page 38: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• In very bright light, chlorophyll accumulates energy faster than it can transfer that energy to the electron transport system.

• As extra energy passes to oxygen molecules, the oxygen may react with water to form hydroxyl ions (OH–) or hydrogen peroxide (H2O2) and a decline in photosynthesis, called photoinhibition, may occur.

4.5 Rate of Photosynthesis (cont.)

Photosynthesis and the Environment

Page 39: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Temperature affects photosynthesis differently from light intensity.

4.5 Rate of Photosynthesis (cont.)

Photosynthesis and the Environment

As temperature increases, the rate of photosynthesis also increases, and then declines. Data are generalized to show trends in C3 plants that grow best between 20˚C and 30˚C.

Page 40: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• An increase in carbon dioxide concentration increases the rate of photosynthesis to a maximum point, after which the rate levels off.

• Above the carbon dioxide saturation point, further increases in carbon dioxide concentration have no effect on photosynthesis.

4.5 Rate of Photosynthesis (cont.)

Photosynthesis and the Environment

Page 41: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The effects of light, temperature, and carbon dioxide all interact with each other.

• The factors in shortest supply have the most effect on the rate of photosynthesis.

• Limiting factors are environmental factors such as food, temperature, water, or sunlight that restrict growth, metabolism, or population size.

4.5 Rate of Photosynthesis (cont.)

Photosynthesis and the Environment

Page 42: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

4.5 Rate of Photosynthesis (cont.)

Photosynthesis and the Environment

At high light intensity, the rate of photosynthesis is greater at 25˚C than at 15˚C. Thus, temperature can be a limiting factor when further increases in light intensity no longer stimulate photosynthesis. Data are generalized for typical C3 plants.

Page 43: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Normal atmospheric concentrations of oxygen (about 21%) can inhibit photosynthesis by up to 50%.

4.6 Photorespiration and Special Adaptations

Photosynthesis and the Environment

Increasing concentrations of oxygen inhibit the rate of photosynthesis in C3 plants.

Page 44: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The enzyme rubisco incorporates carbon dioxide into sugars in the Calvin cycle.

• The molecular structures of oxygen and carbon dioxide are held together by double bonds that keep the atoms about the same distance apart, allowing rubisco to bind to either molecule.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

Page 45: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• When carbon dioxide binds to rubisco and combines with RuBP, two molecules of PGA form.

• When oxygen binds to rubisco and combines with RuBP, one molecule of PGA, and one molecule of the 2-carbon acid glycolate form.

• In a pathway called photorespiration, glycolate is transported out of the chloroplast and partly broken down to carbon dioxide, resulting in a loss of fixed carbon atoms.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

Page 46: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

Photorespiration occurs simultaneously with photosynthesis and results in the loss of previously fixed carbon dioxide. Both processes depend on the enzyme rubisco, which can react with either carbon dioxide or oxygen. High carbon dioxide levels favor photosynthesis over photorespiration. High oxygen levels promote photorespiration.

Page 47: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• C4 plants have adapted to hot, dry, conditions by having two systems of carbon dioxide fixation that occur in different parts of the leaves.

• Surrounding each vein in the leaves is a layer of tightly packed cells, the bundle sheath.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

Page 48: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The mesophyll cells fix carbon dioxide by combining it with a 3-carbon acid.

• The resulting 4-carbon acid is rearranged and then transported to the bundle-sheath cells

• There, carbon dioxide is released from the 4-carbon acid and refixed by rubisco, forming PGA by way of the Calvin cycle.

• Many C4 plants can be about twice as efficient as C3 plants in converting light energy to sugars.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

Page 49: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

Carbon dioxide first combines with a 3-carbon acid in the outside mesophyll cells. The resulting 4-carbon acid is then transported into the bundle-sheath cells, where carbon dioxide is released to the Calvin cycle and refixed by rubisco.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

Page 50: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Another specialization for photosynthesis found in some desert plants is called CAM, for crassulacean acid metabolism.

• CAM plants open their stomates at night and incorporate carbon dioxide into organic acids.

• During the day, the stomates close, conserving water and enzymes then break down the organic acids, releasing carbon dioxide that enters the Calvin cycle.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

Page 51: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• The CAM system is not very efficient and while CAM plants can survive intense heat, they usually grow very slowly.

4.6 Photorespiration and Special Adaptations (cont.)

Photosynthesis and the Environment

The jade plant (Crassula) is an example of a CAM plant.

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• Photosynthesis supplies oxygen gas to Earth’s atmosphere and food to Earth’s organisms.

4.7 Photosynthesis and the Atmosphere

• Most organisms, including plants, use oxygen and release carbon dioxide.

• Photoautotrophs use the carbon dioxide again in photosynthesis, completing the cycle.

Photosynthesis and the Environment

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Summary of carbon, oxygen, and energy cycles in the biosphere

Click the image to view an animated version.

Page 54: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Photosynthesis produces enormous amounts of oxygen.

• Photosynthesis is the largest single biochemical process on Earth, therefore any disruption of that may have dramatic effects.

• The carbon dioxide content of the atmosphere has been increasing steadily at least since 1800.

4.7 Photosynthesis and the Atmosphere (cont.)

Photosynthesis and the Environment

Page 55: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• Preserving the balance of oxygen and carbon dioxide in the atmosphere may be vital to the future of all life on Earth.

• The C4 and CAM pathways are examples of the adaptation of photosynthesis to an oxygen-rich atmosphere.

• Increasing levels of carbon dioxide in the atmosphere favors C3 plants in their competition with C4 plants.

4.7 Photosynthesis and the Atmosphere (cont.)

Photosynthesis and the Environment

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• Chemoautotrophs are bacteria that obtain energy from the oxidation of some substance in the environment, usually an inorganic mineral such as iron or sulfur.

Chemoautotrophy

4.8 Varieties of Chemoautotrophs

• Chemoautotrophy generally does not provide as much energy as photosynthesis or heterotrophy.

• Chemoautotrophs grow best in environments where other organisms cannot survive and light and organic compounds are in short supply.

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• Three questions are important in studying a chemoautotroph:

4.8 Varieties of Chemoautotrophs (cont.)

1. What is its source of energy?

2. What is its source of carbon?

3. What is its source of electrons for reducing carbon?

Chemoautotrophy

Page 59: Splash Contents Chapter Introduction Autotrophy and Photosynthesis 4.1What Are Autotrophs? 4.2Overview of Photosynthesis 4.3The Light Reactions 4.4The.

• While chemoautotrophs fix carbon dioxide, usually with the Calvin cycle, their sources of energy and electrons vary greatly.

4.8 Varieties of Chemoautotrophs (cont.)

Chemoautotrophy

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• Like photoautotrophs, chemoautotrophs have electron transport systems.

• Many chemoautotrophs can adapt to changing environments by switching electron donors or living heterotrophically when food is plentiful.

• Some chemoautotrophs use different energy sources depending on what is available, while others avoid competition by using resources that other organisms ignore.

4.8 Varieties of Chemoautotrophs (cont.)

Chemoautotrophy

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• Chemoautotrophs are not very important in the sun-lit, organic carbon–rich environments familiar to us.

4.9 Chemoautotrophs and the Environment

• Chemoautotrophs are so common underground and deep in the ocean that they may make up the majority of life on Earth.

Chemoautotrophy

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• The oxidized end products of chemoautotrophs form important deposits of oxidized mineral ores, especially iron and sulfur.

• When the same bacteria attack coal that is rich in iron sulfide, or pyrite (FeS2), they oxidize the sulfur in the pyrite, forming sulfuric acid (H2SO4).

4.9 Chemoautotrophs and the Environment (cont.)

Chemoautotrophy

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• Sulfuric acid and dissolved metals may wash into local streams, killing many of the organisms living there.

4.9 Chemoautotrophs and the Environment (cont.)

Chemoautotrophy

Chemoautotrophic bacteria oxidize copper ions in the acidic waste water that drains from copper mines upstream, coloring the water brown in the Queen River in Queenstown, Tasmania (Australia).

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• Nitrogen-oxidizing bacteria contribute to plant growth by oxidizing ammonium ions (NH4

+) to nitrite ions (NO2–), and nitrite to nitrate ions (NO3

–).

• Most plants absorb and use nitrate more effectively than ammonium ions.

4.9 Chemoautotrophs and the Environment (cont.)

Chemoautotrophy

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• Around deep underwater volcanic vents, dissolved minerals and gases support a variety of chemoautotrophs which are the primary producers that support heterotrophs such as tube worms.

4.9 Chemoautotrophs and the Environment (cont.)

Chemoautotrophy

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• Hydrogen-oxidizing bacteria support heterotrophic bacteria and fungi in the pores of rocks as deep as 2,800 m beneath the surface of the earth.

4.9 Chemoautotrophs and the Environment (cont.)

Chemoautotrophy

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Summary

• The cellular processes of photosynthesis include the production of ATP and NADPH.

• NADPH and ATP are used to fix carbon dioxide into sugars during the Calvin cycle.

• In eukaryotes, photosynthesis depends on the structure of the chloroplast.

• Environmental factors that directly influence the rate of photosynthesis in plants include light intensity, temperature, and the concentrations of carbon dioxide and oxygen.

• Photosynthesis transforms sunlight into chemical energy. It also releases the oxygen that many organisms consume.

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Summary (cont.)

• High temperatures usually cause a decline in the rate of reactions. High concentrations of oxygen inhibit the rate of photosynthesis by fueling photorespiration.

• Environmental factors do not act individually but instead interact as limiting factors.

• C4 and CAM plants have evolved specializations that enable them to reduce photorespiration and water loss in hot, dry climates. In CAM plants, the stomates open at night and close during the day, greatly reducing transpiration.

• An increase of light intensity and carbon dioxide concentration tends to increase the rate of photosynthesis.

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Summary (cont.)

• Chemoautotrophs grow best in environments where other organisms cannot survive and light and organic compounds are in short supply.

• Many chemoautotrophs are able to use more than one electron source.

• Chemoautotrophs support communities of organisms around underwater volcanic vents and deep in the earth.

• Chemoautotrophs are bacteria that fix carbon, often by the Calvin cycle, and obtain energy by oxidizing substances in the environment, especially inorganic minerals.

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Reviewing Key TermsMatch the term on the left with the correct description.

___ photoautotroph

___ chemoautotroph

___ photoinhibition

___ photorespiration

___ CAM

___ NADP+

a. an adaptation for photosynthesis in arid conditions

b. occurs when a chloroplast has absorbed too much light energy

c. an organism that derives its energy from light

d. a hydrogen carrier in photosynthesis

e. an organism that derives its energy from the oxidation of inorganic compounds

f. a pathway in plants that consumes oxygen

c

e

b

f

a

d

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Reviewing Ideas1. How does the principle of limiting factors apply

to photosynthesis?

The effects of light, temperature, and carbon dioxide all interact with each other. Any of these factors may be at an ideal level when another is far below optimum. In this case, the factors in shortest supply have the most effect on the rate of photosynthesis.

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Reviewing Ideas2. Why does the rate of photosynthesis level off at

a certain light intensity?

At the light saturation point, the light reactions are saturated with light energy and are proceeding as fast as possible. In light that is more intense than the saturation point, chlorophyll accumulates energy faster than it can transfer that energy to the electron transport system.

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Using Concepts3. How is photosynthesis linked to atmospheric

homeostasis?

Each year plants use as much as 140 billion metric tons of carbon dioxide and 110 billion metric tons of water in photosynthesis. They produce more than 90 billion metric tons each of organic matter and oxygen gas. Because photosynthesis is the largest single biochemical process on Earth, any disruption of that process may have dramatic effects.

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Using Concepts4. Acidic mine runoff pollutes many rivers and streams

around the world. How is this problem linked to chemoautotrophs?

Metal-oxidizing bacteria attack coal that is rich in iron sulfide, or pyrite (FeS2), oxidizing the sulfur in the pyrite which forms sulfuric acid (H2SO4). This strong acid dissolves aluminum and iron from the coal and rock. The acid and dissolved metals wash into local streams, killing many of the organisms living there.

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Synthesize5. How do chemoautotrophs contribute to

agricultural production?

Inorganic nitrogen ions are important plant nutrients. The supply of nitrogen in soil is often a limiting nutrient in plant growth. Chemoautotrophic bacteria contribute to plant growth by oxidizing ammonium ions (NH4

+) to nitrite ions (NO2–), and nitrite to nitrate

ions (NO3–). Most plants absorb and use nitrate

more effectively than ammonium ions.

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Chapter Animations

The light reactions of photosynthesis

Reduction of carbon dioxide to sugars in the Calvin cycle

Summary of carbon, oxygen, and energy cycles in the biosphere

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