Chapter 8 Biology: p 224-243

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Vocabulary Terms:

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Big Idea- Cellular Basis of Life

1. How do plants and other organism capture energy from the sun?

a. How do organisms store energy?b. What cellular structures and molecules are

involved in photosynthesisc. How do photosynthetic organism convert the

sun’s energy into chemical energy?

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8.1 Energy and Life

Key questions:1. What is ATP useful to cells?2. What happens during the process of photosynthesis?

Review: What is homeostasis?Ones ability to regulate internal body conditions in

response to ones environment

What powers so much activity, and where does that power come from?

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Chemical Energy and ATPWhat is Energy?

- ability to do workCells use energy in the form of ATP- Adenosine

Triphosphate, which is made of adenine (nitrogenous base), 5-carbon sugar (ribose), and 3 phosphates

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What do we need energy for?

• Energy is the ability to do work.

• Your cells are busy using energy to build new molecules, contract muscles, and carry out active transport.

• Without the ability to obtain and use energy, life would cease to exist.

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A. Storing Energy

• Adenosine diphosphate (ADP) looks almost like ATP, except that it has two phosphate groups instead of three. ADP contains some energy, but not as much as ATP.

• When a cell has energy available, it can store small amounts of it by adding phosphate groups to ADP, producing ATP.

• ADP is like a rechargeable battery that powers the machinery of the cell.

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B. Releasing Energy

– Cells can release the energy stored in ATP by breaking the bonds between the second and third phosphate groups.

– Because a cell can add or subtract these phosphate groups, it has an efficient way of storing and releasing energy as needed.

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C. Using Biochemical Energy1. One way cells use the energy provided

by ATP is to carry out active transport.

• Many cell membranes contain sodium-potassium pumps. ATP provides the energy that keeps these pumps working, maintaining a balance of ions on both sides of the cell membrane.

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Using Biochemical Energy

2. ATP powers movement, providing the energy for motor proteins that contract muscle and power the movement of cilia and flagella.

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Using Biochemical Energy

3. Energy from ATP powers the synthesis of proteins and responses to chemical signals at the cell surface.

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Using Biochemical Energy

- ATP is not a good molecule for storing large amounts of energy over the long term.

– It is more efficient for cells to keep only a small supply of ATP on hand.

– Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose.

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Heterotrophs Vs. Autotrophs– What happens during the process of

photosynthesis?

– In the process of photosynthesis, plants convert the energy of sunlight into chemical energy stored in the bonds of carbohydrates

Photo- Light

Synthesis- to create

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Heterotrophs– Organisms that obtain food by consuming

other living things are known as heterotrophs.

– Some heterotrophs get their food by eating plants.

– Other heterotrophs, such as this cheetah, obtain food from plants indirectly by feeding on plant-eating animals.

– Still other heterotrophs, such as mushrooms, obtain food by decomposing other organisms.

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Autotrophs

– Organisms that make their own food are called autotrophs.

– Plants, algae, and some bacteria are able to use light energy from the sun to produce food. The process by which autotrophs use the energy of sunlight to produce high-energy carbohydrates that can be used for food is known as photosynthesis.

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8.2 Photosynthesis OverviewKEY QUESTIONS:

1. What role do pigments play in the process of photosynthesis? a. Photosynthetic organisms capture energy from sunlight with

pigments.2. What are electron carrier molecules?a. An electron carrier is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule.

3. What are the reactants and products of photosynthesis?a. Photosynthesis uses the energy of sunlight to convert water and carbon dioxide (reactants) into high-energy sugars and oxygen (products).

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THINK ABOUT IT

– How would you design a system to capture the energy of sunlight and convert it into a useful form?

– Plants have solved these issues—and maybe we can learn a trick or two from them.

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Light– Energy from the sun travels to Earth in

the form of light.– Sunlight is a mixture of different

wavelengths, many of which are visible to our eyes and make up the visible spectrum.

– Our eyes see the different wavelengths of the visible spectrum as different colors: red, orange, yellow, green, blue, indigo, and violet.

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Pigments• Plants gather the sun’s energy with light-absorbing

molecules called pigments.

• The plants’ principal pigment is chlorophyll.

• The two types of chlorophyll found in plants, chlorophyll a and chlorophyll b, absorb light very well in the blue-violet and red regions of the visible spectrum, but not in the green region, as shown in the graph.

• Leaves reflect green light, which is why plants look green.

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Pigments• Plants also contain red and orange pigments such as

carotene that absorb light in other regions of the spectrum.

• Most of the time, the green color of the chlorophyll overwhelms the other pigments, but as temperatures drop and chlorophyll molecules break down, the red and orange pigments may be seen.

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Chloroplasts• Photosynthesis takes place inside organelles called

chloroplasts.

• Chloroplasts contain saclike photosynthetic membranes called thylakoids, which are interconnected and arranged in stacks known as grana.

• Pigments are located in the thylakoid membranes.

• The fluid portion outside of the thylakoids is known as the stroma.

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Energy Collection• Because light is a form of energy, any compound that

absorbs light absorbs energy. Chlorophyll absorbs visible light especially well.

• When chlorophyll absorbs light, a large fraction of the light energy is transferred to electrons. These high-energy electrons make photosynthesis work.

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High-Energy Electrons• The high-energy electrons produced by chlorophyll are

highly reactive and require a special “carrier.”• Think of a high-energy electron as being similar to a hot

potato. If you wanted to move the potato from one place to another, you would use an oven mitt—a carrier—to transport it.

• Plants use electron carriers to transport high-energy electrons from chlorophyll to other molecules.

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High-Energy Electrons• NADP+ (nicotinamide adenine dinucleotide phosphate) is a

carrier molecule.

• NADP+ accepts and holds two high-energy electrons, along with a hydrogen ion (H+). In this way, it is converted into NADPH.

• The NADPH can then carry the high-energy electrons to chemical reactions elsewhere in the cell.

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An Overview of Photosynthesis• Photosynthesis uses the energy of sunlight to convert

water and carbon dioxide into high-energy sugars and oxygen.

In symbols:6 CO2 + 6 H2O C6H12O6 + 6 O2

In words:Carbon dioxide + Water Sugars + Oxygen

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An Overview of Photosynthesis• Plants use the sugars generated by

photosynthesis to produce complex carbohydrates such as starches, and to provide energy for the synthesis of other compounds, including proteins and lipids.

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An Overview of PhotosynthesisHas two major Reactions: (Test Questions)- You must know where each one takes place- What goes in and out of each one

Reactions:1. Light Dependent RXN-

Goes in: water, light, (ADP, NADP+)Comes out: oxygen (ATP, NADPH)Takes place in: thylakoid membranes

2. Light Independent RXN ( dark rxn, Calvin Cycle)Goes in: CO2 (NADPH, ATP)Comes out: Sugar (ADP, NADP+)Takes place in: Stroma

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1. Light-Dependent Reactions• light-dependent reactions- because they require the

direct involvement of light and light-absorbing pigments.• The light-dependent reactions use energy from sunlight

to produce ATP and NADPH. • These reactions take place within the thylakoid

membranes of the chloroplast.• Water is required as a source of electrons and hydrogen

ions. Oxygen is released as a byproduct.

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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.

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

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

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8.3 The Process of PhotosynthesisKey Questions:1. What happens during the light-dependent

reactions?a. use energy from sunlight to produce oxygen and convert

ADP and NADP+ into the energy carriers ATP and NADPH.

2. What happens during the light-independent reactions?

a.ATP and NADPH from the light are used to produce high-energy sugars

3. What factors affect photosynthesis?a. Among the most important factors that affect

photosynthesis are temperature, light intensity, and the availability of water.

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THINK ABOUT IT

Why do chloroplasts contain so many membranes?

• When most pigments absorb light, they eventually lose most of that energy as heat. Chloroplasts avoid such losses. Membranes are the key to capturing light energy in the form of high-energy electrons.

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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.

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Summary of Light-Dependent Reactions

• The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.

• ATP and NADPH provide the energy needed to build

high-energy sugars from low-energy carbon dioxide.

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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 (sugar/starch) that can be stored for a long time.

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Summary of the Calvin Cycle1. The Calvin cycle uses 6

molecules of carbon dioxide to produce a single 6-carbon sugar molecule.

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

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

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

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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.

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Factors Affecting Photosynthesis

1. Temperature2. Light3. Water

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1. Temperature and 2. Light

• 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.

• 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.

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3. 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.

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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.

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C4 Plants

• 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.

• corn, sugar cane, and sorghum.

CAM Plants• Crassulacae family, such as cacti

and succulents, incorporate carbon dioxide into organic acids during photosynthesis in a process called Crassulacean Acid Metabolism (CAM).

• 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.

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