Chapter 8 -Energy and Life

Living things need energy to survive. This energy comes from food. The energy in most food comes from the sun. Where do plants get the energy they need to produce food?

Autotrophs and Heterotrophs Plants and some other types of organisms are able to use light energy from the sun to produce food.

Chemical Energy and ATP Energy comes in many forms including light, heat, and electricity. Energy can be stored in chemical compounds, too.

An important chemical compound that cells use to store and release energy is adenosine triphosphate, abbreviated ATP. ATP is used by all types of cells as their basic energy source.

ATP consists of: adenine ribose (a 5-carbon sugar) 3 phosphate groups Adenine ATP Ribose 3 Phosphate groups

Storing Energy ADP has two phosphate groups instead of three. A cell can store small amounts of energy by adding a phosphate group to ADP. ADP ATP Energy Partially charged battery Fully charged battery + Adenosine Diphosphate (ADP) + Phosphate Adenosine Triphosphate (ATP)

Releasing Energy Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates. P ADP 2 Phosphate groups

What is the role of ATP in cellular activities?

The energy from ATP is needed for many cellular activities, including active transport across cell membranes, protein synthesis and muscle contraction. ATP’s characteristics make it exceptionally useful as the basic energy source of all cells.

Using Biochemical Energy Most cells have only a small amount of ATP, because it is not a good way to store large amounts of energy. Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose.

Quiz 8-1

Organisms that make their own food are called a.autotrophs. b.heterotrophs. c.decomposers. d.consumers.

Most autotrophs obtain their energy from a.chemicals in the environment. b.sunlight. c.carbon dioxide in the air. d.other producers.

How is energy released from ATP? a.A phosphate is added. b.An adenine is added. c.A phosphate is removed. d.A ribose is removed.

How is it possible for most cells to function with only a small amount of ATP? a.Cells do not require ATP for energy. b.ATP can be quickly regenerated from ADP and P. c.Cells use very small amounts of energy. d.ATP stores large amounts of energy.

Compared to the energy stored in a molecule of glucose, ATP stores a.much more energy. b.much less energy. c.about the same amount of energy. d.more energy sometimes and less at others.

The key cellular process identified with energy production is photosynthesis. Photosynthesis is the process in which green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen.

What is the overall equation for photosynthesis?

The Photosynthesis Equation The equation for photosynthesis is: 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 carbon dioxide + water sugars + oxygen Light

Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.

O2O2 CO 2 + H 2 0 Sugar ADP NADP + Light-Dependent Reactions (thylakoids) H2OH2O ATP NADPH Calvin Cycle (stroma) Light energy

What is the role of light and chlorophyll in photosynthesis?

Light and Pigments How do plants capture the energy of sunlight? In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll.

Plants gather the sun's energy with light-absorbing molecules called pigments. The main pigment in plants is chlorophyll. There are two main types of chlorophyll: –chlorophyll a –chlorophyll b

Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum.

Chlorophyll does not absorb light in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green.

Light is a form of energy, so any compound that absorbs light also absorbs energy from that light. When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. These high-energy electrons are what make photosynthesis work. Photosynthesis Video

Quiz 8-2

Most of the added mass of a tree comes from a.soil and carbon dioxide. b.water and carbon dioxide. c.oxygen and carbon dioxide. d.soil and oxygen.

Plants use the sugars produced in photosynthesis to make a.oxygen. b.starches. c.carbon dioxide. d.protein.

The raw materials required for plants to carry out photosynthesis are a.carbon dioxide and oxygen. b.oxygen and sugars. c.carbon dioxide and water. d.oxygen and water.

The principal pigment in plants is a.chloroplast. b.chlorophyll. c.carotene. d.carbohydrate.

The colors of light that are absorbed by chlorophylls are a.green and yellow. b.green, blue, and violet. c.blue, violet, and red. d.red and yellow.

Inside a Chloroplast In plants, photosynthesis takes place inside chloroplasts. Plant Plant cells Chloroplast

Chloroplasts contain thylakoids—saclike photosynthetic membranes. Single thylakoid

Thylakoids are arranged in stacks known as grana. A singular stack is called a granum. Granum

Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast. Chloroplast Photosystems

Chloroplast Light H2OH2O O2O2 CO 2 Sugars NADP + ADP + P Calvin Cycle Light- dependent reactions Calvin cycle

Electron Carriers When electrons in chlorophyll absorb sunlight, the electrons gain a great deal of energy. Cells use electron carriers to transport these high- energy electrons from chlorophyll to other molecules.

One carrier molecule is NADP +. Electron carriers, such as NADP +, transport electrons. NADP + accepts and holds 2 high-energy electrons along with a hydrogen ion (H + ). This converts the NADP + into NADPH.

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

Photosystem II Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level.

Photosystem II These high-energy electrons are passed on to the electron transport chain. Electron carriers High-energy electron

Photosystem II 2H 2 O Enzymes on the thylakoid membrane break water molecules into: Electron carriers High-energy electron

Photosystem II 2H 2 O –hydrogen ions –oxygen atoms –energized electrons + O 2 Electron carriers High-energy electron

Photosystem II 2H 2 O + O 2 The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. High-energy electron

Photosystem II 2H 2 O As plants remove electrons from water, oxygen is left behind and is released into the air. + O 2 High-energy electron

Photosystem II 2H 2 O The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. + O 2 High-energy electron

Photosystem II 2H 2 O Energy from the electrons is used to transport H + ions from the stroma into the inner thylakoid space. + O 2

Photosystem II 2H 2 O High-energy electrons move through the electron transport chain from photosystem II to photosystem I. + O 2 Photosystem I

2H 2 O Pigments in photosystem I use energy from light to re-energize the electrons. + O 2 Photosystem I

2H 2 O NADP + then picks up these high-energy electrons, along with H + ions, and becomes NADPH. + O 2 2 NADP + 2 NADPH 2

2H 2 O As electrons are passed from chlorophyll to NADP +, more H + ions are pumped across the membrane. + O 2 2 NADP + 2 NADPH 2

2H 2 O Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O 2 2 NADP + 2 NADPH 2

2H 2 O The difference in charges across the membrane provides the energy to make ATP + O 2 2 NADP + 2 NADPH 2

2H 2 O H + ions cannot cross the membrane directly. + O 2 ATP synthase 2 NADP + 2 NADPH 2

2H 2 O The cell membrane contains a protein called ATP synthase that allows H + ions to pass through it + O 2 ATP synthase 2 NADP + 2 NADPH 2

2H 2 O As H + ions pass through ATP synthase, the protein rotates. + O 2 ATP synthase 2 NADP + 2 NADPH 2

2H 2 O As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. + O 2 2 NADP + 2 NADPH 2 ATP synthase ADP

2H 2 O Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. + O 2 ATP synthase ADP 2 NADP + 2 NADPH 2

What is the Calvin cycle?

The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. Because the Calvin cycle does not require light, these reactions are also called the light-independent reactions.

Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules. CO 2 Enters the Cycle

The result is twelve 3-carbon molecules, which are then converted into higher-energy forms.

The energy for this conversion comes from ATP and high-energy electrons from NADPH. 12 NADPH ADP 12 NADP + Energy Input

Two of twelve 3-carbon molecules are removed from the cycle. Energy Input 12 NADPH ADP 12 NADP +

The molecules are used to produce sugars, lipids, amino acids and other compounds. 12 NADPH ADP 12 NADP + 6-Carbon sugar produced Sugars and other compounds

The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle. 12 NADPH ADP 12 NADP + 5-Carbon Molecules Regenerated Sugars and other compounds 6 6 ADP

The two sets of photosynthetic reactions work together. –The light-dependent reactions trap sunlight energy in chemical form. –The Calvin Cycle uses that chemical energy to produce stable, high-energy sugars from carbon dioxide and water.

Quiz 8-3

In plants, photosynthesis takes place inside the a.thylakoids. b.chloroplasts. c.photosystems. d.chlorophyll.

Energy to make ATP in the chloroplast comes most directly from a.hydrogen ions flowing through an enzyme in the thylakoid membrane. b.transfer of a phosphate from ADP. c.electrons moving through the electron transport chain. d.electrons transferred directly from NADPH.

NADPH is produced in light-dependent reactions and carries energy in the form of a.ATP. b.high-energy electrons. c.low-energy electrons. d.ADP.

What is another name for the Calvin cycle? a.light-dependent reactions b.light-independent reactions c.electron transport chain d.photosynthesis

Which of the following factors does NOT directly affect photosynthesis? a.wind b.water supply c.temperature d.light intensity