Photosynthesis Chapter 8

Energy and Life Chapter 8.1

Objective  Explain where plants get the energy they need to produce food.  Describe the role of ATP in cellular activities.

Autotrophs and Heterotrophs  Plants and some other types of organisms are able to use light energy from the sun to produce food.  Autotrophs:  Organisms that make their own food  Ex. Plants  Heterotrophs:  Organisms that obtain energy from the food they consume  Ex. Animals

Chemical Energy and ATP  Energy comes in many forms:  Light  Heat  Electricity  Living things also use chemical fuels  Adenosine triphosphate (ATP):  Chemical compound that cells use to store and release energy  Adenine  Ribose: 5-carbon sugar  3 Phosphate groups Adenine Ribose 3 Phosphate groups

Storing Energy  Adenosine diphosphate (ADP):  Similar to ATP except  2 Phosphate groups instead of 3 Partially charged battery Fully charged battery

Releasing Energy  By breaking the chemical bond between the 2 nd and 3 rd phosphates, energy is released.  ATP has enough energy to power a variety of cellular activities:  Ex: Active transport and protein synthesis  The characteristics of ATP make it useful as the basic energy source of all cells

Using Biochemical Energy  Example: Active Transport  Cell membrane contains a sodium-potassium pump  Membrane proteins pump  Sodium ions (Na+) out of the cell  Potassium ions (K+) into the cell  ATP provides the energy that keeps the pump working  Most cells only use a small amount of ATP  ATP is not good at storing large amounts of energy for any long period of time

Photosynthesis: An Overview Chapter 8.2

Objective  Explain what the experiments of van Helmont, Priestly, and Ingenhousz reveal about how plants grow.  State the overall equation for photosynthesis.  Describe the role of light and chlorophyll in photosynthesis.

Investigating Photosynthesis  Photosynthesis:  Plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates (sugars and starches) and oxygen (a waste product).  When a tiny seedling grows into a tall tree with a mass of several tons, where does the tree’s increase in mass come from?

Van Helmont’s Experiment  Jan van Helmont (1600s)  Devised an experiment to find out if plants grew by taking material out of the soil  Concluded that most of the gain in mass had come from water  The experiment accounts for the “Hydrate” or water portion of the carbohydrate produced by photosynthesis

Priestley’s Experiment  Joseph Priestly (1700s)  Gave insight into the process of photosynthesis  Reasoned something was in the air that could keep a candle flame burning  Oxygen  The mint plant had produced the substance required for burning  The mint released oxygen

Jan Ingenhousz  Jan Ingenhousz  Showed the effect by Priestly occurred only when the plant was exposed to light.  Other scientists finally discovered that in the presence of light,  Plants transform CO2 and H2O into carbohydrates, and they also release oxygen.

The Photosynthesis Equation  6CO 2 + 6H 2 O light  C 6 H 12 O 6 + 6O 2  Carbon dioxide + water light  sugars + oxygen  Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high energy sugars and oxygen Copyright Pearson Prentice Hall The Photosynthesis Equation Light energy

Lights and Pigments  In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts.  Pigments:  Plants gather the sun’s energy with light absorbing molecules  Chlorophyll:  The plants principle pigment  Two main types:  Chlorophyll a  Chlorophyll b  When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these molecules.

The Reactions of Photosynthesis Chapter 8.3

Objective  Describe the structure and function of a chloroplast.  Describe what happens in the light-dependent reactions.  Explain what the Calvin cycle is.  Identify factors that affect the rate at which photosynthesis occurs.

Inside a Chloroplast  Photosynthesis occurs inside chloroplasts.  Thylakoids:  Saclike photosynthetic membranes arranged in stacks known as grana.  Photosystems:  Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters.  Light collecting units in chloroplast.  Stroma:  Region outside the thylakoid membranes  Reactions of photosystems have two parts:  Light-dependent reactions  Light-independent reactions (Calvin cycle)

Inside a Chloroplast Light Light- Dependent Reactions CO 2 H2OH2O Sugars O2O2 Chloroplast Calvin Cycle NADP+ ADP + P ATP NADPH

Electron Carriers  Cells use electron carriers to transport high-energy electrons from chlorophyll to other molecules  Electron transport:  A carrier molecule (electron transport chain) is a compound that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule.  NADP + :  A carrier molecule that transfers high-energy electrons from chlorophyll to other molecules

Light-Dependent Reactions  Light-dependent reactions:  Require light in order for plants to grow  Use energy from light to produce ATP and NADPH  The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH  ATP synthase:  Large protein that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP

Light-Dependent Reactions Inner Thylakoid Space Thylakoid Membrane Stroma Photosystem II Electron Transport Chain Hydrogen Ion Movement ATP synthase Chloroplast Photosystem I ATP Formation

The Calvin Cycle  Calvin Cycle:  Plants use the energy that ATP and NADPH contain to build high-energy compounds that can be stored for a long time.  The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars

Calvin Cycle ChloropIast CO 2 Enters the Cycle Energy Input 5-Carbon Molecules Regenerated Sugars and other compounds 6-Carbon Sugar Produced

Factors Affecting Photosynthesis  Water  A shortage of water can slow or even stop photosynthesis  Temperature  Photosynthesis depends on enzymes that function best between 0° C and 35° C  Light intensity  As light increase so does the rate of photosynthesis  However plants reach a maximum rate