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Cell Energy & Photosynthesis Cell Energy Source of Energy In most living organisms the energy in most food comes from? • the sun • autotroph – ‘auto’ – self, ‘troph’ – food. organisms which are able to make their own food – examples? Cell Energy Source of Energy • heterotroph –‘heteros’– other,‘troph’– food. obtain energy from the foods they eat. – Impalas ? – Leopards ? – Mushrooms ? • to live, all organisms must release the energy stored in sugars and other compounds Cell Energy Source of Energy In nature there are many forms that energy can take • examples? – heat – light – nuclear – kinetic – motion – electrical – and chemical Cell Energy Stored Energy One of the principal chemical compounds that living things use to store energy is? • adenosine triphosphate (ATP) • an ATP molecule consists of the following – a nitrogen-containing compound - adenine Cell Energy adenosine tri-phosphate (ATP) Adenine Cell Energy Stored Energy One of the principal chemical compounds that living things use to store energy is? • adenosine triphosphate (ATP) • an ATP molecule consists of the following – a nitrogen-containing compound – adenine – a 5-carbon sugar - ribose Cell Energy adenosine tri-phosphate (ATP) Adenine Ribose Cell Energy Stored Energy One of the principal chemical compounds that living things use to store energy is? • adenosine triphosphate (ATP) • an ATP molecule consists of the following – a nitrogen-containing compound – adenine – a 5-carbon sugar – ribose – and 3 phosphate groups Cell Energy adenosine tri-phosphate (ATP) Adenine Ribose 3 Phosphate groups Cell Energy Stored Energy adenosine diphosphate (ADP) • has a structure similar to ATP but with one important difference – ADP has 2 phosphate groups instead of 3 • the addition of that 3rd phosphate group allows the cell to store small amounts of energy • similar to a battery storing energy Cell Energy ATP – stored energy Adenosine Diphosphate (ADP) + phosphate Cell Energy ATP – stored energy Adenosine Diphosphate (ADP) + phosphate Partially charged battery Cell Energy ATP – stored energy energy Adenosine Diphosphate (ADP) + phosphate Partially charged battery Cell Energy ATP – stored energy energy Adenosine Diphosphate (ADP) + phosphate Partially charged battery Adenosine triphosphate (ATP) Cell Energy ATP – stored energy Adenosine Diphosphate (ADP) + phosphate Partially charged battery energy Adenosine triphosphate (ATP) Fully charged battery Cell Energy Releasing energy from ATP • the energy stored in ATP is released when ATP is converted to ADP and a phosphate group. – this adding and subtracting of a third phosphate group is a way of a cell storing and releasing energy as needed Cell Energy Releasing energy from ATP the ATP molecule carries just enough energy to power a variety of cellular activities • active transport – sodium-potassium pump. enough energy to transport 3 sodium ions and 2 potassium ions • move organelles along microtubules inside cell Cell Energy ATP-ADP cycle Cell Energy ATP and Glucose most cells have only a small amount of ATP – enough to last for a few seconds of activity. – why? • ATP is very efficient at transferring energy but not very good at storing large amounts of energy • what can store lots of energy for a cell? Cell Energy ATP and Glucose • glucose – stores more than 90 times the chemical energy of a molecule of ATP • cells can therefore use carbohydrates like glucose to regenerate ATP from ADP Cell Energy Investigating Photosynthesis Voan Helmont’s experiments (1600’s) • he devised a way to find out if plants grew by taking material out of the soil – determined the mass of a pot of dry soil and a small seedling – planted the seedling in the pot of dry soil – watered the plant regularly Cell Energy Investigating Photosynthesis Voan Helmont’s experiments • results – at the end of 5 years • the seedling had gained about 75 kg. • the mass of the soil was almost unchanged - conclusions - most of the mass gained had come from water Cell Energy Investigating Photosynthesis Voan Helmont’s experiments • conclusions told part of the story of the growth. what was missing? • carbohydrate – – ‘hydrate’ – water – ‘carbo’ – from carbon dioxide Cell Energy Investigating Photosynthesis Joseph Priestley’s experiments • 100 years after Helmont’s experiments • experiment set-up – placed a candle under a glass jar - results - flame of candle eventually goes out - conclusions - something in air was necessary to keep flame burning Cell Energy Investigating Photosynthesis Joseph Priestley’s experiments • additional experiments - if a live sprig of mint is placed under the jar and allowed a few days to pass, the candle could be relighted and remain lighted for a while • conclusions - the mint plant had produced the substance required for burning - oxygen Cell Energy Investigating Photosynthesis Jan Ingenhousz experiments • Dutch scientist who later showed that the effect observed by Priestley occurred only when the plant was exposed to light • conclusion - light is necessary for plants to produce oxygen Cell Energy Investigating Photosynthesis the experiments performed by these and other scientists reveal that • in the presence of light Cell Energy Light energy chloroplast Cell Energy Investigating Photosynthesis the experiments performed by these and other scientists reveal that • in the presence of light – plants transform carbon dioxide and water Cell Energy Light energy chloroplast Carbon dioxide + water Cell Energy Investigating Photosynthesis the experiments performed by these and other scientists reveal that • in the presence of light – plants transform carbon dioxide and water – into carbohydrates and release oxygen Cell Energy Light energy chloroplast Carbon dioxide + water Sugars + oxygen Cell Energy Photosynthesis Equation light 6CO2 + 6H2O carbon dioxide + water C6H12O6 + 6O2 sugar + oxygen Cell Energy Light and Pigments In addition to water and carbon dioxide, photosynthesis requires? • light &? • chlorophyll, a molecule in chloroplasts Cell Energy Light and Pigments energy from the sun travels to the Earth in many forms. • one of these forms is light (sunlight) which your eyes perceive as ‘white light’ – it is actually a mixture of different wavelengths of light – many of these wavelengths are visible to your eyes and are referred to as the visible spectrum –R O Y G B I V Cell Energy Light and Pigments • plants gather the sun’s energy with lightabsorbing molecules called pigments • the plants principal pigment is chlorophyll – there are 2 main types of chlorophyll • chlorophyll a and chlorophyll b Absorption of light by chlorophyll a and chlorophyll b Cell Energy chlorophyll b chlorophyll a chlorophyll absorbs light very well in the blue and red regions however, it does not absorb it very well in the green and yellow regions Cell Energy Light and Pigments • light is a form of energy, any compound that absorbs light also absorbs the energy from that light. • when chlorophyll absorbs light much of the energy is transferred directly to electrons in the chlorophyll molecules, raising the energy levels of these electrons • these high energy electrons make photosynthesis work Cell Energy Inside a Chloroplast • thylakoid membranes – saclike photosynthetic membranes – contain clusters of chlorophyll and other pigments and proteins known as photosystems – able to capture the energy of sunlight • grana – (singular: granum) stacks of thylakoids • stroma – fluid region outside the thylakoid membranes Cell Energy Photosynthesis • light-dependent reactions – occurs in the __________ _________ Cell Energy Photosynthesis • light-dependent reactions – occurs in the thylakoid membranes Cell Energy Photosynthesis lightdependent reactions Chloroplast Cell Energy Photosynthesis • light-dependent reactions – occurs in the thylakoid membranes – requires – ? Cell Energy Photosynthesis • light-dependent reactions – occurs in the thylakoid membranes – requires – light energy, water & raw materials Cell Energy Photosynthesis light H 2O raw materials lightdependent reactions Chloroplast Cell Energy Photosynthesis • light-dependent reactions – occurs in the thylakoid membranes – requires – light energy, water & raw materials – produces – ? Cell Energy Photosynthesis • light-dependent reactions – occurs in the thylakoid membranes – requires – light energy, water & raw materials – produces – oxygen, ATP & NADPH Cell Energy Photosynthesis light H 2O lightdependent reactions Chloroplast O2 ATP NADPH Cell Energy Photosynthesis • light-independent reactions – also referred to as the ? • Calvin cycle – occurs in the ? • stroma Cell Energy Photosynthesis light H 2O lightdependent reactions Chloroplast O2 Calvin Cycle ATP NADPH Cell Energy Photosynthesis • light-independent reactions – also referred to as the ? • Calvin cycle – occurs in the ? • stroma – requires? • carbon dioxide, ATP & NADPH Cell Energy Photosynthesis light lightdependent reactions Chloroplast CO2 H 2O O2 Calvin Cycle ATP NADPH Cell Energy Photosynthesis • light-independent reactions – also referred to as the ? • Calvin cycle – occurs in the ? • stroma – requires? • carbon dioxide, ATP & NADPH – produces? • sugars, NADP+, & ADP + P Cell Energy Photosynthesis light CO2 H 2O NADP + ADP +P lightdependent reactions Chloroplast O2 Calvin Cycle ATP NADPH sugars Cell Energy NADPH • when sunlight excites electrons in chlorophyll, the electrons gain a great deal of energy • a special carrier is needed to move these high-energy electrons – similar to hot coals of a fire Cell Energy NADPH • carrier molecule – compound that can accept a pair of highenergy electrons and transfer them along with most of their energy to another molecule Cell Energy NADPH • NADP+ - carrier molecule that accepts and holds 2 high-energy electrons along with a hydrogen ion (H+) – results in the production of NADPH – this conversion to NADPH allows some energy of light to be trapped in a chemical form – chemical energy can then be used by cell for chemical reactions elsewhere in cell Cell Energy Light-Dependent Reactions • Step A – Photosystem II – pigments in photosystem II absorb light via antenna complexes – energy from light is absorbed by electrons – increasing their energy level – energy is then passed on to the electron transport chain – enzymes break up water molecules into electrons, hydrogen ions (H+), and oxygen Cell Energy Light-Dependent Reactions inner thylakoid membrane thylakoid membrane Stroma Cell Energy Light-Dependent Reactions • Step B – Electron transport chain (ETC) – high-energy electrons move through electron transport chain – energy from electrons is used by molecules to transport H+ ions from stroma to the inner thylakoid Cell Energy Light-Dependent Reactions inner thylakoid membrane thylakoid membrane Stroma Cell Energy Light-Dependent Reactions • Step C – Photosystem I – Pigments in photosystem I use light energy to reenergize the electrons – NADP+ picks up these high-energy electrons plus a H+ ion and becomes NADPH Cell Energy Light-Dependent Reactions inner thylakoid membrane thylakoid membrane Stroma Cell Energy Light-Dependent Reactions • Step D – Hydrogen Ion movement – H+ ions released during water-splitting and electron transport result in a slight positive charge inside the thylakoid membrane and a slight negative charge outside Cell Energy Light-Dependent Reactions inner thylakoid membrane thylakoid membrane Stroma Cell Energy Light-Dependent Reactions • Step D – Hydrogen Ion movement – H+ ions cannot cross the membrane directly – membrane contains a protein called ATP synthase that allows H+ ions to pass through it – as H+ ions pass through the protein, the protein rotates like a turbine – as it turns, ATP synthase binds ADP and a phosphate group to form ATP Cell Energy Light-Dependent Reactions inner thylakoid membrane thylakoid membrane Stroma Cell Energy The Calvin Cycle • Step A – CO2 enter the cycle – six CO2 molecules enter cycle from atmosphere – they combine with six 5-carbon molecules – the end result is twelve 3-carbon molecules Cell Energy The Calvin Cycle Cell Energy The Calvin Cycle • Step B – Energy input – the twelve 3-carbon molecules are converted into higher-energy forms – energy for this conversion comes from ATP and high-energy electrons of NADPH Cell Energy The Calvin Cycle Cell Energy The Calvin Cycle • Step C – 6-carbon sugar produced – two of the twelve 3-carbon molecules are converted into two similar 3-carbon molecules – These molecules are used to form various 6-carbon sugars and other compounds Cell Energy The Calvin Cycle Cell Energy The Calvin Cycle • Step D – 5-carbon molecules regenerated – The remaining ten 3-carbon molecules are converted back into six 5-carbon molecules – These molecules combine with six new CO2 molecules to begin the next cycle Cell Energy The Calvin Cycle Cell Energy Factors affecting photosynthesis • water – because it is a raw material, a shortage can slow or stop process • temperature – enzymes used in process work best between 0o C and 35o C. Temps above or below range may damage enzymes and slow down process • intensity of light – increasing intensity also increases rate of photosynthesis up to a certain point