PHOTOSYNTHESIS Biological Energy Energy and Life AUTOTROPHS HETEROTROPHS

PHOTOSYNTHESIS Biological Energy

Energy and Life • AUTOTROPHS & HETEROTROPHS • To live, all organisms must release the stored chemical energy in carbohydrates & lipids. • Organisms that can make their own nutrients are called autotrophs. • Types of autotrophs: • Chemosynthetic – found in deep water ocean vents or hot springs • Photosynthetic – found all over the world except the arctic • Organisms that cannot use the sun’s energy directly but from nutrients they consume are called heterotrophs. • For example: • Sun < Grass < Rabbit < Timber Wolf • CHEMICAL ENERGY & ATP • Energy is stored in the bonds between atoms. • One of the principal chemical compounds that cells use to store and release energy is adenosine triphosphate abbreviated ATP. • ATP consists of 3 parts: adenine, ribose and 3 phosphate groups. • Adenosine diphosphate, ADP, is similar to ATP but only has 2 phosphate groups.

Energy & Life • USING BIOCHEMICAL ENERGY • By breaking the chemical bond between the 2 nd and 3 rd phosphate group, energy is released as needed. • ATP has enough energy to power: • • Active transport across cell membranes Protein synthesis Muscle contractions Light up a firefly Most cells have only enough ATP to last a few seconds of activity. But Why? It is good at transferring energy but not storing it over the long term. A single glucose molecule store more than 90 times the chemical energy of an ATP molecule. • It is more efficient to keep a small supply of ATP on hand. • Cells regenerate ATP from ADP by using energy from glucose. • •

Photosynthesis: An Overview 6 CO 2 + 12 H 2 O – light energy C 6 H 12 O 6 + 6 O 2 + 6 H 2 O

Photosynthesis: An overview • LIGHT & PIGMENTS • Light is a form of radiation and is energy. The sun provides photosynthetic autotrophs this energy. • Plants gather the sun’s energy with light-absorbing molecules called pigments. • The principle pigment is called chlorophyll. • Chlorophyll is located in the organelle called a chloroplast. • There are two main types of chlorophyll: • Chlorophyll a – absorbs light in violet and regions of visible spectrum • Chlorophyll b – absorbs light in blue and regions of visible spectrum • Chlorophyll does not absorb light in the green region of the visible spectrum which is why plants appear green. • Chlorophyll “reflects” green wavelengths of visible light. • Plants also contain red and orange pigments such as carotene which absorbs light in other regions of the spectrum. • When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising their energy levels. • These high-energy electrons make photosynthesis work!

The Reactions of Photosynthesis • INSIDE A CHLOROPLAST • Thylakoids: saclike photosynthetic membranes. Stacks of thylakoids are called grana (granum = singular). • Photosystems: clusters of chlorophyll and other pigments organized by proteins in the thylakoid membrane. There are two photosystems and each have a different function. • Stroma: the region outside thylakoid membrane. • Two parts to the reactions of photosystems: • Light-dependent reaction (takes place within the thylakoid) • Light-INdependent reaction AKA Calvin Cycle (takes place in the stroma)

The Reactions of Photosynthesis • ELECTRON CARRIERS • Sunlight excites electrons and electrons gain energy. • High-energy electrons require a special carrier. • An electron carrier molecule is a compound that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule – this is called electron transport. • Nicotinamide adenine dinucleotide phosphate, NADP+, is one type of electron carrier molecule. It accepts and holds 2 high-energy electrons and a hydrogen ion (H+). • NADP+ + 2 e- + H+ NADPH • This combination or synthesis reaction is one way in which some of the energy of sunlight is trapped in chemical form. • NADPH then carries high-energy electrons to chemical reactions elsewhere in the cell. • These high energy electrons are used to help build a variety of molecules the cell needs – IE carbohydrates such as……? ? • YES!! GLUCOSE!!

The Reactions of Photosynthesis

The Reactions of Photosynthesis • LIGHT-DEPENDENT REACTIONS • Photosystem II (PS II) absorbs light to break up water molecules into energized electrons, hydrogen ions (H+) and oxygen. • light Pigments + H 2 O electrons (e-) + hydrogen ions (H+) + oxygen (O) • light & pigment 2 H 2 O 4 H+ + O 2 + e- • Electron Transport Chain (ETC) high energy electrons (e-) from PSII move through the ETC to photosystem I using electron carriers. • Energy from the electrons is used by the molecules in the ETC to transport H+ ions from the stroma into the inner thylakoid space. • Photosystem I (PSI) pigments use light to re-energize electrons. NADP+ pics up 2 high energy e- and 1 H+ to form NADPH. • NADP+ + 2 e- + H+ NADPH • NADPH is used to make sugar in the Calvin cycle. • The inside of the thylakoid membrane fills up with H+. Since there are more H+ on the inside of the membrane than the outside, there is now a charge gradient – positive on the inside and negative on the outside. • To neutralize the charge difference, H+ must move to the outside of the thylakoid membrane. • They can only pass through a membrane protein called ATP synthase or ATP’ase. As the H+ ions pass through the protein, the protein spins like a turbine being spun by water. ATP’ase binds ADP and a phosphate to make ATP.

The Reactions of Photosynthesis • LIGHT-INDEPENDENT REACTION (AKA CALVIN CYCLE) • ATP & NADPH have a lot of energy but cannot store it. • Autotrophs use ATP & NADPH to build high-energy compounds that CAN be used to store energy – namely glucose. • CO 2 Enters the Cycle • Six CO 2 molecules enter the cycle from atmosphere and combine with six 5 carbon molecules resulting in 12 3 -carbon molecules. • Energy Input • The 12 3 -carbon molecules are then converted into higher-energy forms by using energy from ATP and high energy electrons from NADPH. • ATP ADP & NADPH NADP+ • 6 -Carbon Sugar Produced • Two 3 -carbon molecules are removed from the cycle to produce sugars and other compounds. • 5 -Carbon Molecules Regenerated • The 10 remaining 3 -carbon molecules are converted back into six 5 -carbon molecules, which are used in the next cycle. • Calvin Cycle uses six molecules of carbon dioxide to produce a single 6 -carbon sugar (glucose), ADP and NADP+

The Reactions of Photosynthesis • SUMMARY • Light-dependent reaction • • Traps sunlight energy and uses water to make high energy electron carrying molecules. Occurs in thylakoid. Reactants = Light energy, H 2 O, NADP+, & ADP Products = H+, O 2, NADPH & ATP • Calvin Cycle • • Uses energy from excited electrons to produce high-energy sugar molecules. Occurs in stroma. Reactants = CO 2, ATP, & NADPH Products = C 6 H 12 O 6, ADP, & NADP+ • FACTORS THAT AFFECT PHOTOSYNTHESIS • Water conditions • Temperature (enzyme Rubisco functions best between 0 C & 35 C) • Light intensity