Photosynthesis & Cellular Respiration These processes are opposites! Chapters 6 & 7 Photosynthesis & Cellular Respiration These processes are opposites!

The equation for photosynthesis: 6CO2 + 6H2O + light energy C6H12O6 + 6O2 Carbon Dioxide + Water + sunlight –make- Organic compounds (sugar) + Oxygen

Photosynthesis & Cellular Respiration are related: The oxygen (O2) and some of the organic compounds produced by photosynthesis are used by cells in a process called cellular respiration.

In which organelles in cells do these process occur? Photosynthesis occurs in the chloroplasts. Cellular respiration occurs in the mitochondria.

Cellular Respiration is basically the opposite of Photosynthesis Photosynthesis creates biomass (organic compounds) by converting light energy into chemical energy (stored as carbohydrate, ATP or other high energy molecule) Cellular respiration is the process by which cells break down organic compounds to produce ATP (energy).

Cellular respiration is essentially photosynthesis in reverse

Photosynthesis Energy from the sun: Photosynthetic organisms are vital to the survival of all life on Earth. For this slide show, Diagrams & information are from Holt biology text

Photosynthesis is vital- because it is beginning of almost all food chains http://www.umaine.edu/umext/earthconnections/images/foodchain.gif

Discuss the following: Name 3 foods you ate today & think about how this food is related to plants. What is the difference between an organic compound and an inorganic compound? What is a carbohydrate? How does photosynthesis cause inorganic compounds to become organic?

Remember: Carbohydrates: Organic Compounds- contain Carbon! Molecules that are a source of energy Example: Glucose General formula for a carbohydrate is [CH2O]n - where n is a number between 3 and 6. Glucose is C6H12O6

Obtaining Energy from the sun to make inorganic compounds into organic compounds: Photosynthesis - converts light energy from the sun into chemical energy in the form of organic compounds through a series of reactions called biochemical pathways.

Part I. The Light Reactions A. All organisms need energy to carry out the functions of life. Where does this energy come from- 1. Directly from the sun- autotrophic organisms- make sugar from sunlight, CO2 & H2O (examples- all plants, algae, cyanobacteria, plant-like protists) 2. Indirectly from the sun- heterotrophic organisms – need to eat autotrophs )

There are 2 parts to photosynthesis Light reactions – Light energy is absorbed form the sun and is converted to chemical energy- temporarily stored in the bonds of ATP and NADPH Calvin cycle – organic compounds are formed using CO2 (now using the chemical energy stored from the light reactions)

B. Capturing Light Energy The light reactions begin with the absorption of light in- Chloroplasts organelles found in the cells of plants, some bacteria, and algae. Inside chloroplasts are Thylakoids, a system of membranes inside the chloroplast that look like flattened sacs

Light and Pigments Chlorophyll a & b Carotenoids the visible spectrum. White light from the sun is composed of an array of colors called the visible spectrum. Pigments absorb certain colors of light and reflect or transmit the other colors. Chlorophyll a & b Carotenoids

The sun emits energy at a range of wavelengths: the visible spectrum is a small part of that range.

Chloroplast Pigments Located in membranes of the thylakoids of chloroplasts are several pigments, including chlorophylls (chlorophyll a and chlorophyll b) and carotenoids.

How light is absorbed

Light Energy into Chemical Energy Photosystems- In the thykaloid membranes of chloroplasts- are the clusters of pigment molecules that harvest light energy for photosynthesis There are 2 photosystems: Photosystem II Photosystem I The 2 photosystems have similar pigments but different jobs in the chloroplast:

Photosystems II & I: Light Energy is absorbed by chlorophyll a molecules. “Excited electrons” in this higher energy level have enough energy to leave the chlorophyll a molecules. the primary electron acceptor donates the electrons to the electron transport chain. NADPH is produced. (now Energy is stored as chemical energy!)

Water is needed: The electrons are replaced by breaking down water The Hydrogen is used to replace the H+ and the e- used in the light reactions Oxygen is a waste product.

Making ATP in Light Reactions An important part of the light reactions is the synthesis of ATP. Chemiosmosis is the movement of protons through ATP synthase (an enzyme) & then into the stroma (This causes a concentration gradient. It releases energy, which is used to produce ATP.) Stroma -the solution that surrounds the thykaloid membrane in chloroplasts.

II. Calvin Cycle (The dark reactions) Carbon Fixation: The ATP and NADPH produced in the light reactions drive the second stage of photosynthesis, the Calvin cycle. In the Calvin cycle, CO2 is incorporated into organic compounds, a process called carbon fixation.

The Calvin cycle is the most common way that plants fix carbon Occurs in the stroma of the chloroplast Is a series of enzyme-assisted chemical reactions that produces a three-carbon sugar called G3P Some G3P sugars are used to make organic compounds, (energy is stored for later use.) Some G3P is converted to a five-carbon sugar (RuBP) to keep the cycle going.

Alternative “Dark” Pathways The C4 Pathway Some plants that evolved in hot, dry climates fix carbon through the C4 pathway. These plants have their stomata partially closed during the hottest part of the day. The CAM Pathway Some plants in hot, dry climates fix carbon through the CAM pathway. These plants carry out carbon fixation at night and the Calvin cycle during the day to minimize water loss

Summary photosynthesis

Chapter 7 is Cellular Respiration Cellular respiration is the process by which cells break down organic compounds to produce ATP. Products of cellular respiration are the reactants in photosynthesis; they are opposites!

Plants & Animals: Both autotrophs and heterotrophs use cellular respiration to get energy from organic compounds and O2 & produce waste products CO2 and water

Cellular respiration can be divided into 2 stages: glycolysis aerobic respiration.

During glycolysis One six-carbon glucose molecule is oxidized to form two three-carbon pyruvic acid molecules. A net yield of two ATP molecules is produced for every molecule of glucose that undergoes glycolysis

Glycolysis takes a 6-carbon sugar & breaks it into 2 3-carbon sugars http://terravivida.com/vivida/glyintro/page01.htm

Remember: lysis means to break up Breaking up the glucose molecule into 2 smaller sugars (pyruvic acid) provides energy to make ATP which is the principle energy 'currency' in the cell http://terravivida.com/vivida/glyintro/page05.htm

What happens after glycolysis? If no oxygen is available- fermentation occurs If oxygen is available- the krebs cycle

1. Fermentation. Lactic Acid Fermentation 2. Alcoholic Fermentation Occurs if oxygen is not present convert pyruvic acid into other compounds For example: Lactic Acid Fermentation an enzyme converts pyruvic acid into another three-carbon compound, called lactic acid. 2. Alcoholic Fermentation Some plants and unicellular organisms, (like yeast) convert pyruvic acid to ethyl alcohol & CO2.

2. Aerobic Respiration Called the Krebs cycle occurs in the mitochondria. occurs only if oxygen is present in the cell. Called the Krebs cycle

The Krebs cycle Also known as the tricarboxylic acid cycle (TCA), was first recognized in 1937 by the man for whom it is named, German biochemist Hans Adolph Krebs

Krebs happens in the mitochondria After the glycolysis takes place in the cell's cytoplasm, the pyruvic acid molecules travel into the interior of the mitochondria.

The Krebs Cycle: (There are actually 8 steps. Not all are show here) Each turn produces 1 ATP 2 CO2 3 NADH 1 ADH2 http://ncam.wgbh.org/publications/stemdx/images/krebs.jpg

The Krebs Cycle. First, pyruvic acid (produced in glycolysis) reacts with coenzyme A to form acetyl CoA. Then, acetyl CoA enters the Krebs cycle. The original glucose becomes completely broken down after 2 turns of the Krebs cycle. 2 turns produce: four CO2 molecules, two ATP molecules, and hydrogen atoms that are used to make six NADH and two FADH2 molecules.

Finally: Electron Transport Chain High-energy electrons in hydrogen atoms from NADH and FADH2 are then passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane

Efficiency of Cellular Respiration Cellular respiration can produce up to 38 ATP molecules from the oxidation of a single molecule of glucose. Most eukaryotic cells produce about 36 ATP molecules per molecule of glucose. Thus, cellular respiration is nearly 20 times more efficient than glycolysis alone.

Summary of Cellular Respiration Providing cells with energy in the form of ATP is an important function of cellular respiration. Also: Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.

Summary diagram- cellular respiration: http://www.chem.uwec.edu/Webpapers2005/mintermm/pages/Intro_media/intro.gif