Cellular Respiration Unit 4, Part 1

Energy in Cells As you know, cells must carry out numerous functions and processes to make its organism run smoothly. They need energy to do this. Some questions to keep in mind during this unit are: Where does this energy come from? What is the main energy form? Where is the energy stored? These processes are called metabolism.

Sources of Energy Chemical reactions that require free energy are called endergonic reactions. Free energy is the energy available to do work in cell processes. Most free energy comes from energy released in other chemical reactions. The reactions that release energy are called exergonic reactions.

The Currency of Energy If energy were something that must be bought by cells, the money would be ATP. ATP is a common result of exergonic reactions. ATP stands for adenosine triphosphate. Its structure is shown on the next slide.

ATP Structure

Energy From ATP When the bond between two phosphate groups in ATP is broken, free energy is released. Usually, this is a hydrolysis reaction in which water is added, resulting in a large molecule breaking apart into smaller ones.

Cellular Respiration When an ATP molecule is broken down, ADP (adenosine diphosphate) and a phosphate remain. If these two can rejoin, they will form ATP again. This requires more free energy. One type of exergonic reaction that can provide free energy is aerobic respiration.

Aerobic Respiration Aerobic respiration is the process of the energy released by breaking the bonds of food molecules such as glucose being used to make ATP from ADP. Aerobic respiration requires the presence of oxygen, and is actually a series of reactions that take place throughout the cell.

Aerobic Respiration Cellular respiration starts in the cytoplasm of a cell, but most of the reactions take place in the mitochondria. In the mitochondria, a process called the citric acid cycle takes place.

Citric Acid Cycle

Anaerobic Respiration Anaerobic respiration takes place without oxygen. (an- means without) An example of an anaerobic reaction is seen when muscles grow tired after working for a long time. They are undergoing anaerobic respiration to release needed energy to keep going. Many bacteria live in anaerobic environments.

Anaerobic Reactions Some more common anaerobic reactions include lactic acid fermentation (causing muscle cramps) and alcohol fermentation.

Energy Yield from Anaerobic Reactions Both types of fermentation mentioned require 2 ATPs to provide the necessary energy. So, since fermentation produces 4 molecules of ATP, the net product is only 2 ATPs because of the 2 used to run the reaction.

Total Energy Yield The total energy yield from the citric acid cycle during aerobic respiration is 2 ATP. The other reactions of aerobic respiration, called the electron transport chain, produce 34 molecules of ATP. So, the total yield of aerobic respiration is 36 molecules of ATP.

Equations To Know Aerobic Respiration: C6H12O6 + 6O2 + 6H2O --> 6CO2 + 12H2O + energy Anaerobic Respiration: C6H12O6 → 2C3H6O3 + 2 ATP (Glucose → Lactic Acid + Energy)

Photosynthesis Unit 4, Part 2

Photosynthesis Photosynthesis is a process that occurs in plant cells, specifically in the chloroplasts found in the cytoplasm of plant cells. Like cellular respiration, photosynthesis is a series of reactions that occur in many different stages. It occurs only in producers - some bacteria, algae, and plants.

Overview of Photosynthesis

Photosynthetic Reactions 6 CO2 + 12 H2O → C6H12O6 + 6 O2 + 6 H2O Photosynthesis requires water, carbon dioxide, and sunlight. Photosynthesis produces glucose, oxygen, and water.

Products of Photosynthesis During photosynthesis, molecules of carbon dioxide and water are combined into simple sugars (like glucose, fructose, or galactose) by enzymes, and oxygen is given off as a by-product. Energy for the process of photosynthesis comes from light energy absorbed by chlorophyll in plant parts that are green.

The Light Reactions Photosynthesis is divided into two parts: the light-dependent reactions and the Calvin cycle (the light-independent reactions). During light reactions, light is absorbed by chlorophyll and carotenoids (red pigments). This energy is passed along until it reaches electrons, making them “excited.” These excited electrons bond ADP to a phosphate molecule to form ATP.

Summarizing the Light Reactions Light energy is absorbed and converted to chemical energy in the bonds of ATP. Water is split into hydrogen ions, electrons, and oxygen. Hydrogen ions from water are attached to carrier coenzymes called NADP for use in later steps.

Light Reactions

The Calvin Cycle

The Calvin Cycle The Calvin cycle is the second set of reactions involved in photosynthesis. It is the process of synthesizing sugars. This is the ‘synthesis’ part of photosynthesis.

Events of the Calvin Cycle Sugars are composed of carbon, hydrogen, and oxygen atoms, so these atoms must be present in the reactants. Remember that the Calvin cycle and the light reactions are related, so the hydrogen ions left over from the first set of reactions can be used here.

Along with the hydrogen ions from the light reactions, the plant has stored up carbon dioxide, which acts as a source of the needed carbon and oxygen atoms. The reactions of the Calvin cycle convert that carbon dioxide to sugars.

Energy Use Photosynthesis uses a total of 54 ATP, but it’s free energy because it comes from the sunlight the chloroplasts absorb. A single molecule of glucose gives off about 38 molecules of ATP.

Relating Energy In some ways, photosynthesis is the opposite of respiration. They are called complementary reactions for this reason. Photosynthesis is an endergonic reaction, while respiration is exergonic. During photosynthesis, low energy carbon dioxide and water are converted to high-energy molecules of sugar. This is an anabolic reaction, since building up occurs. During respiration, high-energy molecules of sugar are converted to the carbon dioxide and water used in photosynthesis. This is a catabolic reaction, since breaking down occurs.

6 CO2 + 12 H2O + energy → C6H12O6 + 6 O2 +6H2O Respiration: The reactions are exactly opposite. Photosynthesis: 6 CO2 + 12 H2O + energy → C6H12O6 + 6 O2 +6H2O Respiration: C6H12O6 + 6O2 + 6H2O --> 6CO2 + 12H2O + energy