Chapter 8.1

How Organisms Obtain Energy

Main Idea

All living organisms use energy to carry out all biological processes.

Energy

Energy is the ability to do work.

Quick Review:

Heterotrophs are organisms that need to ingest or consume food to get energy.

Autotrophs are organisms that make their own food for energy.

Different types of autotrophs:

Photoautotrophs, such as plants, convert light energy from the sun into chemical energy. Chemoautotrophs use inorganic substances (hydrogen sulfide) as a source of energy.

Metabolism

All of the chemical reactions in a cell are referred to as the cell’s metabolism. Chemical reactions can be one of two types. !  Catabolic !  Anabolic

Catabolic pathways

Catabolic pathways release energy by breaking down larger molecules into smaller molecules. In cellular respiration, oxygen is used to break down glucose [a sugar], producing carbon dioxide, water, and energy.

Anabolic Pathways

Anabolic pathways use the energy released by catabolic pathways to build larger molecules from smaller molecules. In photosynthesis, autotrophs use light energy from the Sun, carbon dioxide, and water to form glucose [a sugar] and oxygen.

ATP

Adenosine triphosphate ATP is the most important biological molecule that provides chemical energy.

ATP Structure Three Parts….. !  1. ribose- 5 carbon sugar, !  2. Adenine base and !  3. three phosphate groups

ATP Function

Energy is released when the bond between the second and third phosphate groups is broken. The energy released is used for cellular activities. Energy is stored in the phosphate bond formed when ADP adds on a phosphate group becoming ATP.

8.2 Photosynthesis

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Main Idea

Light energy is trapped and converted into chemical energy during photosynthesis.

Overview of Photosynthesis Most autotrophs make organic compounds, such as sugars, by a process called photosynthesis. Photosynthesis happens in two phases. !  Light dependent phase !  Light independent phase/Calvin cycle

Overall chemical equation:

Phase One: Light Reactions

The absorption of light is the first step to photosynthesis. Large organelles, called chloroplasts, capture the light energy. Chloroplasts are found mainly in the leaves of plants.

Chloroplasts

They contain chlorophyll that allows plants to undergo photosynthesis. They capture light energy from the sun to produce energy for plants. Leaves have large surfaces that act as light collectors for plants. They have two main compartments.

Parts of the chloroplast

First Compartment— ! Thylakoids - Flattened saclike

membranes that are arranged in stacks ! Grana – stacks of thylakoids Second Compartment-- !  Stroma – fluid-filled space that is

outside of the grana

Diagram of chloroplast

Pigments

Pigments are light absorbing molecules. Different pigments absorb different wavelengths of light. Chlorophyll is green. It absorbs red and blue wavelengths best. Chlorophyll is green because the green wavelengths of light are reflected.

Accessory Pigments There are other pigments, accessory pigments, that absorb other wavelengths of light. Carotenoids absorb mainly blue and green regions and reflect red, orange, and yellow. Found in carrots. Trees turn colors in the fall because the chlorophyll is breaking down and the other colors are visible.

Light Reaction

In the light reactions, autotrophs trap and convert light energy into chemical energy in the form of ATP and the chemical compound NADPH.

Phase Two: The Calvin Cycle

ATP and NADPH provide the cells with energy but can’t store energy. The Calvin Cycle stores energy in organic molecules such as glucose, a sugar. Plants use the sugars formed during the Calvin Cycle both as a source of energy and as building blocks for large carbohydrates.

8.3 Cellular Respiration

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Main Idea

Living organisms obtain energy by breaking down organic molecules during cellular respiration.

Cellular Respiration Cellular respiration occurs in the mitochondria, the energy powerhouse organelles of the cell. The function of respiration is to remove high energy electrons from carbon compounds [glucose from photosynthesis] and use that energy to make ATP. ATP is used to as a source of energy for cells to do work.

Cellular Respiration Cellular respiration happens in two main

parts. -glycolysis -aerobic respiration that includes the Krebs cycle and electron transport chain

Overall Equations for Respiration

Glycolysis

Glycolysis is an anaerobic process that does not require oxygen. Glycolysis uses ATP to break a molecule of glucose in half, producing pyruvic acid.

Overall Equations for Respiration

Aerobic respiration Aerobic respiration processes do require oxygen. If oxygen is present, the pyruvate move to the matrix of the mitochondria and are converted into CO2. The two parts of aerobic respiration are the Krebs cycle and the electron transport chain. The Krebs cycle and the electron transport chain take place in the mitochondria.

Aerobic Respiration

CO2 is released after the Krebs cycle. High energy electrons get passed from the pyruvate molecules to electron carriers. These go to the electron transport chain. At the end of the electron transport chain, a total of 38 ATP has been produced from one molecule of glucose.

Fermentation

If no oxygen is present at the end of glycolysis, fermentation occurs. 2 types of fermentation

1.  Lactic acid   Causes muscles to feel sore

2.  Alcoholic   Occurs in some yeast and bacteria

How are photosynthesis and cellular respiration related? The products of photosynthesis are used in cellular respiration. The product of photosynthesis is glucose. Glucose is then the substrate used in photosynthesis.