Chapter 8

 Energy is the ability to do work  All living organisms require energy  To be active (play sports)  Even while resting (cells require energy at all times!)  Without the ability to obtain and utilize energy, life would stop!

 Where does energy come from?  The energy to create most food comes from the sun  Autotrophs – organisms that can produce their own food  Plants and some other types of organisms can use light energy from the sun to produce their own food  Heterotrophs – organisms that cannot produce their own food, but must consume other organisms  Animals, bacteria, fungi

 Energy comes in many forms  Light, heat, electricity  Living organisms use chemical fuel  One of the main chemical compounds used for energy is ATP (adenosine triphosphate)  ATP is exceptionally useful as the basic source of energy of all cells  ATP is made of adenine, ribose, and 3 phosphate groups  The phosphate groups allow ATP to store and release energy

 ADP (adenine diphosphate) is similar to ATP, except it only has 2 phosphate groups  When a cell has energy available, it adds another phosphate group to ADP which produces ATP  ADP = ½ charged battery : ATP = fully charged battery

 When the cell needs energy, the 3 rd phosphate group breaks away from the ATP molecule  Remember energy is created when bonds are broken  Enough energy is released to power cell activities  The molecule then becomes ADP again

 Cells use ATP energy for different functions: 1. Transport across cell membranes  Active Transport - the movement of molecules across the cell membrane from low to high concentration 2. Protein synthesis  Energy is used to respond to chemical signal to produce proteins 3. Muscle contraction  Requires energy from the cell with the use of a sodium/potassium pump

 Even though ATP is an excellent source of energy, cells are not packed with it  Most cells have only a small amount of ATP  Only enough to last a few seconds of activity  ATP is good for transferring energy, but not storing energy  Energy storage is best in carb’s (glucose can store 90 times the chemical energy of an ATP molecule)

 One of the key processes involved with energy production is photosynthesis  Photosynthesis – the process that uses the sun’s energy to convert carbon dioxide and water into oxygen and carbohydrates  There has been much research on photosynthesis  Early research investigated the overall process  Later research investigated the chemical pathways

 In addition to CO2 and H2O, plants require light (to energize the reaction) and chlorophyll for photosynthesis to occur  Plants gather the sun’s energy with light absorbing molecules called pigments  The main pigment of plants is called chlorophyll

 Chlorophyll absorbs light very well in some spectrums (blue-violet and red) and not in others (green)  Green light is reflected, so plants appear green  Since light is a form of energy, any compound that absorbs light also absorbs energy  When chlorophyll absorbs light, it is directed to its electrons which raises their energy levels  These high energy electrons make photosynthesis work

 The requirements for photosynthesis were discovered in the 1800’s  It wasn’t until the mid to late 1900’s that scientists understood the complex chemical reactions of photosynthesis

 Photosynthesis takes place inside organelles called chloroplasts  Chloroplasts contain saclike photosynthetic membranes called thylakoids  Within the thylakoids are proteins called photosystems which organize chlorophyll  They are the light-collecting units of the chloroplast

 There are 2 different types of reactions that take place in order for photosynthesis to happen 1. Light-Dependent Reactions – take place in the thylakoid 2. Light-Independent Reactions – take place in the stroma (the region outside the thylakoid membranes)  Is represented with the Calvin Cycle

 When sunlight excites electrons in chlorophyll, these electrons gain a great deal of energy  These electrons require a special carrier  A 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 process is called electon transport and the carriers are known as the electron transport chain

 One of the electron carriers is NADP +  When an electron needs to be transported, NADP + accepts 2 high energy electrons and 1 hydrogen ion (H + )  This converts NADP + into NAPDH  one way sunlight can be trapped into a chemical form  NADPH carries the electrons to elsewhere in the cell, releases them and returns to the NADP + form

 Light-Dependent Reactions require light  These reactions use energy from light to produce ATP and NADPH and oxygen

 The ATP and NADPH formed by light- dependent reactions contains an abundant amount of chemical energy  These compounds are not stable enough to store that energy for more than a few minutes  The Calvin Cycle uses the ATP and NADPH to produce high-energy sugars which can store energy for long periods of time

 Remember, photosynthesis is possible because of the back and forth relationships of the light- dependent and light-independent (Calvin Cycle) reactions  Light-Dependent traps energy  Calvin Cycle converts energy into sugars

 Water shortage  Why plants that live in dry climates have a waxy covering on their leaves  Temperature  Photosynthesis happens best between 0  C and 35  C (32  F and 95  F)  Anything above or below can damage enzymes which can slow or stop photosynthesis  Light intensity  Photosynthesis happens best only at certain intensity levels