Chapter 5 Photosynthesis & Cellular Respiration

5-1 Energy & Living Things You get energy from the food you eat. Directly or indirectly, all of the Energy in living systems needed for Metabolism comes from the sun.

Metabolism involves either using energy To build molecules or breaking Down molecules in which energy Is stored. Photosynthesis is the process by which Light energy is converted to Chemical energy.

Autotrophs are organisms that use Energy from sunlight or Inorganic substances to make Organic compounds. Like plants use sunlight to Make glucose.

Heterotrphs are organisms that Must get energy from food instead Of directly from sunlight. We are heterotrophs because We can’t make our own food In our cells. Instead we use cellular respiration To “burn” fuel in our bodies.

Almost all of the food we eat goes To heat, but some of the energy Goes into making ATP. ATP (adenosine triphosphate) Provides cells with the energy they Need to carry out life’s processes.

5-2 Photosynthesis

In stage 1, light energy is absorbed. 6CO2 + 6H2O + Light C6H12O6 + 6O2 In stage 1, light energy is absorbed. Structures that will absorb light Contain pigments. Chlorophyll is the primary pigment That absorbs mostly blue and red Light and reflects green and yellow.

That reflection is why plants Are green. Plants contain 2 types of chlorophyll, a and b chlorophyll. Both types of chlorophyll play a Role in photosynthesis.

The pigments that produce yellow And orange colors in fall or In fruits and vegetables Are called carotenoids.

Pigments involved in plant Photosynthesis are located in the Chloroplasts of leaf cells. Clusters of pigments are embedded In the membranes of disk Shaped structures called Thylakoids.

When chlorophyll absorbs light this causes 1 pair of chlorophyll electrons to “bounce around”

Instead of being “trapped” in a wire they are stored in chemical bonds.

These “excited” electrons that leave The chlorophyll molecules are used To produce new molecules that Temporarily store chemical energy, Including ATP. The series of molecules through which Excited electrons are passed along A thylakoid membrane are called Electron transport chains.

-accepts electrons and is converted to NADPH NADP+ (in plants) -accepts electrons and is converted to NADPH NADPH is an electron carrier that Provides the high-energy electrons Needed to make C-H bonds in stage 3.

In stage 3, energy is stored in Organic molecules. In the 1st and 2nd stages of Photosynthesis, light energy is used To make ATP and NADPH, which Temporarily store chemical energy.

In the 3rd stage of photosynthesis, Carbon atoms from the CO2 in The air are used to make Organic compounds in which Chemical energy is stored. This energy is stored in the form Of sugar… Glucose.

The transfer of carbon dioxide To organic compounds is called Carbon fixation. The most common method for Carbon fixation is the Calvin Cycle. The Calvin cycle is a series of enzyme Assisted chemical reactions that Produce 3 carbon sugars.

Photosynthesis is affected by Various types of environmental factors. The most obvious is light Then there is CO2 concentration Also temperature

5-3 Cellular Respiration Cells transfer the energy in organic compounds (carbs, proteins, fats) back to ATP So for the most part, this is the Reverse of photosynthesis.

Metabolic processes that require Oxygen are called aerobic. Metabolic processes that can go On without oxygen are called Anaerobic.

The primary fuel for cellular Respiration is glucose, but fats and Proteins can also be used. In the first step of cellular respiration Glucose is broken down in the Cytoplasm during a process called Glycolysis. Glycolysis is enzyme assisted and Breaks down a 6 carbon glucose To 3 carbon sugars of pyruvate.

As glucose is broken down, some of Its hydrogens are transferred to An electron acceptor, NAD+. This forms the electron carrier NADH. For respiration to continue, the Electrons eventually are donated To other organic compounds, This recycles the NAD+.

In stage 2, more ATP is made By aerobic respiration. When oxygen is present, pyruvate Produced during glycolysis enters a Mitochondria and is converted to A 2 chain compound.

This reaction produces a carbon Dioxide molecule, 1 NADH Molecule and a 2 carbon acetyl group. The acetyl group is attached to a Molecule called coenzyme A, forming A compound called acetyl-CoA. Acetyl-CoA enters a series of enzyme Assisted reactions called the Kreps Cycle.

After the Krebs cycle, NADH and FADH2 now contain much of the Energy that was previously stored In glucose and pyruvate. When the Krebs cycle is completed, The 4 carbon compound that began The cycle is recycled, and Acetyl-CoA can enter the Cycle again.

In aerobic respiration, electrons Donated by NADH and FADH2 Pass through an electron transport Chain. In eukaryotic cells, the electron Transport chain occurs in the Inner membranes of the Mitochondria.

Fermentation follows glycolysis In the absence of oxygen. What happens when there is not Enough oxygen for aerobic Respiration? Then anaerobic respiration occurs.

Two important types of fermentation Are lactic acid fermentation And alcoholic fermentation. During vigorous exercise, pyruvate In muscles is converted to Lactate when there is not Enough oxygen present. The lactic acid then created builds Up and is what causes cramps. 

In other organisms, like yeast, The three carbon pyruvate is Broken down to ethanol, a 2 carbon compound, through a Process called alcoholic fermentation. Carbon dioxide is released During the process.

Ethanol is actually toxic to yeast. Yeast will die with ethanol Concentrations of about 12%. So naturally fermented wine and Beer can only be a maximum Of 12% alcohol.

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