Energy Flow Unit Practice Flashcards

Metabolism and Biochemical Reactions

Metabolism Defined: Metabolism represents all the chemical reactions occurring within each cell of an organism. Its primary functions are to provide energy for life's processes and to create key molecules.
Chemical Reactions: These processes involve the breaking and forming of bonds between different substances during chemical changes.
    * Energy Dynamics: Overall, reactions either absorb or release energy.
    * Bond Breaking: Requires energy to be absorbed.
    * Bond Forming: Allows energy to be released.
Law of Conservation of Energy: No energy in the system is lost; it merely changes forms. It may be released as heat, light, etc.
Classification of Biochemical Reactions:
* Catabolic: Reactions that break down larger molecules into simpler compounds. This results in a release of energy, categorized as exergonic.
* Anabolic: Reactions that build larger molecules from smaller ones. This requires consuming energy, categorized as endergonic.
Activation Energy ( $E_a$ ): The specific amount of energy needed to make a chemical reaction start.
Reaction Components:
* Reactants (Substrates): Substances that are changed during a chemical reaction.
* Products: Substances that are made by a chemical reaction.
Types of Energy Reactions:
* Endothermic: Absorbs energy in the form of heat or light. An example is photosynthesis. In these reactions, there is more energy in the products than in the reactants.
* Exothermic: Releases energy in the form of heat or light. An example is cellular respiration. In these reactions, there is less energy in the products than in the reactants.

Enzymes and Biological Catalysis

Control of Metabolism: Metabolic reactions are controlled by enzymes.
Enzymes Defined: Mostly proteins that speed up biochemical reactions by lowering the activation energy.
Catalysts: Substances that speed up reactions without being permanently altered themselves.
Mechanism of Action: Enzymes are specialized molecules that bind to reactants (substrates) to help break or form bonds, ultimately releasing a newly created product.
    * Reusability: Enzymes are NOT changed in a reaction and can be used over and over again.
    * Specificity: Enzymes are very specific, possessing an active site that fits only one substrate.
    * Induced Fit: Once the substrate connects to the enzyme, the bind tightens, creating an "induced fit."
Functional Variations:
* Bond Breaking: Enzymes can break bonds in a substrate to form two products.
* Bond Forming: Enzymes can make bonds between substrates to form one product.
Denaturation:
    * The enzyme's active site gets deformed and loses its specific shape, leading to a loss of biological activity.
    * Causes: Environmental changes such as extreme changes in temperature, pH, ion strength, and solubility.
    * Renaturation: Some enzymes can be "renatured" back to their original shape, but this is not always possible.
Factors Affecting Reaction Rate:
    * Temperature: Increasing temperature increases the rate of reaction because molecules move faster and collide more frequently.
    * pH: Most enzymes work at specific pH levels; changes can affect reaction speed.
    * Substrate Concentration: The higher the amount of substrate, the faster the reaction due to more particle collisions.
    * Catalysts: Speed up reactions and lower the activation energy.
    * Competitive Inhibitor: Slows down the reaction by competing with the substrate for the active site on the enzyme.

Adenosine Triphosphate (ATP): The Energy Currency

Energy Conversion: The body cannot directly use food for energy. Energy in food is stored in chemical bonds which must be broken and reformed into ATP.
ATP Definition: An energy-carrying molecule that carries/stores energy for cell functions. It is the main energy currency for the cell.
Structure of ATP:
    * A nitrogen base (adenine).
    * A sugar ring (ribose).
    * Three phosphate groups held together with high-energy bonds.
The ATP-ADP Cycle:
    * Energy Release: A significant amount of energy is stored in the bond between the last two phosphates. Energy is released when a phosphate group is removed (and added to another molecule), turning ATP into ADP (Adenosine Diphosphate).
    * Exothermic Nature: Breakdown of ATP is exothermic because more energy is given off than required: $ATP \rightarrow ADP + P + \text{energy}$ .
    * Energy Storage: ADP becomes ATP when a phosphate group is added using energy from broken-down food.
    * Endothermic Nature: Making ATP is endothermic because energy is taken in: $ADP + P + \text{energy} \rightarrow ATP$ .
Macromolecule Energy Sources:
    * Carbohydrates: Most commonly broken down for ATP. Yields approximately $4\,cal/g$ . One glucose molecule can produce $36\,ATP$ .
    * Lipids (Fats): Broken down after carbohydrates. Stores the most energy at $9\,cal/g$ .
    * Proteins: Least likely to be broken down for energy. Stores $4\,cal/g$ .

Energy Flow through Ecosystems

Primary Source: All energy originates from the sun.
Producers (Autotrophs): Get energy from nonliving sources. Examples include plants, some bacteria, and algae.
* Photosynthesis: Capturing sunlight to make simple sugars: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$ .
* Chemosynthesis: Using chemicals like sulfur and methane for energy. Example: deep sea vent bacteria. Sulfur-based equation: $6CO_2 + 18H_2S + 3O_2 \rightarrow C_6H_{12}O_6 + 12H_2O + 18S$ .
Consumers (Heterotrophs): Get energy from living or once-living organisms. Examples include animals, most bacteria, and fungi.
    * Types of Consumers:
        1. Herbivores: Eat only vegetation.
        2. Carnivores: Eat only meat.
        3. Omnivores: Eat meat and vegetation.
        4. Detritivores (Decomposers): Eat dead materials.
Food Chains and Trophic Levels:
    * A food chain traces a single flow of energy showing trophic levels (levels of nourishment).
    * Rule of 10: Only $10\%$ of the energy obtained at one level is transferred to the next. The other $90\%$ is used for metabolism or lost as heat.
    * Hierarchy: (1) Producers (Grass) \rightarrow (2) Primary Consumers (Grasshopper) \rightarrow (3) Secondary Consumers (Mouse) \rightarrow (4) Tertiary Consumers (Owl).
Trophic Pyramids:
    * Energy Pyramid: Represents available energy; levels always get smaller ascending the pyramid.
    * Numbers Pyramid: Represents the number of organisms; fewer organisms can be supported as you move up.
    * Biomass Pyramid: Represents the total mass of living organic matter.

Photosynthesis: Solar to Chemical Energy

Process: Solar/light energy, water, and carbon dioxide are converted into chemical energy stored in glucose ( $C_6H_{12}O_6$ ).
Equation: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$ .
* Reactants: Carbon dioxide (absorbed through stomata) and Water (absorbed through roots).
* Products: Glucose and Oxygen.
Chloroplast Structure:
* Grana: Pancake-like stacks of thylakoid membrane.
* Stroma: Fluid-like substance filling the space between grana.
Chlorophyll: Pigment that absorbs every color of sunlight except green, which is reflected.
Rate Factors: Light intensity, amount of $CO_2$ , and temperature.
Alternate Pathways and Issues:
* Stomata: Pores on leaves for gas exchange ( $CO_2$ in, $O_2$ out). If closed to prevent dehydration in heat, gas exchange stops.
* Photorespiration: Occurs when $O_2$ levels rise inside the leaf; oxygen is added to the Calvin Cycle instead of $CO_2$ , wasting resources and producing no sugar or ATP.

Cellular Respiration: ATP Production

Goal: Convert chemical energy in food (glucose) to energy stored in ATP.
Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$ .
Mitochondria Structure:
* Inner Membrane: Folded membranes.
* Matrix: Fluid-like substance.
Glycolysis: The first stage; splitting 6-carbon glucose into two 3-carbon Pyruvates. It is anaerobic, occurs in the cytoplasm, and produces a total of $2\,ATP$ and $2\,NADH$ .
Respiration Pathways:
    * Aerobic Respiration: If oxygen is present. Yields $36-38\,ATP$ .
    * Anaerobic Respiration (Fermentation): If oxygen is absent. Yields $2-4\,ATP$ .
        * Lactic Acid Fermentation: Occurs in bacteria and animal muscle cells. Pyruvate is converted to lactic acid and $2\,ATP$ . Equation: $C_6H_{12}O_6 \rightarrow 2C_3H_6O_3 + 2\,ATP$ .
        * Alcohol Fermentation: Occurs in yeast. Pyruvate is broken down into alcohol, $CO_2$ , and $2\,ATP$ . Equation: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + 2\,ATP$ .

Biogeochemical Cycles: Carbon and Nitrogen

The Carbon Cycle:
* Reservoirs: Rocks ( $60,000,000\,Gt$ ), Ocean ( $41,000\,Gt$ ), Fossil Fuels ( $10,000\,Gt$ ), Land Biomass ( $2,500\,Gt$ ), Atmosphere ( $840\,Gt$ ).
* Processes: Photosynthesis (plants/plankton absorb carbon), Respiration (organisms release carbon), Fossilization (organic matter buried without decomposing), Combustion (burning fossils/biomass releasing $CO_2$ ).
The Nitrogen Cycle:
    * Atmospheric Nitrogen ( $N_2$ ): Comprises $78\%$ of the atmosphere but is unreactive due to a triple bond.
    * Nitrogen Fixation: Bacteria in soil/root nodules convert $N_2$ gas into ammonia ( $NH_3$ ) or ammonium ( $NH_4^+$ ).
    * Assimilation: Plants take up ammonia to build DNA, RNA, and proteins.
    * Nitrification: Nitrifying bacteria convert ammonia into nitrites ( $NO_2^-$ ) and then nitrates ( $NO_3^-$ ).
    * Ammonification: Decomposers return nitrogen to the soil as ammonia when organisms die.
    * Denitrification: Denitrifying bacteria convert nitrates back into $N_2$ gas, occurring best in low-oxygen environments like waterlogged soil.
Human Impact:
* Fertilizers: Excess nitrogen ends up in waterways, depleting oxygen and harming aquatic life.
* Emissions: Combustion in automobiles and factories contributes nitrous oxide to the atmosphere.

Questions & Discussion

Q: Why do humans impact the carbon cycle?
* A: Humans change where carbon is located by drilling/burning fossil fuels and through deforestation, moving carbon from ground reservoirs to the atmosphere.
Q: What is biometry in the context of the carbon cycle?
* A: Measuring living things (like tree circumferences) to estimate stored carbon.
Q: Why don't root cells need chloroplasts?
* A: Chloroplasts catch sunlight. Since roots are underground and not exposed to the sun, they cannot perform photosynthesis.
Q: Does loss of energy in a pyramid violate the Law of Conservation of Energy?
* A: No. Energy is not destroyed; it changes form into heat, which is lost to the environment but still exists within the total energy of the universe.
Q: How do animals obtain nitrogen?
* A: They obtain it through the food chain by eating plants or other animals.
Q: What happens if the nitrogen cycle stopped?
* A: Life would end because all living things require nitrogen for DNA and protein synthesis.