Lesson 6 Cellular Respiration and Fermentation

Overview of Energy Conversion

Energy conversion is a vital biological process that transforms light energy from the sun into cellular energy in the form of adenosine triphosphate (ATP). This conversion is crucial for various cellular functions, including growth, metabolism, and overall cellular maintenance. When glucose is broken down during cellular respiration, energy is released, which cells use for various activities necessary for life.

Cellular Respiration

Cellular respiration is a metabolic process that changes glucose into ATP, primarily occurring in two forms:

• Aerobic Respiration: This type requires oxygen and takes place in the mitochondria. It is very efficient, producing around 36 to 38 ATP from one glucose molecule.

• Anaerobic Respiration: This occurs when oxygen is limited, leading to the production of only about 2 ATP per glucose molecule. This type of respiration includes processes such as alcohol fermentation in yeast and lactic acid fermentation in muscle cells during strenuous activity.

Mitochondria and ATP Production

Mitochondria, known as the "powerhouses of the cell," play a central role in ATP production. They contain structures necessary for ATP synthesis, essential for a variety of cellular processes, including the assembly of biological polymers, material transport, and cellular movement.

Energy Flow in Ecosystems

In ecosystems, energy flows in a linear path from producers, like plants that convert sunlight into chemical energy by photosynthesis, to consumers (animals) and eventually to decomposers (microorganisms) that recycle nutrients back into the system.

Photosynthesis vs. Cellular Respiration

• Cellular Respiration Equation: C6H12O6 + O2 -> CO2 + H2O + ATP

• Photosynthesis Equation: H2O + CO2 + light energy -> C6H12O6 + O2These two processes are interdependent, forming a cyclical relationship that sustains life on Earth by converting energy in different forms.

Catabolic Pathways

Catabolic pathways involve breaking down larger molecules, such as glucose, to release energy. Aerobic respiration is more effective in terms of ATP yield compared to fermentation, which happens in low oxygen environments.

Glycolysis and Subsequent Steps

Glycolysis occurs in the cytoplasm, converting one glucose molecule into two pyruvate molecules while producing a net of 2 ATP. Following glycolysis, the pyruvate is oxidized, entering the Krebs cycle, which generates high-energy electron carriers (NADH, FADH2) and releases carbon dioxide as a waste product.

Oxidative Phosphorylation

During oxidative phosphorylation, oxygen functions as the final electron acceptor in the electron transport chain, enabling the production of 26 to 28 ATP molecules per glucose molecule. This step is crucial for meeting the energy demands of aerobic organisms.

Fermentation Processes

• Alcohol Fermentation: Takes place in yeast, converting pyruvate into ethanol and carbon dioxide in the absence of oxygen.

• Lactic Acid Fermentation: Occurs in muscle cells during vigorous exercise when oxygen is scarce, leading to the conversion of pyruvate into lactic acid.

Importance of Electron Carriers

Electron carriers such as NADH and FADH2 are essential to the process of cellular respiration, as they transport high-energy electrons to the electron transport chain, thereby facilitating ATP production by creating a proton gradient necessary for ATP synthesis.

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the biochemical process by which green plants, algae, and certain bacteria transform light energy into chemical energy stored in the form of glucose. This essential process not only provides the primary energy source for all living organisms but also releases oxygen into the atmosphere, which is crucial for the survival of aerobic life forms.

Key Concepts

Cellular Respiration Review

• Process: Glucose (C6H12O6) + Oxygen → Carbon Dioxide + Water + Energy (ATP)

• Type: Exergonic (energy is released as a byproduct).

• Location: In eukaryotic cells, cellular respiration occurs in the mitochondria; for prokaryotes, the process takes place across the cell membrane.

• ATP Production: Aerobic respiration results in the production of significantly more ATP (30-38 ATP) compared to fermentation, which produces only 2 ATP.

Photosynthesis Definition

• Equation: Carbon Dioxide + Water + Light Energy → Glucose + Oxygen

• Type: Endergonic (energy is required to synthesize glucose from simpler molecules).

• Organelles Involved:

  • In eukaryotic cells, photosynthesis occurs in chloroplasts containing chlorophyll, which captures light energy.

  • In prokaryotic organisms, such as cyanobacteria, the reactions take place in the cytoplasm due to the absence of chloroplasts.

Roles of Producers and Consumers

• Producers (Autotrophs): Organisms, primarily plants and some algae, that synthesize their own food using light energy (photoautotrophs) or chemical energy (chemoautotrophs).

• Consumers (Heterotrophs): Organisms that rely on consuming other living entities (plants, animals) to obtain their energy. They cannot produce their own food.

• Decomposers: Fungi and bacteria that break down dead organic matter, recycling nutrients back into the ecosystem and enriching the soil.

Light Energy & Photosynthesis

• Photon: The basic unit of light energy absorbed by chlorophyll during photosynthesis, initiating the conversion of light energy into chemical energy.

• UV Radiation: The ultraviolet spectrum comprises three types - UVA, UVB, and UVC; while UVC is absorbed by the ozone layer, UVA contributes to skin aging and increases the risk of skin cancer.

Plant Structure Related to Photosynthesis

• Stomata: Tiny openings on the leaf surface that facilitate gas exchange; allowing carbon dioxide to enter and oxygen to exit during photosynthesis.

• Chloroplasts Structure:

  • Outer and Inner Membranes: Protective layers surrounding the chloroplast.

  • Thylakoids: Membrane-bound sacs where the light-dependent reactions transpire; these are stacked in structures known as grana.

  • Stroma: A semi-fluid surrounding thylakoids where light-independent reactions (Calvin Cycle) take place.

Photosynthesis Phases

1. Light-Dependent Reactions:

   • Capture light energy using chlorophyll.

   • Convert this energy into chemical energy in the form of ATP and NADPH.

   • Water molecules are split (photolysis), releasing electrons for energy production and oxygen as a byproduct

   • electron transport chain - 7 proteins

2. Light-Independent Reactions (Calvin Cycle):

   • Utilize ATP and NADPH generated from light-dependent reactions to convert carbon dioxide into glucose.

   • Carbon fixation occurs through the enzyme Rubisco, which catalyzes the reaction between carbon dioxide and ribulose bisphosphate.

Energy Relationships

• Both cellular respiration and photosynthesis feature electron transport chains that play a pivotal role in ATP production.

• Light-Dependent Reaction Products: Produce ATP and NADPH that are essential for the Calvin Cycle.

• Calvin Cycle Requirements: Needs ATP and NADPH generated during light-dependent reactions to drive the formation of glucose.

  • light independent reaction

  • 3 stops: carbon fixation, reduction, renegeration of RUBIP

  • Carbon Fixation: using smaller carbon compounds to make larger carbon compounds (ex: CO2 tadd it to a 5 carbon molecule to make a 6carbon molecule [Glucose])

  • carbon dionxide binds to RUBP - the enzyme that binds it is called rubisco

  • Rubisco starts the calvin cycle

  • 2nd stage is reduction ( adding electrons)

  • 3rd stage is regeneration of RuBP

  • IT TAKES 6 TURNS FOR THE CALVIN CYCLE TO GENERATE GLUCOSE because each cycle only makes 1 carbon

Important Terms

• Carbon Fixation: The process of converting inorganic carbon (CO2) into organic compounds during the Calvin Cycle, critical for forming sugars.

• Rubisco: The prominent enzyme in photosynthesis that catalyzes the initial reaction of the Calvin Cycle. It is crucial for integrating CO2 into organic compounds.

• G3P (Glyceraldehyde 3 Phosphate): A three-carbon sugar produced in the Calvin Cycle; it serves as a building block for glucose and other carbohydrates.

Environmental Impact

• Increasing CO2 levels driven by human activities, such as fossil fuel combustion and deforestation, are major contributors to climate change.

• Plants, especially trees, play a vital role in sequestering CO2 from the atmosphere, and their removal exacerbates environmental issues such as global warming and habitat loss.

  Pigments absorb or reflect light

  • green is reflected

  • red, orange, yellow, blue, indigo, and violet is absorbed

• pigments in plants

  • chlorophyll A - Maint pigments -reflects green

    • the only pigment that can transfer light energy to an electron.

    • Gives electrons to B, replaces it with electrons from water

    • if there is no passing of electrons, they cannot move due to lack of energy

  • Chlorophyll B- accessory pigments - reflects green

  • Both absorb light energy

  • both degrades, so energy cannot transfer energy electrons unless there chlorophyll A

  • carotenoids - accessory pigment

phtotsyterm II provides energy for the production of ATP and NADPH during the light-dependent reactions of photosynthesis.