Photosynthesis & Cellular Respiration

Unit 6: Photosynthesis & Cellular Respiration

Light Energy

  • Key Components:
      - CO₂
      - Water
      - CELL RESPIRATION
      - Mitochondria
      - Glucose
      - Chemical energy
      - PHOTOSYNTHESIS

The Big Picture

Energy and Life

  • Forms of Energy:
      - Light
      - Heat
      - Electricity
      - Chemical

  • All living things must obtain and use energy.
      - Heterotrophs: Organisms that obtain energy by consuming other living things.
      - Autotrophs: Organisms that obtain energy by making their own food, typically in the form of glucose via photosynthesis.

Chemical Energy and ATP

  • ATP (Adenosine Triphosphate):
      - One of the most important compounds that cells use to store and release energy.
      - Composition:
        - Nitrogen base: Adenine
        - Pentose (5C) sugar: Ribose
        - Three Phosphate groups

Storing and Releasing Energy

  • Energy is stored in phosphate bonds of ATP.

  • Release Process:
      - Energy is released when a phosphate bond is broken, resulting in ADP (Adenosine Diphosphate).
      - A free-floating phosphate can reattach to ADP, reforming ATP in a process called Phosphorylation.

Photosynthesis

Photosynthesis Big Picture

  • All energy in food originates from the sun.

  • Autotrophs capture energy from the sun to produce glucose through photosynthesis.

Cell Interpretation of Photosynthesis

  • Glucose produced from photosynthesis is broken down in a process called Cellular Respiration to create ATP (the energy currency of the cell).

History of Photosynthesis

  • Contribution of Key Scientists:
      - Jan van Helmont: Helped relate plant mass to water absorption.
      - Joseph Priestley: Discovered that plants produce oxygen.
      - Jan Ingenhousz: Demonstrated that light is essential for plants to produce oxygen.

Plant Structures

Basic Plant Structures

  • Roots: Absorb water from the ground.

  • Leaves: Capture sunlight and exchange CO₂/O₂ between the plant and atmosphere, where photosynthesis occurs.

  • Stem: Provides structure and transports sugar and water throughout the plant (via adhesion).

Stomata

  • Definition: Pores located in a plant's cuticle that facilitate the exchange of water vapor and gases (Oxygen and Carbon Dioxide) between the plant and the atmosphere.

Parts of a Plant Cell

  • Components:
      - Nucleus
      - Cell wall
      - Vacuole
      - Mitochondria
      - Cytoplasm
      - Chloroplasts:
        - Function: Food producers of the cell, containing chlorophyll (the green pigment essential for photosynthesis).

Chloroplast Structure

  • Chloroplast: Organelle where photosynthesis occurs.

  • Key structures include:
      - Outer Membrane
      - Inner Membrane
      - Granum
      - Lumen
      - Stroma
      - Thylakoids

Chlorophyll

  • Definition: Main green pigment responsible for light absorption during photosynthesis, located in thylakoid membranes.

  • Plants appear green because they reflect the green wavelength rather than absorb it.

Absorption of Light by Chlorophyll

  • Absorption Spectrum:
      - Violet
      - Blue
      - Green
      - Yellow
      - Orange
      - Red

Accessory Pigments

  • Example: Carotenoids (red/orange/yellow pigments).

  • Function: Assist in absorbing various wavelengths of light.

Steps of Photosynthesis

Overview of Photosynthesis

  • Photosynthesis utilizes sunlight energy to convert water and carbon dioxide (reactants) into high-energy sugars and oxygen (products).

Photosynthesis Involves Two Sets of Reactions

  1. Light-Dependent Reactions

  2. Light-Independent Reactions (Calvin Cycle)

Light-Dependent Reactions

  1. Occur in thylakoid membranes inside chloroplasts.

  2. Sun energy is harnessed to produce energy-rich compounds (including ATP).

  3. Water (H₂O) is required, and oxygen (O₂) is released as a byproduct.

Light-Independent Reactions (Calvin Cycle)

  1. Occur in the stroma (the fluid inside chloroplasts).

  2. No light is necessary to power this reaction.

  3. Atmospheric carbon dioxide (CO₂) is utilized to produce high-energy sugars like glucose (plant food).

Factors Affecting Rate of Photosynthesis

Factors Affecting Photosynthesis

  1. Amount of Light:
      - The photosynthesis rate increases with light intensity until all pigments are utilized - this point is referred to as the “saturation point.”

Factors Affecting Photosynthesis

  1. CO₂ Concentration:
      - At saturation point, the Calvin Cycle cannot proceed more quickly due to limited reactants.

Factors Affecting Photosynthesis

  1. Temperature:
      - Photosynthesis involves enzymes, which are only effective within certain temperature ranges.
      - Similar effects occur based on pH levels for the same reasons.

Factors Affecting Photosynthesis

  1. Color of Light:
      - Different wavelengths of light can increase or decrease the rate of photosynthesis.

Cellular Respiration

Overview of Cellular Respiration

  • Definition: Cellular respiration is the process that releases energy from food in the presence of oxygen.

  • Chemical Equation:
      C6H12O6+6O2<br>ightarrow6CO2+6H2O+extEnergy(ATP)C_6H_{12}O_6 + 6O_2 <br>ightarrow 6CO_2 + 6H_2O + ext{Energy (ATP)}

Comparing Photosynthesis and Cellular Respiration

  • Photosynthesis removes CO₂ from the atmosphere, whereas cellular respiration releases it back.

  • Photosynthesis generates O₂, which cellular respiration uses to extract energy from food (glucose).

Aerobic Respiration

Overview of Aerobic Cellular Respiration

  • Big Idea: CR releases energy from food in an oxygen-rich environment.

  • Overall Reaction:
      C6H12O6+6O2<br>ightarrow6CO2+6H2O+extATPC_6H_{12}O_6 + 6O_2 <br>ightarrow 6CO_2 + 6H_2O + ext{ATP}

Characteristics of Aerobic Respiration

  • Occurs in eukaryotes.

  • Requires oxygen.

  • Goal: Breakdown glucose to synthesize usable energy (ATP).

  • Begins in the cytoplasm and concludes in the mitochondria.

Stages of Aerobic Respiration

  • Consists of three stages:
      1. Glycolysis
      2. Krebs Cycle
      3. Electron Transport Chain (ETC)

Stage 1: Glycolysis

  • Definition: The “sugar-breaking” process.

  • Location: Occurs in the cytoplasm.

  • Process: Glucose is broken down into two smaller carbon-containing molecules known as pyruvate.

  • Big Picture:
      - Reactants: Glucose
      - Products: 2 pyruvate molecules, ATP

Stage 2: Krebs Cycle

  • Location: Occurs in the mitochondrial matrix.

  • If oxygen is present, the pyruvate is further broken down.

  • Big Picture:
      - Reactants: 2 pyruvate molecules from glycolysis
      - Products: CO₂, ATP

Stage 3: Electron Transport Chain

  • Location: Occurs in the inner mitochondrial membrane.

  • Process: Hydrogen ions combine with oxygen to produce water (H₂O).

  • Big Picture:
      - Reactants: O₂
      - Products: H₂O, ATP

Summary of Inputs and Outputs of Aerobic Respiration

  • Step: Reactants/Inputs
      - Glycolysis: Glucose
      - Krebs Cycle: Pyruvate
      - Electron Transport: O₂

  • Products/Outputs:
      - Glycolysis: 2 pyruvate, ATP
      - Krebs Cycle: CO₂, ATP
      - Electron Transport: H₂O, ATP

Anaerobic Respiration

Definition of Anaerobic Respiration

  • Also known as fermentation.

  • Occurs in the absence of oxygen.

  • Two types are:
      - Lactic Acid Fermentation
      - Alcoholic Fermentation

  • Both processes initiate with glycolysis.

  • Purpose: To regenerate NAD+ needed to restart glycolysis, allowing minimal ATP production (net gain of 2 ATP).

Overview of Anaerobic Respiration Process

  • General Steps:
      1. Glucose undergoes glycolysis.
      2. Pyruvate enters either lactic acid or alcoholic fermentation pathway.

Example: Lactic Acid Fermentation

  1. Glycolysis produces pyruvate and a small number of ATP.

  2. Pyruvate then enters lactic acid fermentation pathway, producing lactic acid.

Characteristics of Lactic Acid Fermentation

  • Occurs in muscles during strenuous exercise when oxygen supply is insufficient.

  • Lactic acid accumulation leads to muscle soreness.

  • Also utilized in cheese and yogurt production.

Example: Alcoholic Fermentation

  1. Glycolysis generates pyruvate and some ATP.

  2. Pyruvate enters the alcoholic fermentation pathway, leading to the production of ethyl alcohol and CO₂.

Characteristics of Alcoholic Fermentation

  • Used in alcoholic beverages.

  • Yeast activity causes bread to rise, resulting in its spongy texture due to CO₂ production.

Aerobic vs. Anaerobic Respiration

  • Aerobic Respiration:
      - Requires oxygen
      - Occurs in eukaryotic organisms; partially takes place in mitochondria
      - Consists of 3 stages: Glycolysis, Krebs Cycle, Electron Transport Chain
      - Produces a total of 36 NET ATP per glucose

  • Anaerobic Respiration:
      - Occurs without oxygen
      - Seen in prokaryotes and some eukaryotic cells; occurs in cytoplasm
      - Comprises 2 stages: Glycolysis and fermentation (either lactic acid or alcoholic)
      - Produces 2 NET ATP per glucose.