Biology 111 lecture 8

Mesophyll of the Leaves

  • The mesophyll is the space between leaf cell walls.

Evolutionary Profile of Cyanobacteria

  • Provides insights into the timeline of cyanobacteria evolution.

  • The Great Oxidation Event is a key point in this timeline:

    • It represents the first mass extinction event on Earth.

    • Cyanobacteria oxygenated the atmosphere, leading to toxicity for most existing life forms.

Cyanobacteria and Mass Extinction

  • Evidence of cyanobacteria exists in the form of biochemical markers.

  • The oxygen produced by cyanobacteria during photosynthesis led to widespread extinction as life had to adapt to a new, oxygenated environment. This event had significant implications for future life forms and evolutionary paths.

Stoma and Guard Cells

  • Stoma: Small openings on the underside of the leaf that facilitate gas exchange.

  • Guard Cells are present on either side of the stoma:

    • They control the opening and closing of the stoma, thereby regulating the exchange of gases with the environment.

Chloroplast Structure

  • Chloroplast: The site of photosynthesis in plant cells.

    • Thylakoids: Disc-like structures stacked to form grana within the chloroplast; the double membranes where photosynthesis occurs.

    • Lumen: The internal space within the thylakoid.

    • Stroma: The liquid-filled area surrounding the thylakoids, comparable to cytoplasm in other cells.

Photosynthesis: Light and Dark Reactions

  • Two stages of photosynthesis: Light-dependent reactions and Light-independent reactions (dark reactions).

    • Light-independent reactions can occur in sunlight; they are not strictly nocturnal.

Light-Dependent Reactions

  • Capture energy from sunlight, producing ATP and NADPH.

  • Involves chlorophyll pigments absorbing light energy.

Light-Independent Reactions (Calvin Cycle)

  • Converts CO₂ into sugar (G3P).

    • Uses NADPH and ATP produced in the light-dependent reactions.

    • Carbon fixation process through Rubisco enzyme.

Understanding Light and Photons

  • Light: Electromagnetic radiation; the visible part is a fraction of the entire electromagnetic spectrum (includes UV, infrared, X-rays, microwaves, etc.).

  • Photon: A single packet of light energy.

  • Wavelength: Distance between crests of waves determines light energy:

    • Shorter wavelengths correspond to higher energy (e.g., X-rays).

    • Longer wavelengths correspond to lower energy (e.g., radio waves).

Pigments and Their Function

  • Pigments absorb specific wavelengths of light:

    • Chlorophyll a and Chlorophyll b are the main pigments in plants.

    • Carotenoids, such as beta-carotene and lycopene, absorb excess energy and can appear orange or red.

    • Important for plant heat generation by dissipating excess absorbed energy as heat.

Photosystems in Photosynthesis

  • Photosystems are multi-protein complexes in the thylakoid membrane, categorized as:

    • Photosystem II (PSII) and Photosystem I (PSI).

    • PSII is the first in the sequential order; its discovery was reversed in sequence.

  • Light-Harvesting Complex: Transfers light energy to the reaction center.

  • Photoact: The process of utilizing photon energy to oxidize molecules and drive reactions.

Photosynthetic Electron Transport Chain (ETC)

  • Involves PSII and PSI, cytochrome, and plastocyanin that help produce ATP and NADPH:

    • Water molecules are split to release oxygen and hydrogen.

  • The electron transport chain re-energizes electrons for further reactions while pumping hydrogens to create a chemiosmotic gradient.

Calvin Cycle Breakdown

  • Occurs in three stages: Fixation, Reduction, and Regeneration:

    • Fixation stage involves Rubisco enzyme to integrate CO₂ into organic structures.

    • Six CO₂ molecules are needed to produce glucose (G3P), requiring six turns of the cycle.

    • Each turn utilizes ATP and NADPH from light-dependent reactions.

Overall Energy Cycle in Photosynthesis

  • Plants consume CO₂ and release oxygen; animals do the reverse (consuming oxygen and releasing CO₂).

  • This interdependent energy cycle is essential for sustaining life on Earth.

Spectrophotometer Functionality

  • A device to measure absorbance and transmittance of light through samples:

    • A lamp provides light which is separated by a diffraction grating to isolate specific wavelengths.

    • Absorbance measures how much light is absorbed by the sample, essential for studying pigments and photosynthesis efficiency.

Laboratory Experiment Insights

  • Discussion of experimental setups to measure photosynthetic rates and resolve data discrepancies in previous labs.

  • Mention of yeast experiments to demonstrate fermentation and related biochemical processes.

Exam Information

  • Upcoming exam covers cellular respiration, metabolism, and plasma membrane topics.

  • Format includes approximately 62 questions with free response sections, evenly distributed without focusing more on specific chapters.

Miscellaneous Observations

  • Various plant pigments, including their roles and colors, have practical applications in cooking, such as the color characteristics of carrots and tomatoes.

  • Conversations on fermentation and its contributions to sourdough bread flavor.