Midterm Practice Exam #1 (Hard)

Levels of Organization in Biology

  • Organismic Level: Focus on ecology and broader biological interactions.

  • Cellular and Molecular Level: Focus on physiological processes and biochemistry.

Key Concepts in Plant Physiology

  • Discussed in relation to photosynthesis, respiration, and growth.

  • Physiological processes explained at a molecular level but contextualized within cellular activities and organismal levels.

Melvin Calvin

Biography

  • Born: April 1911, Minnesota

  • Ph.D.: Chemistry from the University of Minnesota

  • Career: Professor of Chemistry at University of California, Berkeley

Significant Contributions

  • Conducted research on photosynthesis using radioisotopes, particularly C14 labeling of carbon dioxide.

  • Proposed mechanisms for converting light energy to chemical energy via electron transfer among pigment molecules.

  • Awarded the Nobel Prize in 1961 for mapping carbon assimilation pathways in photosynthesis.

  • Calvin's principles remain relevant in renewable energy and solar studies.

Photosynthesis in Higher Plants

Importance of Photosynthesis

  • Role of Green Plants:

    • Autotrophs: Make their own food through photosynthesis.

    • Heterotrophs: Provide food for other organisms.

  • Process Summary:

    • A light-driven physico-chemical process that converts light energy into organic compounds, essential for food production and oxygen release.

Key Components of Photosynthesis

Initial Requirements

  • Essential components: Chlorophyll, light, and CO2.

  • Historical Experiments:

    • Joseph Priestley (1770): Established that plants restore air quality.

    • Jan Ingenhousz: Demonstrated the necessity of sunlight for photosynthesis; identified oxygen bubbles.

    • Julius von Sachs (1854): Discovered glucose production and the importance of chlorophyll in chloroplasts.

    • T.W. Engelmann: Identified chlorophyll's absorption characteristics through light spectra experiments.

Photosynthetic Process

  • Photosynthesis Equation:

    • General: CO2 + H2O --(light)--> (CH2O) + O2.

  • Location: Primarily in green leaves and other green parts of the plant.

  • Chloroplast Structure: Composed of grana and stroma.

Pigments in Photosynthesis

  • Types of Main Pigments:

    • Chlorophyll a (blue-green), chlorophyll b (yellow-green), xanthophylls, carotenoids.

  • Role: Absorb different wavelengths of light.

Light Reaction Phase

  • Captures light energy, splits water molecules, and releases oxygen.

  • Light-harvesting complexes in Photosystem I (PS I) and Photosystem II (PS II) are crucial.

Electron Transport and ATP Production

  • Process Flow:

    • Excited electrons in PS II lead to ATP and NADPH synthesis.

    • Water splitting via PS II is vital for electron supply.

    • Cyclic vs. Non-Cyclic Photophosphorylation:

      • Non-cyclic: Involves PS I and PS II, producing both ATP and NADPH.

      • Cyclic: Only PS I active, producing ATP without NADPH.

Chemiosmotic Hypothesis

  • Links ATP synthesis to the proton gradient across the thylakoid membrane, producing ATP via proton flow through ATP synthase.

Dark Reactions - Calvin Cycle

  • Stages:

    1. Carboxylation

    2. Reduction

    3. Regeneration of RuBP.

  • Utilizes ATP and NADPH from light reactions for sugar synthesis.

C3 vs. C4 Pathways

  • C3 Plants: Initial CO2 product is 3-phosphoglycerate (PGA).

  • C4 Plants: Initial fixation produces oxaloacetic acid (OAA), minimizing photorespiration; efficient in warm climates.

Factors Affecting Photosynthesis

  • Light: Affects the rate; saturation occurs at low levels.

  • Carbon Dioxide: Optimal levels vary between C3 and C4 plants.

  • Temperature: Influences enzymatic processes; C4 plants thrive in warmth.

  • Water: Essential for structure and function; impacts stomata and metabolic activity.

Summary

  • Photosynthesis is vital for food production and oxygen release, involving complex interactions between environmental factors and plant adaptations.