Coping with Environmental Variation: Energy

Coping with Environmental Variation: Energy

Autotrophs

  • Definition: Organisms that synthesize their own food from inorganic substances.

    • Energy Source:

    • Photosynthesis: Utilizes sunlight to convert light energy into chemical energy.

    • Chemosynthesis:

      • Process of converting inorganic compounds into carbohydrates using energy from chemical reactions.

      • Significance: Important in nutrient cycling and in ecosystems such as hydrothermal vent communities.

    • Energy Storage: Converts energy into chemical energy stored in organic molecules.

Heterotrophs

  • Definition: Organisms that cannot produce their own food and instead consume organic compounds from other organisms.

    • Energy Origin: The energy heterotrophs consume originated from autotrophs that synthesized organic compounds.

  • Types of Heterotrophs:

    • Detritivores: Consume non-living organic matter.

    • Parasites: Feed on live hosts without necessarily killing them.

    • Herbivores: Generally consume live plant material.

    • Predators: Capture and consume live prey.

Plant Parasitism

  • Holoparasites: Plants that lack photosynthetic pigments and receive nutrients from other plants (e.g., dodder).

    • Impact: Can significantly reduce the biomass of host plants.

  • Hemiparasites: Produce some of their own energy through photosynthesis but rely on host plants for nutrients and water (e.g., mistletoe).

Unique Examples of Energy Acquisition

  • Sea Slugs: Have functional chloroplasts obtained from the algae they consume, allowing them to perform photosynthesis.

Chemosynthesis& Photosynthesis

  • Chemosynthesis (Chemolithotrophy): Involves using inorganic compounds to produce carbohydrates. Substrates include:

    • Ammonium (NH₄⁺)

    • Nitrite (NO₂⁻)

    • Hydrogen Sulfide (H₂S)

    • Sulfur (S)

    • Ferrous Iron (Fe²⁺)

Photosynthesis

  • Overview: Most biologically available energy on Earth comes from photosynthesis which occurs in:

    • Archaea, bacteria, protists, algae, and plants.

  • Two Major Steps of Photosynthesis:

    1. Light Reaction: Light energy splits water molecules, providing electrons to produce ATP and NADPH.

    2. Dark Reaction: Also known as the Calvin cycle, where CO₂ is fixed, leading to carbohydrate synthesis.

Environmental Impact on Photosynthesis

  • Photosynthetic Rate: Determines energy supply, influencing growth and reproduction in plants.

    • Important topic in physiological ecology.

    • Light Response Curves: Illustrate the effect of light intensity on photosynthetic rate.

    • Key Points:

      • Light Compensation Point: Level where CO₂ uptake is equal to CO₂ loss.

      • Saturation Point: Maximal effect where increasing light does not raise photosynthesis further.

Acclimatization to Light

  • Plants can modify their morphology and physiology in response to varying light intensities.

    • Thicker Leaves: More chloroplasts can develop in leaves grown in high light conditions.

Water Availability and CO₂ Supply

  • Low water availability results in stomatal closure, leading to restricted CO₂ uptake to save water, posing a trade-off between water conservation and energy gain.

  • Risks of Stomatal Closure: Increases susceptibility to light damage, with excess energy potentially harming photosynthetic membranes.

    • Mechanisms to dissipate excess energy include carotenoids.

Temperature and Enzyme Activity

  • Plants in different climates adapt their enzyme forms to optimize performance in respective temperatures, allowing for enzyme functioning suited to their environments.

Nitrogen and Nutrient Influence on Photosynthesis

  • Nitrogen is crucial as it often associates with photosynthetic enzymes like ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco). Higher nitrogen levels correlate with heightened photosynthetic rates.

Trade-offs in Nitrogen Acquisition

  • Increased nitrogen may heighten plant vulnerability to herbivores, as they often are also nitrogen-deficient.

Metabolic Constraints on Photosynthetic Efficiency

  • Rubisco Enzyme: Key for carbon fixation, can catalyze two reactions:

    • Carboxylase Reaction: Promotes photosynthesis.

    • Oxygenase Reaction: Involves the uptake of O₂, leading to photorespiration, which breaks down carbon compounds.

Photorespiration

  • Benefits of photorespiration were examined through experiments on the model plant Arabidopsis thaliana, revealing that plants lacking photorespiration capabilities struggle under typical light and CO₂ conditions.

  • Hypothesis: Suggests that photorespiration could serve to protect plants from light damage during high light conditions.

    • Supporting Evidence: Altered tobacco plants showing high photorespiration rates experienced less light damage compared to plants with normal or reduced rates.

C4 Photosynthesis Evolution

  • Emergence of C4 pathway occurred approximately 7 million years ago as a response to low CO₂ and high-temperature conditions. C4 plants characterized by:

    • Independently evolving multiple forms.

    • Common in many grass species, including corn, sugarcane, and sorghum.

Mechanism of C4 Photosynthesis

  • Separation of CO₂ uptake and Calvin cycle processes across different leaf structures.

    • CO₂ absorbed in mesophyll by phosphoenolpyruvate carboxylase (PEPcase), which shows a preference for CO₂ over O₂.

    • Concentrated CO₂ is then directed to bundle sheath cells where rubisco operates in the Calvin cycle, minimizing O₂ interference.

Energy Considerations and Environmental Adaptations

  • While higher ATP consumption occurs in the C4 pathway, increased photosynthetic efficiency gives C4 plants a competitive edge in high-temperature environments.

  • Reduced transpiration losses due to efficient CO₂ uptake even when stomates are partially closed.

    • Close correlation observed between temperature and community C4 plant presence.

Crassulacean Acid Metabolism (CAM) Adaptation

  • CAM plants adapt to arid conditions by timing CO₂ uptake (night) and Calvin cycle operation (day) to minimize water loss, maintaining stomata open at night for gas exchange.

    • Common examples include succulent plants with fleshy structures like the pineapple and certain cacti.

Heterotrophic Energy Acquisition

  • Heterotrophs possess diverse feeding strategies to acquire organic compounds and convert them into usable energy (ATP).

    • Energy derived varies based on food chemistry and the energy investment needed for acquisition.

Diverse Feeding Strategies Among Heterotrophs

  • Microorganisms: Utilize little energy to acquire low-energy detritus.

  • Predators like Cheetahs: Invest considerable energy tracking and capturing high-energy prey.

Morphological and Physiological Adaptations

  • Multicellular animals have developed specialized tissues for efficient absorption, digestion, transport, and excretion, showcasing adaptation efficiency.

Examples of Dietary Variation

  • Migrating warblers adapt their diets according to their geographical location, indicating variations in metabolic efficiency alongside different diets.

Tool Use and Energy Gain

  • Appearance and use of tools among humans and certain animals illustrates a sophisticated approach to accessing energy-rich food resources, potentially influencing evolutionary paths.

Note: This study guide is an extensive resource summarizing the ecological and physiological principles related to energy acquisition and coping with environmental variation based on autotrophic and heterotrophic strategies. Each section is carefully elaborated upon to capture essential information and interconnections, ensuring thorough comprehension of the material.