Body plans & regulation in multicellular organisms I (4/2)

Molecule Forms in Multicellular Life

• Focus on how fungi, plants, and animals develop body structures and solve the problem of resource acquisition.

• Emphasis on comparing and contrasting the strategies of fungi, plants, and animals.

Filamentous Fungi

• Definition & Structure:

  • Multicellular filamentous fungi consist of hyphae, which are long filaments that remain attached after cell division.

  • Hyphae are branched and create a large surface area to volume ratio, optimizing nutrient absorption.

• Key Characteristics:

  • Mycelium: The main part of the fungal body, functioning in nutrient absorption and growth.

  • The structure is one cell thick, allowing efficient nutrient and water uptake.

  • The shared cytosol of the mycelium facilitates flow of nutrients, leading to more effective resource management.

• Nutrition Strategy:

  • Fungi digest through external digestion (excrete enzymes to break down macromolecules in the environment).

  • Nutrient transport: Nutrients absorbed through mycelium (e.g., sugars). Regions touching resources act as sugar "sources," while other parts act as "sinks" needing sugars.

• Resource Acquisition:

  • Growth towards resources (positive autotropism) is driven by environmental signals.

  • Negative autotropism occurs when hyphae avoid overlapping, maximizing ground coverage.

Plant Structures and Growth

• Vascular Plants:

  • Focus on vascular plants, which leverage bulk flow for resource distribution, primarily utilizing light as their energy source.

  • The body's structure is heavily dependent on environmental conditions (light, water).

• Meristems:

  • Meristems represent regions of active growth (stem cells).

  • Shoot Apical Meristem: Responsible for vertical growth and production of auxin (hormone regulating growth).

• Hormonal Control:

  • Hormones like auxin regulate growth patterns and inhibit lateral bud development via apical dominance.

  • Cutting the shoot apical meristem removes the hindrance on lateral growth, promoting branching.

• Response to Environmental Signals:

  • Plants respond to light (positive phototropism): Shoots grow towards light, enhancing energy acquisition.

  • Roots grow downwards, aided by auxin that inhibits elongation in roots to enhance water and nutrient absorption.

Growth Mechanisms

• Auxin Functions:

  • Auxin promotes elongation in stem cells and inhibits it in root cells for better resource allocation.

  • Light signals lead to movement of auxin, influencing growth direction (polar transport).

• Tropism in Plants:

  • Plants exhibit positive and negative tropism based on resource availability and environmental signals.

  • Root hairs increase surface area for enhanced nutrient absorption, particularly in shaded roots.

Summary of Influences on Body Plans

• Body plans of both filamentous fungi and vascular plants are highly influenced by resource availability and environmental factors.

• The strategies developed by each organism group (fungi, plants, animals) showcase a variety of adaptations to optimize resource use and ensure survival in their respective habitats.