Plant Transport and Mechanisms

Plant Transport

• Water is transported upwards in the xylem, a unidirectional process.
• Water movement is driven by transpiration, the evaporation of water from leaves, creating a pulling force.
• Minerals are transported with water. This process is called translocation.
• Xylem cells are dead at maturity, enabling efficient water movement.
• Xylem cells have thick, lignin-rich walls for structural support.

Water Adhesion and Cohesion in Xylem

• Cohesion: Water molecules stick together due to their polarity, forming a continuous chain.
• Adhesion: Water molecules stick to the xylem walls, resisting downward pull of gravity.

Transport Mechanisms

• Passive Transport: Movement of molecules along a concentration gradient (no energy needed).
• Active Transport: Movement of molecules against a concentration gradient (requires energy).

Translocation (Phloem Transport)

• Phloem transports sugars from sources (production sites, like leaves) to sinks (areas needing resources, like roots or developing fruits).
• This is an active process.
• Companion cells use active transport to load sugars into sieve tube elements, creating a pressure difference driving transport.

Asexual Reproduction (Mitosis)

• Asexual reproduction produces clones (genetically identical offspring).
• Advantages include adaptation to specific environments and fewer energy requirements.
• Disadvantages include limited adaptability to changing conditions due to lack of genetic diversity.
• Examples include runners in strawberries, root fragments in dandelions and modified stems in potatoes.

Sexual Reproduction (Meiosis)

• Sexual reproduction involves meiosis.
• Flowers are the reproductive organs.
• Advantages include adaptability to new environments and enhanced resilience during stress.
• Disadvantages include the high energy expenditure for meiosis and pollination.
• Example: Pollination in flowering plants.

Flower Anatomy

• Sepals: Protect the flower bud.
• Petals: Attract pollinators.
• Stamen (male): Anther (pollen producer) and filament.
• Carpel/Pistil (female): Stigma, style, and ovary.

Pollination

• Self-Pollination: Pollen transfer within the same flower or plant.
• Cross-Pollination: Pollen transfer between different flowers or plants (usually by wind or animals).

Seed Dispersal

• Seeds disperse to prevent competition and expand the plant's range.
• Methods include:
  • Fruit (transport by animals)
  • Lightweight seeds (wind dispersal)
  • Sticky seeds (animal dispersal)

Leaf Structure

• Upper epidermis/cuticle: Protect against water loss and pathogens.
• Chloroplasts: Carry out photosynthesis.
• Palisade mesophyll: Maximize light absorption.
• Veins: Contain xylem and phloem for transport.
• Spongy mesophyll/air spaces: Facilitate gas exchange.
• Guard cells: Regulate stomata opening/closing.
• Stomata: Allow gas exchange (CO2 in, O2 out) and transpiration (water out).

Osmosis

• Osmosis is the movement of water across a selectively permeable membrane from a high water concentration to a low water concentration.
• Key terms include:
  • Solute: Dissolved substance
  • Hypertonic: Higher solute concentration
  • Isotonic: Equal solute concentration
  • Hypotonic: Lower solute concentration