Plant Cell Structure and Function

Plant Cell Structure and Function

• Cell Hierarchy: Molecules, organelles, cells, tissues, organs, organ systems, organisms

• Unicellular vs. Multicellular Organisms:

  • Unicellular: A single-celled living organism. Not 'simple'.
  • Multicellular: Organisms composed of multiple cells. Specialized cells carry out specific functions.
  • Advantages of Multicellular Organisms: Division of labor (specialized cells), increased size (better nutrient transport), interdependence of cells (resistance to damage to a single cell, but vulnerable to problems in any one).

Plant Organ Systems

• Shoot System: Includes leaves, stems, buds, flowers, fruit, and tubers (swollen stems for food storage, e.g., potatoes). Specialized for photosynthesis, reproduction, food and water storage, & transportation.

• Root System: Includes aerial roots. Specialized for anchorage, water and mineral absorption, and food and water transport.

Plant Tissues

• Dermal Tissue (Epidermis): Outermost covering of herbaceous (non-woody) plants.

  • Single cell layer thick, waxy cuticle (outer layer) reduces water loss and protects from disease.
  • Shoot epidermis: Gas exchange (O2, CO2), cuticle secretion.
  • Root epidermis: Water and nutrient uptake.

• Ground Tissue: Makes up bulk of plant. Directly beneath epidermis, loosely packed for air diffusion.

  • Shoot ground tissue: Strength & support (stem), photosynthesis (leaves).
  • Root ground tissue: Food and water storage.

• Vascular Tissue: Transport system with xylem and phloem.

  • Xylem: Transports water and dissolved minerals from roots to leaves. Non-living cells.
  • Phloem: Transports sucrose and other sugars from leaves to other parts of the plant (including storage). Sieve tube cells (long, connected cells) require companion cells for survival and direction.

Cell Specialization and Growth

• Differentiation: Cells become specialized for specific functions as they develop.
• Root Hairs: Tiny projections on root cells that increase surface area for nutrient and water absorption.
• Guard Cells: Specific cells in leaf epidermis that form pores called stomata for gas exchange. They contain chloroplasts.

Gas Exchange and Water Regulation

• Stomata: One pore surrounded by two guard cells; stomata open and close to regulate gas exchange.
• Turgor Pressure: Pressure from water against cell walls; turgid when swollen with water (in guard cells to open stomata).
• Stomata Opening (Swelling of Guard Cells): Accumulation of potassium ions (active transport), increased water entry (osmosis) resulting in turgidity, and outward bulging.
• Stomata closing (Shrinking of Guard Cells): Potassium ions diffuse out, decreasing water entry, resulting in loss of turgidity.

Photosynthesis and Cellular Respiration

• Photosynthesis: Occurs in chloroplasts; uses light energy to convert CO2 and water into glucose and oxygen.
  • Word equation: Carbon dioxide + water → glucose + oxygen + energy
  • Balanced equation: 6CO₂(g)+ 6H₂O(l) +light → C₆H₁₂O₆(s) + 6O₂.(g)
• Cellular Respiration: Reverse of photosynthesis; occurs in mitochondria; converts glucose and oxygen into CO2, water, and ATP.
  • Word equation: glucose + oxygen → carbon dioxide + water + energy
  • Balanced equation: C6H12O6 + 6O2 -> 6CO2 + 6H2O
• Difference between photosynthesis and cellular respiration: Photosynthesis is daytime plant only; cellular respiration is continuous in all cells.

Leaf Structure and Function

• Mesophyll Tissue: Photosynthesis occurs here.
  • Spongy mesophyll: Loosely packed cells with air spaces for gas exchange.
  • Palisade mesophyll: Tightly packed cells with many chloroplasts, maximizing light absorption.
• Vascular Bundle (Vein): Contains xylem and phloem, embedded in mesophyll, transport system.

Water Transport Mechanisms

• Transpiration: Water evaporation from leaves. Affects water transport.
  • Factors: Hot/cold temperature; higher rate in hot.
• Cohesion: Attraction between water molecules.
• Adhesion: Attraction between water and other substances (e.g., plant cell walls).
• Tension (Transpiration Pull): Tension created by transpiration, pulling water up the xylem.

Root Pressure and Other Processes

• Root Pressure: Upward force in transport tubes from water entry into roots.
• Plasmolysis: Cell shrinking in a hypertonic environment.
• Hypotonic Solution: Cell swelling in a hypotonic environment.

Sugar Transport

• Pressure-Flow Theory: Sugars are actively loaded into phloem, increasing water intake, and water pressure pushes them through the plant.
• Source: Location of sugar production (leaves).
• Sink: Location of sugar use/storage.

Plant Responses to Stimuli

• Stimulus: Signal triggering a reaction.
• Tropism: Plant response to an external stimulus.
• Positive Tropism: Growth toward a stimulus.
• Negative Tropism: Growth away from a stimulus.
• Phototropism: Response to light, stems positive (toward), roots negative (away).
• Gravitropism: Response to gravity, roots positive (toward), stems negative (away).
• Auxin: Plant hormone stimulating cell growth, causing stems to grow toward light.
• How Plants Detect Up/Down: Starch granules move based on gravity to inform the plant about orientation.

This quiz explores the intricate structures and functions of plant cells, highlighting the differences between unicellular and multicellular organisms. It also covers the various plant organ systems, including the shoot and root systems, and the specialized functions of plant tissues. Test your knowledge on how these components work together for plant survival.