Plant Anatomy and Photosynthesis

The Leaf

• The leaf is the site of photosynthesis in plants.
• It is composed of an upper and lower epidermis, a mesophyll layer, and vascular tissue.
• The upper and lower epidermis are covered by a waxy cuticle that prevents water loss.
• Stomata, tiny openings in the epidermis, allow for gas exchange and transpiration.
• Guard cells, containing chloroplasts, regulate the opening and closing of stomata.

Mesophyll

• The mesophyll layer is divided into the palisade layer and the spongy layer.
• The palisade layer, containing many chloroplasts, is responsible for photosynthesis.
• The spongy layer, with large air spaces, facilitates gas exchange.

Roots

• Roots anchor the plant, absorb nutrients from the soil, and store food.
• The root structure consists of an epidermis, cortex, vascular cylinder, and endoderm.
• The epidermis, with root hairs, increases the absorptive surface area.
• The cortex contains parenchyma cells with plastids for starch storage.
• The vascular cylinder, containing xylem and phloem, is surrounded by the pericycle, which gives rise to lateral roots.
• The endoderm, with a Casparian strip, controls mineral entry into the vascular cylinder.

Nutrient and Water Absorption

• The symplast, a continuous cytoplasmic network connected by plasmodesmata, allows for cell communication.
• The apoplast, a network of cell walls and intercellular spaces, facilitates water movement within the plant.

Root Types

• Taproot: A single, large root with lateral branches, common in dicots.
• Aerial Root: Roots that grow above water in swampy or salt marsh environments, like mangroves, to aerate root cells.
• Fibrous Root: Many thin roots, common in monocots like grasses, providing strong anchorage and minimizing soil erosion.

Stems

• Stems support the plant, transport water and nutrients, and store food in some cases.

Plant Tissue Types

• Dermal Tissue: The outermost protective layer of plants, typically composed of epidermal cells.
  • Cuticle: A waxy layer protecting the leaf surface.
  • Trichomes: Spike-like projections providing protection.
  • Guard Cells: The only dermal cells with chloroplasts, regulating stomata.
• Vascular Tissue: Responsible for transport.
  • Xylem: Transports water and nutrients from roots to leaves.
    • Tracheids: Cells with thickened, lignified secondary cell walls for structural support and water transport.
    • Vessel Elements: Also thickened with lignin, contribute to water transport.
  • Phloem: Transports sugars and other organic compounds throughout the plant.
    • Sieve Tube Elements: Lack a nucleus, forming chains for long-distance transport.
    • Companion Cells: Adjacent to sieve tube elements, providing metabolic support.
• Ground Tissue: All other plant tissues besides vascular and dermal.
  • Parenchyma Cells: Traditional plant cells, with some containing chloroplasts for photosynthesis.
  • Collenchyma Cells: Have unevenly thickened primary walls, providing structural support.
  • Sclerenchyma Cells: Very thick primary and secondary walls fortified with lignin, purely for support.

Additional Notes

• Symbiotic organisms (Mutualism): An example is lichen, a combination of a fungus (absorbs water) and algae cells (photosynthesize).
• Turgor Pressure: Pressure inside a cell caused by water or other factors.
• Light Spectrum:
  • Red light has the longest wavelength, while violet light has the shortest.
  • Green plants reflect green light, which is why they appear green.
• Photoperiodism: The flowering response of plants to the length of daylight. Plants are categorized as:
  • Long-day plants: Require more light than their critical photoperiod to flower.
  • Short-day plants: Require less light than their critical photoperiod to flower.
  • Neutral-day plants: Flowering is independent of daylight length.
• Auxin: A plant hormone involved in elongation and tropism.
• Chromatography: A technique used to separate pigments.
• Plasmodesmata: Narrow cytoplasmic threads connecting adjacent plant cells, facilitating communication.