Study guide: Angiosperm Functional Organization

📋 Course Outline

1. Plant Organs and Fixed Lifestyle
2. Root and Fungal Exchange Surfaces
3. Leaf Structure and Gas Exchange
4. Sap Transport and Vascular Tissues
5. Protection from Environmental Stress
6. Meristems and Plant Growth
7. Hormones and Environmental Responses

📖 1. Plant Organs and Fixed Lifestyle

🔑 Key Concepts & Definitions

• Vegetative apparatus: Consists of its roots, stem, and leaves.

★ Must-know

• Roots anchor the plant and provide resistance to wind, but anchoring also makes the plant immobile and dependent on its environment.

• Roots absorb water and mineral ions from the soil, providing mineral nutrition needed for plant life and photosynthesis.

• Leaves are the main sites of gas exchange and photosynthesis.

Further detail

• The stem contains rigid supporting tissues that help the plant resist gravity and transports raw and elaborated sap between roots and aerial organs.

📌 Herbaceous flowering plants are small, with flexible, chlorophyll-bearing, sparsely branched stems, whereas woody plants are large, with rigid, brown, highly branched stems.

💡 Memory Hook

Roots anchor the plant but also make it immobile.

📖 2. Root and Fungal Exchange Surfaces

🔑 Key Concepts & Definitions

• Mycorrhiza: An intimate, lasting, mutually beneficial association between a plant root and a fungus of a different species.

📝 Essential Points

• Fine, long roots and numerous elongated root hairs near their tips greatly increase contact with soil water and minerals.

• About 90% of plants associate with fungi at their roots to form mycorrhizae.

📌 In mycorrhizae, the plant supplies the fungus with leaf-produced organic matter, while the fungus increases the plant’s uptake of water and mineral salts by expanding its exchange surface.

💡 Memory Hook

The plant supplies organic matter; the fungus expands mineral and water uptake.

📖 3. Leaf Structure and Gas Exchange

🔑 Key Concepts & Definitions

• Stoma: An epidermal opening, usually bounded by two guard cells and opening into an ostiole, through which gases exchange with the atmosphere when conditions are favorable.

★ Must-know

• Chlorophyll-bearing cells, particularly on the upper side of the leaf, contain chloroplasts whose thylakoid pigments capture photons for photosynthesis.

• During the day, leaves show net CO₂ uptake and release water and O₂ through stomata.

📌 Stomatal opening responds to light and the plant’s CO₂ needs: the ostiole closes in darkness and opens in light.

Further detail

• Numerous leaves with flattened blades provide a large surface for capturing light.

• Stomata are mainly, sometimes only, on the lower leaf surface, while the upper epidermis is often covered by a cuticle that limits water loss.

💡 Memory Hook

The cuticle limits water loss, while stomata permit regulated gas exchange.

📖 4. Sap Transport and Vascular Tissues

🔑 Key Concepts & Definitions

• Xylem: The vascular tissue that transports raw sap and consists of files of elongated dead cells whose remaining lateral walls are reinforced with lignin.
• Phloem: The vascular tissue that transports elaborated sap and consists of files of elongated living cells with cellulose walls and perforated transverse walls.

★ Must-know

• Raw sap forms in roots from absorbed water and mineral salts and moves upward toward leaves, where photosynthesis occurs.

• Elaborated sap contains organic molecules made by photosynthesis in leaves and moves from photosynthetic cells to non-photosynthetic cells, including roots and buds.

Further detail

• Xylem and phloem vessels are grouped into vascular bundles.

💡 Memory Hook

Xylem carries raw sap upward; phloem carries elaborated sap from photosynthetic cells.

📖 5. Protection from Environmental Stress

★ Must-know

• A hydrophobic, lipid-rich cuticle covers the outer epidermal cell surfaces and limits dehydration.

📌 During drought, stomata close to limit water loss, and their predominantly lower-surface position helps shield them from the Sun.

• Some trees shed their frost-sensitive leaves in autumn and enter dormancy during the cold period.

Further detail

• Some species limit evaporation with stomata enclosed in crypts, and the leaves of marram grass can roll up.

• Buds resist cold with thick, impermeable scales and down, then produce leaves in spring; some plants keep their buds underground, as in hyacinth bulbs and potato tubers.

• Seeds can survive winter through stored reserves and a dormant state.

💡 Memory Hook

Cold or drought triggers protective strategies that reduce exposure and water loss.

📖 6. Meristems and Plant Growth

🔑 Key Concepts & Definitions

• Meristem: A group of small, dividing, undifferentiated cells found at the ends of stems or roots.
• Phytomer: A repeated plant module made of a section of stem, a bud, and a leaf.

★ Must-know

• 🔄 Plant development proceeds through:
  1. Cell multiplication by mitosis in meristems
  2. Cell elongation
  3. Differentiation into stems, leaves, flowers, and roots

📌 Primary meristems drive lengthwise growth of stems and roots, whereas secondary meristems in many shrubs and trees drive growth in width.

Further detail

• Plant growth is organized through the repetition and stacking of phytomers.

• The root apex has a cell-proliferation meristem beneath the root cap and a zone of cell elongation where cells no longer proliferate.

💡 Memory Hook

Mitosis → cell elongation → organ differentiation.

📖 7. Hormones and Environmental Responses

🔑 Key Concepts & Definitions

• Phytohormone: A plant-produced molecule that communicates between cells and acts at a distance at low concentration, without requiring specialized hormone-producing organs or cells.
• Positive phototropism: The bending of a plant toward a unidirectional light source, caused by different auxin production on the illuminated and shaded sides of the apex.

★ Must-know

• Auxin promotes plant-cell elongation and secondary-root formation, and a greater auxin concentration produces a stronger effect.

📌 Root-produced cytokinins promote axillary bud development, opposing the effect of auxin produced at shoot apices; removing an apex allows axillary buds to take over growth.

Further detail

• The main phytohormones are:

  • Auxin (AIA, indole-3-acetic acid)
  • Gibberellins
  • Cytokinins
  • Abscisic acid (ABA)
  • Ethylene

• Environmental cues that can trigger phytohormone synthesis include:

  • Light intensity
  • Day length
  • Gravity
  • Temperature
  • Molecules produced by symbionts or parasites
  • Soil mineral availability
  • Soil water availability

💡 Memory Hook

Auxin promotes elongation, whereas root-produced cytokinins promote axillary bud development.