Plant Form and Function: Study Guide

Study Guide - Smart Notes

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Plants are composed of specialized cells, tissues, and organs that work together to support growth, reproduction, and survival.

Three Basic Types of Plant Cells:
- Parenchyma: Thin-walled, living cells involved in photosynthesis, storage, and tissue repair. Found throughout the plant, especially in leaves, stems, and roots.
- Collenchyma: Elongated cells with unevenly thickened cell walls, providing flexible support. Common in young stems and petioles.
- Sclerenchyma: Thick, lignified cell walls; often dead at maturity. Provide rigid support (e.g., fibers, sclereids).
Three Basic Types of Plant Tissues:
- Dermal Tissue: Outer protective covering (epidermis, periderm).
- Vascular Tissue: Conducts water, minerals, and food (xylem and phloem).
- Ground Tissue: Functions in photosynthesis, storage, and support (parenchyma, collenchyma, sclerenchyma).
Three Basic Organs of a Plant: Root, stem, and leaf.

Meristems are regions of undifferentiated cells that enable plant growth.

Meristem: A region of actively dividing cells.
Apical Meristems: Located at the tips of roots and shoots; responsible for primary (lengthwise) growth.
Lateral Meristems: Found along the sides of stems and roots; responsible for secondary (thickness) growth (e.g., vascular cambium, cork cambium).
Primary Growth: Increases length of roots and shoots via apical meristems.
Secondary Growth: Increases girth of stems and roots via lateral meristems.

Woody plants display distinct growth patterns and structures.

Early Wood: Formed in spring; cells are larger with thinner walls for rapid water transport.
Late Wood: Formed in late summer; cells are smaller and thicker-walled for support.
Growth Rings: Alternating patterns of early and late wood, visible as rings in cross-sections of trees; indicate age and growth conditions.
Bark: Composed of all tissues outside the vascular cambium (phloem, cork cambium, cork).
Heartwood: Older, non-conducting xylem in the center; provides structural support.
Sapwood: Younger, outer xylem that conducts water and minerals.

Monocots and dicots are two major groups of angiosperms with distinct features.

Number of Cotyledons: Monocots have one; dicots have two.
Leaf Venation: Monocots have parallel veins; dicots have net-like veins.
Stems: Monocot vascular bundles scattered; dicot bundles arranged in a ring.
Roots: Monocots have fibrous roots; dicots have a taproot system.
Flowers: Monocot floral parts in multiples of 3; dicots in multiples of 4 or 5.

Plants use specialized mechanisms to move water, minerals, and sugars.

Root Pressure: Osmotic pressure in roots that pushes water upward; can cause guttation (exudation of water droplets).
Transpirational Pull: Evaporation of water from leaves creates negative pressure, pulling water up through xylem.
Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to xylem walls (adhesion), aiding upward flow.
Phloem Translocation: Movement of sugars from sources (leaves) to sinks (roots, fruits) via phloem, driven by pressure flow.

Stomata regulate gas exchange and water loss; xerophytes are adapted to dry environments.

Stomata: Pores in the epidermis controlled by guard cells; open/close in response to light, CO2, water status, and hormones.
Xerophyte: Plant adapted to arid conditions; adaptations include thick cuticles, reduced leaf area, sunken stomata, and CAM photosynthesis.

Plants require essential elements for growth, classified by the amount needed.

Macronutrients: Needed in large amounts (e.g., N, P, K, Ca, Mg, S).
Micronutrients: Needed in trace amounts (e.g., Fe, Mn, Zn, Cu, B, Mo, Cl, Ni).

Some plants have unique strategies for obtaining nutrients.

Epiphyte: Plant that grows on another plant for support but is not parasitic (e.g., orchids).
Parasitic Plants: Obtain nutrients from host plants (e.g., mistletoe).
Carnivorous Plants: Trap and digest insects/animals to supplement nutrient intake (e.g., Venus flytrap).

Angiosperms have distinct male and female gametophyte development.

Male Gametophyte (Pollen Grain): Develops from microspores in anthers; contains two sperm cells.
Female Gametophyte (Embryo Sac): Develops from megaspore in ovule; typically contains egg cell and other supporting cells.

Plants have evolved mechanisms to promote genetic diversity and conserve resources.

Avoiding Self-Fertilization: Mechanisms include spatial separation of sex organs, temporal separation, and self-incompatibility genes.
Double Fertilization: One sperm fertilizes egg (zygote), another fuses with two nuclei to form endosperm (nutritive tissue).
Advantage of Seed Dormancy: Allows seeds to survive unfavorable conditions and germinate when conditions improve.

Plants can reproduce without seeds through various mechanisms.

Mechanisms: Runners (stolons), rhizomes, tubers, bulbs, fragmentation, and apomixis (seed formation without fertilization).

Genetically modified (transgenic) plants are a topic of scientific and public debate.

Major Concerns: Environmental impact, gene flow to wild relatives, food safety, ethical issues, and socioeconomic effects.

Plant hormones regulate growth, development, and responses to stimuli.

Hormone	Major Functions
Auxin	Cell elongation, apical dominance, root initiation
Gibberellin	Stem elongation, seed germination, flowering
Cytokinin	Cell division, delay of senescence, shoot formation
Abscisic Acid (ABA)	Stomatal closure, seed dormancy, stress responses
Ethylene	Fruit ripening, leaf abscission, response to stress

Leaf loss in autumn is a controlled process with adaptive advantages.

Process: Abscission layer forms at base of petiole; cells weaken and leaf detaches.
Advantage: Reduces water loss and prevents damage during winter.
Hormones Involved: Ethylene (promotes abscission), abscisic acid (promotes dormancy).