Plant Cell Biology

• Plant biology is the scientific study of plants, including their physiology, structure, genetics, ecology, distribution, classification, and economic importance
• Plant anatomy is a subdiscipline that focuses on the internal structure of plants

Plant Cells

• Plant cells are eukaryotic cells that contain various organelles specialized for specific functions
• The major components and organelles include:
  • Cell wall: a rigid outer layer composed mainly of cellulose, providing support and shape to the cell
  • Plasma membrane: a selectively permeable membrane that regulates the movement of substances in and out of the cell
  • Cytoplasm: the gel-like substance within the cell, containing organelles and various molecules
  • Nucleus: contains the cell's genetic material (DNA) and controls cell activities
  • Vacuole: a large, fluid-filled sac that stores water, nutrients, and waste products and helps maintain cell turgor
  • Chloroplasts: organelles responsible for photosynthesis, containing chlorophyll
  • Mitochondria: organelles responsible for cellular respiration, producing energy (ATP)
  • Ribosomes: sites of protein synthesis
  • Endoplasmic reticulum (ER): a network of membranes involved in protein and lipid synthesis
  • Golgi apparatus: modifies, sorts, and packages proteins and lipids
  • Peroxisomes: involved in various metabolic processes, including photorespiration in plant cells
  • Plasmodesmata: channels through cell walls that connect adjacent cells, allowing communication and transport

Plant Tissues

Meristematic Tissues

• Meristematic tissues are regions of actively dividing cells that give rise to new plant cells
• Apical meristems: located at the tips of roots and shoots, responsible for primary growth (increase in length)
• Lateral meristems (cambium): found in woody plants, responsible for secondary growth (increase in thickness)
• Intercalary meristems: found in some monocots, responsible for regrowth after damage (e.g., mowing)

Permanent Tissues

• Permanent tissues are differentiated tissues that perform specific functions within the plant

Simple Tissues

• Parenchyma:
  • Composed of living cells with thin walls
  • Involved in photosynthesis, storage, and secretion
  • Found in various parts of the plant, including leaves, stems, and roots
• Collenchyma:
  • Composed of living cells with unevenly thickened walls
  • Provides flexible support to young plant organs
  • Found beneath the epidermis in stems and leaves
• Sclerenchyma:
  • Composed of dead cells with thick, lignified walls
  • Provides rigid support and protection
  • Includes fibers and sclereids (stone cells)

Complex Tissues

• Xylem: transports water and minerals from the roots to the rest of the plant
  • Tracheids and vessel elements are the main conducting cells
  • Also provides structural support
• Phloem: transports sugars (produced during photosynthesis) from the leaves to other parts of the plant
  • Sieve tube elements and companion cells are the main conducting cells
• Epidermis:
  • Outermost layer of cells covering the plant body
  • Provides protection and prevents water loss
  • May contain specialized cells such as stomata (for gas exchange) and trichomes (hairs)
• Periderm:
  • Replaces the epidermis in woody plants, providing protection
  • Includes cork cells (phellem), cork cambium (phellogen), and phelloderm

Plant Organs

Roots

• Anchor the plant in the soil
• Absorb water and nutrients from the soil
• Transport water and nutrients to the stem
• Some plants have specialized roots for storage, aeration, or support
• Root cap: a protective layer of cells covering the root tip
• Root hairs: extensions of epidermal cells that increase the surface area for absorption

Stems

• Support the leaves, flowers, and fruits
• Transport water, nutrients, and sugars between the roots and the rest of the plant
• Some plants have specialized stems for storage, propagation, or protection
• Nodes: points where leaves are attached
• Internodes: regions between nodes
• Buds: undeveloped shoots that can develop into new leaves, stems, or flowers
• Vascular bundles: contain xylem and phloem, arranged differently in monocots and dicots

Leaves

• Primary site of photosynthesis
• Capture sunlight and convert it into chemical energy (sugars)
• Regulate gas exchange and water loss through stomata
• Blade (lamina): the broad, flat part of the leaf
• Petiole: the stalk that attaches the leaf to the stem
• Veins: vascular bundles that transport water and nutrients within the leaf
• Mesophyll: the photosynthetic tissue of the leaf, containing chloroplasts

Flowers

• Reproductive structures of angiosperms (flowering plants)
• Involved in pollination and fertilization, leading to the formation of seeds and fruits
• Sepals: protect the developing flower bud
• Petals: attract pollinators
• Stamens: male reproductive organs, consisting of anther (where pollen is produced) and filament
• Pistil (carpel): female reproductive organ, consisting of stigma (receives pollen), style, and ovary (contains ovules)

Seeds

• Mature ovules containing an embryo and stored food reserves
• Dispersed away from the parent plant, allowing for colonization of new areas
• Seed coat (testa): protects the embryo
• Embryo: develops into a new plant
• Endosperm: provides nutrients to the developing embryo

Fruits

• Mature ovaries containing seeds
• Protect the seeds and aid in their dispersal
• Various types of fruits, including fleshy fruits (e.g., berries, drupes) and dry fruits (e.g., legumes, nuts)
• Pericarp: the fruit wall, derived from the ovary wall

Vascular Tissue Arrangement

Roots

• Stele: The central vascular cylinder
• Xylem: Often in the center, forming a star shape in dicots
• Phloem: Located between the arms of the xylem star
• Endodermis: A layer of cells surrounding the stele, regulating water and nutrient uptake

Stems

• Dicots: Vascular bundles arranged in a ring around the pith (central core)
• Monocots: Scattered vascular bundles throughout the stem

Leaves

• Veins: Contain xylem (on the upper side) and phloem (on the lower side)
• Mesophyll: Located between the upper and lower epidermis, containing chloroplasts
• Stomata: Pores in the epidermis that regulate gas exchange

Plant Development

• Plant development involves growth, differentiation, and morphogenesis
• Growth: increase in size and mass due to cell division and expansion
• Differentiation: cells become specialized for specific functions
• Morphogenesis: the development of plant form and structure

Factors Influencing Development

Genetic Factors

• Genes regulate various aspects of plant development, including cell division, differentiation, and morphogenesis

Environmental Factors

• Light: influences photosynthesis, phototropism, and photoperiodism
• Temperature: affects enzyme activity, growth rate, and flowering time
• Water: essential for cell turgor, nutrient transport, and photosynthesis
• Nutrients: required for various metabolic processes and plant growth
• Gravity: influences gravitropism (growth response to gravity)

Hormonal Regulation

• Plant hormones (phytohormones) regulate various aspects of plant development
  • Auxins: promote cell elongation, apical dominance, and root formation
  • Cytokinins: promote cell division, delay senescence, and stimulate bud growth
  • Gibberellins: promote stem elongation, seed germination, and flowering
  • Abscisic acid (ABA): promotes dormancy, closes stomata, and inhibits growth
  • Ethylene: promotes fruit ripening, senescence, and abscission

Specialized Plant Structures and Adaptations

• Modified leaves (e.g., spines, tendrils, bracts)
• Modified stems (e.g., rhizomes, tubers, corms)
• Modified roots (e.g., storage roots, aerial roots, pneumatophores)
• Adaptations to specific environments (e.g., xerophytes in dry environments, hydrophytes in aquatic environments)
• Carnivorous plants: adapted to nutrient-poor environments by trapping and digesting insects
• Parasitic plants: obtain nutrients from other plants
• Mycorrhizae: symbiotic associations between plant roots and fungi, enhancing nutrient uptake
• Nitrogen-fixing bacteria: convert atmospheric nitrogen into a form that plants can use

Plant cells are eukaryotic cells which contain organelles specialized for specific functions. The major components and organelles include the cell wall, plasma membrane, cytoplasm and nucleus. Chloroplasts are the organelles responsible for photosynthesis.