Plant Diversity and Land Colonization

Plant Diversity and Colonization of Land

• Kingdom Plantae includes algae, bryophytes, ferns, gymnosperms, and angiosperms
• Plants evolved and adapted from aquatic to terrestrial environments
• Key defining characteristics of land plants include being eukaryotic, predominantly photoautotrophic, multicellular with cell walls, sessile, undergoing alternation of generations, and retaining the embryo within gametophyte tissue
• Plant adaptations for terrestrial life include root and shoot systems for nutrition and support, and an evolutionary trend toward diploid dominance
• Kingdom Plantae includes approximately 300,000 species across 10 phyla
• Plants demonstrate adaptations for desiccation avoidance, physical support, nutrient uptake, and sexual reproduction without water

Plant Groups and Characteristics

• Algae are a diverse group of aquatic, photosynthetic organisms, and can be single-celled to multicellular forms
• Bryophytes are nonvascular plants, such as mosses, liverworts, and hornworts, and are characterized by poikilohydric nature, small size, preference for wet habitats, a lack of vascular tissue, and structures enclosing plant gametes
• Ferns are seedless vascular plants possessing fronds which reproduce with spores
• Gymnosperms are seed-bearing plants with "naked" seeds or seeds not enclosed in an ovary
• Angiosperms are seed-bearing plants that feature seeds enclosed in an ovary, otherwise known as flowering plants
• Lycophytes are small seedless vascular plants with simple vascular tissues that grow on forest floors, featuring upright or horizontal stems and sporophylls, and strobil or cones which are clusters of sporophylls
• Most Lycophytes are homosporous
• Ferns typically have a familiar sporophyte stage and are frequently found in habitats from wet to arid, demonstrating finely divided leaves known as fronds, with sporangia often in sori

Reproduction and Life Cycle of Flowering Plants (Angiosperms)

• Flowering plants reproductive strategies involve flower structure, pollen development in the anther, megaspore and embryo sac development in the ovule, as well as pollination and double fertilization
• Flowers are composed of sepals, petals, anthers, and a pistil, arranged in different patterns, known as inflorescence
• Pollen, otherwise known as microspores, develop in the anther, while the megaspore and embryo sac develop in the ovule
• Pollination and fertilization are key reproductive processes that occur in plants
• Embryo development in plants includes that of endosperm and embryo development in both monocots and dicots
• Seed and Fruit Formation is defined as, the ovary walls developing into fruit
• Vegetative plant formation involves the development of a plant body through non-sexual means
• Defining flower structures:
  • Sepals - the outer, protective leaf-like structures of a flower
  • Petals - the brightly colored parts of a flower that attract pollinators
  • Anthers - pollen-producing part of the stamen which is the male reproductive organ
  • Pistil - the female reproductive organ (stigma, style, and ovary)
• Inflorescence refers to the arrangement of flowers on a plant
• Pollen is the male gametophyte of seed plants that carries sperm cells
• Ovule is the structure in the ovary with the female gametophyte, otherwise known as the embryo sac, which is capable of developing into a seed
• Pollination is the transfer of pollen from the anther to the stigma
• Double Fertilization is a unique process that occurs in angiosperms and includes one sperm fertilizing the egg and another fertilizing the central cell to form the endosperm
• Endosperm is nutritive tissue in the seed which supports embryo development
• Monocots are types of angiosperms containing one cotyledon, or seed leaf
• Dicots are angiosperms containing two cotyledons also known as seed leaves

Seed Development

• Seed Dormancy is a period of suspended growth in seeds
• Germination is the process by which a seed begins to grow and develop
• A simple fruit develops from a single ovary of one flower
• Naked seed plants (gymnosperms) feature pollen grains that produce nonmotile sperm and require no water for pollination
• Gymnosperm ovules are sporophyte structures that produce the female gametophyte with an egg

Vegetative Plant Growth

• Plant growth, cell types, tissue systems, and shoot and root development are different for vegetative plants
• Basic plant cell and tissue types include parenchyma, collenchyma, sclerenchyma, epidermal cells, phloem (sieve tube cells and companion cells), xylem (tracheids and vessel element cells), cork cells, and periderm
• Apical meristems facilitate primary growth, while lateral meristems facilitate secondary growth
• Cell development consists of cell elongation, differentiation, and maturation
• The shoot system consists of leaf components and modifications in both angiosperms and gymnosperms, as well as stem structure in angiosperms such as monocots and dicots
• The root system is made up of the primary root in monocot and dicot plants
• Secondary growth in plants encompasses the comparison of angiosperm dicot stems and roots with gymnosperms, growth rings, rays, and periderm

Plant Cellular Definitions

• Parenchyma are plant cells that have thin walls and participate in storage, photosynthesis, and secretion
• Collenchyma are plant cells with thicker walls that provide flexible support
• Sclerenchyma are plant cells with very thick, lignified walls which provide rigid support
• Epidermal cells are the outer protective cell layer of plants
• The phloem is a vascular tissue responsible for transport of sugars and other organic nutrients
• Sieve tube cells are phloem cells specialized for transport that otherwise lack a nucleus at maturity
• Companion cells are phloem cells which support the function of sieve tube cells
• Xylem is vascular tissue responsible for the transport of water and minerals
• Tracheids are elongated xylem cells with tapered ends
• Vessel element cells are shorter, wider xylem cells that form vessels
• Cork cells are protective cells located in the outer bark of woody plants
• Periderm is the protective outer layer of woody stems and roots, which comprise cork, cork cambium, and phelloderm
• Plant meristems consist of plant tissue that is capable of continuous cell division and responsible for plant growth
• Shoot and root tips consist of apical meristems, and are responsible for primary growth
• Lateral meristems facilitate secondary growth, or increased thickness

Plant Growth Characteristics

• Primary growth increases the length of a plant
• Secondary growth increases the plant's thickness
• Growth rings are visible in woody stems and roots, as a result of seasonal growth variations
• Rays are parenchyma cells that extend radially within woody stems which facilitate water and nutrient transport
• The shoot system consists of stems, leaves, buds, and flowers, all of which are adapted for photosynthesis and pollination
• Stem organization consists of nodes, internodes, and terminal and lateral buds
• Stem arrangements can be described by protoderm, procambium, and ground meristem
• Vascular bundle arrangement types include monocots and eudicots
• Roots have a taproot and fibrous root system which anchor the plant, absorb water and minerals, and facilitate storage of carbohydrates
• Zones of cell division, elongation, and maturation describe root structures
• Stele refers to the central cylinder, while exodermis, endodermis, and pericycle describe other root structures
• Secondary growth is defined by the increase of girth and includes vascular cambium that produces secondary xylem (wood) and secondary phloem, and cork cambium that produces cork which is part of the bark
• Improved light interception and better means for resource acquisition and reproduction describe the adaptive significance Plant Cells
• Plant cells consist of a primary cell wall constructed from cellulose, plus plasmodesmata
• Some types of plant cells also have secondary cell walls containing lignin
• The role of plant meristems is to provide indeterminate growth to height and girth
• Monocots and eudicots describe the two main structural forms of flowering plants
• Plant lifespans can be annual, biennial, or perennial

Plant Tissue Types

• Ground tissue consists of parenchyma, collenchyma, and sclerenchyma
• Vascular tissue consists of xylem which conducts water and minerals and comprises tracheids and vessel members and phloem which conducts sugars and other solutes
• Dermal tissue comprises the epidermis which covers the primary plant body, a waxy cuticle which restricts water loss, stomata that facilitate gas exchange, and trichomes (hairs) that can act as absorbent root hairs

Transport in Plants

• Osmosis is diffusion of water across a semipermeable membrane, from an area of low solute concentration to an area of high solute concentration
• Symplasts are transported and cross no membranes, instead flow continuously into different cells
• Passive transport does not require metabolic energy as substances move along concentration or electrochemical gradients
• Active transport requires metabolic energy and moves substances in opposition to gradient by assisted transport proteins in electrochemical gradients
• Xylem sap is a dilute water movement from roots to shoot parts
• Water potential (Ψ) acts a plant driving force
• Aquaporin proteins influence through which a hydrophobic membrane the rate that water moves
• Apoplastic pathways include water not crossing a cell membrane but diffusing through all nonliving regions including any cell walls or air spaces

Transmembrane Pathways

• Symplastic pathways include water crossing the membrane that tends to use plasmodesmata and diffuses across a fluid
• Transmembrane pathways include water crossing the plasma membrane as well as the tonoplasts
• Cohesion tension consists of evaporation creating tension
• Stomata regulates the amounts of loss via transpiration
• In dry climates plant adaptations for conserving water include various adaptation to thrive well

Plant Hormones

• Source: Any region of a plant where organic substances are loaded into Phloem
• Sink: Any region of a plant where organic substances are unloaded from Phloem

Auxin and Plant Hormones

• Polar Transport from tip to base: Auxin has influx carriers and efflux carriers where they create downwards flow
• Gibberellins: Commonly GA1 and stem elongation/ seed dormancy is affected
• Cytokinins affect cell division leaf expansion and leaf growth aging
• Ethylene: Presence affects the plant by helping in ripening aging abscission

The Function of Jasmonates

• Synthesis: Shoots and leaves,
• Growth light: Responds to gravity
• The cells of these plants in leaves have these certain acids
• Chemical defenses, the genes for genes affect plants and gives defense recognition to them
• System Acquired Resistance is for infections to help the salicylic acid in long lasting attack

Chemical Environmental Signals and Defense Mechanisms

• Growth responses to light are seen in phototropism, and gravitropism orients the plant according to gravity. Stems exhibit negative gravitropism. Mechanical stimulus induces auxin distribution, which changes cell growth, for which Thigmotropism creates thigmorphogenesis if damaged by farm machinery
• Circadian rhythms regulate day and sunlight exposure. By changes in daylight they can be changed or reset or also are altered by blue green pigment affecting
• Stomata’s actions also involve hormonal adjustments along which mesophyll cells take up A B A
• Plants under water are adapted