🔬General Biology I Unit 32 – Plant Reproduction

Key Concepts

• Plant reproduction involves the creation of new individuals from parent plants and ensures the continuation of species
• Two main types of plant reproduction: asexual reproduction and sexual reproduction
• Asexual reproduction produces genetically identical offspring from a single parent plant without the fusion of gametes
• Sexual reproduction involves the fusion of male and female gametes to produce genetically diverse offspring
• Plant life cycles can be divided into two main categories: haploid-dominant (gametophyte) and diploid-dominant (sporophyte)
• Flowers are the reproductive structures of angiosperms and consist of sepals, petals, stamens, and carpels
• Pollination is the transfer of pollen grains from the male anther to the female stigma, which can occur through various agents such as wind, water, or animals
• Fertilization occurs when the male gamete (sperm) fuses with the female gamete (egg) to form a zygote, which develops into a seed

Types of Plant Reproduction

• Asexual reproduction involves the creation of new individuals from a single parent plant without the fusion of gametes
  • Produces genetically identical offspring, also known as clones
  • Advantageous in stable environments as it allows for rapid colonization and growth
• Sexual reproduction involves the fusion of male and female gametes to produce genetically diverse offspring
  • Requires the production of specialized reproductive structures such as flowers or cones
  • Advantageous in changing environments as genetic diversity increases adaptability
• Some plants can reproduce both asexually and sexually, depending on environmental conditions and the stage of their life cycle
• Asexual reproduction is more common in lower plants (mosses, ferns) while sexual reproduction is more prevalent in higher plants (gymnosperms, angiosperms)
• The type of reproduction employed by a plant species can have significant implications for its evolutionary success and distribution

Asexual Reproduction in Plants

• Vegetative reproduction is a form of asexual reproduction in which new plants grow from vegetative parts of the parent plant (stems, roots, or leaves)
  • Examples include runners (strawberries), rhizomes (ginger), and tubers (potatoes)
• Fragmentation occurs when a plant is broken into smaller pieces, each capable of growing into a new individual
  • Common in aquatic plants such as water hyacinth and bladderwort
• Budding involves the formation of new individuals from outgrowths or buds on the parent plant
  • Seen in plants like kalanchoe and bryophyllum
• Spore production is another form of asexual reproduction in which single-celled reproductive units called spores are released and can develop into new individuals
  • Prevalent in non-flowering plants such as ferns and mosses
• Asexual reproduction allows for rapid colonization of new areas and can be advantageous in stable environments where the parent plant is well-adapted
• However, asexual reproduction limits genetic diversity, which can make populations more vulnerable to environmental changes or disease outbreaks

Sexual Reproduction in Plants

• Involves the fusion of male and female gametes to produce genetically diverse offspring
• Requires the production of specialized reproductive structures such as flowers (angiosperms) or cones (gymnosperms)
• The male reproductive structures, called stamens, produce pollen grains containing the male gametes (sperm)
• The female reproductive structures, called carpels, contain ovules that house the female gametes (eggs)
• Pollination is the transfer of pollen grains from the male anther to the female stigma
  • Can occur through various agents such as wind (grasses), water (seagrasses), or animals (bees, birds)
• Fertilization occurs when the male gamete (sperm) fuses with the female gamete (egg) to form a zygote
  • The zygote develops into an embryo, which is enclosed within a seed
• Sexual reproduction promotes genetic diversity, which can increase a species' adaptability to changing environments
• However, sexual reproduction is often more energy-intensive and time-consuming compared to asexual reproduction

Plant Life Cycles

• Plant life cycles can be divided into two main categories: haploid-dominant (gametophyte) and diploid-dominant (sporophyte)
• In haploid-dominant life cycles, the multicellular haploid gametophyte is the dominant phase
  • The diploid sporophyte is short-lived and dependent on the gametophyte for nutrition
  • Examples include mosses and liverworts
• In diploid-dominant life cycles, the multicellular diploid sporophyte is the dominant phase
  • The haploid gametophyte is reduced and short-lived
  • Examples include ferns, gymnosperms, and angiosperms
• Alternation of generations is a key feature of plant life cycles, involving the alternation between the haploid gametophyte and diploid sporophyte phases
• The duration and prominence of each phase vary among different plant groups, reflecting their evolutionary history and adaptations to various environments
• Understanding plant life cycles is crucial for the study of plant reproduction, as it provides a framework for understanding the timing and location of reproductive events

Flower Structure and Function

• Flowers are the reproductive structures of angiosperms (flowering plants) and consist of four main parts: sepals, petals, stamens, and carpels
• Sepals are the outermost part of the flower and protect the developing flower bud
  • Often green and leaf-like in appearance
• Petals are the colorful, often showy parts of the flower that attract pollinators
  • Their shape, color, and scent can vary depending on the specific pollinator the plant aims to attract
• Stamens are the male reproductive structures and consist of a filament and an anther
  • The anther produces and releases pollen grains containing the male gametes (sperm)
• Carpels are the female reproductive structures and consist of a stigma, style, and ovary
  • The stigma receives pollen grains during pollination
  • The style is a long tube that connects the stigma to the ovary
  • The ovary contains ovules, which house the female gametes (eggs) and develop into seeds after fertilization
• The arrangement and number of floral parts can vary among different plant species, reflecting their evolutionary history and adaptations to different pollinators and environments

Pollination and Fertilization

• Pollination is the transfer of pollen grains from the male anther to the female stigma
• Can occur through various agents such as wind (anemophily), water (hydrophily), or animals (zoophily)
  • Wind pollination is common in grasses, sedges, and many trees (pine, oak)
  • Water pollination is rare but occurs in some aquatic plants (seagrasses, pondweeds)
  • Animal pollination is the most common and involves a wide range of animals (bees, butterflies, birds, bats)
• Cross-pollination occurs when pollen is transferred from one plant to another, promoting genetic diversity
• Self-pollination occurs when pollen is transferred within the same flower or between flowers on the same plant, leading to less genetic diversity
• After pollination, pollen grains germinate on the stigma and produce a pollen tube that grows through the style towards the ovary
• The pollen tube delivers the male gametes (sperm) to the ovule, where fertilization occurs
• Double fertilization is unique to angiosperms and involves the fusion of one sperm with the egg to form a zygote and the fusion of the other sperm with two polar nuclei to form the endosperm
  • The zygote develops into the embryo, while the endosperm provides nutrition for the developing embryo

Seed Formation and Dispersal

• After fertilization, the ovule develops into a seed, which contains the embryo, endosperm (in angiosperms), and a protective seed coat
• The ovary wall develops into the fruit, which can be dry (nuts, pods) or fleshy (berries, drupes)
• Seeds represent the dormant stage of the plant life cycle and can remain viable for extended periods until suitable conditions for germination occur
• Seed dispersal is the process by which seeds are spread from the parent plant to new locations, reducing competition and increasing the chances of survival
• Dispersal can occur through various means, depending on the specific adaptations of the plant species
  • Wind dispersal (dandelion, maple)
  • Water dispersal (coconut, mangrove)
  • Animal dispersal (through consumption or attachment to fur/feathers)
    • Examples include berries (birds), burrs (mammals), and elaiosomes (ants)
• Some plants have evolved specialized mechanisms for seed dispersal, such as explosive dehiscence (impatiens) or drill-shaped fruits (geranium)
• Effective seed dispersal is crucial for the colonization of new habitats, gene flow between populations, and the long-term survival of plant species