Ch 10: Flowers and Reproduction
Concepts
Reproduction can serve two different functions. Producing offspring that have identical copies of the parental genes or generating individuals that are genetically different from their parents.
If the environment is stable during several lifetimes, it is selectively advantageous for an organism to reproduce asexually by budding or sending out runners.
In asexual reproduction the offspring are never more fit than the parent- take the parent genes.
If some of the plants in an area are different genetically they have a better chance of surviving overall
Sex cells are so small that many can be produced by a single plant. This allows for experimentation of different genes for "cheap"
Sexual reproduction allows for a Genetically diverse species.
Two individuals are required in sex cells must move from one Plant to another. In seed plants, pollen can be carried by wind, insects, and birds. The pollen can be lost or eaten before it makes its way to another plant or tree
Seeds- Produced by sexual reproduction, often have a means of long-distance dispersal. This can cause the seeds to become widely scattered and germinate in many diverse sites. In these new sites, it could face new microclimates, soil conditions, and new predators and pathogens.
Fragmentation- A large spreading or Vining plant grows to several meters in length, and individual parts become self-sufficient by establishing adventitious roots
The Plant Life Cycle
Sporophytes are always diploid and have organs with cells capable of undergoing meiosis which results in haploid spores. Gametes can fuse with other gametes in a process called syngamy or fertilization
If all of the plants in An area are genetically identical, Something such as a rare freeze could wipe all of them out.
during sexual reproduction sex cells of one plant combined with those of one or several others resulting in new gene combinations
Alternation of generations- life cycle with two generations- sporophyte and gametophyte. This is an alternation of heteromorphic generations since they do not resemble each other.
Flower Structure
Stalk- Pedicel
Receptacle where the other flower parts attach
There are four types of flower appendages: sepals, petals, stamens, and carpels. Complete flowers have all 4.
Sepals- The lowest and outer most of the four floral appendages. They are modified leaves that surround and enclose the other flower parts as they mature. Also the thickest, toughest, and waxiest of the flower parts. Protects the flowering bud. Also referred to as calyx
Petals- Make up the corolla. Sepals and petals both make up the perianth.
Stamens- together known as the androecium. Commonly referred to as the male part of the flower. 2 parts- filament and anther (where pollen is produced.)
Anther is composed Of diploid cells and in each anther For long columns of tissue become distant as some cells enlarge and prepare for meiosis. These microspore mother cells or microsporocytes Continue to enlarge and then undergo meiosis.
tapetum- Neighbors anther Cells and acts as a nurse, contributing to microspore development and maturation
carpels- constitute the gynoecium, Located at the highest level of the receptacle. Three main parts including a stigma that catches pollen grains, a style that elevates the stigma to a useful position, and an ovary where megaspores are produced.
Inside the ovary are placentae, Regions of tissue that bear small structures called ovules.
Gametophytes
Embryo sac- Technical term for a multi. nucleate megagametophyte
Plasmogamy- the protoplasm of two parent cells (usually from the mycelia) fuses together without the fusion of nuclei, effectively bringing two haploid nuclei close together in the same cell.
In angiosperms only the second sperm nucleus released from the pollen tube my grades into the central. It undergoes karyogamy With both polar nuclei, establishing a large endosperm nucleus
suspensor is delicate and ephemeral in angiosperms. The end of the embryo farther from the suspensor initiates 2 primordia that grow into cotyledons
In the torpedo stage, the embryo is an elongate cylinder: A short axis is established, consisting of radicle, epicotyl, and hypocotyl.
If endosperm is abundant the seed is albuminous
If endosperm is sparse or absent at maturity the seat is exalbuminous
The integuments That surround the nucleus expand and mature into the seed coat (testa)
fruit
As the ovule develops into a seed, the ovary matures into a fruit. The exocarp is the outer layer, the middle is the mesocarp, and the inner most is the Endocarp. The entire fruit wall is called the pericarp
Flower structure and cross pollination
cross-pollination- Pollination of a carpel by pollen from a different individual
Self-pollination- Pollination of a carpel by pollen from the same flower or another flower on the same plant
Compatibility barriers- Inhibits Self pollination in many species, especially mini important crop species. Inhibited by chemical reactions between pollen and carpels that prevent pollen growth
If a flower lacks stamens or carpels, Sexual reproduction is dramatically affected. The flower would be incomplete and imperfect. If a flower has both it is a perfect flower.
Dioecious life cycle- microgametophytes, megagametophytes, staminate sporophytes, and carpellate sporophytes.
Animal pollinated flowers
flowers underwent coevolution due to insects choosing the most nutritious flowers to visit and distributing pollen among them from other flowers
Most flowers are Radially symmetrical and called actinomorphic or regular
In many species flowers and pollinators have coevolved in such a way that the flowers are now also bilaterally symmetrical- zygomorphic
Inflorescences and pollination
If many flowers are grouped together it is called an inflorescence. They gave a collective visual signal to pollinators; one small flower may be overlooked, but not 100 close together
Determinant inflorescences- Has only a limited potential for growth because the inflorescences Apex is converted to a flower, ending its possibilities for continued growth.
Indeterminant inflorescence- The lowest or outer most flowers open first, and even while these flowers are open, new flowers are still being initiated at the Apex
fruit types and seed dispersal
The term true fruit Is used to refer to fruits containing only ovarian tissue and accessory fruit or false fruit Is used if any non-ovarian tissue is present.
If the fruit develops from a single ovary or the fused ovaries of one flower, it is a simple fruit.
If the separate carpels of one gynoecium fuse during development, an aggregate fruit results.
Fruits can be grouped or classified in several ways. In one method, emphasis is placed on whether the fruit is dry or fleshy
A dry fruit Is one that is not typically eaten by the natural seed distributing animals
A fleshy fruit Is one that is eaten during a natural seed distribution process.
The further classification of dry fruit emphasizes fruit opening. dehiscent fruit Break open and release the seeds, whereas indehiscent do not.