Chapter 38 Notes

Plant-Animal Relationships

• Some plants rely on animals for seed dispersal, nutrients, and protection, in exchange for edible parts; humans and crops exemplify this relationship.

Artificial Selection & Genetic Engineering

• Plant breeders have used artificial selection for 10,000 years to modify angiosperms; genetic engineering has accelerated this process.

Angiosperm Reproduction: Flowers, Double Fertilization, and Fruits

• Angiosperms, vital in agriculture, reproduce sexually and asexually; humans influence crop genetics, sparking biotechnology debates.

Alternation of Generations

• Plant life cycles alternate between haploid (n) and diploid (2n) phases. Angiosperms are sporophyte-dominant, featuring flowers, double fertilization, and fruits.

Flower Structure and Function

• Flowers, specialized for sexual reproduction, consist of carpels, stamens, petals, and sepals. Complete flowers have all organs; incomplete ones lack some.

Pollination

• Angiosperms mainly depend on biotic agents (animals) or abiotic agents (wind, water) for pollination. Some self-pollinate, limiting genetic diversity.

Abiotic Pollination by Wind

• Wind-pollinated plants (20% of angiosperms) have small, scentless flowers and rely on copious pollen.

Pollination by Bees

• Bees pollinate 65% of flowering plants, attracted to sweet-smelling, bright (yellow/blue) flowers, using UV nectar guides.

Pollination by Moths and Butterflies

• Moth/butterfly-pollinated flowers are fragrant; butterflies prefer bright colors, moths like white/yellow.

Pollination by Bats

• Bat-pollinated flowers are light, aromatic, attracting nocturnal pollinators.

Pollination by Flies

• Fly-pollinated flowers mimic rotten meat with reddish color and odor, deceiving blowflies.

Pollination by Birds

• Bird-pollinated flowers are large, red/yellow, odorless, with nectar for energy, and have fused petals for bird beaks.

Methods of Pollination

• Pollination is pollen transfer via wind, water, or animals.

Evolution and Coevolution

• Animal pollination drives natural selection and coevolution, influencing floral and pollinator traits; climate change may affect these relationships.

Angiosperm Life Cycle Overview

• The angiosperm life cycle includes gametophyte development, sperm delivery via pollen tubes, double fertilization, and seed development; gametophytes are sporophyte-dependent.

Development of Female Gametophytes (Embryo Sacs)

• Female gametophytes develop within ovules inside the ovary, forming embryo sacs with synergid, antipodal cells, and polar nuclei.

Development of Male Gametophytes in Pollen Grains

• Male gametophytes develop in anthers' microsporangia, forming microspores that produce generative and tube cells within pollen grains.

Sperm Delivery by Pollen Tubes

• Pollen grains germinate, forming pollen tubes to deliver sperm to the embryo sac, initiating synergid death for entry.

Double Fertilization

• One sperm fertilizes the egg (zygote), another combines with polar nuclei (endosperm), ensuring endosperm development only upon fertilization.

Seed Development

• After fertilization, ovules become seeds, ovaries become fruits, and embryos stockpile nutrients.

Seed Development and Structure: A Closer Look

• Seeds develop post-fertilization, containing a dormant embryo, food reserves, and protective layers.

Endosperm Development

• Endosperm develops before the embryo, storing nutrients for the seedling; cotyledons may later take over this function.

Embryo Development

• Zygotes divide into basal and terminal cells, forming suspensors and proembryos; cotyledons and apical meristems develop.

Structure of the Mature Seed

• Mature seeds dehydrate, enclosing an embryo with food supply in a protective coat; hypocotyl, radicle, epicotyl, and plumule are key structures.

Seed Dormancy: An Adaptation for Tough Times

• Seed dormancy is broken by specific environmental cues, ensuring germination at optimal times and places.

Sporophyte Development from Seed to Mature Plant

• Seed dormancy ends with germination, followed by vegetative growth and eventual flowering.

Seed Germination

• Germination begins with imbibition, followed by enzyme activity, radicle emergence, and root system development.

Growth and Flowering

• Post-germination, resources support vegetative growth from meristems; flowering is triggered by environmental cues.

Fruit Structure and Function

• Fruits, from mature ovaries, protect and aid seed dispersal, classified as simple, aggregate, multiple, or accessory.

Seed and Fruit Dispersal

• Plants disperse seeds/fruits via biotic/abiotic agents like wind, water, or animals.

Asexual Reproduction

• Asexual reproduction produces clones from a single parent, common in angiosperms.

Mechanisms of Asexual Reproduction

• Asexual reproduction involves fragmentation, adventitious shoots, or apomixis.

Advantages and Disadvantages of Asexual and Sexual Reproduction

• Asexual reproduction advantages include no need for pollinators and strong progeny, while sexual reproduction generates genetic variation.

Mechanisms That Prevent Self-Fertilization

• Self-fertilization is prevented by dioecious species, varied maturation times, or self-incompatibility.

Totipotency, Vegetative Reproduction, and Tissue Culture

• Totipotency allows cells to clone organisms; vegetative propagation and tissue culture are based on this.

Vegetative Propagation and Grafting

• Vegetative propagation is human-facilitated asexual reproduction via cuttings and grafting.

Test-Tube Cloning and Related Techniques

• In vitro methods clone plants via tissue culture and genetic engineering.

Modifying Crops

• Crops are modified through breeding and genetic engineering.

Plant Breeding

• Plant breeding changes plant traits to achieve desired characteristics.

Plant Biotechnology and Genetic Engineering

• Plant biotechnology uses GM organisms in agriculture, enabling gene transfer across species.

Reducing World Hunger and Malnutrition

• Plant biotechnology enhances crop yields and nutritional value.

Reducing Fossil Fuel Dependency

• Biofuels from biomass could significantly contribute to energy needs.

Debate over Plant Biotechnology

• GMO debates encompass political, social, economic, and ethical aspects.

Issues of Human Health

• Concerns exist over allergen transfer in GMOs, though efforts are made to remove allergenic genes, and some GM foods are healthier.