Alternation of generations Sporophyte Dominant in flowering plants Bears flowers – reproductive structure Diploid or 2n Produces haploid microspores and megaspores by meiosis Gametophyte Haploid or 1n Produces gametes Microspore undergoes mitosis and become a pollen grain, a male gametophyte Megaspore undergoes mitosis to become embryo sac, a female gametophyte Upon fertilization, the cycle returns to the 2n sporophyte 24-2
Plant Reproduction, cont. Once a sperm fertilizes an egg, the zygote becomes an embryo, still within an ovule Ovule develops into a seed, which contains the embryo and stored food surrounded by a seed coat Ovary becomes a fruit, which aids in dispersing the seeds When a seed germinates, a new sporophyte emerges and, through mitosis and growth, becomes a mature organism Sexual life cycle of flowering plants is adapted to land 24-3
Figure 24.1D A corn plant is monoecious (flowers that are only male or only femalea. The staminate flowers produce pollen that is carried by wind tob. the carpellate flowers, where ears of corn develop. 24-8
Figure 24BButterflies, birds, and bats are adapted for acquiring nectar from certain flowers.Flowers that attract beetles produce much pollen and those that attract flies have 24-9the smell of rotting flesh
Sexual reproduction involves 1. Production of pollen grains (male gametophytes) in the anthers of stamens 2. Production of an embryo sac (female gametophyte) in an ovule located within the ovary of a carpel Pollination Pollen transferred from anther to stigma so an egg within female gametophyte is fertilized Most angiosperms use animals to carry out pollination 24-10
Double fertilization is unique in angiosperms Results in not only a zygote but also a food source for the developing zygote Endosperm – nutritive tissue developing embryonic sporophyte uses as energy source Mature seed contains Embryo – will develop into the plant Stored food – endosperm Seed coat – develops from ovule wall for protection 24-15
Simple Versus Aggregate & Multiple Fruits Simple fruits are derived from the simple ovary of a single carpel Exs: grapes, tomatoes Accessory fruits form from other flower parts in addition to ovary Exs: strawberry, apple Aggregate and multiple fruits are examples of compound fruits derived from several individual ovaries Strawberry – aggregate fruit, each ovary becomes a one- seeded fruit called an achene Pineapple – a multiple fruit derived from many individual flowers, each with its own carpel 24-21
Germination – seeds form into a seedling Doesn’t usually take place until there is sufficient water, warmth, and oxygen to sustain growth For seeds, dormancy is the time during which no growth occurs, even though conditions may be favorable for growth 24-25
24.6 Plants have various ways of reproducing asexually Also called vegetative reproduction Type of cloning – offspring exactly like parent Plants can grow from axillary buds of above or below ground stems Rhizome – underground horizontal stem (iris, many grasses) Tuber – enlarged portion of rhizome (potato) Corm – bulbous underground stems (onion) 24-29
24.7 Cloning of plants in tissue culture assists agriculture Tissue culture Growth of a tissue in an artificial liquid or on agar 3 methods Somatic embryogenesis – technique that uses hormones to cause plant tissues to generate small masses of cells Meristem tissue culture – many new shoot tips from a single shoot tip Anther tissue culture – produces haploid plantlets or chromosomal doubling chemically induced 24-32
Figure 24.7B Producing whole plants from meristem tissue 24-36
Connecting the Concepts: Chapter 24 Life, as we know it, would not be possible without vascular plants Although we now live in an industrialized society, we are still dependent on plants and have put them to many more uses We grow plants for food, shelter, beauty and substances for industry Half of all pharmaceutical drugs have their origin in plants 24-37
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