Lab 4 (plants) Flashcards
why do seasonal allergies exist
Seasonal allergies can result from the pollen produced by male trees, weeds, and grasses. Airborne pollen can cause allergy symptoms such as sneezing, nasal congestion, and irritated, watery eyes. This is because the immune system mounts an immune response to the harmless pollen. Allergy treatment involves inhibiting various aspects of the immune systems when it encounters pollen.
how does the pollen tube influence the success of seed plants
The evolution of a pollen tube, a tubular structure that transports sperm to the ovule, the structure containing female gametes, eliminates the need for water in the transfer of sperm in dry terrestrial environments
how does evolving away from spores let seed plants be successful
Simpler plants use spores, haploid cells that require moisture to give rise to a gametophyte, a haploid multicellular organism that develops sex organs to produce gametes. Gametes are haploid cells that fuse with other haploid cells during fertilization in organisms that reproduce sexually. In contrast to these plants that use spores, seed plants have evolved to produce seeds, protective structures that contain a diploid embryo. The structure of seeds prevents desiccation, reducing reliance on water in dry terrestrial environments. Seeds can rest dormant till conditions are suitable for their continued growth.
how does the endosperm lead to seed plant success
Within the seed, the embryo is surrounded by endosperm, tissues that serves as a source of nutrients that fuels initial growth of the sporophyte, the diploid multicellular stage of a plant that emerges from the plant embryo.
what kind of sporophytes do seed plants have
Seed plants are heterosporous, meaning that the sporophyte produces both female and male spores. The larger female spores are called megaspores, and the smaller male spores are called microspores.
How are seed plants divided
Seed plants are traditionally divided into Angiosperms and Gymnosperms. Angiosperms are flowering plants whose seeds are enclosed within a reproductive structure called the fruit of angiosperms. Gymnosperms are nonflowering plants whose seeds are not protected.
what is the ovule
The female reproductive structure of a seed plant is the ovule. After fertilization the ovule develops into a seed that contains the female reproductive cells and consists of three parts:
what are the three parts of seeds
the integument layer, nucellus, and megagametophyte / embryo
what is the micropyle
The micropyle, a narrow canal in the integument, provides an open pathway for the microspores to enter the internal megasporangium and magaspores.
what is the male reproductive structure of seed plants
The male reproductive structures of seed plants are called microsporangia. Microsporangia produce microsporocytes, also called pollen mother cells, diploid microspore mother cells that undergo meiosis to produce four microspores. Because there are hundreds or thousands of microsporocyte cells within each microsporangium, many thousands of microspores are produced.
what is pollen
Within the cytoplasm of each microspore, a microscopic, multicellular, male microgametophyte develops by mitosis. This entire structure is what is commonly called a pollen grain. The pollen tube, the tube that transports two sperm cells of the microgametophyte to the egg cell of the megagametophyte in the ovule, is a unicellular outgrowth of the inner wall of the pollen grain. Pollen is the powdery substance that contains pollen grains.
what are cones
Gymnosperm means naked seed. Conifers, such as redwoods, giant sequoias, and bristlecone pine trees, are the largest and most important group of gymnosperms. Conifers have two types of organs that contain reproductive structures: male cones, which produce pollen, and female cones, which produce seeds.
where are male cones typically found
The male cones are typically found in clusters at the base of lower side branches, although in some species they can be found on higher branches as well.
what are Microsporophylls
Microsporophylls, modified leaves also called scales, extend out from a central axis and bear one or more microsporangia. Inside each Microsporangium, microsporocytes undergo meiosis produce four haploid microspores that develop into pollen grains.
what does mitosis of the microspore produce
Mitosis of the microspore produces the generative cell, which gives rise to the sperm, and the tube cell, which grows the pollen tube.
what does the pollen grain also consist of in conifers
In conifers, pollen grains also consist of an outer wall, called the exine, an inner wall, called the intine, and a pair of air sacs that make the pollen grains buoyant in the wind.
where do female cones typically form
Female cones typically form higher up in the tree
what are Megasporophyll
the modified leaves or scales of female cones are called megasporophylls. Each scale has two ovules where megaspores can develop.
what does the megasporocute produce
The megasporangium, the middle layer of the ovule, contains a megasporocyte that undergoes meiosis to produced four megaspores. Each ovule also has a micropyle, a small canal in the outer envelope for sperm to enter.
