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Primary producers are those organisms in an ecosystem that produce biomass from inorganic compounds (autotrophs). In almost all cases these are photosynthetically active organisms (plants, cyanobacteria and a number of other unicellular organisms; see article on photosynthesis). However, there are examples of archea (unicellular organisms) that produce biomass from the oxidation of inorganic chemical compounds (chemoautotrophs) in hydrothermal vents in the deep ocean.
Fungi and other organisms who gain their biomass from oxidizing organic materials are called reducers and are not primary producers.
Vascular plants (also known as tracheophytes or higher plants) are those plants that have lignifiedtissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the ferns, clubmosses, flowering plants, conifers and other gymnosperms. Scientific names for the group include Tracheophyta and Tracheobionta, but neither name is very widely used.
Vascular plants are distinguished by two primary characteristics:
- Vascular plants have vascular tissues, which circulate resources through the plant. This feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are therefore restricted to relatively small sizes.
- In vascular plants, the principal generation phase is the sporophyte, which is usuallydiploid with two sets of chromosomes per cell. Only the germ cells and gametophytes are haploid. By contrast, the principal generation phase in non-vascular plants is usually the gametophyte, which ishaploid with one set of chromosomes per cell. In these plants, generally only the spore stalk and capsule are diploid.
One possible mechanism for the presumed switch from emphasis on the haploid generation to emphasis on the diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. In other words, elaboration of the spore stalk enabled the production of more spore and the ability to release it higher and to broadcast it farther. Such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, and more branching.
Water transport happens in either xylem or phloem: xylem carries water and inorganic solutes upward toward the leaves from the roots, while phloem carries organic solutes throughout the plant. Group of plants having lignified conducting tissue (xylem vessels or tracheids).
A proposed phylogeny of the vascular plants after Kenrick and Crane is as follows, with modification to the Pteridophyta from Smith et al.
This phylogeny is supported by several molecular studies. Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns (Pteridophyta) are not monophyletic.
Nutrients and water from the soil and the organic compounds produced in leaves are distributed to specific areas in the plant through the xylem and phloem. The xylem draws water and nutrients up from the roots to the upper sections of the plant's body, and the phloem conducts other materials, such as the sucrose produced during photosynthesis, which gives the plant energy to keep growing and seeding.
The xylem consists of tracheids, which are dead hard-walled hollow cells arranged to form tiny tubes to function in water transport. A tracheid cell wall usually contains the polymer lignin. The phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
The movement of nutrients, water and sugars is affected by transpiration, conduction and absorption of water.
The most abundant compound in all plants, as in all life, is water which serves an important role in the various processes taking place. Transpiration is the main process a plant can call upon to move compounds within its tissues. The basic minerals and nutrients a plant is composed of remain, generally, within the plant. Water is constantly lost from the plant through its stomata to the atmosphere.
Water is transpired from the plants leaves via stomata, carried there via leaf veins and vascular bundles within the plants cambium layer. The movement of water out of the leaf stomata creates, when the leaves are considered collectively, a transpiration pull. The pull is created through water surface tension within the plant cells. The draw of water upwards is assisted by the movement of water into the roots via osmosis. This process also assists the plant in absorbing nutrients from the soil as soluble salts, a process known as absorption. Surprisingly, the movement of water upwards requires very little or no energy from the plant. Hydrogen bonds exist between watermolecules, causing them to line up; as the molecules at the top of the plant evaporate, each pulls the next one up to replace it, which in turn pulls on the next one in line.
Xylem vessels allow the movement of water and nutrients upwards towards the shoots and seeds, cuttings, bulbs and other plant parts. Plant propagation can also refer to the artificial or natural dispersal of plants.
Sexual propagation (seed)
Seeds and spores can be used for reproduction (through e.g. sowing). Seeds are typically produced from sexual reproduction within a species, because genetic recombination has occurred plants grown from seeds may have different characteristics from its parents. Some species produce seeds that require special conditions to germinate, such as cold treatment. The seeds of many Australian plants and plants from southern Africa and the American west require smoke or fire to germinate. Some plant species, including many trees do not produce seeds until they reach maturity, which may take many years. Seeds can be difficult to acquire and some plants do not produce seed at all.
Commonly used by both hobby gardeners, and in large scale industrial facilities, an electrical propagator is a low-cost, efficient and safe method of encouraging seed growth.
Plants have a number of mechanisms for asexual or vegetative reproduction. Some of these have been taken advantage of by horticulturists and gardeners to multiply or clone plants rapidly. People also use methods that plants do not use, such as tissue culture and grafting. Plants are produced using material from a single parent and as such there is no exchange of genetic material, therefore vegetative propagation methods almost always produce plants that are identical to the parent. Vegetative reproduction uses plants parts such as roots, stems and leaves. In some plants seeds can be produced without fertilization and the seeds contain only the genetic material of the parent plant. Therefore, propagation via asexual seeds or apomixis is asexual reproduction but not vegetative propagation.
Techniques for vegetative propagation include:
- Air or ground layering
- Grafting and bud grafting, widely used in fruit tree propagation
- Stolons or runners
- Storage organs such as bulbs, corms, tubers and rhizomes
- Striking or cuttings
This can be in the form of a clear enclosed bin sitting over a hotpad, or even a portable heater pointed at the bin. the key is to keep the moisture in the clear bin, while keeping lighting over the top of it, usually
Seed propagation mat
An electricseed-propagation mat is a heated rubber mat covered by a metal cage which is used in gardening. The mats are made so that planters containing seedlings can be placed on top of the metal cage without the risk of starting a fire. In extreme cold, gardeners place a loose plastic cover over the planters/mats which creates a sort of miniature greenhouse. The constant and predictable heat allows people to garden in the winter months when the weather is generally too cold for seedlings to survive naturally. When combined with a lighting system, many plants can be grown indoors using these mats.
Plant pathology (also phytopathology) is the scientific study of plant diseases caused by pathogens (infectious diseases) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrate or other pests that affect plant health by consumption of plant tissues. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.
The fungi reproduce both sexually and asexually via the production of spores. These spores may be spread long distances by air or water, or they may be soil borne. Many soil borne spores, normally zoospores, are capable of living saprotrophically, carrying out the first part of their lifecycle in the soil.
Biotrophic fungal pathogens colonize living plant tissue and obtain nutrients from living host cells. Necrotrophic fungal pathogens infect and kill host tissue and extract nutrients from the dead host cells. See Powdery Mildew and Rice Blast images below.
Significant fungal plant pathogens include:
- Fusariumspp. (causal agents of Fusarium wilt disease)
- Thielaviopsisspp. (causal agents of: canker rot, black root rot, Thielaviopsis root rot)
- Magnaporthe grisea(causal agent of blast of rice and gray leaf spot in turfgrasses)
- Phakospora pachyrhizi(causal agent of soybean rust)
- Pucciniaspp. (causal agents of severe rusts of virtually all cereal grains and cultivated grasses)
The oomycetes are not true fungi but are fungal-like organisms. They include some of the most destructive plant pathogens including the genusPhytophthora which includes the causal agents of potato late blight and sudden oak death.
Despite not being closely related to the fungi, the oomycetes have developed very similar infection strategies and so many plant pathologists group them with fungal pathogens.
Significant oomycete plant pathogens
Most bacteria that are associated with plants are actually saprotrophic, and do no harm to the plant itself. However, a small number, around 100 species, are able to cause disease. Bacterial diseases are much more prevalent in sub-tropical and tropical regions of the world.
Most plant pathogenic bacteria are rod shaped (bacilli). In order to be able to colonize the plant they have specific pathogenicity factors. Five main types of bacterial pathogenicity factors are known:
2. ToxinsThese can be non-host specific, and damage all plants, or host specific and only cause damage on a host plant.
3. Effector proteins These can be secreted into the extracellular environment or directly into the host cell, often via the Type three secretion system. Some effectors are known to suppress host defense processes.
Answers:Australian Tree Fern Loblolly Pine Bird of Paradise and for a non vascular plant Sphagnum Moss
Answers:It helps if you know a little bit about the origins of these words. The easiest to remember is that the "-phyte" part of sporophyte means "plant". So the sporophyte is always diploid and is the life-phase that produces spores (which are haploid). The sporangium is the container that holds and releases the spores (the "-angium" part is taken from a Greek word meaning container or vessel; it becomes "-angia" in the plural) In some texts you will see the terms "microspore" and "megaspore". These are easier to remember because everyone knows that micro means small and mega means large. They are used for the small reproductive cells (pollen) and the relatively large ones (egg cells) in higher plants.
Answers:Yea i know it can get confusing in a regular bio class. I didn't fully understand the alternation of generations in plants until i took a botany class. Basically, plants have two stages in their life cycle, they can appear as a gametophyte or a sporophyte. They are both multicellular but depending on what phylum of plants we're talking about, either a gametophyte will be dominant or a sporophyte will be. If we're talking about any plants that came before vascular plants ( ferns, conifers and flowering plants and ect.), then the gametophyte will be dominant. That is the case for bryophytes, the three phylum of non-vascular plants that includes liverworts, hornworts and mosses. In bryophytes, the gametophyte stage is bigger and live longer, while the sporophyte is attached and dependent on the gametophyte for most of its water and nutrition. Two gametophytes, one a female and one a male produces sperm and egg which will fertilize and creates a zygote which at this stage is a diploid (since fertilization is 1n +1n = 2n). The zygote will go through mitosis (basically cell replication with daughter cells identical to parents) to form a small sporophyte that attaches itself to the gametophyte for its entire life. The sporophyte will go through meiosis which basically splits the sets of chromosomes creating spores which are haploid (1n). (i suggest you go back and review meiosis...you cannot understand the alt. of gen. without understanding meiosis). The spores then leave its parents and form other gametophytes through mitosis. The spores change into a gametophyte by basically diving its cells and having the cells differentiate and get more specialized. It's the same thing in humans when we're an embryo...embryonic stem cells divide and differentiate into different layers and eventually forms organs and ect. You should already know that mitosis is basically the parent cell reproducing replicas of itself. Meiosis are only used for sex cells in which the parent cells divide their chromosome sets in half. This is why a diploid organism undergoing meiosis will create a haploid product. If we're talking about vascular plants here...plants with a conducting system xylem and phloem, The sporophyte is dominant and the gametophyte will be independent in some species and dependent on the sporophyte in others. If the gametophyte is independent in these vascular plants, it'll be be very small and live very short compared to its sporophyte stage--which it will look like the typical plants we see. The stages are basically the same. The only difference are the reproductive structures. Gymnosperms and angiosperms will have the more complex structures. I can go on about this but you just wanted an explanation on the stages. Just know that a sporophyte will create spores by meiosis and the spores then go through mitosis to form a gametophyte. Two gametophytes will produce sperm and egg and they will fertilize and form a zygote. the zygote then is a diploid and only need to go through mitosis to form a sporophyte. Oh and the zygote is form on the gametophyte where the egg is formed. Like humans i guess--where the egg after being fertilized develops into an embryo). And yea just realize that the gametophyte and sporophyte are two muticellular structures.
Answers:In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many plants, algae, fungi and some protozoans. A chief difference between spores and seeds as dispersal units is that spores have very little stored food resources compared with seeds. Spores are usually haploid and unicellular and are produced by meiosis in the sporophyte. Once conditions are favorable, the spore can develop into a new organism using mitotic division, producing a multicellular gametophyte, which eventually goes on to produce gametes. Pollen is a fine to coarse powder consisting of microgametophytes (pollen grains), which produce the male gametes (sperm cells) of seed plants. A hard coat covering the pollen grain protects the sperm cells during the process of their movement between the stamens of the flower to the pistil of the next flower.