Divyanshu67/squad_v2 huggingface dataset:
Antenna_(radio)

Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization is elliptical, meaning that the polarization of the radio waves varies over time. Two special cases are linear polarization (the ellipse collapses into a line) as we have discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates back and forth along one direction; this can be affected by the mounting of the antenna but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field (and magnetic field) of the radio wave rotates at the radio frequency circularly around the axis of propagation. Circular or elliptically polarized radio waves are designated as right-handed or left-handed using the "thumb in the direction of the propagation" rule. Note that for circular polarization, optical researchers use the opposite right hand rule from the one used by radio engineers.

Question: What are electrical fields projected on to?
Answer: imaginary plane

Question: What is the imagenary plane perpindicular to?
Answer: radio wave

Question: What is the name to describe polarization of radio waves varies over times?
Answer: elliptical

Question: How many directions does the E-plane of the radio waves oscillates back and forth?
Answer: one direction
Antenna_(radio)

It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception. Intermediate matchings will lose some signal strength, but not as much as a complete mismatch. A circularly polarized antenna can be used to equally well match vertical or horizontal linear polarizations. Transmission from a circularly polarized antenna received by a linearly polarized antenna (or vice versa) entails a 3 dB reduction in signal-to-noise ratio as the received power has thereby been cut in half.

Question: What is the best for an recieving antenna for optimum reception?
Answer: match the polarization

Question: What loses signal strength?
Answer: Intermediate matchings

Question: What is used to match vertical and horizontal linear polarizations?
Answer: circularly polarized

Question: A transmission can cause reduction in what?
Answer: signal-to-noise ratio
Antenna_(radio)

Maximum power transfer requires matching the impedance of an antenna system (as seen looking into the transmission line) to the complex conjugate of the impedance of the receiver or transmitter. In the case of a transmitter, however, the desired matching impedance might not correspond to the dynamic output impedance of the transmitter as analyzed as a source impedance but rather the design value (typically 50 ohms) required for efficient and safe operation of the transmitting circuitry. The intended impedance is normally resistive but a transmitter (and some receivers) may have additional adjustments to cancel a certain amount of reactance in order to "tweak" the match. When a transmission line is used in between the antenna and the transmitter (or receiver) one generally would like an antenna system whose impedance is resistive and near the characteristic impedance of that transmission line in order to minimize the standing wave ratio (SWR) and the increase in transmission line losses it entails, in addition to supplying a good match at the transmitter or receiver itself.

Question: What requires matching of the empedance to an antenna system?
Answer: Maximum power transfer

Question: What is the desired design value for transmmiting circuitry?
Answer: 50 ohms

Question: Why would a transmitter have additional adjustments?
Answer: "tweak" the match

Question: What is SWR?
Answer: standing wave ratio
Antenna_(radio)

In some cases this is done in a more extreme manner, not simply to cancel a small amount of residual reactance, but to resonate an antenna whose resonance frequency is quite different from the intended frequency of operation. For instance, a "whip antenna" can be made significantly shorter than 1/4 wavelength long, for practical reasons, and then resonated using a so-called loading coil. This physically large inductor at the base of the antenna has an inductive reactance which is the opposite of the capacitative reactance that such a vertical antenna has at the desired operating frequency. The result is a pure resistance seen at feedpoint of the loading coil; unfortunately that resistance is somewhat lower than would be desired to match commercial coax.[citation needed]

Question: What can be shorter than 1/4 wavelength long?
Answer: whip antenna

Question: What is the opposite of inductive reactance?
Answer: capacitative reactance

Question: What is at the base of the antenna?
Answer: loading coil

Question: Where is the resistance seen on the loading foil?
Answer: feedpoint
Antenna_(radio)

So an additional problem beyond canceling the unwanted reactance is of matching the remaining resistive impedance to the characteristic impedance of the transmission line. In principle this can always be done with a transformer, however the turns ratio of a transformer is not adjustable. A general matching network with at least two adjustments can be made to correct both components of impedance. Matching networks using discrete inductors and capacitors will have losses associated with those components, and will have power restrictions when used for transmitting. Avoiding these difficulties, commercial antennas are generally designed with fixed matching elements or feeding strategies to get an approximate match to standard coax, such as 50 or 75 Ohms. Antennas based on the dipole (rather than vertical antennas) should include a balun in between the transmission line and antenna element, which may be integrated into any such matching network.

Question: What is not adjustable when it comes to a transformer?
Answer: turns ratio

Question: A general matching network needs a minimum of how many adjustments to correct all components of impedance?
Answer: two adjustments

Question: How many ohms are in are in a standard coax?
Answer: 50 or 75

Question: What is included between the transmission line and the antenna element?
Answer: balun

Question: A balun should be integrated into what?
Answer: matching network
Antenna_(radio)

Unlike the above antennas, traveling wave antennas are nonresonant so they have inherently broad bandwidth. They are typically wire antennas multiple wavelengths long, through which the voltage and current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas. They have linear polarization (except for the helical antenna). Unidirectional traveling wave antennas are terminated by a resistor at one end equal to the antenna's characteristic resistance, to absorb the waves from one direction. This makes them inefficient as transmitting antennas.

Question: What antenna's are nonresonant?
Answer: traveling wave antennas

Question: How long are the wire antenna's that the voltage and current waves travel in the same direction?
Answer: one direction

Question: What antenna does not have linear polarization?
Answer: helical antenna

Question: What are undirectional traveling wave directions terminated by?
Answer: resistor

Question: What is the resistor equal to?
Answer: antenna's characteristic resistance
Antenna_(radio)

The radiation pattern and even the driving point impedance of an antenna can be influenced by the dielectric constant and especially conductivity of nearby objects. For a terrestrial antenna, the ground is usually one such object of importance. The antenna's height above the ground, as well as the electrical properties (permittivity and conductivity) of the ground, can then be important. Also, in the particular case of a monopole antenna, the ground (or an artificial ground plane) serves as the return connection for the antenna current thus having an additional effect, particularly on the impedance seen by the feed line.

Question: What is the radiation patter influenced by?
Answer: dielectric constant

Question: The ground is important for what antenna?
Answer: terrestrial antenna

Question: Whats another name for the ground?
Answer: artificial ground plane

Question: What does the artificial ground plane do for the antenna current?
Answer: return connection
Antenna_(radio)

The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, we are in the regime of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.

Question: What is the net quality of the ground dependent of?
Answer: topography

Question: What is the reason for the receiver seeing both the ral antenna and image of the antenna?
Answer: reflection

Question: What frequencies is associated with shorter wavelengths?
Answer: higher frequencies

Question: When will reflections not be coherent?
Answer: ground has irregularities
Antenna_(radio)

The phase of reflection of electromagnetic waves depends on the polarization of the incident wave. Given the larger refractive index of the ground (typically n=2) compared to air (n=1), the phase of horizontally polarized radiation is reversed upon reflection (a phase shift of  radians or 180°). On the other hand, the vertical component of the wave's electric field is reflected at grazing angles of incidence approximately in phase. These phase shifts apply as well to a ground modelled as a good electrical conductor.

Question: What is the refractive index of the ground?
Answer: n=2

Question: What is the refractive index of air?
Answer: n=1

Question: When is polarized radiation reversed?
Answer: reflection

Question: Besides a ground, what has these phases apply well to?
Answer: electrical conductor
Antenna_(radio)

When an electromagnetic wave strikes a plane surface such as the ground, part of the wave is transmitted into the ground and part of it is reflected, according to the Fresnel coefficients. If the ground is a very good conductor then almost all of the wave is reflected (180° out of phase), whereas a ground modeled as a (lossy) dielectric can absorb a large amount of the wave's power. The power remaining in the reflected wave, and the phase shift upon reflection, strongly depend on the wave's angle of incidence and polarization. The dielectric constant and conductivity (or simply the complex dielectric constant) is dependent on the soil type and is a function of frequency.

Question: what is reflected and transmitted into the ground when a plane surface is struck?
Answer: electromagnetic wave

Question: Who proposed this theory?
Answer: Fresnel coefficients

Question: Is the ground has a great conductor, how much of the wave will be reflected?
Answer: 180° out of phase

Question: What depends on the polarization and waves angle?
Answer: power remaining
Antenna_(radio)

The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which it delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has a flux of 1 pW / m2 (10−12 watts per square meter) and an antenna has an effective area of 12 m2, then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts rms at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source.

Question: What is the portion of something that is reached by the radio transmission called?
Answer: aperture

Question: What is a measure of the power of an antenna?
Answer: microvolts

Question: What effects the function of signals received by an antenna?
Answer: direction

Question: How much power will be delivered to the reciever if the antenna has an effective area of 12 m/2?
Answer: 12 pW of RF power
Antenna_(radio)

The bandwidth characteristics of a resonant antenna element can be characterized according to its Q, just as one uses to characterize the sharpness of an L-C resonant circuit. However it is often assumed that there is an advantage in an antenna having a high Q. After all, Q is short for "quality factor" and a low Q typically signifies excessive loss (due to unwanted resistance) in a resonant L-C circuit. However this understanding does not apply to resonant antennas where the resistance involved is the radiation resistance, a desired quantity which removes energy from the resonant element in order to radiate it (the purpose of an antenna, after all!). The Q is a measure of the ratio of reactance to resistance, so with a fixed radiation resistance (an element's radiation resistance is almost independent of its diameter) a greater reactance off-resonance corresponds to the poorer bandwidth of a very thin conductor. The Q of such a narrowband antenna can be as high as 15. On the other hand, a thick element presents less reactance at an off-resonant frequency, and consequently a Q as low as 5. These two antennas will perform equivalently at the resonant frequency, but the second antenna will perform over a bandwidth 3 times as wide as the "hi-Q" antenna consisting of a thin conductor.

Question: The properties of a usable radio frequency can be called its?
Answer: Q

Question: What is a measure of the comparison between reactance and resistance?
Answer: Q

Question: What is the largest Q that could be achieved with a slimmer band antenna?
Answer: 15

Question: What type of element would be used to encounter less reactance?
Answer: thick
Antenna_(radio)

For example, at 30 MHz (10 m wavelength) a true resonant 1⁄4-wavelength monopole would be almost 2.5 meters long, and using an antenna only 1.5 meters tall would require the addition of a loading coil. Then it may be said that the coil has lengthened the antenna to achieve an electrical length of 2.5 meters. However, the resulting resistive impedance achieved will be quite a bit lower than the impedance of a resonant monopole, likely requiring further impedance matching. In addition to a lower radiation resistance, the reactance becomes higher as the antenna size is reduced, and the resonant circuit formed by the antenna and the tuning coil has a Q factor that rises and eventually causes the bandwidth of the antenna to be inadequate for the signal being transmitted. This is the major factor that sets the size of antennas at 1 MHz and lower frequencies.

Question: What can be added to allow for an antenna shorter than the needed height to produce desired results?
Answer: loading coil

Question: How would the resistive impedance from this scenario compare to if the antenna was the proper height?
Answer: lower

Question: The coil has lengthed the antenna to reach how much length electrically?
Answer: 2.5 meters

Question: What is the major thing that sets the size of antennas at lower frequencies?
Answer: reactance
Antenna_(radio)

Consider a half-wave dipole designed to work with signals 1 m wavelength, meaning the antenna would be approximately 50 cm across. If the element has a length-to-diameter ratio of 1000, it will have an inherent resistance of about 63 ohms. Using the appropriate transmission wire or balun, we match that resistance to ensure minimum signal loss. Feeding that antenna with a current of 1 ampere will require 63 volts of RF, and the antenna will radiate 63 watts (ignoring losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; in this case the reflected current would arrive at the feed out-of-phase with the signal, causing the net current to drop while the voltage remains the same. Electrically this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance, and the signal will be reflected back into the antenna, reducing output. This could be addressed by changing the matching system between the antenna and transmission line, but that solution only works well at the new design frequency.

Question: How big would an antenna be used to with with one m wavelengths?
Answer: 50 cm

Question: How could the rection of output be adressed by?
Answer: changing the matching system

Question:  What unit is used to measure current?
Answer: ampere

Question: What effect occurs when the signal is reflected back into the antenna?
Answer: reducing output
Antenna_(radio)

Recall that a current will reflect when there are changes in the electrical properties of the material. In order to efficiently send the signal into the transmission line, it is important that the transmission line has the same impedance as the elements, otherwise some of the signal will be reflected back into the antenna. This leads to the concept of impedance matching, the design of the overall system of antenna and transmission line so the impedance is as close as possible, thereby reducing these losses. Impedance matching between antennas and transmission lines is commonly handled through the use of a balun, although other solutions are also used in certain roles. An important measure of this basic concept is the standing wave ratio, which measures the magnitude of the reflected signal.

Question: What sort of changes in material would a current reflect?
Answer: electrical

Question:  What must match between the transmission line and elements?
Answer: impedance

Question: What technique is used to prevent unintentional decrease in signal?
Answer: Impedance matching

Question: How is this process usually used for transmission lines and antennas?
Answer: balun
Antenna_(radio)

An electromagnetic wave refractor in some aperture antennas is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This is the radio equivalent of an optical lens.

Question: What is used to allow one to control the function of wave fronts moving through an antenna?
Answer: selectively delay

Question: What changes the structuak traits of a wave on either side?
Answer: refractor

Question: What is the main purpose of a refractor?
Answer: spatial characteristics

Question: A refractor can be compared to what type of viewing?
Answer: optical lens
Antenna_(radio)

The actual antenna which is transmitting the original wave then also may receive a strong signal from its own image from the ground. This will induce an additional current in the antenna element, changing the current at the feedpoint for a given feedpoint voltage. Thus the antenna's impedance, given by the ratio of feedpoint voltage to current, is altered due to the antenna's proximity to the ground. This can be quite a significant effect when the antenna is within a wavelength or two of the ground. But as the antenna height is increased, the reduced power of the reflected wave (due to the inverse square law) allows the antenna to approach its asymptotic feedpoint impedance given by theory. At lower heights, the effect on the antenna's impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the antenna. Changing the antenna's height by a quarter wavelength, then changes the phase of the reflection by 180°, with a completely different effect on the antenna's impedance.

Question: What can receive a stron signal by transmitting an original wave?
Answer: actual antenna

Question: Where will the additional current be induced?
Answer: antenna element

Question: What is altered because of the proximity to the ground?
Answer: antenna's impedance

Question: what happens to the reflected wave which allows the antenna to reach its asympotic feedpoint impedance?
Answer: reduced power
Antenna_(radio)

For horizontal propagation between transmitting and receiving antennas situated near the ground reasonably far from each other, the distances traveled by tne direct and reflected rays are nearly the same. There is almost no relative phase shift. If the emission is polarized vertically, the two fields (direct and reflected) add and there is maximum of received signal. If the signal is polarized horizontally, the two signals subtract and the received signal is largely cancelled. The vertical plane radiation patterns are shown in the image at right. With vertical polarization there is always a maximum for θ=0, horizontal propagation (left pattern). For horizontal polarization, there is cancellation at that angle. Note that the above formulae and these plots assume the ground as a perfect conductor. These plots of the radiation pattern correspond to a distance between the antenna and its image of 2.5λ. As the antenna height is increased, the number of lobes increases as well.

Question: What is between recieving and transmitting antenna's?
Answer: horizontal propagation

Question: When is the emission at maximized recieved signal?
Answer: polarized vertically

Question: Where is the radiation patterns in the vertical plane shown?
Answer: image at right

Question: What is also increased along with the antenna's height?
Answer: lobes
Antenna_(radio)

On the other hand, classical (analog) television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection of electromagnetic waves in the p polarization (horizontal polarization off the side of a building) is generally less than s (vertical, in this case) polarization. Vertically polarized analog television has nevertheless been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.

Question: What is another name for classical television transmissions?
Answer: analog

Question: Buildings can create ghost images because of what?
Answer: multipath propagation

Question: When is ghosting reduced?
Answer: horizontal polarization

Question: What cause less problems in digital terrestrial television?
Answer: Vertically polarized analog television
Antenna_(radio)

Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna elements. The mathematics presented below are useful in analyzing the electrical behaviour of antenna arrays, where the properties of the individual array elements (such as half wave dipoles) are already known. If those elements were widely separated and driven in a certain amplitude and phase, then each would act independently as that element is known to. However, because of the mutual interaction between their electric and magnetic fields due to proximity, the currents in each element are not simply a function of the applied voltage (according to its driving point impedance), but depend on the currents in the other nearby elements. Note that this now is a near field phenomenon which could not be properly accounted for using the Friis transmission equation for instance.

Question: Where are the indiviual array elements known?
Answer: antenna arrays

Question: What induces a feedpoint to antennas nearby?
Answer: Current circulating

Question: What are the mathmatic useful towards?
Answer: electrical behaviour

Question: What cause mutual interactions between the elements electric and magnetic fields?
Answer: proximity
Antenna_(radio)

This is a consequence of Lorentz reciprocity. For an antenna element  not connected to anything (open circuited) one can write . But for an element  which is short circuited, a current is generated across that short but no voltage is allowed, so the corresponding . This is the case, for instance, with the so-called parasitic elements of a Yagi-Uda antenna where the solid rod can be viewed as a dipole antenna shorted across its feedpoint. Parasitic elements are unpowered elements that absorb and reradiate RF energy according to the induced current calculated using such a system of equations.

Question: a antenna element not connected to anything is circuited how?
Answer: open circuited

Question: When is the element not allowed voltage?
Answer: short circuited

Question: What element absorbs and reradiate RF-energy?
Answer: Parasitic

Question: What antenna can the solid rod be viewed as a dipole antenna?
Answer: Yagi-Uda

Question: Where can this solid rod be viewed?
Answer: feedpoint
Antenna_(radio)

The difference in the above factors for the case of θ=0 is the reason that most broadcasting (transmissions intended for the public) uses vertical polarization. For receivers near the ground, horizontally polarized transmissions suffer cancellation. For best reception the receiving antennas for these signals are likewise vertically polarized. In some applications where the receiving antenna must work in any position, as in mobile phones, the base station antennas use mixed polarization, such as linear polarization at an angle (with both vertical and horizontal components) or circular polarization.

Question: What type of programmin relies on vertical polarization?
Answer: broadcasting

Question: If you were to position your receiver closer to the ground what might be a negative of this placement?
Answer: cancellation

Question: What is one use that would require an antenna to receive signals in various ways at once?
Answer: mobile phones

Question: If you were to develop a signal to be used with mobile phones what would be an effective antenna type?
Answer: circular polarization.

Question: What would the antenna you are using take advantage of to allow it to work in multiple locations?
Answer: mixed polarization
Antenna_(radio)

Loop antennas consist of a loop or coil of wire. Loops with circumference of a wavelength or larger act similarly to dipole antennas. However loops small in comparison to a wavelength act differently. They interact with the magnetic field of the radio wave instead of the electric field as other antennas do, and so are relatively insensitive to nearby electrical noise. However they have low radiation resistance, and so are inefficient for transmitting. They are used as receiving antennas at low frequencies, and also as direction finding antennas.

Question: What type of antenna can be formed by a circular segment of wire?
Answer: Loop antennas

Question: What is a loop antenna compared with to determine its beahvior?
Answer: circumference of a wavelength

Question: If you needed to place an antenna somewhere with a large amount of interference, which type would be best?
Answer: loops small

Question: Why would this type be good for receiving but not transmtting?
Answer: low radiation resistance

Question: What else would be an effective application of this antenna type?
Answer: direction finding
Antenna_(radio)

It is a fundamental property of antennas that the electrical characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth, resonant frequency and polarization, are the same whether the antenna is transmitting or receiving. For example, the "receiving pattern" (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of the reciprocity theorem of electromagnetics. Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.

Question: Are essential properties of an antenna changed based on what fungtion they are performing
Answer: the same

Question: What proposition explains the equivalency of the recieving pattern of an antenna?
Answer: reciprocity theorem of electromagnetics

Question: Can the antenna serve more than one fungtion at a time?
Answer: either transmitting or receiving

Question: What is one electrical trait of an antenna?
Answer: radiation pattern
Flowering_plant

The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with about 350,000 species. Like gymnosperms, angiosperms are seed-producing plants; they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term "angiosperm" comes from the Greek composite word (angeion-, "case" or "casing", and sperma, "seed") meaning "enclosed seeds", after the enclosed condition of the seeds.

Question: What are the most diverse group of land plants?
Answer: angiosperms

Question: How many species of flowering plants are there about?
Answer: 350,000

Question: What do angiosperms have in common with gymnosperms?
Answer: seed-producing plants

Question: What does an angiosperm produce its seeds within?
Answer: an enclosure

Question: What is the Greek word for "case" or "casing"?
Answer: angeion

Question: Where does the term gymnosperm originate?

Question: What are gymnosperms known as?

Question: What do angeion have in common with angiosperms?

Question: How is production of fruits distinguished from a fruiting plant?

Question: What does gymnosperm mean etymologically?
Flowering_plant

Fossilized spores suggest that higher plants (embryophytes) have lived on land for at least 475 million years. Early land plants reproduced sexually with flagellated, swimming sperm, like the green algae from which they evolved. An adaptation to terrestrialization was the development of upright meiosporangia for dispersal by spores to new habitats. This feature is lacking in the descendants of their nearest algal relatives, the Charophycean green algae. A later terrestrial adaptation took place with retention of the delicate, avascular sexual stage, the gametophyte, within the tissues of the vascular sporophyte. This occurred by spore germination within sporangia rather than spore release, as in non-seed plants. A current example of how this might have happened can be seen in the precocious spore germination in Selaginella, the spike-moss. The result for the ancestors of angiosperms was enclosing them in a case, the seed. The first seed bearing plants, like the ginkgo, and conifers (such as pines and firs), did not produce flowers. The pollen grains (males) of Ginkgo and cycads produce a pair of flagellated, mobile sperm cells that "swim" down the developing pollen tube to the female and her eggs.

Question: How long have higher plants lived on land?
Answer: at least 475 million years

Question: How did early plants reproduce sexually?
Answer: with flagellated, swimming sperm

Question: Upright meisporangia allowed what to be dispersed to new habitats?
Answer: spores

Question: What are the nearest algal relatives existing today?
Answer: Charophycean green algae

Question: What is the common name for Selaginella?
Answer: the spike-moss

Question: What do the first green algae not produce?

Question: What does the pollen of spike-moss produce for reproduction?

Question: What does the pollen of spike-moss do to reach the female?

Question: What suggests that confiers have lived on land for 475 million years?

Question: What did Charophycean green algae develop to disperse by spores into new habitats?
Flowering_plant

The apparently sudden appearance of nearly modern flowers in the fossil record initially posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin. However, the fossil record has considerably grown since the time of Darwin, and recently discovered angiosperm fossils such as Archaefructus, along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps. Several groups of extinct gymnosperms, in particular seed ferns, have been proposed as the ancestors of flowering plants, but there is no continuous fossil evidence showing exactly how flowers evolved. Some older fossils, such as the upper Triassic Sanmiguelia, have been suggested. Based on current evidence, some propose that the ancestors of the angiosperms diverged from an unknown group of gymnosperms in the Triassic period (245–202 million years ago). Fossil angiosperm-like pollen from the Middle Triassic (247.2–242.0 Ma) suggests an older date for their origin. A close relationship between angiosperms and gnetophytes, proposed on the basis of morphological evidence, has more recently been disputed on the basis of molecular evidence that suggest gnetophytes are instead more closely related to other gymnosperms.[citation needed]

Question: What did Charles Darwin call the sudden appearance of nearly modern flowers in the fossil record?
Answer: abominable mystery

Question: What type of fossil is the recently discovered Archaefructus?
Answer: angiosperm

Question: What fossil evidence is lacking when it comes to flowers?
Answer: evidence showing exactly how flowers evolved

Question: From what period does fossilized pollen suggest an older date for angiosperm origin?
Answer: Middle Triassic

Question: What relationship proposed on the basis of morphological evidence has recently been disputed?
Answer: relationship between angiosperms and gnetophytes

Question: What was ancestors of angiosperms suddenly appearing called by Charles Darwin?

Question: What have several groups of Archaefructus been proposed to be?

Question: What is missing to show how ancestors of angiosperms diverged from an unknown group?

Question: Why has the relationship between gnetophytes and gymnosperms been disputed?

Question: What type of fossil is the recently discovered Sanmiguelia?
Flowering_plant

The evolution of seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. These occurred at 319 million years ago and 192 million years ago. Another possible whole genome duplication event at 160 million years ago perhaps created the ancestral line that led to all modern flowering plants. That event was studied by sequencing the genome of an ancient flowering plant, Amborella trichopoda, and directly addresses Darwin's "abominable mystery."

Question: How many distinct rounds of genome duplication events are suspected in the evolution of seed plants?
Answer: two

Question: When did the first whole genome duplication event occur?
Answer: 319 million years ago

Question: What type of event perhaps created the line which led to modern flowering plants?
Answer: whole genome duplication

Question: How are duplication events studied?
Answer: by sequencing the genome of an ancient flowering plant

Question: Who coined the term "abominable mystery"?
Answer: Darwin

Question: What appears to be the cause of duplicaton of seed plants?

Question: When did Darwin's "abominable mystery first appear?

Question: When was the ancient plant used in the study dated to?

Question: How are modern plants studied?

Question: Who coined the term duplication event?
Flowering_plant

The earliest known macrofossil confidently identified as an angiosperm, Archaefructus liaoningensis, is dated to about 125 million years BP (the Cretaceous period), whereas pollen considered to be of angiosperm origin takes the fossil record back to about 130 million years BP. However, one study has suggested that the early-middle Jurassic plant Schmeissneria, traditionally considered a type of ginkgo, may be the earliest known angiosperm, or at least a close relative. In addition, circumstantial chemical evidence has been found for the existence of angiosperms as early as 250 million years ago. Oleanane, a secondary metabolite produced by many flowering plants, has been found in Permian deposits of that age together with fossils of gigantopterids. Gigantopterids are a group of extinct seed plants that share many morphological traits with flowering plants, although they are not known to have been flowering plants themselves.

Question: When is the earliest known macrofossil identified as an angiosperm dated?
Answer: about 125 million years BP

Question: What is the earliest known angiosperm?
Answer: Archaefructus liaoningensis

Question: What pushes the age of angiosperm 5 million years further back?
Answer: pollen

Question: How long ago has circumstantial evidence has been found for the existence of angiosperms?
Answer: 250 million years ago

Question: What group of now extinct seed plants had many of the traits of what are now flowering plants?
Answer: Gigantopterids

Question: What is Oleanne, the earliest macrofossil, traditionally considered to be?

Question: What evidence has shown that flowering plants existed 125 million years BP?

Question: What has been found in ginko deposits of that age with gigantopterid fossils?

Question: What do Oleanne share morphological traits with?

Question: What are not known to have Permian deposits themselves?
Flowering_plant

The great angiosperm radiation, when a great diversity of angiosperms appears in the fossil record, occurred in the mid-Cretaceous (approximately 100 million years ago). However, a study in 2007 estimated that the division of the five most recent (the genus Ceratophyllum, the family Chloranthaceae, the eudicots, the magnoliids, and the monocots) of the eight main groups occurred around 140 million years ago. By the late Cretaceous, angiosperms appear to have dominated environments formerly occupied by ferns and cycadophytes, but large canopy-forming trees replaced conifers as the dominant trees only close to the end of the Cretaceous 66 million years ago or even later, at the beginning of the Tertiary. The radiation of herbaceous angiosperms occurred much later. Yet, many fossil plants recognizable as belonging to modern families (including beech, oak, maple, and magnolia) had already appeared by the late Cretaceous.

Question: When does a great diversity of angiosperms appear in the fossil record?
Answer: approximately 100 million years ago

Question: What is the appearance of a large amount of angiosperms in the fossil record known as?
Answer: great angiosperm radiation,

Question: When did the division of the eight main groups of angiosperms occur?
Answer: 40 million years ago

Question: What were the angiosperms up to by the late Cretaceous?
Answer: dominated environments

Question: Beech and maple had already appeared by what period?
Answer: Cretaceous

Question: When does a diversity of magnoliids appear in the fossil record?

Question: What is the appearance of ferns in the fossil record called?

Question: By the end of the Tertiary, what did angiosperms dominate?

Question: When did eudicots replace conifers as dominant trees?

Question: When had eight main groups of Chloranthaceae recognizable as belonging to modern families appear?
Flowering_plant

Island genetics provides one proposed explanation for the sudden, fully developed appearance of flowering plants. Island genetics is believed to be a common source of speciation in general, especially when it comes to radical adaptations that seem to have required inferior transitional forms. Flowering plants may have evolved in an isolated setting like an island or island chain, where the plants bearing them were able to develop a highly specialized relationship with some specific animal (a wasp, for example). Such a relationship, with a hypothetical wasp carrying pollen from one plant to another much the way fig wasps do today, could result in the development of a high degree of specialization in both the plant(s) and their partners. Note that the wasp example is not incidental; bees, which, it is postulated, evolved specifically due to mutualistic plant relationships, are descended from wasps.

Question: What is one proposed explanation for the instant appearance of flowering plants?
Answer: Island genetics

Question: What is island genetics thought to be a default source of?
Answer: speciation

Question: What did radical adaptations seem to have required?
Answer: inferior transitional forms

Question: How did an isolated setting like an island help flowering plants evolve?
Answer: highly specialized relationship with some specific animal

Question: What are bees descended from?
Answer: wasps

Question: What are transitional forms descended from?

Question: What is an explanation for the sudden appearance of fig wasps?

Question: What does a relationship between bees and wasps result in?

Question: What is carrying pollen thought to be a common source of?

Question: How did flowering plants help transitional forms evolve?
Flowering_plant

Animals are also involved in the distribution of seeds. Fruit, which is formed by the enlargement of flower parts, is frequently a seed-dispersal tool that attracts animals to eat or otherwise disturb it, incidentally scattering the seeds it contains (see frugivory). Although many such mutualistic relationships remain too fragile to survive competition and to spread widely, flowering proved to be an unusually effective means of reproduction, spreading (whatever its origin) to become the dominant form of land plant life.

Question: What are animals also a part of?
Answer: distribution of seeds

Question: What did the enlargement of flower parts evolve to form?
Answer: Fruit

Question: What does a plant get out of forming fruit?
Answer: seed-dispersal

Question: What are many mutualistic relationships, thus failing to survive competition? 
Answer: fragile

Question: What turned out to be unusually effective for plants to reproduce?
Answer: flowering

Question: What did competition prove to be effective at doing?

Question: What did mutualistic relationships spread to eventually become?

Question: How does a plant benefit from competition?

Question: What reproductive method spread widely but made plants fragile?

Question: What did accidentally scattering seeds help flower parts evolve to form?
Flowering_plant

Flower ontogeny uses a combination of genes normally responsible for forming new shoots. The most primitive flowers probably had a variable number of flower parts, often separate from (but in contact with) each other. The flowers tended to grow in a spiral pattern, to be bisexual (in plants, this means both male and female parts on the same flower), and to be dominated by the ovary (female part). As flowers evolved, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant or at least "ovary-inferior".

Question: What uses a combination of genes to form new shoots?
Answer: Flower ontogeny

Question: What were plant parts like in their primitive days?
Answer: separate from (but in contact with) each other

Question: How did flowers become bixsexual?
Answer: grow in a spiral pattern

Question: What did some plant parts do as they evolved?
Answer: fused together

Question: What is a term for a plant with a specific sex per flower?
Answer: "ovary-inferior"

Question: What was dominated by the male parts?

Question: How did flowers tend to grow when they were male dominant?

Question: What did some plant parts do when the flower had only male parts?

Question: During flower ontogeny, what was a plant of a specific sex called?

Question: What do ovary inferior plants use to form new shoots?
Flowering_plant

Flower evolution continues to the present day; modern flowers have been so profoundly influenced by humans that some of them cannot be pollinated in nature. Many modern domesticated flower species were formerly simple weeds, which sprouted only when the ground was disturbed. Some of them tended to grow with human crops, perhaps already having symbiotic companion plant relationships with them, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection.

Question: How long has flower evolution occurred? 
Answer: present day

Question: Humans have effected some flowers so much they can no longer do what in nature?
Answer: pollinated

Question: What heritage do many modern domesticated flower species have?
Answer: formerly simple weeds

Question: Why did weeds grow with human crops?
Answer: symbiotic companion plant relationships

Question: What feature helped flowers not get plucked?
Answer: prettiest

Question: What has happened to weeds due to human influence?

Question: How long has weed evolution occurred?

Question: What was the origin of many simple weeds?

Question: What have weeds developed a dependence on?

Question: What characteristic caused crops not to be harvested?
Flowering_plant

The exact relationship between these eight groups is not yet clear, although there is agreement that the first three groups to diverge from the ancestral angiosperm were Amborellales, Nymphaeales, and Austrobaileyales. The term basal angiosperms refers to these three groups. Among the rest, the relationship between the three broadest of these groups (magnoliids, monocots, and eudicots) remains unclear. Some analyses make the magnoliids the first to diverge, others the monocots. Ceratophyllum seems to group with the eudicots rather than with the monocots.

Question: What three groups were the first to diverge from angiosperm?
Answer: Amborellales, Nymphaeales, and Austrobaileyales

Question: What term refers to the first three groups to diverge from angiosperm?
Answer: basal

Question: How clear is the relationship between the broadest of the three non-basal angiosperm groups?
Answer: unclear

Question: What group do some analyses seem to indicate diverged first?
Answer: magnoliids

Question: What were the first three groups to diverge from magnoliids?

Question: What do Amborellales tend to group with instead of monocots?

Question: What is the status of the relationship between Nymphaeales and monocots?

Question: What attitude is there about the first magnoliids diverging from the ancestral angiosperm?

Question: What do some eudicots indicate diverged first?
Flowering_plant

The botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon (bottle, vessel) and σπέρμα, (seed), was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked. The term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any approach to its modern scope became possible only after 1827, when Robert Brown established the existence of truly naked ovules in the Cycadeae and Coniferae, and applied to them the name Gymnosperms.[citation needed] From that time onward, as long as these Gymnosperms were, as was usual, reckoned as dicotyledonous flowering plants, the term Angiosperm was used antithetically by botanical writers, with varying scope, as a group-name for other dicotyledonous plants.

Question: What term did Paul Hermann come up with in 1690?
Answer: Angiosperm

Question: What did Hermann use the term angiosperm a primary division of in the plant kingdom?
Answer: primary

Question: Who restricted the application of the angiosperm term?
Answer: Carl Linnaeus

Question: What did Robert Brown establish the existence of in Cycadeae and Coniferae?
Answer: naked ovules

Question: What is the group-name angiosperm has been used for by botanical writers?
Answer: other dicotyledonous plants

Question: Who coined the term dicotyledonous?

Question: In what year was the term dicotyledonous created?

Question: Why did Robert Brown use the term dicotyledonous?

Question: How was the term angeion maintained by Robert Brown?

Question: In 1690 what happened to the term angeion as used by Robert Brown?