Answer:
Cycads /ˈsaɪkædz/ are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, therefore the individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly[3] and live very long, with some specimens known to be as much as 1,000 years old.[citation needed] Because of their superficial resemblance, they are sometimes mistaken for palms or ferns, but they are not closely related to either group.
Cycads are gymnosperms (naked seeded), meaning their unfertilized seeds are open to the air to be directly fertilized by pollination, as contrasted with angiosperms, which have enclosed seeds with more complex fertilization arrangements. Cycads have very specialized pollinators, usually a specific species of beetle. Both male and female cycads bear cones (strobili), somewhat similar to conifer cones.
Cycads have been reported to fix nitrogen in association with various cyanobacteria living in the roots (the "coralloid" roots).[4] These photosynthetic bacteria produce a neurotoxin called BMAA that is found in the seeds of cycads. This neurotoxin may enter a human food chain as the cycad seeds may be eaten directly as a source of flour by humans or by wild or feral animals such as bats, and humans may eat these animals. It is hypothesized that this is a source of some neurological diseases in humans.[5][6]
Cycads all over the world are in decline, with four species on the brink of extinction and seven species having fewer than 100 plants left in the wild.[7] The plant has a very long fossil history, with evidence that they existed in greater abundance and in greater diversity before the Jurassic and late Triassic mass extinction events.
Explanation:
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(Jane)
Answer:
Compression is a reverse fault, tension is normal fault and shear is strike slip fault.
Explanation:
Compression is a reverse fault, tension is normal fault and shear is strike slip fault. Reverse fault is opposite of normal fault which occurs due to the stress of compression on an object in which both object come close together. Due to tension stress, rocks pulling apart from each other, produces a normal fault. Shear is strike slip fault because in strike-slip fault, the two blocks slide over one another
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Polyploidy (more than two complete sets of chromosomes) is not rare among plants. For example, pollen grains may reach female flowers via animals or wind. In some cases, pollen grains from species with 4 complete sets of chromosomes will have 2 sets of chromosomes. Pollen grains may fuse with a female reproductive organ with 1 set of chromosome (so, female plant must have 2 sets of chromosomes). The resulting zygote will have 2 + 1 sets of chromosomes, so the plant will have 3 complete sets of chromosomes.
