A solar-powered airplane finished crossing the United States on Saturday, landing in New York City after flying over the Statue of Liberty during its historic bid to circle the globe, the project team said. The spindly, single-seat experimental aircraft, dubbed Solar Impulse 2, arrived at New York's John F. Kennedy International Airport at about 4 a.m. local time after it took off about five hours beforehand at Lehigh Valley International Airport in Pennsylvania, the team reported on the airplane's website. Such a pleasure to land in New York! For the 14th time we celebrate sustainability," said the project's co-founder Andre Borschberg on Twitter after flying over the city and the Statue of Liberty during the 14th leg of the trip around the globe. The Swiss team flying the aircraft in a campaign to build support for clean energy technologies hopes eventually to complete its circumnavigation in Abu Dhabi, where the journey began in March 2015. The solar cr...
Reproduction (or procreation) is the biological process by which new individual organisms – "offspring" – are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: sexual and asexual.
In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction is not limited to single-celled organisms. The cloning of an organism is a form of asexual reproduction. By asexual reproduction an organism creates a genetically similar or identical copy of itself.
Sexual reproduction typically requires the sexual interaction of two organisms or gametes of the same species, one from each sex, to produce offspring organisms whose genetic characteristics are derived from those of the parent organisms.
Asexual Reproduction
Asexual reproduction involves one parent. As a result, the offspring tend to have the same genotype and phenotype; they lack variation.
It is advantageous in a constant environment because a large number of offspring can be produced in a short time.
Examples:
Flatworms can divide into 2 halves; each half grows into a separate organism.
Cnidarians undergo budding where a new individual grows from and then breaks off of the parent individual.
Echinoderms can be cut to form new individuals.
Insects- parthenogenesis (unfertilized egg develops)
Sexual Reproduction
Sexual reproduction involves the fusion of two gametes.Sperm and eggs are sometimes produced by the same individual and sometimes produced by different individuals.
The sexes of vertebrates are separate but some vertebrates can change sex and others are both male and female.
Variation
Sexual reproduction promotes variation because offspring inherit genes from two different parents.
In addition, when an individual produces gametes, crossing-over and independent assortment mix genes from that individuals parents. Gametes are haploid; they contain some genes from the individuals mother and some from the father.
Variation is advantageous to species in fluctuating environments.
Reproductive cycles
Reproductive cycles in many vertebrates and invertebrates are related to changes in day length.
Day length is a reliable indicator of season for timing circannual events such as reproductive behavior and migration.
In many species, the pineal gland secretes melatonin in the dark. Increasing day length (decreased melatonin levels) triggers reproductive behavior.
Fertilization
External fertilization
During external fertilization, many gametes are released into the water by each sex at the same time and place.
This type of fertilization requires water because animal sperm must swim to the eggs. Water also protects the gametes from drying out.
Species which have external fertilization are either aquatic or return to water for reproduction.
Internal fertilization
Internal fertilization is practiced by species that lay shelled eggs or have a period of internal embryonic development.
terrestrial environment because it enables sperm to swim to the egg and it prevents gametes from drying out.
The male often has a copulatory organ (a penis) for transferring sperm.
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