Chantay Gros November 22, 2019 Fruit
As the ovules develop into seeds, the ovary begins to ripen and the ovary wall, the pericarp, may become fleshy (as in berries or drupes), or form a hard outer covering (as in nuts). In some multi seeded fruits, the extent to which the flesh develops is proportional to the number of fertilized ovules. The pericarp is often differentiated into two or three distinct layers called the exocarp (outer layer, also called epicarp), mesocarp (middle layer), and endocarp (inner layer). In some fruits, especially simple fruits derived from an inferior ovary, other parts of the flower (such as the floral tube, including the petals, sepals, and stamens), fuse with the ovary and ripen with it. In other cases, the sepals, petals and/or stamens and style of the flower fall off. When such other floral parts are a significant part of the fruit, it is called an accessory fruit. Since other parts of the flower may contribute to the structure of the fruit, it is important to study flower structure to understand how a particular fruit forms.
Selflessness is an important feature of some fruits of commerce. Commercial cultivars of bananas and pineapples are examples of seedless fruits. Some cultivars of citrus fruits (especially grapefruit, mandarin oranges, navel oranges), satsumas, table grapes, and watermelons are valued for their selflessness. In some species, selflessness is the result of parthenogenesis, where fruits set without fertilization. Parthenogenesis fruit set may or may not require pollination, but most seedless citrus fruits require a stimulus from pollination to produce fruit.
Darwin explained such male-female differences in his theory of sexual selection in his book The Descent of Man. Once the females begin to select males according to any particular characteristic, such as a long tail or a colored crest, that characteristic is emphasized more and more in the males. Eventually all the males will have the characteristics that the females are sexually selecting for, as only those males can reproduce. This mechanism is powerful enough to create features that are strongly disadvantageous to the males in other ways. For example, some male birds of paradise have wing or tail streamers that are so long that they impede flight, while their brilliant colors may make the males more vulnerable to predators. In the extreme, sexual selection may drive species to extinction, as has been argued for the enormous horns of the male Irish elk, which may have made it difficult for mature males to move and feed.
Some prey animals such as zebra are marked with high-contrast patterns which possibly help to confuse their predators, such as lions, during a chase. The bold stripes of a herd of running Zebra have been claimed make it difficult for predators to estimate the prey’s speed and direction accurately, or to identify individual animals, giving the prey an improved chance of escape. Since dazzle patterns (such as the Zebra’s stripes) make animals harder to catch when moving, but easier to detect when stationary, there is an evolutionary trade-off between dazzle and camouflage. Another theory is that the zebra’s stripes could provide some protection from flies and biting insects.
Bio luminescence is the production of light, such as by the photosensor of marine animals, and the tails of glow-worms and fireflies. Bio luminescence, like other forms of metabolism, releases energy derived from the chemical energy of food. A pigment, luciferin is catalysed by the enzyme luciferase to react with oxygen, releasing light. Comb jellies such as Euphemisms are bio luminescent, creating blue and green light, especially when stressed; when disturbed, they secrete an ink which luminescence in the same colors. Since comb jellies are not very sensitive to light, their bio luminescence is unlikely to be used to signal to other members of the same species (e.g. to attract mates or repel rivals); more likely, the light helps to distract predators or parasites. Some species of squid have light-producing organs (photophores) scattered all over their undersides that create a sparkling glow. This provides counter-illumination camouflage, preventing the animal from appearing as a dark shape when seen from below. Some anglerfish of the deep sea, where it is too dark to hunt by sight, contain symbiotic bacteria in the ’bait’ on their ’fishing rods’. These emit light to attract prey.
While many animals are unable to synthesize carotene pigments to create red and yellow surfaces, the green and blue colors of bird feathers and insect carapaces are usually not produced by pigments at all, but by structural coloration. Structural coloration means the production of color by microscopically-structured surfaces fine enough to interfere with visible light, sometimes in combination with pigments: for example, peacock tail feathers are pigmented brown, but their structure makes them appear blue, turquoise and green. Structural coloration can produce the most brilliant colors, often iridescent. For example, the blue green gloss on the plumage of birds such as ducks, and the purple blue green red colors of many beetles and butterflies are created by structural coloration. Animals use several methods to produce structural color, as described in the table.
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