BIOLOGY

• Coevolution is the joint evolution of two unrelated species that have a close ecological relationship, where the evolution of one species depends in part on the evolution of the other.
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• Some herbivores are able to breach these defenses and attack the plant.
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• Plants have acquired defensive mechanisms such as thorns, spines, hard seed-coats, and poisonous or ill-tasting sap that deter would-be consumers.
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• Certain insects, such as the monarch butterfly, can incorporate poisonous substances found in food plants into their own tissues and use them as a defense against predators.
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• Coevolution is also involved in predator-prey relations, where over time, as predators evolve more efficient ways of capturing or consuming prey, the prey evolves ways to escape predation.
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• Commensalism is an association between two different kinds of nonparasitic animals, called commensals, that is harmless to both and in which one of the organism benefits.
• Predation is the consumption of one living organism, plant or animal, by another, serving to move energy and nutrients through the ecosystem, but it may also regulate population and promote natural selection by weeding the unfit from a population.
• In some communities, predators may so reduce populations of prey species that a number of competing species can coexist in the same area because none is abundant enough to control the resource.
• Parasites include viruses and bacteria that cause many diseases; certain protozoans that can infect plants and animals; tapeworms and flukes that infest the intestinal tracks and internal organs of animals; and external parasites such as lice and ticks.
• Commensalism is most common among marine invertebrates, but it often occurs among land animals, such as in the association of ants with other insects like aphids and beetles.
• When predators are reduced or removed, the dominant species tend to crowd out other competitors, thereby reducing species diversity.
• Many commensals are free to separate, while others function together so completely that they cannot separate.
• A rabbit is a predator on grass, just as the fox is a predator on the rabbit.
• Predation on plants involves defoliation by grazers and the consumption of seeds and fruits.
• Predator-prey interactions at one feeding level influence the predator-prey relations at the next feeding level.
• Parasitism, also known as antagonistic symbiosis, is an association between two organisms where one organism receives no benefits and is often injured while supplying nutrients or shelter for the other organism.
• The association of colon bacteria with humans and other animals, especially plant-eating animals, is also a type of commensalism.
• There are also parasitic plants like mistletoe that draw their nourishment from the branches of other plants.
• The abundance of plant predators, or herbivores, directly influences the growth and survival of the carnivores.
• Competition occurs when a shared resource is in short supply, and organisms compete, with the more successful surviving.
• Sperm pass through a long duct called the vas deferens to the seminal vesicles, a pair of sacs that lies behind the bladder.
• These sacs produce seminal fluid, which mixes with sperm to produce semen.
• Ovulation, the release of an egg into the uterus, occurs approximately every 28 days; during the same period the uterus is prepared for the implantation of a fertilized ovum by the action of estrogens.
• After childbirth, prolactin, a hormone secreted by the pituitary, activates the production of milk.
• Reproduction is accomplished by the union of male sperm and the female ovum.
• Leading away from the ovaries are the fallopian tubes, or oviducts, the site of fertilization.
• The organs of the male reproductive system enable a man to have sexual intercourse and to fertilize female sex cells (eggs) with sperm.
• The pituitary secretes hormones that control the activity of other endocrine glands and regulate various biological processes.
• In coitus, the male organ ejaculates more than 250 million sperm into the vagina, from which some make their way to the uterus.
• During male orgasm the penis ejaculates semen.
• If a male cell fails to unite with a female cell, other hormones cause the uterine wall to slough off during menstruation.
• The gonads, called testicles, produce sperm.