Crossing over happens in prophase I when the homologous chromosomes are sy naps ed. The two inner chromoatids exchanges sections with each other. This means that after the exchange the inner two chromatids have new combinations of alleles than their parents had. The two outer chromatids still have the parental combinations.So there are more kinds of chromatids ready to go into the gametes than there were before. This is an increase in variation.
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The basic processes of life include organization, metabolism, responsiveness, movements, and reproduction. In humans, who represent the most complex form of life, there are additional requirements such as growth, differentiation, respiration, digestion, and excretion.
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The crust, mantle and inner core are defined by chemical composition
Parasitism is when one organism benefits at the cost of it's host. Like fleas on a dog or intestinal parasites to livestock. Fleas and intestinal worms get food and a nice place to livr, while the dogs and the livestock are being leeched off of and malnourished.
Commensalism is when one organism benefits, while the host is left unharmed- but also doesn't really get anything in return, unlike mutualism. Like a shark and remoras (those fish with suction-cup heads & hitchhike). Sharks aren't hurt, but the remoras get free transportation and access to food scraps.
Hope this helps!