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Sound is a type of energy made by vibration . How sound is produced Sound is produced when an object vibrates, creating a pressure wave . The loudness of a sound refers to how strong the sound seems to us when it reaches to our ears . The softness and loudness of sound is called volume . some sound may be too loud while other may be too soft . the volume of the sound depends on the strength of a vibration . when sound come in contact with different material like wall or carpets , they are reflected absorbed . some materials reflect sound and cause echoes , head surface like Flat concrete wall are good at reflecting sounds . Loudness is a measure of how strong a sound seems to us .if we apply greater force in an object we produce loud sounds .if we apply laser force in an object we produce soft sounds .

#ArtificialSelection #Biology #SelectiveBreeding Selective Breeding • Selective breeding means to select individuals with desirable characteristics and breed them together • The process doesn’t stop there though because it’s likely that not all of the offspring will show the characteristics you want so offspring that do show the desired characteristics are selected and bred together • This process has to be repeated for many successive generations before you can definitely say you have a ‘new breed’ which will reliably show those selected characteristics in all offspring Selective breeding in domesticated animals • An example of selective breeding is dog breeders who select which dogs can mate together to increase the likelihood of puppies displaying desirable characteristics eg. coat colour • This has given rise to the many recognisable dog breeds of today, all the same species (Canis familiaris) and all descended from one breed  Selective breeding in crop plants • Plants are selectively bred by humans for the development of many characteristics, including: • disease resistance in food crops • increased crop yield • hardiness to weather conditions (e.g. drought tolerance) • better tasting fruits • large or unusual flowers • An example of a plant that has been selectively bred in multiple ways is wild brassica, which has given rise to cauliflower, cabbage, broccoli, Brussels sprouts, kale and kohlrabi:

#NaturalSelection #Biology #VariationAndSelection Natural Selection • In any environment, the individuals that have the best adaptive features are the ones most likely to survive and reproduce • This results in natural selection: • Individuals in a species show a range of variation caused by differences in genes • When organisms reproduce, they produce more offspring than the environment is able to support • This leads to competition for food and other resources which results in a ‘struggle for survival’ • Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce • Therefore the alleles resulting in these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival • This means that in the next generation, there will be a greater number of individuals with the better adapted variations in characteristics • This theory of natural selection was put forward by Charles Darwin and became known as ‘survival of the fittest’ • Within the population of snails there is variation in shell colour • Normal varieties of shell colours in this snail species is black or grey (as evidenced by the first picture) • Chance mutations lead to a small number of snails / one snail having a white shell • This ‘small number’ is shown in the second diagram where there are less white shelled snails than black or grey shelled snails • The white shelled snail(s) survive longer • This is the ‘survival of the fittest’, a term used to explain why some organisms succeed in the competitive struggle for survival against other members of their population • The reason the white shelled snail(s) survive longer is because they are better camouflaged • This means that they are less likely to be seen by predators and eaten • As they survive longer they get more opportunities to reproduce • And so the allele for white shells is passed onto offspring more frequently than the alleles for black or grey shells • Over generations, this is repeated until the majority of snails in the population have white shells Adaptation by Natural Selection •  If the environment does not change, selection does not change • This will favour individuals with the same characteristics as their parents • If the environment changes, or a chance mutation produces a new allele, selection might now favour individuals with different characteristics or with the new allele • So the individuals that survive and reproduce will have a different set of alleles that they pass on to their offspring • Over time, this will bring about a change in the characteristics of the species - it will produce evolution • Evolution is defined as the change in adaptive features of a population over time as a result of natural selection • Natural selection results in a process of adaptation, which means that, over generations, those features that are better adapted to the environment become more common • This is how evolution occurs • This means populations of organisms become better suited to their environment • A good example of this is the development of antibiotic resistance by bacteria