Answer:
Mesopelagic zone
Explanation:
The Mesopelagic zone, also referred to as the Twilight zone, is the second oceanic zone from the top, lying just bellow the Epipelagic zone. It is occupying the waters at depths between 200 meters and 1,000 meters. The sunlight is only managing to reach the top few meters of this zone, while the rest is not receiving any sunlight, thus this zone is not supporting the plant species because they need sunlight for the process of photosynthesis. There are lot of animal species that live in this zone though, and they are ll very well adapted for it, often having hard shells or heavily scaled bodies, larger lungs and heart, and very well developed gills. Some of the animals that live in here are the crabs and the clams. They have developed all the needed characteristics to live in this zone. Because they are prey to lot of larger animals, both the crabs and the clams have started to use the soft sediments at the bottom as cover, digging themselves below it, and mostly managing to evade trouble and end up as food for the other species.
Natural selection is the process by which individuals with characteristics that are advantageous for reproduction in a specific environment leave more offspring in the next generation, thereby increasing the proportion of their genes in the population gene pool over time. Natural selection is the principal mechanism of evolutionary change, and is the most important idea in all biology. Natural selection, the unifying concept of life, was first proposed by Charles Darwin, and represents his single greatest contribution to science.
Natural selection occurs in any reproducing population faced with a changing or variable environment. The environment includes not only physical factors such as climate or terrain, but also living factors such as predators, prey, and other members of a population.
Mechanism of Natural Selection
The mechanism of natural selection depends on several phenomena:
• Heredity: Offspring inherit their traits from their parents, in the form of genes.
• Heritable individual variation: Members of a population have slight differences among them, whether in height, eyesight acuity, beak shape, rate of egg production, or other traits that may affect survival and reproduction. If a trait has a genetic basis, it can be passed on to offspring.
• Overproduction of offspring: In any given generation, populations tend to create more progeny than can survive to reproductive age.
• Competition for resources: Because of excess population, individuals must compete for food, nesting sites, mates, or other resources that affect their ability to successfully reproduce.
Given all these factors, natural selection unavoidably occurs. Those members of a population that reproduce the most will, by definition, leave more offspring for the next generation. These offspring inherit their parents' traits, and are therefore also likely to succeed in competition for resources (assuming the environment continues to pose the same challenges as those faced by parents). Over several generations, the proportion of offspring in a population that are descended from the successful ancestor

Uloborid spider eggs and spiderlings. In any given generation, populations tend to create more offspring than can survive to reproductive age.
increases, and traits that made the ancestor successful therefore also increase in frequency. Natural selection leads to adaptation, in which an organism's traits conform to the environment's conditions for existence.
There are all sorts of ways to reconstruct the history of life on Earth. Pinning down when specific events occurred is often tricky, though. For this, biologists depend mainly on dating the rocks in which fossils are found, and by looking at the “molecular clocks” in the DNA of living organisms.
There are problems with each of these methods. The fossil record is like a movie with most of the frames cut out. Because it is so incomplete, it can be difficult to establish exactly when particular evolutionary changes happened.
Modern genetics allows scientists to measure how different species are from each other at a molecular level, and thus to estimate how much time has passed since a single lineage split into different species. Confounding factors rack up for species that are very distantly related, making the earlier dates more uncertain.
These difficulties mean that the dates in the timeline should be taken as approximate. As a general rule, they become more uncertain the further back along the geological timescale we look. Dates that are very uncertain are marked with a question mark.
Answer:
Explanation:
Given that,
The mass of a sample, m = 16.7 grams
Volume of the sample, V = 4.4 cm³
We need to find the density of the metal sample.
Density = mass/volume
Substituting all the values,
So, the density of the metal sample is 
.
Phenotype - short , Tall
Genotype - tt (short) , TT or Tt (tall)
<u>Explanation:</u>
In Mendelian Genetics, <em>Dominant traits</em> are represented by capital letters and <em>Recessive traits</em> are represented by small letters.
So if height is the character considered, then the traits would be short and tall.
Tall is the dominant phenotype and short is the recessive phenotype.
The alleles of the gene for height are T and t.
The genotype for Tall trait is TT or Tt.
The genotype for short trait is tt.
Therefore, the symbol representation of phenotype (Tall) is TT or Tt and for phenotype (short) is tt.
