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lesya [120]
3 years ago
8

You walk outside on a sunny day and have to squint until you put sunglasses on. What is the stimulus that causes the response of

squinting? the outside temperature the bright sunlight the surrounding air
Biology
1 answer:
-Dominant- [34]3 years ago
6 0

Answer:

The correct answer is: the bright sunlight.

Explanation:

The bright sunlight on a sunny day is the stimulus that causes the response of squinting, which is necessary for us to protect our eyes from different conditions that can be caused by extreme sun exposure.

This stimulus is transmitted to the Central Nervous System by sensory neurons, so the information can be processed in the brain and the response to squint our eyes to receive less light can be performed by the orbicularis oculi muscle (the one that closes the eyelids).

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Consider a species of sparrow that originally lived only in Alaska but recently expanded its range through North America, then C
Shtirlitz [24]

Answer:

North America is the one with the highest heterozygosity frequency for most loci, followed by Central America, and finally, South America with the lowest heterozygosity level.  

Explanation:

Some different forces or mechanisms might alter H-W equilibrium and lead to evolution, such as mutation, natural selection, migration, and genetic drift.

In the exposed example, we have a species of sparrow that migrates from Alaska to North America. Migration is unidirectional, which means that the movement occurs in only one direction: from Alaska to North America. We should also consider that the first immigrants colonized the area for the first time, meaning that there was not a receiving population of the same species already established. Finally, we need to consider that Alaska´s environmental conditions are very different from North America´s environmental conditions.

When a species arrives at a new place, it needs to adapt. The establishment and dispersion of the species in the new area depend on previous adaptation. So, when the firsts sparrow individuals arrived in North America, they faced new environmental conditions that acted as selective pressures that drove to the occurrence of mutations. A mutation implicates a stable and inheritable change in the genetic material. A mutation introduces changes, new alleles in the population, variability. But mutation rates are very low and have no evolutive direction, so they need another force to increase or decrease the mutant allelic frequencies. Natural selection benefits new advantageous alleles and transmits them to new generations changing their relative frequencies. <em>So, sparrows arrive in North America, mutated, and natural selection favored the beneficial mutations leading to a better adaptation to the environment.</em> This means that the heterozygosity level in this new recent population is very high.

As animals adapt to the new habitat and have better dispersal genes, they get to disperse even more. So they start new migration south, to Central America and South America. Again, they are moving to new regions with new conditions, and to establish they need to suffer new adaptations. But remember that we are talking about a recent event in time. Probably the animals migrating south are just a few.  They have not spent enough time yet in the new area, to adapt to the new environment and to include new genes into their population. What is even more, as they are a small new population moving south, they are more vulnerable to genetic drift events. Genetic drift acts on a population decreasing the variability between individuals, hence, decreasing the heterozygosity. <em>This small population suffers low mutation, has not enough time to establish, and is more vulnerable to genetic drift events.</em> The heterozygosity level is probably inferior to North America´s one.

Comparing the three areas, we could say that North America is the one with the highest heterozygosity frequency, followed by Central America, and finally, South America with the lowest level of heterozygosity.

8 0
2 years ago
what is the characteristic of a cell membrane that controls which substances can enter and exit the cell
lorasvet [3.4K]

Answer:

selective permeability

Explanation:

The property or characteristic of cellular membrane to allow certain substances to pass through the cell is known as selective permeability. The movement of molecules and ions across the cell can be active or passive.

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Answer:

I believe the answer is a single bacteria cell.

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