The correct answer is D. Cell Membrane because the cell membrane contains two phospholipid layers with the protein molecules attached to them throughout.
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Answer:
The main function of viagra is to relax the muscles of the blood vessels in some areas of the body. It is used for the treatment of erectile dysfunction and for high blood pressure. The component of viagra is a competitor to the enzyme PDE5, breaking down cGMP. In the penis, blood is trapped, which results in the erection being maintained. When cGMP levels decrease, the concentration of calcium ions increases, causing smooth muscle contraction.
Explanation:
I think it's fight or flight
Answer:
Explanation:
Domain. A domain is the most inclusive of the levels (meaning it has the most number of individuals in the group).
Human skin pigmentation is the product of two clines produced by natural selection to adjust levels of constitutive pigmentation to levels of UV radiation (UVR). One cline was generated by high UVR near the equator and led to the evolution of dark, photoprotective, eumelanin-rich pigmentation. The other was produced by the requirement for UVB photons to sustain cutaneous photosynthesis of vitamin D3 in low-UVB environments, and resulted in the evolution of depigmented skin. As hominins dispersed outside of the tropics, they experienced different intensities and seasonal mixtures of UVA and UVB. Extreme UVA throughout the year and two equinoctial peaks of UVB prevail within the tropics. Under these conditions, the primary selective pressure was to protect folate by maintaining dark pigmentation. Photolysis of folate and its main serum form of 5-methylhydrofolate is caused by UVR and by reactive oxygen species generated by UVA. Competition for folate between the needs for cell division, DNA repair, and melanogenesis is severe under stressful, high-UVR conditions and is exacerbated by dietary insufficiency. Outside of tropical latitudes, UVB levels are generally low and peak only once during the year. The populations exhibiting maximally depigmented skin are those inhabiting environments with the lowest annual and summer peak levels of UVB. Development of facultative pigmentation (tanning) was important to populations settling between roughly 23° and 46° , where levels of UVB varied strongly according to season. Depigmented and tannable skin evolved numerous times in hominin evolution via independent genetic pathways under positive selection.
<span>folatevitamin DmelanintanningUVB</span>
