Answer:
The correct answer is b. He determined that DNA contains four nitrogenous bases.
Explanation:
Levene was an American biochemist who studied the structure of DNA in the early 1900s and in 1920 he found that DNA consists of four nitrogenous bases that are Adenine, Guanine, Thymine, Cytosine.
He also found deoxyribose sugar and phosphate group and said that nucleotide is the basic unit of DNA which contains a ribose sugar with attached nitrogenous base and phosphate group.
He also concludes that an equal amount of adenine, guanine, thymine, and cytosine makes the DNA which is now known as tetranucleotide hypothesis. So the correct answer is b. He determined that DNA contains four nitrogenous bases.
Answer:
Among others, two adaptations might be
- Avoiding corporal heat loss
- Increasing oxygen absorption
Explanation:
Up in the mountains, there is low oxygen, food is scarce, and adverse meteorological conditions. Animals and plants need to develop different strategies to survive. These adaptations involve not only physical and physiological changes but also behavioral changes. To mention a few adaptations, we can name:
- Avoiding heat loss. Temperature tends to be very low at highs, so, to <u>avoid heat loss,</u> animals develop shorter legs, tails, and ears. By doing this they reduce the area or surface of heat loss and also avoid getting frozen. In mammals, the coat is also very important. A thick coat helps them maintain a constant body temperature and keep warm. Some amphibians might also develop a thicker skin as they can not regulate their temperature, and it also helps them not to dehydrate.
- Camouflage: Coat is also helpful in camouflaging. Mammals´ hair color depends on their environment. Some animals, such as hares, can also change their fur color depending on the season. During snow seasons they turn white, and during the warmer season, they turn yellow or brown.
- Size and metabolism: Small mammals lose heat very fast, so they need to keep active and feeding most of the time. They have an elevated metabolism to keep warm. On the contrary, big animals, such as bears, need to hibernate to reduce their metabolism and get to survive, otherwise, they would need many reserves to cover their energetic requirements.
- Oxygen absorption: Some animals have adapted to the lack of oxygen by increasing their heart and lungs capacity as well as their capability to absorbing more oxygen from the blood.
Answer:
Metamorphic rocks are changed by the heat and pressure inside Earth.
Explanation:
Es | HIV.gov
There is currently no vaccine available that will prevent HIV infection or treat those who have it. However, scientists are working to develop one.
<h2>Vasa recta </h2>
Explanation:
The vasa recta is a specialized capillary that branches from the efferent arteriole; The blood flow in the vasa recta runs parallel, but in the opposite direction to the flow of tubular filtrate within the nephron loop
- The vasa recta capillaries are long, hairpin-shaped blood vessels that run parallel to the loops of Henle
- The hairpin turns slow the rate of blood flow, which helps maintain the osmotic gradient required for water reabsorption
- Absorbed water is returned to the circulatory system via the vasa recta, which surrounds the tips of the loops of Henle
- Because the blood flow through these capillaries is very slow, any solutes that are reabsorbed into the bloodstream have time to diffuse back into the interstitial fluid, which maintains the solute concentration gradient in the medulla; this passive process is known as counter-current exchange
