Lets look at your first question. A food chain is a linear (line) relationship between organisms. It shows who eats what and who gets eaten. The energy is passed up the chain from one organisms to the next. A food web is a series of interconnected food chains. It can show one organism being preyed upon by several predators. The answer choice A is really referring to an energy pyramid, but it is true in any ecosystem that only 10% of available energy is passed to the next trophic level. B and C are both true statements as well. D is completely false because 90% of energy is lost, not retained. So with that said, there is more than one correct answer here. I have included a diagram so you can see the difference between the two.
For Question 8, the key to understanding this is that sunlight is the main source of energy for any ecosystem. Plants (autotrophs) use the sunlight to convert it to sugars (glucose) which is a compound that heterotrophs can utilize. This process is called photosynthesis. :-)
Question 9: So in a food chain, you typically start with the producers (plants), then to the primary consumer, then secondary consumer, then tertiary consumer, and in some cases you may have a quaternary consumer. That is 4 links. However, we are forgetting the role of decomposers at all levels of this food chain, and that would add an extra link. In summary, you wouldn't typically see more than 5 links in a food chain.
I hope all of my explanations are helpful! Good luck! :-)
<span>Active transport works to conserve homeostasis. When cells are doing something they typically receive a signal causing channels to open, which in turn lets in a flood of molecules down their chemical gradients. Hope this answers the question.</span>
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.