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! :-)
