Answer:
The food web provides a better model of an ecosystem because the food web is a model between MANY different consumers and producers in an ecosystem.
Explanation
While the food chain is a model for just one consumer and producer. energy moves up a food chain.
Answer:
Your heart changes its rate depending on the activity, so that it can carry blood to your muscles, and therefore it needs to beat stronger if you are performing some exercise, or not so strong if you are sleeping, for example.
Explanation:
Your heart is continuously beating to keep blood circulating throughout your body.
So, here it is why your heart changes its rate: Its rate changes depending on your activity level; it is lower while you are asleep and at rest and higher while you exercise to supply your muscles with enough freshly oxygenated blood to keep the functioning at a high level.
And how: depending on your activity level, your heart has to pump enough blood to your muscles. Blood carries needed oxygen and other nutrients. Muscles need more blood sugar than any other tissue especially when working hard. To supply your muscles with oxygen your heart needs to beat faster, and this builds up your heart muscles.
Answer:
C
Explanation:
Nuclear fusion is the process by which the Sun produces its energy. It converts mass into energy, which is radiated over most of our solar system. The pressure from the fusion reactions keeps the star from collapsing.
Without the Sun's energy, in the amount we receive, the Earth would likely be entirely frozen and beyond deathly cold. Take Pluto as an example :)
