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.
I believe its false. I Thought it was time over distance
Answer:
Spider has a circulatory system
Answer:
A callus is a hardening of skin, keratin is the protein which is abundant in callus. Skin is a protective layer against a external environment. Outer layer of skin consist of keratin which is also found in hair. Callus is the accumulation of dead cells result due to friction and pressure exerts on the part in which they are present. The keratin component (keratinocytes) remains undifferentiated in these dead cells which causes hardening in callus.
I believe the answer is D. Earthworms.
