Answer:
If semen gets in the vagina, the sperm cells can swim up through the cervix and uterus and into the fallopian tubes, looking for an egg. They have up to 6 days to find an egg before they die. When a sperm cell joins with an egg, it's called fertilization. Fertilization doesn't happen right away.
Explanation:
This is how reproduction works.
Answer:
Higher levels of organization are built from lower levels. Therefore, molecules combine to form cells, cells combine to form tissues, tissues combine to form organs, organs combine to form organ systems, and organ systems combine to form organisms.
Explanation:
The nervous system takes in information through our senses, processes the information and triggers reactions, such as making your muscles move or causing you to feel pain. For example, if you touch a hot plate, you reflexively pull back your hand and your nerves simultaneously send pain signals to your brain.
Answer:
Subtract your heart's resting rate from your maximum rate. For example, if you are 40 years old, subtract that number from 220; your maximum rate is 180. Next, subtract your resting rate or 80 in this example. Your heart-rate reserve is 100 beats per minute.
