1. Explain how muscles work in pairs in moving limbs.

Because one muscle move your limb one way and the other muscle move it to the other way because the muscles can only pull and not push. The muscles work in opposite ways for example when one contracts the other one relax

2. Identify the structures that make up a skeletal muscle. Include these terms: muscle fiber, fascicle, myofibrils, actin, myosin, sarcomere.

The skeletal muscle is made up of muscle fibers which contain nuclei and the nuclei contains myofibrils. The unit of muscle fibers are sarcomeres that are made up of myosin (thick) and actin (thin).

3. Identify at least 3 organ systems involved in a handshake. Describe WHAT each system contributes to the handshake.

In the handshake involves first the skeletal system because without it you cannot put your hand in shape so you can shape your hand the way you want, second you use the muscles to move your hand and third the nervous system so you can feel the other person hand.

4. Explain how actin and myosin interact as a muscle cell contracts.

They help in muscle contraction because myosin attaches to actin, then the actin moves to the sarcomere and then the ATP attaches to the myosin and then because of this reaction the myosin and the actin separate. The myosin then would pull the filaments and they would overlap, the sarcomere becomes shorter and that cause the muscle cells to contract