AP Biology : Understanding Muscle Cells

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #556 : Cellular Biology

Which of the following characteristics of smooth muscle is false?

Possible Answers:

Smooth muscle is striated

Smooth muscle is moved via involuntary movement

Smooth muscle cells have a single, central corkscrew nucleus

All choices reflect true characteristics of smooth muscle

Correct answer:

Smooth muscle is striated

Explanation:

Smooth muscle is used for numerous involuntary actions of the body. It is not striated and has a single, central corkscrew nucleus.

Example Question #557 : Cellular Biology

Which of the following characteristics of skeletal muscle is false?

Possible Answers:

Skeletal muscles are moved by the body voluntarily

Skeletal muscle cells have multiple nuclei

All of the choices reflect true characteristics of skeletal muscle

Skeletal muscle is striated

Correct answer:

All of the choices reflect true characteristics of skeletal muscle

Explanation:

Skeletal muscles are used for voluntary movement of the body. They are striated and have multiple nuclei at the periphery of each cell.

Example Question #558 : Cellular Biology

Which of the following characteristics of cardiac muscle is false?

Possible Answers:

Cardiac muscle is controlled by voluntary movements

Cardiac muscle is striated

All answer choices reflect true characteristics of cardiac muscle

Cardiac muscle cells have a single nucleus

Correct answer:

Cardiac muscle is controlled by voluntary movements

Explanation:

Cardiac muscle is used for involuntary contractions of the heart, allowing for the movement of blood. Cardiac muscles are striated and have a single, central nucleus in each cell.

Example Question #559 : Cellular Biology

The basic contractile unit of a muscle is known as a __________.

Possible Answers:

Myofibril

Muscle fiber

Bundle

Sarcomere

Correct answer:

Sarcomere

Explanation:

Sarcomeres represent the basic contractile unit of the muscle and can be used to show the process of contraction. Numerous sarcomeres make up myofibril, which combine to form a muscle fiber (myocyte), which combine to form a fasciculus, which combine to form muscle.

Example Question #560 : Cellular Biology

Which of the muscle types is controlled by voluntary motion?

Possible Answers:

Cardiac muscle

Smooth muscle

Skeletal muscle

Connective muscle

Correct answer:

Skeletal muscle

Explanation:

Skeletal muscle is attached to bones by tendons, allowing you to move around. These are the muscles that you can consciously control.

Smooth muscle and cardiac muscle are not controlled consciously. You cannot consciously control your heart beat or your blood vessels constriction.

Example Question #1 : Understanding Muscle Cells

The body constantly secretes saliva into the mouth. Muscular contractions eliminate the accumulated saliva by passing it down the throat and into the stomach. Even when an acrobat is hanging upside down, their body is able to counter-act gravity and move the saliva toward the stomach.

Which of the three muscle types controls the muscles in your throat involved in swallowing?

Possible Answers:

Smooth muscle

Smooth muscle and skeletal muscle

Skeletal muscle

Neither smooth muscle, nor skeletal muscle

Correct answer:

Smooth muscle and skeletal muscle

Explanation:

Swallowing involves both skeletal muscle and smooth muscle. While skeletal muscle is voluntary (somatic), smooth muscle is involuntary (autonomic). Swallowing involves both of these systems. One can voluntarily induce swallowing, but will also swallow involuntarily, such as while sleeping.

Most of the muscles in the esophagus are smooth muscle; these will be the muscles largely responsible for counter-acting gravity in the example. The upper region of the esophagus (the pharynx) and the tongue are composed of skeletal muscle, allowing us to induce the swallowing motion voluntarily.

Example Question #2 : Understanding Muscle Cells

What is the functional unit of a muscle cell?

Possible Answers:

Sarcoplasm

Sarcomere

Muscle belly

Sarcolemma

Endomysium

Correct answer:

Sarcomere

Explanation:

A muscle consists of millions of tiny subunits called sarcomeres. This is the functional unit of the muscle cell responsible for shortening and causing contractile force. Sarcomeres combine to form myofibrils, which form together to become a single muscle fiber, or muscle cell. Multiple muscle fibers form a muscle belly, the macrostructure of the muscle.

Example Question #3 : Understanding Muscle Cells

What is the scientific term for a muscle cell?

Possible Answers:

Acanthocyte

Melanocyte

Astrocyte

Sarcomere

Myocyte

Correct answer:

Myocyte

Explanation:

Muscle cells are called myocytes. "Myo" is a prefix for anything related to muscles. Terms such as myoblasts and myogenesis are related to muscle cells. "Cyte" means cell, and therefore "myo" and "cyte" means "muscle cell."

Melanocytes are found in the skin, and are responsible for producing the pigment melanin. Astrocytes are glial cells in the nervous system that create the blood-brain barrier. Acanthocytes are abnormal red blood cells that have become damaged, resulting in a change in their appearance.

Sarcomeres are not cells; they are a structure found in myocytes. Sarcomeres are composed of actin and myosin filaments, and are the fundamental contractile unit of the muscle fiber.

Example Question #4 : Understanding Muscle Cells

Calcium ions are necessary for the formation of cross-bridges between the myosin head of the thick filament and the actin subunits of the thin filament. In order to end cross-bridge cycling calcium ions must follow which of the listed processes?

Possible Answers:

Return to the blood via ribosomal transport

Return to the sarcoplasmic reticulum via active transport

Return to the sarcoplasmic reticulum via ribosomal transport

Return to the extracellular space via active transport

Correct answer:

Return to the sarcoplasmic reticulum via active transport

Explanation:

Calcium ions facilitate the translocation of the troponin-tropomyosin complex, which inhibits cross-bridge formation between the myosin head (thick filament) and actin (thin filament). In order to inhibit muscle contraction, the troponin-tropomyosin must slide back into its original position, thereby inhibiting physical and chemical contact between the thick and thin filaments. In order to accomplish this, the calcium ions must be actively pumped out of the cytoplasm and into the sarcoplasmic reticulum (SR). It is important to remember that in a muscle fiber, the SR acts as a reservoir to store calcium ions. In order for them to be stored in a concentration greater than that in the cytoplasm, active transport must be involved to pump the ions against their gradient.

Example Question #9 : Understanding Muscle Cells

What ultimately allows muscle contraction to occur?

Possible Answers:

Release of calcium ions from the sarcoplasmic reticulum 

Hydrolysis of ATP by actin

Hydrolysis of GTP

Degradation of troponin

Correct answer:

Release of calcium ions from the sarcoplasmic reticulum 

Explanation:

In order for muscle contraction to occur, myosin binding sites must be exposed on actin filaments. This is accomplished by releasing calcium ions from the sarcoplasmic reticulum. Calcium interacts with troponin, which in turn allows the myosin binding site to be exposed via interaction with tropomyosin. Troponin is not degraded during this process, only used to move tropomyosin out of the way. Myosin can then bind actin, hydrolyze ATP, and begin contraction.

GTP is not involved in the process and actin does not have an ATPase function.

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