High School Biology : Musculoskeletal System

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Understanding Sliding Filament Theory

In sarcomeres, the thick filament is composed of which protein?

Possible Answers:

Actin

Myosin

Collagen

Titin

Correct answer:

Myosin

Explanation:

Sarcomeres are composed of thick and thin filaments. The thin filament is composed of polymerized actin, while the thick filament is composed of myosin. Titin is a protein that spans the full range of the sarcomere, and is involved in stability and elasticity in the muscle. Collagen is not a primary component of sarcomeres.

Example Question #1 : Understanding Sliding Filament Theory

Which statement is incorrect in describing sliding filament theory?

Possible Answers:

The actin filaments lengthen, while the myosin filaments shorten

The protein complex formed is classically named actomyosin and helps facilitate the "stroke" part of muscle contraction

Actin and myosin form a "crossbridge" when myosin binds to actin

The actin and myosin filaments slide past one another

Actin and myosin filaments stay the same size during contraction

Correct answer:

The actin filaments lengthen, while the myosin filaments shorten

Explanation:

The sliding filament theory describes the mechanism that allows muscles to contract. According to this theory, myosin (a motor protein) binds to actin. The myosin then alters its configuration, resulting in a "stroke" that pulls on the actin filament and causes it to slide across the myosin filament. The overall process shortens the sarcomere structure, but does not change the actual length of either filament.

Example Question #1 : Understanding Sliding Filament Theory

In order for muscle contraction to occur, what molecules/ions must be readily available?

Possible Answers:

ADP + Pi

GTP and chloride ions

NADPH and GADPH

Glycogen

Calcium ions and ATP

Correct answer:

Calcium ions and ATP

Explanation:

The correct answer is ATP and calcium ions. Myosin head activation to form a cross-bridge with actin requires ATP, and the cleavage of ATP to ADP + Pi contracts the myosin head and pulls the actin. Calcium is required to expose actin binding sites for myosin in conjunction with troponin. 

Example Question #1 : Understanding Sliding Filament Theory

Muscles require a supply of ATP in order to contract. What function is enabled by the release of energy from ATP?

Possible Answers:

Myosin bending to pull actin

Shortening of myosin

Myosin attaching to actin

Myosin attaching to the Z-disc

Myosin detaching from actin

Correct answer:

Myosin detaching from actin

Explanation:

In the sliding filament theory, myosin heads attach to an actin filament, bend to pull the actin filaments closer together, then release, reattach, and pull again. Energy from ATP is required for the myosin head to release from the actin filament—otherwise the myosin heads would remain in the same place, and the muscle would not contract. Even though the filaments are moving, the filaments themselves never actually get shorter or longer.

When ATP stores are depleted, myosin becomes incapable of detaching from actin, and the muscle remains in a taut, flexed state. This is the cause of rigor mortis.

Example Question #5 : Understanding Sliding Filament Theory

When is ATP required for muscles according to the sliding filament theory?

Possible Answers:

For the myosin heads to bind the actin

To perform the power stroke, where the myosin heads rotate toward the sarcomere

To perform the power stroke, where the myosin heads rotate away from the sarcomere

For the crossbridges to detach from the actin and eventually reorient the myosin heads.

For crossbridge formation

Correct answer:

For the crossbridges to detach from the actin and eventually reorient the myosin heads.

Explanation:

The myosin head will hydrolyze the . Being bound to ADP, this allows the myosin head to form crossbridges by binding to actin. As ADP detaches from the myosin head, the head will produce the power stroke motion, where the myosin heads will rotate toward the sarcomeres. The myosin head will be locked in this position, attached to the actin, until another ATP molecule comes and attaches to the myosin head. This will allow the head to detach from actin and reorient itself to complete the process again. 

Example Question #1 : Musculoskeletal System

Which bone cell is responsible for resorbing bone matrix and releasing calcium into the blood?

Possible Answers:

Osteogenic cells

Osteoclasts

Osteoblasts

Osteocytes

Correct answer:

Osteoclasts

Explanation:

Osteogenic cells are a type of stem cell that differentiate into osteoblasts, which allow bone to form. Eventually, osteoblasts will become enveloped into the bone matrix and differentiate into osteocytes. Osteoclasts have the opposite function of osteoblasts, and are responsible for the resorption of bone matrix. This releases calcium into the bloodstream by breaking down bone.

Example Question #1 : Understanding Bones

Which of the following is NOT a function of the skeletal system?

Possible Answers:

Supporting soft tissue

Generating heat

Blood cell production

Mineral storage

Correct answer:

Generating heat

Explanation:

The skeletal system has a variety of functions, including protecting internal organs, storing minerals and energy molecules, and assisting in movement.

The production of heat, however, is a function of the muscular system.

Example Question #1 : Musculoskeletal System

Red blood cell development takes place in what structure in bones?

Possible Answers:

Osteons

Cartilage

Yellow bone marrow

Red bone marrow

Correct answer:

Red bone marrow

Explanation:

Red bone marrow is found in the epiphyses, or ends of long bones. It is the site of hematopoiesis, or red blood cell development.

Yellow bone marrow is primarily composed of fat. Osteons are the functional units of bone, and house the cells that build and break down the bony matrix. Cartilage is found on the articular surfaces of bone, and helps provide support for joints.

Example Question #1 : Understanding Bones

Which of the following is a primary function of bone marrow?

Possible Answers:

Blood cell production

Mineral storage

Movement

Detoxification

Protection

Correct answer:

Blood cell production

Explanation:

Bone marrow is the major producer of blood cells, including most of those in the immune system.

The other answer options listed are functions of the bones in the skeletal system, but are not directly linked to the bone marrow. The skeletal system stores calcium and phosphorus, which in turn make the bones strong. Bones can complement to liver to detoxify blood by removing metals such as lead and radium. Muscles attach to bones and generate movement. The skull protects the brain. The rib cage protects the heart and lungs. 

Example Question #2 : Musculoskeletal System

Ligaments connect __________.

Possible Answers:

muscle to muscle

bone to muscle

muscle to tendon

bone to bone

muscle to muscle

Correct answer:

bone to bone

Explanation:

Ligaments are made of dense connective tissue and connect bone to bone. Have you ever sprained your ankle? Chances are you partially or fully tore some ligaments in your ankle. Unfortunately, ligaments do not heal very well since there is almost no blood supply to them, and instead lay down scar tissue. Tendons connect bone to muscle. Muscles are already attached to tendons.

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