21.3B Text B

What is the primary characteristic that distinguishes cardiac muscle from skeletal muscle?

• Cardiac muscle has multiple nuclei
• Cardiac muscle can contract without nervous system stimulation
• Cardiac muscle is not striated
• Cardiac muscle is larger in size

Which protein interaction is essential for muscle contraction?

• Melanin and keratin
• Myosin and actin
• Sarcomere and nucleus
• Epidermis and dermis

The sliding-filament model of muscle contraction involves:

• Permanent bonds between proteins
• Random movement of muscle fibers
• Cross-bridges forming and detaching repeatedly
• Direct nervous system control

Why can humans both push and pull with their muscles?

• Because muscles can stretch infinitely
• Because muscles work in opposing pairs
• Because muscles have multiple nuclei
• Because muscles contain melanin

What is the main function of melanin in the skin?

• Produces vitamin D
• Regulates body temperature
• Protects against ultraviolet radiation
• Removes waste products

Which layer of skin contains blood vessels and nerve endings?

• Epidermis
• Dermis
• Hypodermis
• Outer layer

How do blood vessels in the dermis help regulate body temperature?

• By producing sweat
• By generating melanin
• By widening and narrowing
• By creating new cells

What is the primary component of human hair and nails?

• Melanin
• Actin
• Myosin
• Keratin

The endocrine system primarily functions by:

• Producing and releasing hormones
• Generating muscle contractions
• Creating new blood cells
• Forming protective barriers

Where do most endocrine glands release their hormones?

• Into the lymphatic system
• Directly into organs
• Into the blood
• Into the nervous system