Problem 10 - Campbell Biology Concepts & Connections

Question

Which of the following statements about skeletons is true? a. Chitin is a major component of vertebrate skeletons. b. Loss of forelimbs in snakes involved little change in the axial skeleton. c. Most cnidarians must shed their skeleton periodically to grow. d. Vertebrate bones contain living cells

Step-by-Step Solution

Answer

Statement 'd' is true: Vertebrate bones contain living cells.

Step 1: Understand the Question

Read the given statements about skeletons carefully. Determine what each statement implies about skeleton composition and growth.

Step 2: Analyze Statement a

Chitin is a major component of invertebrate exoskeletons, particularly in arthropods, not vertebrate skeletons. Therefore, statement 'a' is false.

Step 3: Analyze Statement b

The loss of forelimbs in snakes involved significant evolutionary changes in the axial skeleton. Therefore, statement 'b' is false.

Step 4: Analyze Statement c

Cnidarians, such as jellyfish, generally do not have skeletons that they need to shed periodically. Therefore, statement 'c' is false.

Step 5: Analyze Statement d

Vertebrate bones contain living cells, such as osteocytes, which are essential for bone maintenance and repair. Therefore, statement 'd' is true.

Step 6: Verify the Answer

Confirm that statement 'd' is indeed aligned with known biological facts about vertebrates and their skeletal structures.

Key Concepts

Vertebrate Skeleton

Vertebrate skeletons are internal frameworks that support the bodies of animals with backbones, like mammals, birds, reptiles, amphibians, and fish. These skeletons are primarily composed of bones and cartilage.
Bones are hard and rigid structures made primarily of calcium phosphate. They provide structural support and protection for vital organs. For instance, the rib cage protects the heart and lungs.
Cartilage, on the other hand, is a flexible yet sturdy tissue that reduces friction in joints and provides cushioning. Examples include the cartilage in your nose and ears.
Vertebrate skeletons also enable movement by acting as levers for muscles. Muscles are attached to bones, and when they contract, they move the bones, allowing actions like walking, jumping, or flying.

Invertebrate Exoskeleton

Invertebrates, such as insects, arachnids, and crustaceans, have exoskeletons instead of internal skeletons. An exoskeleton is a tough outer covering made primarily of a material called chitin.
Chitin is a polysaccharide, a type of carbohydrate that provides strength and protection. This rigid exterior serves as a support structure, helping to shape the body and protect internal organs.
Since exoskeletons cannot grow, invertebrates must shed them periodically in a process known as molting. After shedding, they produce a new, larger exoskeleton to accommodate growth.
Exoskeletons play a critical role in the survival of invertebrates by offering protection against predators and environmental hazards. Additionally, they provide points of connection for muscles, enabling movement.

Bone Cells

Vertebrate bones are not just static structures; they contain living cells essential for the bone's function and health. The main types of bone cells include:

• Osteocytes: These are mature bone cells embedded within the bone matrix. They help maintain bone tissue and communicate with other bone cells.


• Osteoblasts: These cells are responsible for forming new bone. They secrete the bone matrix and facilitate the mineralization process.


• Osteoclasts: These are large cells that break down bone tissue. They play a crucial role in bone remodeling, which allows bones to grow and adapt to new stresses.

Bone cells continuously remodel bone tissue to ensure it remains strong and functional. This process is vital for growth, healing, and adaptation to physical activity.

Evolutionary Biology

Evolutionary biology studies how organisms change over time through genetic variations and natural selection. The study of skeletons in both vertebrates and invertebrates provides significant insights into evolutionary processes.
For instance, the loss of forelimbs in snakes involved significant changes in their axial skeleton (the skeleton running along the body's central axis). These changes illustrate how species can evolve different structural adaptations for survival.
Similarly, the evolution of bone cells in vertebrates shows how complex internal structures have developed to support larger bodies and more active lifestyles.
Understanding evolutionary biology helps explain the diversity of life on Earth and how various adaptations, like skeletons, have allowed organisms to thrive in different environments.