Question

Which of the following statements about movement and locomotion is false? a. Terrestrial animals and flying animals expend energy to provide lift. b. Swimming animals typically expend energy to provide thrust but not lift. c. Flexors and extensors are examples of muscles called agonists. d. Flexors cause bending at a joint. e. Extensors cause straightening of a limb.

Short answer

The false statement is: Flexors and extensors are examples of muscles called agonists.

Step-by-step solution

Analyse the Statements Regarding Active Lift

The first statement claims that terrestrial and flying animals expend energy to provide lift. This is true because flight requires lift to overcome gravity, and climbing or leaping terrestrial animals also use energy to 'lift' their body mass against gravity. The second statement asserts that swimming animals usually use energy for thrust, but not lift. This is also accurate as buoyancy typically aids swimming animals in maintaining their depth, so they focus their energy on forward propulsion or thrust.

Evaluate the Claims about Muscular Action

The third statement designates flexors and extensors as examples of agonist muscles. While it is true that flexor and extensor muscles work in opposition, they are not both agonists—instead, one acts as the agonist and the other as the antagonist during motion. Therefore, this statement is false. The fourth and fifth statements correctly identify the actions of flexor and extensor muscles, respectively—flexors facilitate joint bending, while extensors aid in limb straightening.

Key concepts

Muscle Action

Muscle action is a fundamental aspect of animal movement. Every muscle is designed to either contract or relax, leading to motion. Muscles are composed of fibers that generate force when they contract, which is necessary for movement. In animals, these contractions allow for various activities such as running, flying, and even subtle movements like blinking. Understanding muscle action involves recognizing both the types and roles of muscles involved.

• Muscle contractions can be voluntary, like moving an arm, or involuntary, such as the heartbeat.
• Muscles work by pulling on bones, which act as levers, resulting in movement.

Muscles can only pull; they never push, which is why they often work in pairs. This leads us into the concept of agonist and antagonist muscles.

Lift and Thrust in Locomotion

To move efficiently, animals must overcome various forces like gravity and friction. Lift and thrust are essential components in this process. Flying animals, such as birds, must produce lift to counteract gravity. This lift is generated by their wings, which change the air pressure above and below, enabling flight. Thrust, on the other hand, propels them forward. In flying creatures, wing flapping or gliding aids in achieving thrust.

• Thrust in flying animals is usually a result of both muscle action and aerodynamic design of wings.
• For terrestrial animals, thrust is produced by the legs, pushing against the ground to move forward.

Swimmers focus more on thrust since the buoyancy helps with lift, making it less energy-intensive to stay afloat.

Agonist and Antagonist Muscles

Agonist and antagonist muscles work in pairs to facilitate movement in animals. This pairing is essential because each muscle in the pair has a distinct role during the motion of a limb.

• The agonist muscle is primarily responsible for a specific movement, contracting to initiate the motion.
• The antagonist muscle opposes this action, stretching and controlling the motion to provide balance.

For example, when bending the elbow, the bicep acts as the agonist by contracting, while the tricep serves as the antagonist, relaxing to allow the bending motion. This balancing act ensures smooth and controlled movements.

Buoyancy in Swimming Animals

Buoyancy is a crucial factor that aids swimming animals in maintaining their position in water. Unlike flying or terrestrial animals, swimmers don't need to expend as much energy on lift. This feature is particularly helpful as it allows these animals to focus more on thrust. Water has natural buoyant properties, which means it can naturally support the animal's weight. Most swimming animals have adapted features, such as flattened bodies and fins, to maximize the benefit of buoyancy.

• Buoyancy helps reduce the energy needed to stay afloat, allowing for more efficient movement through water.
• Thrust is then generated through the motion of fins, tails, or limbs, enabling forward motion.

Consequently, swimming animals can travel long distances with less energy expended on staying buoyant, freeing more resources for navigation and speed through the water.