Problem 13 - Biology Today and Tomorrow with Physiology

Question

Birds and placental mammals ______. a. are ectotherms b. lay eggs c. have mammary glands d. have a four-chambered heart

Step-by-Step Solution

Answer

Birds and placental mammals both have a four-chambered heart (option d).

Step 1: Understanding the Terms

First, let's understand what each term means in the context of birds and placental mammals. Both groups are endotherms, not ectotherms, meaning they regulate their body temperature internally rather than relying on the environment. Many birds lay eggs, while placental mammals typically give birth to live young. Mammary glands are specific to mammals for feeding milk to their young, which birds do not have. However, a four-chambered heart is present in both birds and placental mammals, separating oxygen-rich blood from oxygen-poor blood for efficient circulation.

Step 2: Evaluating Each Option

Now, let's evaluate each option: - Option (a) 'are ectotherms' is incorrect as both are endotherms. - Option (b) 'lay eggs' is incorrect because only birds lay eggs, while placental mammals do not. - Option (c) 'have mammary glands' is incorrect since only mammals have these glands, not birds. - Option (d) 'have a four-chambered heart' is correct because both birds and placental mammals share this cardiovascular feature.

Step 3: Choosing the Correct Answer

Based on the evaluations, the correct choice is option (d) 'have a four-chambered heart'. This is the common feature that both birds and placental mammals share.

Key Concepts

Endothermy

Endothermy refers to the ability of an organism to regulate its body temperature internally, rather than relying on external environmental temperatures. This trait is vital for maintaining a stable temperature that supports high metabolic and activity levels. Animals that are endothermic can remain active in a broader range of environmental conditions.

• Both birds and placental mammals are endotherms. They generate heat through metabolic processes to maintain a constant body temperature, usually higher than that of their surroundings.
• This characteristic differentiates them from ectotherms, like reptiles and amphibians, which depend on external heat sources.

Being endothermic has allowed birds and mammals to exploit a wide range of habitats and adapt to various climates.

Egg-laying vs Live Birth

A significant distinction between birds and placental mammals is their method of reproduction. Birds are oviparous, meaning they lay eggs.

• The eggs are typically incubated outside the body until hatching.
• This method ensures that offspring development occurs while the mother continues her regular activities.

On the other hand, placental mammals are known for viviparity, or giving birth to live young.

• In these species, the developing embryos are nourished inside the mother’s body through the placenta until birth.
• This method provides a protective environment and continuous nourishment for the young, increasing their survival chances.

These reproductive strategies reflect adaptations to diverse ecological niches.

Mammary Glands

Mammary glands are specialized organs in mammals used to produce milk, a process known as lactation. This adaptation provides a significant evolutionary advantage.

• Mammary glands are exclusive to mammals and facilitate feeding the young after birth.
• Milk is rich in nutrients necessary for the growth and development of the newborn.
• The presence of mammary glands enables mammals to supply a consistent food source regardless of environmental conditions.

This feature is absent in birds, which instead use methods like regurgitation to feed their young.

Four-Chambered Heart

Both birds and placental mammals possess a four-chambered heart, a feature that allows for highly efficient circulation of blood. This cardiovascular adaptation consists of two atria and two ventricles.

• It effectively separates oxygen-rich blood from oxygen-poor blood, improving oxygen delivery to cells and tissues.
• This separation helps sustain the high energy demands of endothermy.
• A four-chambered heart supports active lifestyles and rapid response to environmental challenges.

This sophisticated organ system has evolved independently in birds and mammals, reflecting convergent evolution aimed at optimizing circulatory function.