Problem 12 - Biology Today and Tomorrow with Physiology

Question

No animal cell has a ______. a. plasma membrane b. flagellum c. nucleic acids d. hormones

Step-by-Step Solution

Answer

No animal cell has a flagellum.

Step 1: Understanding the Options

Let's understand what each option represents: - Option a: Plasma membrane is the boundary that separates the interior of all cells from the outside environment. - Option b: Flagellum is a whip-like structure that allows a cell to move. - Option c: Nucleic acids are biomolecules essential for all forms of life, including DNA and RNA. - Option d: Hormones are signaling molecules produced by glands in multicellular organisms to regulate physiology and behavior.

Step 2: Analyzing Animal Cells

Analyze what animal cells typically have: - Animal cells have a plasma membrane, which is essential for protecting the cell and controlling what enters and exits. - Some animal cells (like sperm cells) have a flagellum for movement. - Animal cells contain nucleic acids (DNA in the nucleus, RNA in various parts). - Animal cells can produce and respond to hormones, which are critical for the regulation of biological processes.

Step 3: Identifying What's Missing

Determine which of the options is not typically part of an animal cell: Based on our analysis: - Plasma membranes are present. - Flagella can be present in certain animal cells, like sperm. - Nucleic acids are present in all animal cells. - Hormones are part of many processes in animal cells, but they are not structural or inherent parts of individual cells.

Key Concepts

Plasma Membrane

The plasma membrane serves as the boundary between the cell's interior and its external environment. It plays a critical role in protecting the cell and maintaining its integrity. This thin, flexible barrier is composed of a bilayer of lipids, interspersed with proteins that contribute to various functions.

• Selective Permeability: The plasma membrane controls what substances can enter and leave the cell, allowing only specific substances to pass through.
• Cell Communication: Embedded proteins in the plasma membrane help in communicating signals from the outside to the inside of the cell.

These functions are essential for the cell's survival and its ability to interact with its environment.

Flagellum

Flagella are whip-like structures that provide motility to certain cells. In the animal kingdom, flagella are most commonly associated with the movement of sperm cells. Their structure is particularly interesting due to the way they assist in movement.

• Structure: Flagella are made up of a protein called flagellin. They are supported by a complex arrangement of microtubules.
• Function: By whipping back and forth, flagella propel cells forward, allowing for movement in fluid environments.

While not all animal cells possess a flagellum, it is crucial for the reproductive processes of animals.

Nucleic Acids

Nucleic acids are biomolecules that store and transmit genetic information. They are critical for coding the instructions crucial for individual cell functions and overall organism growth and maintenance. There are two primary types of nucleic acids: DNA and RNA.

• DNA (Deoxyribonucleic Acid): DNA resides in the nucleus and carries the instructions for the development, function, growth, and reproduction of all living organisms.
• RNA (Ribonucleic Acid): RNA plays a key role in the manufacture of proteins, transferring the genetic code from the DNA to the ribosomes where proteins are synthesized.

These molecules are found in all animal cells, highlighting their universal and fundamental importance to life.

Hormones

Hormones are vital chemical messengers within an organism that regulate a wide array of bodily functions. Produced by glands, they travel through the bloodstream to target organs and tissues, exerting influence over numerous physiological activities.

• Regulatory Role: Hormones are involved in processes like metabolism, growth, and mood regulation.
• Response Mechanism: Cells respond to hormones through specific receptor proteins, initiating a cellular response that can lead to changes in cell function.

While hormones themselves are not part of the structural components of an animal cell, their impact on cell behavior is profound and crucial in maintaining homeostasis within the organism.