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Chapter 4: Problem 23

What type of junctions prevent the movement of chemicals between two adjacent animal cells? a. desmosomes b. gap junctions c. plasmodesmata d. tight junctions

Short Answer

Expert verified
d. tight junctions

Step by step solution

01

Introduce the Question

The task is to identify the type of junctions that prevent the movement of chemicals between adjacent animal cells.
02

Understand the Types of Junctions

First, review different types of cell junctions: desmosomes, gap junctions, plasmodesmata, and tight junctions.
03

Describe Desmosomes

Desmosomes are adhesive junctions that help to mechanically link cells to one another, but they do not prevent movement of chemicals between cells.
04

Describe Gap Junctions

Gap junctions are channels that allow ions and small molecules to move between adjacent cells, facilitating communication but not preventing movement.
05

Describe Plasmodesmata

Plasmodesmata are channels between plant cells that allow molecules and ions to pass through, not found in animal cells and do not prevent movement in this context.
06

Describe Tight Junctions

Tight junctions create a seal between adjacent animal cells and prevent the movement of substances through the space between cells. This is the type of junctions that prevent the movement of chemicals between adjacent cells.
07

Conclusion

After analyzing all four types of junctions, tight junctions are the ones that prevent the movement of chemicals between two adjacent animal cells.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Desmosomes
Desmosomes are specialized structures that serve as anchoring junctions. They act like spot welds between adjacent animal cells, providing mechanical strength.
Desmosomes are made of protein complexes that include cadherins and cytoplasmic anchor proteins.
This junction type is critical in tissues that experience significant stress, such as the skin and heart. Although desmosomes are essential for cell integrity and binding, they do not prevent the passage of molecules or chemicals between cells.
Instead, they focus on maintaining cellular cohesion, ensuring that cells stay tightly bound together.
Gap Junctions
Gap junctions are specialized intercellular connections that form channels between adjacent animal cells.
These channels are composed of connexin proteins, creating pores that allow ions, nutrients, and small molecules to travel directly from one cell to another.
Gap junctions are vital for cell communication, especially in tissues requiring synchronized activity like heart and smooth muscle.
However, they do not prevent the passage of substances between cells. Instead, they facilitate the direct transfer of electrical and chemical signals, making them crucial for coordinated cellular activities.
Tight Junctions
Tight junctions are crucial for creating a barrier between adjacent animal cells.
These junctions seal the space between cells and prevent the movement of chemicals, ions, and other substances through the intercellular space.
Tight junctions are composed of occludin and claudin proteins, and they form a nearly impermeable seal.
This is essential for maintaining distinct environments on either side of the cell layer, such as in the cells lining the intestines or blood-brain barrier.
Thus, tight junctions are vital in controlling the flow of molecules between cells and maintaining cellular polarity.
Plasmodesmata
Plasmodesmata are channels that traverse the cell walls of plant cells and allow the direct passage of molecules and ions between them.
These structures are not found in animal cells, but they serve a comparable function to gap junctions in animals.
Plasmodesmata enable plant cells to communicate and transport necessary substances, facilitating coordination and function throughout the plant.
However, unlike tight junctions, plasmodesmata do not act as barriers and can even dilate to allow larger molecules to pass through.
They are key in ensuring that plant cells work in concert, distributing nutrients and signals effectively between them.

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Most popular questions from this chapter

Mammalian red blood cells have no nuclei, must originate in other tissue systems, are relatively long-lived, are small with shapes that actively respond to their environment, and are metabolic anaerobes. Other vertebrates have red blood cells that are usually nucleated and are often relatively large, aerobic, self-replicating, and short-lived. To connect these facts to biology, questions need to be asked. The questions that you pose will depend on the path your class is taking through the curriculum. Begin by summarizing what you know: What are the functions of a eukaryotic cell nucleus? What is the approximate average size of a human red blood cell? What is the range of blood vessel diameters in adult humans? What is the range of red blood cell size in vertebrates? What is the average lifetime of a human red blood cell? How can you show how cell production is stimulated using examples from particular systems? How is cell death controlled? What biochemical cycles are associated with anaerobic and aerobic respiration, and what are the important differences between these? What process is involved in the transport of oxygen and carbon dioxide into and out of red blood cells? What behaviors and dynamic homeostatic processes might be associated with the properties of red blood cells in mammalian and nonmammalian organisms? What do you know about the evolutionary divergences among vertebrates? Your summary has revealed some similarities and differences among vertebrate erythrocyte and circulatory system structures. Scientific questions are testable. They can be addressed by making observations and measurements and analyzing the resulting data. A. Pose three scientific questions that arise from your summaries of what you know about erythrocytes and capillary size. B. For each question you pose, predict what you believe would be the answer and provide reasoning for your prediction. C. Describe an approach you think can be used to obtain data to test your prediction. D. In the production of mammalian red blood cells, erythrocytes that have not yet matured and are still synthesizing heme proteins are surrounded by a macrophage. Predict the role of the macrophage in the maturation of a red blood cell.

Where would you find DNA, the genetic material, in an animal cell? a. in the centriole b. only in the mitochondria c. in the mitochondria and the nucleus

We have discussed the upper limits of cell size; yet, there is a lower limit to cell size. What determines how small a cell can be? a. The cell should be large enough to escape detection. b. The cell should be able to accommodate all the structures and metabolic activities necessary to survival. c. The size of the cell should be large enough to reproduce itself. d. The cell should be large enough to adapt to the changing environmental conditions.

Which of the following organisms appear first in the fossil record? a. archaea b. fish c. protists d. plants

Bacteria do not have organelles; yet, the same reactions that take place on the mitochondria inner membrane, the phosphorylation of ADP to ATP, and chloroplasts, photosynthesis, take place in bacteria. Where do these reactions take place? a. These reactions take place in the nucleoid of the bacteria. b. These reactions occur in the cytoplasm present in the bacteria. c. These reactions occur on the plasma membrane of bacteria. d. These reactions take place in the mesosomes
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