Study Guide Section 5.5: Multicellularity

Vocabulary

• Tissue

• Organ

• Organ system

• Cell differentiation

• Stem cell

• Homeostasis (review)

Review Questions

1. How are tissues, organs, and organ systems related?

Cells make tissues; tissues make up organs; and organs make up organ systems.

2. How do organ systems work together and communicate so that an organism maintains homeostasis?

Organ systems are made up of organs, which are made up of cells. The cells of one tissue communicate among themselves; and cells of different tissues communicate with one another. The communication among cells of the same tissue and different tissues is responsible for maintaining the body’s internal environment – and thus homeostasis.

3. Suppose your family goes out of town and forgets to ask your neighbor to water the plants. Do you think the plants’ stomata, an organ system in plants, will be open or closed? Explain how this is related to organ systems and homeostasis. Since the plants are not receiving any water, they will need to conserve the water that they have. Therefore, the stomata will close to conserve water.

4. What is cell differentiation and why does it occur? Explain why cell differentiation is an important part of the development of a multicellular organism.

Cell differentiation is the process by which undifferentiated stem cells develop into specialized, mature cells with specific functions. Cell differentiation is needed in order to create cells that perform distinct jobs or tasks in the body. Multicellular (complex) organisms could not exist without cell differentiation because one cell type cannot perform all the activities required by multicellular life.

5. Why is regulation of the differentiation process during the early stages of development in a multicellular organism so critical?

The early stages of differentiation lead to the development of progressively more specialized tissues and organs. Errors in cell differentiation in the early stages could cause severe abnormalities in an organism’s body structure.

6. Do different types of cells have different DNA? Explain.

All cells have the same number of chromosomes (a complete set of genes); however, each cell uses only a small number those genes based on the kind of cell it is. A liver cell is only going to use genes that pertain to the functioning of a liver.

7. What are the defining characteristics of stem cells and why are they important? Stem cells can divide continually, while remaining undifferentiated (capable of becoming any kind of cell). When differentiation is desired, then they can develop into all specialized cell types.

8. How are stem cells classified and what is the difference among the varying classes of stem cells (see page 154)? The classifications are totipotent stem cell (only the zygote), pluripotent (embryonic) stem cells, and multipotent (adult) stem cells. Totipotent cells (the fertilized egg) can grow into any other type of cell; pluripotent, embryonic, stem cells (the blastula) can grow into any cell type except a totipotent cell; and multipotent stem cells can only grow into cells of a closely related cell family.

9. What are the differences between adult stem cells and embryonic stem cells?

Adult stem cells are only multipotent; they are only able to grow into cells of a closely related family of cells (example, adult blood stem cells can only develop into red and white blood cells and platelets. Embryonic stem cells are pluripotent and can grow into any cell type except for totipotent stem cells.

10. Choose an animal and give an example of how its behavior reflects its need to maintain homeostasis.

Sample Answer: bears store large amounts of energy in fat tissue during warm months; then sleep through much of the winter, conserving energy while living off the fat when food is scarce. 11.

The small little red ball is a blastula (photographed on the lip of a small gage needle), which means that it is a 5 day old embryo. The cells of the embryo are undifferentiated and pluripotent. What does pluripotent mean? What are the next steps in development of the blastula? How can the pluripotent nature of the cells be used in medicine? Do you think embryonic stem cells (from an embryo that is only 5 days old) should be used for therapeutic treatments in medicine? Please support your answer.