KEY CONCEPT Cells work together to carry out complex functions.

Objectives Describe the specialization in multicellular organisms. Identify different types of stem cells.

Vocabulary Tissue Group of cells that work together to perform a similar function. Organ Group of different types of tissues that work together to perform a specific function or related functions. Organ System Two or more organs that work in a coordinated way to carry out similar functions.

Vocabulary Cell Differentiation Processes by which unspecialized cells develop into their mature form and function. Stem Cell Cell that can divide for long periods of time while remaining undifferentiated.

Tissues are groups of cells that perform a similar function. Multicellular organisms depend on interactions among different cell types. vascular tissue leaf stem lateral roots primary root SYSTEMS root system shoot system Tissues are groups of cells that perform a similar function. Organs are groups of tissues that perform a specific or related function. Organ systems are groups of organs that carry out similar functions. CELL TISSUE ORGAN

Specialized cells perform specific functions. Cells develop into their mature forms through the process of cell differentiation. Cells differ because different combinations of genes are expressed. A cell’s location in an embryo helps determine how it will differentiate. Outer: skin cells Middle: bone cells Inner: intestines

Stem cells are unique body cells. Stem cells have the ability to divide and renew themselves remain undifferentiated in form develop into a variety of specialized cell types

Stem cells are classified into three types. totipotent, or growing into any other cell type pluripotent, or growing into any cell type but a totipotent cell multipotent, or growing into cells of a closely related cell family

Stem cells come from adults and embryos. Adult stem cells can be hard to isolate and grow. The use of adult stem cells may prevent transplant rejection. The use of embryonic stem cells raises ethical issues Embryonic stem cells are pluripotent and can be grown indefinitely in culture. First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules.

The use of stem cells offers many currently realized and potential benefits. Stem cells are used to treat leukemia and lymphoma. Stem cells may cure disease or replace damaged organs. Stem cells may revolutionize the drug development process.

Question/Answer Suppose your family goes out of town and forgets to ask your neighbor to water the plants. Do you think the plants’ stomata will be open or closed? Explain. Because the plants are not receiving any water, they will need to conserve the water that they have. The stomata will most likely be closed. Why is regulation of the differentiation process during the early stages of development so critical? The early stages of differentiation lead to the development of progressively more specialized tissues and organs. Distribution of cell differentiation in the early stages could cause severe abnormalities in an organism’s body structure.

Question/Answer List treatment benefits and risks of both types of stem cells. Adult stem cells taken from a patient’s body are less likely to be rejected. However, they can be difficult to isolate and grow, and have limited potential as far as what tissue can develop. Embryonic stem cells can develop into almost any cell type. However, they may be rejected by a patient’s body.