Multicellular Life

Section 5.5

Objectives

• SWBAT describe the specialization in multicellular organisms.

• SWBAT identify different types of stem cells.

Vocabulary

• Tissue• Organ • Organ system• Cell differentiation• Stem cell

Starter

• Alone or with a partner, come up with as many different types of cells in your body (or the body of any multicellular organism) as you can.

• How did all of those different cells come about? What do those cells make up?

Multicellularity

• As near as we can tell, multicellularity has arisen naturally, throughout evolutionary history, 20 different times (the last time being 200 million years ago).

• Interestingly, researchers in the United States have created multicellularity twice in laboratories.

Multicellularity

• Multicellularity means that cells communicate with one another and work together, in groups, forming increasingly larger and more complex structures (and more complex organisms).

• In multicellular organisms we see: cells forming tissues, tissues forming organs, and organs forming organ systems.

Tissues, Organs, Organ Systems

Tissues, Organs, Organ Systems

• Within multicellular organisms, cells communicate and work together in groups that form increasingly larger, more complex structures.

• Tissues – groups of cells that work together to perform a similar function.

• Organs – groups of tissues that work together to perform a specific function or related functions.

Tissues, Organs, Organ Systems

The tissues of a leaf work together to form a plant’s food-producing organ.

Tissues, Organs, Organ Systems

• Organ Systems – organs that carry out similar functions are grouped into organ systems.

• Examples of a plant’s organ systems would be the plant’s root system and its shoot system that includes reproductive structures (seeds, fruit, flower, etc.).

Tissues, Organs, Organ Systems

Cell Differentiation

• Cell differentiation – the process by which unspecialized cells develop into their mature forms and functions.– This result is cell specialization.– Each cell in your body has a full set of your DNA –

but it only utilizes specific genes that correspond to its function (that of its tissue).

– DNA can be thought of as a cookbook – full of many different “recipes” (the tissues and how they are arranged are the result of the “recipes.”)

Cell Differentiation (Stem Cells)

• Stem Cells – cells that have the ability to:– divide and renew themselves for long periods of

time;– remain undifferentiated in form; – and develop into a variety of specialized cell

types.

Stem Cells

• Stem cells can divide to form either two stem cells or one stem cell and one specialized cell.

Stem Cell Classification

• Classified based on their potential to develop into differentiated cell types of different tissues. – Totipotent stem cells can grow into any other cell type

(example: the fertilized egg – also known as a zygote).– Pluripotent stem cells can grow into any cell type but a

totipotent cell (example: a blastula – embryonic stem cells)

– Multipotent stem cells can grow into only of a closely related cell family (example: adult stem cells).

Stem Cell Classification

A blastula (a 5 day old embryo) – a hollow mass of pluripotent cells)

The cells of this embryo have not started to differentiate yet. Fertilization clinics use blastulas in in vitro fertilization. The embryos can be frozen at this stage and “thawed out” for later use. They are also of great value to science.

Adult Stem Cells

• They are partially undifferentiated cells located among specialized cells of many organs and tissues. – They are found all over the body.– These stem cells are also found in children and

umbilical cord blood (which leads some to save the umbilical cord after a child’s birth).

– Advantage – can be taken from a patient, cultured, and then put back in the patient.

Adult Stem Cells

– The risk of rejection by a patient’s immune system is low because it comes from the patient (it should be a perfect match).

– Disadvantage – The utilization of adult stem cells has shown promise in the creation of new medical therapies but few have been truly effective.

– Currently, blood stem cells are the only type of adult stem cell commonly used – they are employed in bone marrow transplants.

Adult Stem Cells

– There has been a great deal of research into using neural stem cells to treat Parkinson disease and spinal cord injury, though treatments are only in the trial phase.

– For more info., visit http://stemcell.childrenshospital.org/about-stem-cells/adult-somatic-stem-cells-101/how-do-adult-stem-cells-get-turned-into-treatments/

Pluripotent Stem Cells

• Pluripotent Stem Cells (embryonic stem cells) are master cells potentially able to produce any type of tissue the body needs. – Embryonic stem cells are procured from unused embryos

created in vitro at fertility clinics (blastulas are created and frozen – then implanted in the uterus when needed).

– If reliable techniques can be developed, pluripotent stem cells could someday allow doctors to create customized, rejection-proof transplants to patch a scarred heart, reawaken damaged nerves or reboot an immune system incapable of fighting infection.

Pluripotent Stem Cells

• To know more, this is a good place to start: http://stemcell.childrenshospital.org/about-stem-cells/pluripotent-stem-cells-101/