B2.3  Cell Specialization

Theme:  Form and Function

Cell structure becomes specialized for specific functions through differentiation that transforms unspecialized cells into highly adapted forms optimized for particular biological roles.

• Totipotent embryonic cells can become any cell type, pluripotent cells have reduced options, and multipotent adult stem cells have limited pathways, showing how structural potential determines functional possibilities.
• Cell size specialization ranges from tiny red blood cells optimized for circulation to massive muscle fibers built for contraction, with each size perfectly matched to functional requirements.
• Surface area-to-volume ratios constrain cell function. Larger cells need structural adaptations like flattening, microvilli, and invagination to maintain efficient exchange.
• Type I Pneumocyte cells are extremely thin for gas diffusion while Type II Pneumocyte cells contain secretory vesicles for surfactant production.
• Muscle cell adaptations include contractile myofibrils. Cardiac muscle are branched cells with single nuclei while skeletal muscle are unbranched fibers with multiple nuclei.
• Gamete adaptations create complementary functions. Sperm are streamlined for motility while eggs are large with nutrient stores for development.

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• What are the roles of stem cells in multicellular organisms?
• How are differentiated cells adapted to their specialized functions? 

​​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What are the advantages of small size and large size in biological systems?
• How do cells become differentiated? ​

Key Terms to Know: * higher level only

Alveoli*
Bone Marrow
Cardiac Muscle Cell*
Chemical Gradients
Cytoplasm*
Differentiation
Diffusion*
Egg Cell
Embryo
Epithelium*
Erythrocyte*
Exchange
Fertilization
Gamete

Gene Expression
Hair Follicle
Invagination*
Lumen*
Microvilli
Multipotent
Myofibril*
Nephron*
Neuron
Pluripotent
Proximal Convoluted Tubule Cell*
Red Blood Cell
Scientific Model
Secretory Vesicle*

Specialized
Sperm Cell
Stem Cell
Stem Cell Niche
Striated Muscle Fibre
Surface Area
Surface-Area-To-Volume Ratio
Surfactant*
Totipotent
Type I Pneumocyte*
Type II Pneumocyte*
Volume
White Blood Cell

B2.3.1— Production of unspecialized cells following fertilization and their development into specialized cells by differentiation.

• State that a zygote is an unspecialized cell produced from fertilization. 
• Outline the impact of chemical gradients on gene expression within an early-stage embryo. ​

B2.3.2— Properties of stem cells.

• Outline two properties of stem cells. 
  

B2.3.3—  Location and function of stem cell niches in adult humans.

• Define stem cell niche.
  
• Outline the location and function of two types of multipotent stem cells in an adult human body.​​

B2.3.4— Differences between totipotent, pluripotent and multipotent stem cells.

• Define totipotent, multipotent and pluripotent.
• List an example of a totipotent, multipotent and pluripotent stem cell. 
• Explain why pluripotent stem cells are most prevalent in the early embryonic development of a multicellular organism.​

​​B2.3.5— Cell size as an aspect of specialization.

• Relate the relative cell size to the specialized function of sperm, egg, red blood cell, white blood cell, neuron and striated muscle fibers.​

B2.3.6- Surface area-to-volume ratios and constraints on cell size.

• Outline the activities occurring in the volume and at the surface of the cell.
• Calculate the surface area, volume and SA:V ratio of a cube.
• Explain the benefits and limitations of using cubes to model the surface area and volume of a cell.
• Describe the relationship between cell size and the SA:V ratio of the cell.
• Explain why cells are often limited in size by the SA:V ratio.

AHL ​​B2.3.7— Adaptations to increase surface area-to-volume ratios of cells.

• List two examples of cells that are specialized for exchange of materials and have adaptations to increase the SA:V ratio.
• Outline three adaptations of cells that maximize the SA: volume ratio.

AHL ​​B2.3.8- Adaptations of type I and type II pneumocytes in alveoli.

• Define “alveolar epithelium.”
• Outline the structure and function of type I pneumocytes.
• Outline the structure and function of type II pneumocytes.
• Describe two functions of the fluid secreted by type II pneumocytes.
• Label the following structures on a micrograph of lung tissue:  type 1 pneumocyte, type 2 pneumocyte, capillary endothelium, basement membrane and blood cells.

AHL ​​B2.3.9- Adaptations of cardiac muscle cells and striated muscle fibers.

• List three types of muscle tissue found in the human body.
• Outline the relationship between skeletal muscles, muscle fibre cells and myofibrils.
• Label a diagram of a  skeletal muscle fibre cell, including the sarcolemma, nuclei, sarcoplasmic reticulum and mitochondria.
• Compare and contrast cardiac muscle tissue and skeletal muscle tissue.
• Describe how the branching and intercalated discs of cardiac muscle cells allow for propagation of the stimulus to contract.

AHL ​​B2.3.10- Adaptations of sperm and egg cells.

• State the function of gamete cells.
• Compare the size, and motility of egg and sperm cells.  
• State the function of each of the following egg structures:  haploid nucleus, binding proteins, zona pellucida, cortical granules, yolk, mitochondria and centrioles.
• State the function of each of the following sperm structures:  head, acrosome, plasma membrane receptors, binding proteins in the acrosome, haploid nucleus, midpiece, helical mitochondria, microtubules and tail.