A2.2:  Cell Structure

Theme:  Unity and Diversity

The tools and methods used to study cells demonstrate how scientific investigation uncovers both themes:

• Light and electron microscopy allow direct observation of both the common structures that unite all cells and the unique features that distinguish different cell types
• Studying cells from different organisms reveals both shared fundamental features and remarkable adaptations to specific environments and lifestyles

Unity:

• All living organisms, regardless of size or complexity, are composed of one or more cells, establishing the most fundamental unity among all life forms
• Every cell contains DNA as genetic material, cytoplasm composed mainly of water, and a plasma membrane made of lipids, showing that all life shares the same basic molecular building blocks
• All organisms must perform the same essential functions: homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli, and reproduction
• Evidence from endosymbiotic theory suggests all eukaryotic cells evolved from a common ancestor, with mitochondria and chloroplasts representing ancient bacterial partners that became permanent cellular residents

Diversity:

• There are two primary types of cells, with prokaryotes achieving efficiency through simplicity while eukaryotes developed complex internal compartmentalization
• Plant cells evolved cell walls and chloroplasts for photosynthesis, fungal cells developed different wall compositions for structural support, and animal cells created specialized structures for movement and communication
• Different cell types within the same organism express different genes to create neurons, muscle cells, immune cells, and hundreds of other specialized cell types, each adapted for specific functions
• Evolution has produced remarkable variations like multinucleated muscle cells, enucleated red blood cells, and other specialized structures that modify the basic cellular plan for specific purposes
• Cells range in size and structures based on function 

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 features common to all cells and the features that differ? 
• How is microscopy used to investigate cell structure? 

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

• What explains the use of certain molecular building blocks in all living cells?
• What are some features of a compelling theory?
• What are examples of structure–function correlations at each level of biological organization? (B2.2)
• How is the structure of specialized cells related to function?  (C2.2)​

Key Terms to Know: * higher level only

70S Ribosome
80S Ribosome
Animal
Aseptate Fungal Hyphae
Capsule
Deductive Reasoning
Cell Specialization*
Cell Theory
Cell Wall
Centriole
Chlamydomonas
Chloroplast
Chromosome
Cilia
Cryogenic Electron Microscopy
Cytoplasm
Cytoskeleton
Differentiation*
Deoxyribonucleic Acid (DNA)
Electron Microscope
Endosymbiosis*
Eukaryote
Excretion
Eyepiece Graticule
Field of View
Flagellum

Freeze-Fracture
Fungus/Fungi
Gene Expression*
Golgi Apparatus
Gram Positive
Growth
Histone
Homeostasis
Immunofluorescence
Inductive Reasoning
Light Microscope
Lysosome
Magnification
Metabolism
Microfilaments
Micrograph
Microtubule
Microvilli
Mitochondrion
Movement
Multicellular
Naked DNA
Nucleoid
Nucleus
Nutrition
Objective Lens

Ocular Lens
Organelle
Paramecium
Phloem Sieve Tube Element
Pili
Plant
Plasma Membrane
Plasmid
Plastid
Prokaryote
Quantitative
Red Blood Cell
Reproduction
Resolution
Response
Ribosome
Rough Endoplasmic Reticulum
Scale
Skeletal Muscle Fibre
Smooth Endoplasmic Reticulum
Ultrastructure
Unicellular
Vacuole
Vesicle
Wet Mount

A2.2.1— Cells as the basic structural unit of all living organisms. 

• State the three parts of the cell theory.
• Compare the use of the word theory in daily language and scientific language.
• Distinguish inductive from deductive reasoning. 
• Outline the process of inductive reasoning that led to the development of the cell theory. 
• ​Outline how deductive reasoning can be used to predict characteristics of a newly discovered organism.​

A2.2.2— Microscopy skills.

• Given the magnification of the ocular and objective lenses, calculate the total microscope magnification.
• Demonstrate how to focus the microscope on a sample.
• Demonstrate how to make a temporary wet mount and stain a microscopic sample. 
• Demonstrate how to draw cell structures seen with a microscope using sharp, carefully joined lines and straight edge lines for labels.
• Measure the field of view diameter of a microscope under low power.
• Calculate the field of view diameter of a microscope under medium or high power.
• Use a formula to calculate the magnification of a micrograph or drawing.
• If given the magnification of a micrograph or drawing, use a formula to calculate the actual size of a specimen.
• Compare quantitative and qualitative observations.

A2.2.3— Developments in microscopy. 

• Define resolution and magnification.  
• Compare the functionality of light and electron microscopes.
• State a benefit of using fluorescent stains to visualize cell structures. 
• Outline the process of visualizing specific proteins in cells using immunofluorescence technology. 
• Outline the process of producing images of cell surfaces using freeze-fracture electron microscopy.  
• Outline the process of visualizing specific proteins using cryogenic electron microscopy.  

A2.2.4— Structures common to cells in all living organisms.

• Outline the function of structures that are common to all cells.

A2.2.5— Prokaryote cell structure.

• ​Outline the functions of the following structures of an example prokaryotic cell:  cell wall, plasma membrane, cytoplasm, 70s ribosome, and nucleoid DNA.
• Define the term “naked” in relation to prokaryotic DNA.

A2.2.6 —Eukaryote cell structure.  

• Compare and contrast prokaryotic and eukaryotic cell structure. 
• Label a diagram of a eukaryotic cell.
• Outline the function of the following structures in the eukaryotic cell:  plasma membrane, cytoplasm, 80s ribosomes, nucleus, mitochondria, chloroplast, endoplasmic reticulum, Golgi apparatus , vesicles,  vacuoles, lysosomes, cytoskeleton of microtubules and microfilaments.​

A2.2.7— Processes of life in unicellular organisms.

• List the common processes carried out by all  life.
• Define metabolism, homeostasis, excretion, growth, nutrition, movement, reproduction and response to stimuli.
• Describe characteristics of Paramecium or Chlamydomonas that enable it to perform the functions of life.

A2.2.8— Differences in eukaryotic cell structure between animals, fungi and plants.

• Compare and contrast the structures of plant, animal and fungal cells with reference to cell walls, vacuoles, chloroplasts, centrioles, cilia and flagella.

A2.2.9— Atypical cell structure in eukaryotes.

• Describe features of skeletal muscle fibers that make them an atypical cell.
• Describe features of aseptate fungal hyphae that make them an atypical cell.
• Describe features of red blood cells that make them an atypical cell.
• Describe features of phloem sieve tube elements that make them an atypical cell.​
• Compare the number of nuclei in aseptate fungal hyphae, skeletal muscle, red blood cells and phloem sieve tube elements.
  

A2.2.10— Cell types and cell structures viewed in light and electron micrographs. 

• Recognize features and identify structures in micrographs of prokaryotic cells (inclusive of the plasma membrane, nucleoid region, ribosomes and cell wall).
• Recognize features and identify structures in micrographs of eukaryotic cells (inclusive of the plasma membrane, nucleus, mitochondrion, chloroplast, vacuole, rough and smooth endoplasmic reticulum, Golgi apparatus, secretory vesicle, ribosomes, cell wall, cilia, flagella and microvilli).

A2.2.11— Drawing and annotation based on electron micrographs.

• Given a micrograph, draw and label the ultrastructure of a prokaryotic cell.
  
• Given a micrograph, draw and label the ultrastructure of a eukaryotic cell.

AHL A2.2.12— Origin of eukaryotic cells by endosymbiosis.

• Explain the origin of mitochondria and chloroplast with reference to the endosymbiosis.
• Describe the genetic, structural and behavioral evidence for the endosymbiotic theory.​​

AHL A2.2.13— Cell differentiation as the process for developing specialized tissues in multicellular organisms. 

• Outline the benefits of cell specialization in a multicellular organism.
• Define differentiation.
• Describe the relationship between cell differentiation and gene expression.​​

AHL A2.2.14— Evolution of multicellularity.​

• State that multicellularity has evolved repeatedly. 
• List groups of organisms that are multicellular.
• Outline the steps in the evolution of multicellularity.