Category: Microscope

No, centrioles are not typically visible under a light microscope.

Centrioles are small, cylindrical structures found in animal cells, and they play a crucial role in the organization of microtubules during cell division. However, centrioles are very small and are below the resolution limit of a light microscope, which is approximately 200 nanometers. Therefore, they cannot be resolved and visualized using a standard light microscope.

Parameter	Value
Magnification Range	40x – 1000x
Resolution	Approximately 200 nanometers
Maximum Useful Magnifica	500x – 600x for most details
Illumination Source	Visible light
Sample Preparation	Usually requires staining
Cost	Relatively inexpensive
Common Applications	Biological and medical studies
Limitations	Limited resolution for small structures like centrioles

Understanding Centrioles

Centrioles, small but essential cellular structures, are key players in the intricate choreography of cell division and cytoskeletal organization. Comprising cylindrical tubes, centrioles are typically found in pairs near the cell’s nucleus. Understanding the structure and functions of centrioles provides insights into their significance in cellular processes.

What are Centrioles?

Centrioles are microtubule-based organelles, typically organized in pairs called centrosomes. Structurally, they consist of nine triplets of microtubules arranged in a cylindrical pattern, often likened to the blades of a turbine. This unique arrangement contributes to their role as microtubule organizers within the cell.

Centriole Functions

The primary role of centrioles lies in orchestrating cell division. During mitosis and meiosis, centrioles play a vital role in forming the spindle apparatus, a structure that segregates chromosomes into daughter cells. Additionally, centrioles are involved in the formation of cilia and flagella – cellular projections crucial for cell movement and sensory functions.

Centrioles and Cellular Organization

Beyond their role in cell division, centrioles contribute significantly to the organization of the cytoskeleton. The cytoskeleton is a dynamic network of protein filaments that gives the cell its shape, provides mechanical support, and facilitates intracellular transport. Centrioles help anchor microtubules, influencing the overall structural integrity of the cell.

Understanding the significance of centrioles in cellular processes sheds light on their indispensable functions. The intricacies of their structure and their involvement in vital cellular activities emphasize the importance of studying these organelles to unravel the mysteries of cell biology.

Challenges of Light Microscopy

Light microscopy, a cornerstone in the realm of biology, has been instrumental in studying various cellular structures. However, when it comes to observing structures as small as centrioles, inherent limitations arise. This section explores the challenges posed by light microscopy in the quest to visualize centrioles.

Limitations of Light Microscopy

One of the fundamental challenges lies in the resolution of light microscopes. The wavelength of visible light imposes a limit on the smallest structures that can be resolved. Centrioles, with their diminutive size and intricate structure, often fall below this limit, making them challenging to observe accurately.

To illustrate this limitation, consider the typical resolution of a light microscope, which is around 200 nanometers. Given that centrioles are on the order of 100 nanometers in diameter, pushing the boundaries of light microscopy, the fine details may remain elusive under conventional observation.

The Size of Centrioles

Centrioles, measuring approximately 200 to 250 nanometers in length, pose a size challenge when viewed through light microscopes. The optical limitations make it difficult to discern these structures with the clarity required for comprehensive analysis.

Let’s visualize this in a table:

Parameter	Centriole Diameter	Light Microscope Resolution
Approximate Size	200-250 nanometers	~200 nanometers

This comparison underscores the tight margins within which light microscopy operates concerning centriole observation.

Optical Challenges

The optical properties of centrioles further complicate their visibility under light microscopes. The refractive index mismatch between the centrioles and the surrounding cellular environment leads to distortions and reduced image clarity. This phenomenon hampers the accurate depiction of centriolar structures, making their observation a nuanced task.

Let’s summarize the optical challenges in a table:

Optical Challenge	Impact on Visibility
Refractive Index Mismatch	Distortions and reduced image clarity

Can Centrioles be Observed Using a Light Microscope?

Centrioles, unfortunately, are not readily visible under a standard light microscope. Their size and structure make them challenging to discern with the limited resolution of a light microscope, which typically ranges between 200 and 300 nanometers.

Microscope Type	Visibility of Centrioles
Light Microscope	Not Visible
Electron Microscope	Clearly Visible

Why are Centrioles Difficult to See with a Light Microscope?

Centrioles, being small organelles with dimensions below the resolving power of a light microscope, lack the contrast necessary for clear observation. Their size falls below the wavelength of visible light, making it challenging to distinguish them from the surrounding cellular structures.

Size of Centrioles	Light Microscope Resolution
< 200 nm	Limited Visibility

What Microscope Can be Used to Visualize Centrioles?

To observe centrioles effectively, an electron microscope is recommended. The higher resolution of electron microscopes, which can reach below 1 nanometer, allows for the detailed imaging of centrioles and other subcellular structures.

Microscope Type	Suitable for Centriole Observation
Light Microscope	Inadequate Resolution
Electron Microscope	Recommended

Can Special Staining Techniques Enhance Centriole Visibility?

Yes, employing specific staining techniques can enhance the visibility of centrioles under a light microscope. Dyes and stains that selectively bind to centriolar components can improve contrast, making these organelles more distinguishable.

Staining Technique	Effect on Centriole Visibility
Centriole Staining	Enhanced Contrast
Immunofluorescence	Improved Visibility

What is the Size of Centrioles, and How Does it Affect Visibility?

Centrioles typically have a diameter of about 250 nanometers and a length of approximately 500 nanometers. Their small size poses a challenge for light microscopy, where the resolution limit often exceeds the dimensions of these organelles.

Centriole Dimensions	Light Microscope Resolution
250 nm (diameter)	Limited Visibility

Are Centrioles Important Despite Their Limited Visibility?

Despite their challenge to observe directly, centrioles play a crucial role in cell division, organizing the microtubules of the mitotic spindle. Their significance lies in their contribution to the proper segregation of chromosomes during cell division, ensuring the formation of genetically identical daughter cells.

Centriole Importance	Visibility Challenge
Crucial for Cell Division	Limited Direct Observation

Can Advances in Microscopy Technology Improve Centriole Visibility?

Advancements in microscopy techniques, such as super-resolution microscopy, hold promise for improving centriole visibility. These techniques surpass the diffraction limit of traditional light microscopy, potentially allowing for clearer imaging of centrioles.

Microscopy Advancements	Potential for Improved Visibility
Super-Resolution Microscopy	Promising for Enhanced Clarity

Conclusion

To unravel the mysteries of centrioles, we have navigated through their intricate structures, vital functions in cell biology, and the challenges posed by light microscopy. The limitations inherent in the resolution of light microscopes, coupled with the small size and optical challenges presented by centrioles, underscore the complexity of studying these cellular components.

As we conclude, it is evident that pushing the boundaries of traditional light microscopy is essential for a comprehensive understanding of centrioles. Prospects hinge on advancements in microscopy techniques, with electron and super-resolution microscopy offering promising avenues. By surpassing light microscopy’s limitations, these methods provide more precise insights into the elusive world of centrioles.

As scientific knowledge expands and technology continues to evolve, the potential for studying centrioles through light microscopy may improve.

No, electron microscopes cannot generally be used to observe living cells.

The preparation process for electron microscopy involves dehydration and vacuum conditions that are incompatible with maintaining living cells.

Electron microscopes use electron beams instead of light to achieve much higher resolution images than light microscopes. However, the sample preparation for electron microscopy involves fixing, dehydrating, and embedding the specimen in a resin. This process is unsuitable for preserving living cells’ delicate structures and functions. Dehydration and exposure to a vacuum can cause cellular structures to collapse and lose their natural state.

Other techniques, such as light or confocal microscopy, are typically used to visualize living cells. These methods allow real-time observation of dynamic cellular processes without extensive sample preparation.

Characteristic	Transmission Electron Microscope (TEM)	Scanning Electron Microscope (SEM)
Resolution	0.1 nanometers or better	1-10 nanometers
Magnification	Up to 50 million times	Up to 2 million times
Sample Preparation	Thin sectioning and staining	Coating with a thin layer of metal
3D Imaging Capability	Limited	Yes
Depth of Field	Narrow	Broad
Types of Specimens	Thin sections of biological samples	Solid surfaces
Image Type	2D cross-sectional images	3D surface images
Applications	Subcellular structures, viruses, etc.	Surface morphology, material science
Vacuum Requirement	High vacuum	High vacuum
Cost	Expensive	Expensive

Basics of Electron Microscopy

In microscopic exploration, electron microscopy stands as a paramount tool, revealing the hidden intricacies of the nanoscale world. This section will delve into the fundamental principles of electron microscopy, outlining the two primary types—Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM).

Types of Electron Microscopes

Electron microscopes, owing to their exceptional resolution, are categorized into two main types: Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM).

Transmission Electron Microscope (TEM)

TEM operates on the principle of transmission, where a beam of electrons passes through an ultrathin specimen. The interaction of electrons with the specimen provides detailed insights into its internal structures. This type of electron microscope has been instrumental in unraveling the ultrastructure of cells, showcasing cellular components with remarkable detail.

Scanning Electron Microscope (SEM)

On the other hand, SEM employs a different approach. Instead of transmitting electrons through the specimen, SEM scans its surface. This scanning process generates a 3D image, revealing the topography of the specimen. SEM is particularly useful for studying the surface features of cells and other microscopic structures.

Sample Preparation in Electron Microscopy

A critical aspect of electron microscopy is the preparation of biological samples, which significantly influences the quality of the obtained images.

Fixation and Staining Techniques

Researchers employ fixation and staining techniques to enhance contrast and reveal specific cellular structures. Chemical fixatives, such as formaldehyde, stabilize cellular structures, preventing degradation during the imaging process. Additionally, heavy metal stains, like osmium tetroxide, interact with specific cellular components, further enhancing contrast.

Types of Electron Microscopes

Microscope Type	Operating Principle	Main Application
TEM	Transmission of Electrons through Specimen	Internal Structure of Cells
SEM	Scanning Surface with Electrons	Surface Topography of Cells

Fixation and Staining Techniques

Technique	Purpose	Examples
Chemical Fixation	Stabilize Cellular Structures	Formaldehyde
Heavy Metal Stains	Enhance Contrast	Osmium Tetroxide

Advances in Live Cell Imaging with Electron Microscopy

Cryo-Electron Microscopy (Cryo-EM)

Innovative techniques have propelled advancements in live cell imaging, and one notable breakthrough is cryo-electron microscopy (Cryo-EM). This method addresses the challenges faced by traditional electron microscopy when observing living cells.

Preservation of Cell Structures at Low Temperatures

Cryo-EM involves rapidly freezing biological samples, preserving them at ultra-low temperatures. This process, known as vitrification, retains cellular structures in a near-native state. By avoiding the distortions caused by conventional sample preparation methods, Cryo-EM provides a unique opportunity to capture dynamic cellular processes without compromising structural integrity.

Cryo-Electron Microscopy (Cryo-EM)

Advancement	Description
Preservation of Cell Structures	Rapid freezing preserves cellular structures at low temps.
Near-Native State Imaging	Retains cellular integrity for studying dynamic processes.

Cryo-EM Applications in Studying Living Cells

Cryo-EM has found diverse applications in the realm of live cell imaging. From unraveling the intricacies of cell division to examining viral infection mechanisms, this technique offers a new dimension in understanding the dynamic nature of living cells.

Applications of Cryo-Electron Microscopy

Cellular Process	Cryo-EM Application
Cell Division	Study of dynamic events during cell division.
Viral Infection	Unraveling mechanisms of viral entry and replication.

Correlative Light and Electron Microscopy (CLEM)

Another significant stride in live cell imaging is the integration of correlative light and electron microscopy (CLEM). This approach seamlessly merges the strengths of light microscopy with the high resolution of electron microscopy.

Integration of Light and Electron Microscopy

CLEM begins with live-cell imaging using light microscopy, capturing dynamic events in real time. Once specific structures of interest are identified, the specimen transitions to an electron microscope for high-resolution imaging. This integration allows researchers to correlate real-time observations with detailed structural information.

Correlative Light and Electron Microscopy (CLEM)

Integration Process	Benefits
Light Microscopy Observation	Real-time capture of dynamic cellular events.
Transition to Electron Microscopy	High-resolution imaging for detailed structural information.

Real-time Imaging of Living Cells

The real strength of CLEM lies in its ability to provide a comprehensive understanding of living cells. By bridging the gap between dynamic processes observed through light microscopy and detailed structural analysis via electron microscopy, CLEM has become an invaluable tool in the study of cellular dynamics.

Real-time Imaging in Correlative Light and Electron Microscopy

Observation Technique	Strengths
Light Microscopy	Real-time observation of dynamic cellular processes.
Electron Microscopy	High-resolution imaging for detailed structural analysis.

Limitations and Future Prospects

While the recent advancements in live cell electron microscopy have been groundbreaking, certain limitations still hinder its widespread application.

Technical Constraints

One primary challenge is the existence of technical constraints. The resolution achieved in live cell electron microscopy is often lower compared to static samples. This limitation poses challenges in capturing the intricate details of dynamic cellular processes.

Resolution Challenges

The quest for higher resolution remains an ongoing pursuit. Achieving atomic-level resolution in live cell imaging proves to be particularly challenging due to the dynamic nature of biological samples and the potential damage caused by electron beams.

Table 1: Current Limitations of Live Cell Electron Microscopy

Challenges	Description
Technical Constraints	Limitations in resolution for dynamic cellular processes.
Resolution Challenges	Difficulty in achieving atomic-level resolution in vivo.

Emerging Technologies and Future Directions

Despite the current limitations, the field of live cell electron microscopy is dynamic, with ongoing research and emerging technologies pointing towards a promising future.

Advancements in Microscopy Techniques

Researchers are actively exploring advancements in microscopy techniques, aiming to overcome current limitations. Adaptive optics and novel sample preparation methods are being investigated to enhance resolution and minimize potential damage to living cells.

Potential Breakthroughs in Live Cell Imaging

The future holds exciting prospects for live cell imaging. Continued innovation may lead to breakthroughs that enable researchers to explore cellular dynamics with unprecedented clarity. The integration of artificial intelligence (AI) for real-time analysis and improved environmental control chambers are among the potential avenues that could shape the future of live cell electron microscopy.

Future Directions in Live Cell Electron Microscopy

Technological Advances	Potential Impact
Adaptive Optics	Enhanced resolution for dynamic cellular processes.
AI Integration	Real-time analysis for improved understanding of dynamics.
Advanced Environmental Control	Minimizing environmental impact on living cell integrity.

Conclusion

Electron microscopes have revolutionized our understanding of living cells by allowing us to observe their intricate structures and processes. These powerful instruments have pushed the boundaries of scientific exploration, enabling researchers to delve deeper into the world of microscopic organisms.

Through their high-resolution imaging capabilities, electron microscopes have provided invaluable insights into the behavior and characteristics of living cells. With continued advancements in technology, we can expect even greater discoveries and advancements in our knowledge of these fascinating building blocks of life.

Staphylococcus bacteria appear as spherical clusters or grape-like structures under a microscope.

Staphylococcus, commonly known as staph, is a genus of bacteria characterized by its round shape and tendency to form clusters. When viewed under a microscope, these bacteria appear as spherical clusters resembling grapes or bunches. The name “staphylococcus” is derived from the Greek words “staphyle,” meaning bunch of grapes, and “kokkos,” meaning berry.

Staphylococcus bacteria are Gram-positive, meaning they retain the violet stain in the Gram-staining process. This is due to the thick layer of peptidoglycan in their cell walls. The grape-like clusters result from the bacteria dividing into multiple planes.

Characteristic	Description
Shape	Spherical (cocci)
Arrangement	Clustered (staphylo arrangement)
Gram Staining	Gram-positive
Size	Approximately 0.5 to 1.5 micrometers in diameter
Color (Gram Staining)	Purple

Understanding Staphylococcus

Structure of Staph Bacteria

Staphylococcus bacteria exhibit a distinct spherical cluster structure, resembling a bunch of grapes under the microscope. The cells are arranged in irregular, non-motile clusters, a defining feature that aids in their identification. Each individual Staph cell possesses a cell wall, membrane, and cytoplasm.

Types of Staph Bacteria

Staphylococcus aureus is the most well-known species among the Staph genus. Recognizing its golden appearance on agar plates is a common method of identification. However, various other Staph species exist, each with unique characteristics and health implications. Differentiation between these species becomes crucial in understanding and treating Staph infections.

Staph bacteria, when observed under a microscope, exhibit distinct morphological features crucial for identification. Their spherical shapes, often arranged in characteristic clusters, set them apart from other bacterial species.

Gram Staining and Its Significance in Staph Identification

Staphylococcus Type	Gram Staining Result	Cell Wall Characteristics
Staphylococcus aureus	Gram-Positive	Thick peptidoglycan layer
Staphylococcus epidermidis	Gram-Positive	Thinner peptidoglycan layer, biofilm-forming
Staphylococcus saprophyticus	Gram-Positive	Thicker peptidoglycan layer, uropathogenic

Gram staining is a fundamental technique aiding in the categorization of staphylococci based on their cell wall composition. Staphylococcus aureus, a Gram-positive bacterium, possesses a thick peptidoglycan layer, contributing to its pathogenicity. Other staphylococci, like Staphylococcus epidermidis and Staphylococcus saprophyticus, exhibit variations in peptidoglycan thickness, influencing their roles in infections.

Detailed Examination of Staph Cells and Clusters

Microscopic analysis allows for a detailed inspection of various components within staph cells. The cytoplasmic content, presence of appendages, and the arrangement of cells in clusters provide additional insights.

Microscopic Features of Different Staph Strains

Staphylococcus Type	Cytoplasmic Details	Cluster Arrangement
Staphylococcus aureus	Abundant cytoplasm, potential for toxins	Grape-like clusters (staphylococcal clusters)
Staphylococcus epidermidis	Sparse cytoplasm, biofilm-producing	Irregular clusters (biofilm matrix)
Staphylococcus saprophyticus	Plentiful cytoplasm, uropathogenic	Small clusters with uropathogenic features

The examination of cytoplasmic content allows differentiation between strains. Staphylococcus aureus, with abundant cytoplasm, may produce toxins influencing its virulence. Staphylococcus epidermidis, known for biofilm formation, shows sparse cytoplasm emphasizing biofilm matrix production. Staphylococcus saprophyticus, associated with urinary tract infections, exhibits distinctive uropathogenic features.

Highlighting Unique Features Based on Staph Type

Different staph strains may present unique microscopic features that impact their clinical significance. For instance, methicillin-resistant Staphylococcus aureus (MRSA) may exhibit altered cell structures or arrangements not found in other staphylococci. These variations become crucial markers for both identification and the development of targeted treatment strategies, especially in the context of antibiotic resistance.

Microscopic Variances in MRSA

MRSA Characteristics	Microscopic Features
Altered cell wall structure	Irregular cell wall thickness
Unique cluster arrangements	Clusters with irregular shapes
Potential presence of toxins	Increased cytoplasmic complexity

Microscopic analysis of MRSA reveals deviations in cell wall structures, cluster arrangements, and cytoplasmic content. Recognizing these unique features aids in accurately identifying MRSA strains and informs clinicians about potential challenges in treatment due to antibiotic resistance.

Visualizing staph under a microscope provides invaluable insights into the diverse world of these bacteria. Microscopic analysis and advanced staining techniques allow for precise identification and characterization, enabling healthcare professionals to tailor effective treatment strategies for staph infections. Understanding the microscopic nuances of different staph strains, including MRSA, is pivotal in the ongoing battle against antibiotic-resistant bacteria.

The Gram stain is a critical test performed in microbiology to classify bacteria into two groups based on the characteristics of their cell walls, giving clues to their identification. Staphylococcus species are Gram-positive, which means they hold onto the primary dye (crystal violet) and appear purple under the microscope. Here’s a look at the Gram stain procedure:

Step	Description
1. Crystal Violet	Application of the crystal violet dye which is taken up by all bacteria.
2. Iodine Treatment	Iodine is applied to form a complex with the crystal violet, which becomes trapped in the thick peptidoglycan layer of Gram-positive bacteria.
3. Alcohol Decolorization	Alcohol is used to wash the slide; it decolorizes Gram-negative bacteria while Gram-positive bacteria retain the crystal violet-iodine complex.
4. Counterstain (Safranin)	A counterstain, typically safranin, is applied, which dyes the now colorless Gram-negative bacteria a different color for differentiation.

Visual Characteristics Under High Magnification

• Staphylococcus appear as purple, round cells in clusters when stained with Gram stain.
• They may also display a golden color on agar plates, leading to the name Staphylococcus aureus for some strains.
• Their cluster formation can sometimes be differentiated from streptococci, which are typically found in chains.

Common Species Of Staphylococcus

While Staphylococcus aureus is the most renowned pathogenic species due to its association with numerous infections, there are other species that are also important in clinical diagnostics:

Species	Commonly Associated With
Staphylococcus epidermidis	Skin flora, contaminant in blood cultures, device-related infections
Staphylococcus saprophyticus	Urinary tract infections, particularly in young women
Staphylococcus haemolyticus	Healthcare-associated infections, multi-drug resistant

Challenges and Limitations in Microscopic Staph Analysis 

Microscopic analysis of Staphylococcus encounters several challenges and limitations that may impact identification accuracy and subsequent treatment strategies.

Challenges in Microscopic Staph Analysis

Challenges	Impact on Microscopic Analysis
Variation in Sample Preparation	Inconsistent staining and visualization of cellular structures
Overlapping Morphological Features	Difficulty in distinguishing between different staphylococcal strains
Limited Resolution in Light Microscopy	Inability to discern finer details, affecting accurate identification
Artifacts in Electron Microscopy	Presence of distortions or artifacts, compromising image reliability

Consistent sample preparation is crucial, as variations can lead to unreliable staining and visualization. Overlapping morphological features pose challenges in distinguishing closely related staphylococcal strains. Light microscopy’s limited resolution can hinder detailed examination, while artifacts in electron microscopy may compromise the reliability of captured images. Addressing these challenges is essential for enhancing the precision of microscopic staph analysis and improving diagnostic and therapeutic outcomes.

How does Staphylococcus appear under a microscope?

Staphylococcus bacteria, commonly known as Staph, is observable under a microscope in clusters resembling grapes. These clusters have a distinctive round shape, appearing as cocci, or spherical cells. The typical arrangement of Staphylococcus cells is in irregular, nonuniform clusters.

Characteristics	Description
Shape	Spherical (cocci)
Arrangement	Irregular clusters resembling grapes

What staining techniques are used to visualize Staph under a microscope?

Gram staining is commonly employed to visualize Staphylococcus bacteria under a microscope. Staphylococci can be classified as either Gram-positive or Gram-negative based on their response to this staining technique. Staphylococci typically appear purple when stained, indicating a positive Gram reaction.

Staining Technique	Result for Staphylococcus
Gram Staining	Purple (Gram-positive reaction)

What is the size of Staph cells when observed under a microscope?

Staphylococcus cells are generally small, with an average diameter ranging from 0.5 to 1.0 micrometers when viewed under a microscope. The relatively compact size of these cocci contributes to their ability to form clusters and survive in various environments.

Size Range (Diameter)	Description
0.5 to 1.0 micrometers	Small spherical cells

Can the appearance of Staph under a microscope vary among different species?

Yes, the appearance of Staphylococcus can vary among different species. While the general characteristics such as spherical shape and cluster arrangement remain consistent, there may be subtle differences in size and specific arrangements depending on the Staph species.

Variations in Appearance	Description
Size and Arrangement	Slight variations depending on Staph species

How does Methicillin-Resistant Staphylococcus aureus (MRSA) appear under a microscope?

MRSA, a strain of Staphylococcus aureus resistant to many antibiotics, retains the typical appearance of Staph under a microscope. However, due to its resistance to methicillin, it is specifically identified through additional laboratory tests. Under a microscope, MRSA appears as Gram-positive cocci in clusters, similar to other Staph species.

MRSA under Microscope	Description
Gram Staining	Purple (Gram-positive reaction)
Cocci in Clusters	Similar to other Staph species

How does Staphylococcus epidermidis differ in appearance from other Staph species under a microscope?

Staphylococcus epidermidis, a common skin bacterium, shares the general characteristics of Staph under a microscope. However, subtle differences may exist in its arrangement and size. Staphylococcus epidermidis tends to form more regular clusters and may have a slightly smaller size compared to some other Staph species.

Staphylococcus epidermidis	Description
Cluster Arrangement	More regular clusters
Size	Slightly smaller than some other Staph species

Final Words

The microscopic world of bacteria is complex and fascinating. When viewed under a microscope, Staphylococcus species can be readily identified by their grape-like clusters and purple hue following a Gram stain. Understanding what these microscopic organisms look like and how to identify them plays a crucial role in microbiology and medical diagnostics, ultimately aiding in the effective treatment and control of infections.

Resources and References

1. MicrobeWiki
2. Journal of Bacteriology