A2.2 cell structure Flashcards
Cytology
Cytology is the branch of biology that studies all facets of the cell.
As our understanding of the cell has increased, so has our ability to understand all forms of life and diseases that occur on planet Earth.
units and their measurement
1 metre (m) (100 cm = 1,000 mm)
1 centimetre (cm) (0.01 m)
1 millimetre (mm) (0.001 m)
1 micrometre (um) (0.000001 m)
1 nanometre (nm) (0.000000001 m)
What is magnification in microscopy?
Magnification refers to the increase in an object’s image size compared to its actual size.
It’s represented in numbers like 500× or 100,000×, indicating how much larger the image is than the actual object.
Define resolution in microscopy.
Resolution is the minimal distance between two distinguishable points or objects. Higher resolution microscopes reveal greater detail, often compared to clarity, with increased resolution providing clearer images.
How do light microscopes operate, and what do they use to enhance visibility?
Light microscopes use light to pass through specimens, living or dead, to form an image. Stains might be applied to improve the visibility of structures within the specimen.
What distinguishes electron microscopes (EMs) from light microscopes?
Electron microscopes provide the highest magnification (over 100,000×) and resolution. They use electron beams passing through specimens to form images, enabling ultra-high magnification and detailed views.
Light microscope
Inexpensive to purchase and operate
Simple and easy specimen preparation
Magnifies up to 2,000×
Electron microscope
Expensive to purchase and operate
Complex and lengthy specimen preparation
Magnifies over 500,000x
What is the order of sizes from largest to smallest, in terms of cells and their components?
Cells > Organelles > Bacteria (some similar in size to organelles) > Viruses > Membranes > Molecules.
What is the field of view in a microscope, and how is its diameter calculated?
The field of view is the total visible area through a microscope’s ocular or eyepiece. Its diameter is calculated using specialized micrometers, such as ocular and stage micrometers.
What is an ocular micrometer, and how is it calibrated?
The ocular micrometer, located in the eyepiece, is engraved with equal units, but these units are arbitrary. Calibration is done using a stage micrometer with defined units, typically calibrated with a ruler or a special slide with known units (usually millimeters).
How is the magnification of a specimen calculated using a microscope?
Measured size of image / Actual size of specimen = Magnification.
What significant advancements have been made in microscopy since Robert Hooke’s microscope in 1665?
Electron microscopy, including techniques like freeze fracture and cryogenic electron microscopy, has significantly progressed since early microscopes.
What distinguishes an electron microscope (EM) from a light microscope in terms of its operating principle?
EMs use a beam of electrons, which have a shorter wavelength than light, providing over a 1,000 times greater resolving power and magnification up to 500,000× compared to a light microscope’s maximum of 2,000×.
What are the two types of electron microscopes and how do they differ?
Scanning electron microscopes (SEM) scan a specimen’s surface with an electron beam, while transmission electron microscopes (TEM) pass electrons through thin sections for internal structure examination.
What are the techniques employed in electron microscopy and their contributions?
Freeze fracture reveals a plane through a specimen for examining structures like the cell membrane, while cryogenic electron microscopy provides a three-dimensional view of proteins involved in cellular function.
What are advantages and limitations of electron microscopy compared to light microscopy?
EMs offer higher resolution but are expensive,
require extensive training,
and often involve non-living specimens, with artefacts sometimes present.
Light microscopy is used for living samples and employs techniques like fluorescent stains and immunofluorescence for enhanced visibility.
How do fluorescent stains and immunofluorescence contribute to the study of living cells using light microscopy?
Fluorescent stains bind with cellular components, fluorescing when exposed to specific light, while immunofluorescence uses antibodies with dyes to detect target molecules, such as proteins, in living tissues or infected cells.
What recent advancements have been made in fluorescence-based methods?
Modern fluorescence-based techniques allow visualization of single RNA molecules within single cells and viruses, expanding our ability to study RNA in detail.
What is a characteristic of a brightfield microscope?
It uses visible light, the specimen is viewed against a light background, and it’s the most common and user-friendly light microscope.
What distinguishes a darkfield microscope?
A darkfield microscope utilizes a special opaque lens in the condenser, blocking direct light from entering the specimen, resulting in the specimen appearing light against a dark background.
What is a feature of a phase-contrast microscope?
It employs a special condenser with a circular diaphragm and a modified objective lens, allowing detailed imaging of specimens without staining.
How are cells often categorized, and what are two major groups?
Cells are categorized into prokaryotic and eukaryotic cells. Prokaryotic cells are simpler and smaller than eukaryotic cells.
What defines prokaryotic cells, and what organisms fall into this category?
Prokaryotic cells are typically less than 1 μm in diameter and include bacteria and archaea, which are mostly small, unicellular organisms.
How do prokaryotic organisms relate to the evolution of life?
Bacteria and archaea, both prokaryotes, followed different evolutionary paths from eukaryotes (in the domain Eukarya). They play a significant role in the world today and exhibit vast diversity in factors like nutrition, energy sources, composition, and morphology.
What are the features of a prokaryotic cell?
Cell wall
Plasma membrane
Flagella
Pili
Ribosomes
Nucleoid (region containing free DNA)
What are the functions of the prokaryotic cell wall?
The prokaryotic cell wall protects and maintains the cell’s shape, preventing it from rupturing due to internal water pressure. It’s primarily composed of peptidoglycan and, in some bacteria, contains an additional outer layer called the capsule, aiding in adhesion to surfaces.
Describe the composition and function of the plasma membrane in prokaryotic cells.
The plasma membrane, similar to eukaryotic cells, is found just inside the cell wall. It controls material movement in and out of the cell and plays a role in prokaryotic cell division (binary fission).
How is bacteria classification based on their dye retention?
Bacteria can be classified as “Gram-positive” or “Gram-negative” based on their reaction to crystal violet dye. Gram-positive bacteria retain the dye, appearing violet or blue, while Gram-negative bacteria do not retain the dye and do not appear violet or blue under a microscope.
Can you provide examples of Gram-positive bacteria?
Bacillus and Staphylococcus are examples of Gram-positive bacteria.
What are pili, and what functions do they serve in bacterial cells?
Pili are hair-like structures found on some bacterial cells, primarily used for attachment. Their main function involves joining bacterial cells in preparation for DNA transfer, facilitating a form of sexual reproduction.
What purpose do flagella serve in bacterial cells?
Flagella, longer than pili, enable bacterial cells to move. They are anchored to the cell wall and plasma membrane, providing mobility to the cell.
Describe the cytoplasm in prokaryotic cells.
The cytoplasm fills the entire interior of a prokaryotic cell. Under high-magnification microscopes, the most visible structure in the cytoplasm is the chromosome or DNA molecule. Prokaryotic cells lack internal membranes or specialized compartments within the cytoplasm where cellular processes occur.
What role do ribosomes play in prokaryotic cells?
Ribosomes are the sites of protein synthesis in prokaryotic cells. Composed of protein and ribosomal RNA, they occur in large numbers in cells producing significant amounts of protein.
Describe the nucleoid region in a bacterial cell.
The nucleoid region contains a single, continuous circular thread of DNA known as the bacterial chromosome. It lacks a surrounding membrane and is involved in cell control and reproduction. Prokaryotic DNA isn’t associated with histones like in eukaryotes, hence bacterial chromosomes are often referred to as “naked loops”.
What are plasmids, and how do they differ from the bacterial chromosome?
Plasmids are small, circular DNA molecules independent of the main bacterial chromosome. They replicate separately and aren’t necessary under normal conditions but aid the cell in adapting to unusual circumstances.
Explain the process of binary fission in prokaryotic cell division
Prokaryotic cells divide through binary fission, where DNA is copied, resulting in two daughter chromosomes. These daughters attach to different regions on the plasma membrane, leading to the division of the cell into two genetically identical daughter cells.
What distinguishes eukaryotic cells from prokaryotic cells?
Eukaryotic cells are found in organisms like algae, protozoa, fungi, plants, and animals, ranging in diameter from 5 to 100 μm. They contain a nucleus, noticeable at higher magnification, and various organelles that carry out specific functions, providing compartmentalization, unlike prokaryotic cells.
