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Who first discovered cells, and what did he observe them in?
Robert Hooke (1665) discovered cells when he examined thin sections of cork under a microscope. He called them "cells" because they reminded him of the small compartments in a monastery.
What is the Cell Theory?
Cell theory is the concept that all living organisms are made up of cells, and cells are the basic units of structure, function, and organization in living things.
How much can a light microscope magnify?
A light microscope can magnify objects up to 1,500 times, allowing us to see cells clearly.
How powerful is an electron microscope?
An electron microscope can magnify objects up to 500,000 times, revealing incredibly detailed structures inside cells.
How does an electron microscope compare to a light microscope?
An electron microscope can magnify up to 500,000 times, much more than a light microscope, allowing scientists to see fine details of cell structures.
Why was the development of better lenses and staining techniques important for cell studies?
Improved lenses and staining techniques allowed scientists to see cells more clearly, enhancing our understanding of their structure and function.
How does a light microscope illuminate a specimen?
A light microscope illuminates the specimen from underneath using either sunlight reflected with a mirror or a built-in light source.
What happens after the objective lens magnifies a specimen?
The objective lens produces a magnified and inverted image, which is then focused by the eyepiece lens for the viewer to see.
How is the total magnification of a specimen calculated using a light microscope?
Total magnification = magnification of objective lens × magnification of eyepiece lens.
Example: X10 (objective) × X10 (eyepiece) = X100 total magnification.
How can you calculate the actual size of a specimen under a light microscope?
Actual size = image size ÷ magnification.
What is the importance of recording magnification when using a light microscope?
Recording the magnification allows you to calculate the actual size of the specimen and ensure accurate measurements.
Why are most specimens for light microscopes dead, stained, and specially preserved?
Specimens are often dead, stained, and specially preserved to make them easier to observe and to highlight specific structures within cells or tissues.
What is the purpose of staining specimens under a light microscope?
Staining is used to make it easier to identify types of cells or parts of cells by adding color to certain structures.
What does haematoxylin stain
Haematoxylin stains the nuclei of plant and animal cells purple, blue, or brown.
What does methylene blue stain
Methylene blue stains the nuclei of animal cells blue.
What does acetocarmine stain?
Acetocarmine stains the chromosomes in dividing nuclei in both plant and animal cells.
What does iodine stain in plant cells?
Iodine stains starch-containing material in plant cells blue-black.
What is one advantage of using a light microscope for studying living organisms?
Light microscopes allow you to see living plants and animals (or parts of them) directly, which is useful for real-time observation and comparison.Light microscopes are relatively cheap, making them accessible for use in various educational and research settings.They are relatively light and portable, allowing them to be used in various locations, like in the field for identifying diseases such as malaria.
What are some disadvantages of using light microscopes?
Preserving and staining tissue can produce artefacts, which are not part of the living tissue but result from the preparation process. These artefacts can sometimes be mistaken for actual features of the tissue.Limited powers of resolution (and magnification).
Why are light microscopes widely used in schools, universities, and hospitals?
Light microscopes are relatively cheap, making them accessible for use in various educational and research settings.
Can light microscopes be used to examine living tissue?
Yes, light microscopes can be used with prepared slides of living tissue, although many specimens are stained and preserved.
What makes light microscopes portable and versatile?
They are relatively light and portable, allowing them to be used in various locations, like in the field for identifying diseases such as malaria.
What is a potential issue with preserving and staining tissue for light microscopy?
Preserving and staining tissue can produce artefacts, which are not part of the living tissue but result from the preparation process. These artefacts can sometimes be mistaken for actual features of the tissue.
How do the limited resolution and magnification of light microscopes affect their use?
They restrict the ability to view very small structures like viruses or certain cell components.
What technological development has improved the information we can get from light microscopes?
Confocal microscopy.
How does the electron microscope form an image?
It uses a beam of electrons, which are scattered by the specimen in a similar way to how light is scattered in a light microscope.
What is the key difference between the behavior of electrons in an electron microscope and light in a light microscope?
Electrons in an electron microscope behave like light waves but have a much smaller wavelength, allowing for greater resolution.
Why must specimens be in a vacuum for the electron microscope to work?
Specimens must be in a vacuum because the electrons can’t travel through air, and the vacuum prevents interference that would distort the electron beam.
What types of specimen preparation are required for electron microscopy?
The preparation process can include chemical preservation, freeze-drying, freeze-fracturing, dehydration, embedding, sectioning, and mounting on a metal grid.
Why are heavy metal ions like lead and uranium used in electron microscopy?
Heavy metal ions are used to stain the specimens to improve the scattering of electrons, enhancing contrast and clarity in the final image.
How is the image from an electron microscope displayed?
The image is displayed on a monitor or computer screen for analysis.
What is the difference between magnification and resolution?
Magnification makes an object appear larger, while resolution determines how much detail is visible and whether two close points can be distinguished as separate.
What are the two types of electron micrographs?
Transmission Electron Micrographs (TEMs) – 2D images, and Scanning Electron Micrographs (SEMs) – 3D images.
What is the difference between TEMs and SEMs?
TEMs are 2D images created by passing electrons through the specimen, while SEMs are 3D images created by scanning the surface of the specimen with electrons.
Why are false colors added to electron micrographs?
False colors are added digitally to help differentiate various features or cells, making the image easier to interpret, but they do not reflect actual staining.
What are some advantages of using an electron microscope?
It provides huge magnification and resolution, revealing many details of cell structure for the first time.
What are the disadvantages of using an electron microscope?
Specimens must be in a vacuum, so living tissue can't be observed.
Complex specimen preparation often results in artefacts.
They are extremely expensive and require skilled handling.
The instrument is large and requires precise environmental conditions.
What is mitosis ?
Mitosis is a process of nuclear division where chromosomes are duplicated and the genetic material is equally shared between two daughter cells. It is involved in asexual reproduction, growth, and the production of new cells after gametes fuse during sexual reproduction.
What is the result of asexual reproduction?
Asexual reproduction results in genetically identical offspring from a single parent cell or organism, and it relies on mitosis.
How does mitosis contribute to growth?
Mitosis contributes to growth by increasing cell numbers through the division of cells.
How is sexual reproduction dependent on mitosis?
After the fusion of gametes (sex cells), mitosis is used to produce new cells for growth and development of the offspring.
What is meiosis ?
Meiosis is a type of nuclear division involved in the formation of sex cells (gametes), which reduces the chromosome number by half, different from mitosis.
How does mitosis ensure genetic material is equally shared?
During mitosis, the chromosomes are duplicated and then equally distributed between two daughter cells, ensuring both receive the same genetic material.
What is a chromosome made of?
A chromosome is made up of coiled threads of DNA and proteins.
What happens to chromosomes when a cell starts to divide?
The chromosomes condense, becoming much shorter, denser, and easier to stain and identify.
Why are chromosomes easier to identify when a cell is dividing?
Chromosomes condense and absorb stains readily, making them visible under a microscope.
What role do histones play in chromosome structure?
Histones are positively charged proteins that help package DNA by binding to it, forming nucleosomes that aid in the DNA's efficient coiling.
What are nucleosomes?
Nucleosomes are clusters of DNA wrapped around histone proteins, which help in the condensation of DNA during cell division.
What happens to genes in the supercoiled areas of chromosomes?
In the supercoiled areas, the genes are not available to be transcribed into proteins.
Why are chromosomes not easily seen in a non-dividing cell?
In a non-dividing cell, chromosomes are translucent to both light and electrons, so they cannot be easily seen or identified.
How many chromosomes do human cells have?
Human cells have 46 chromosomes.
How do chromosomes occur in human cells?
Chromosomes occur in matching pairs, with one chromosome from each pair originating from each parent.
hat must a cell do before it divides in mitosis?
Before a cell divides, it must duplicate the original set of chromosomes.
How are chromosomes divided during mitosis?
During mitosis, chromosomes are divided equally between the two new cells, ensuring that each cell has a complete and identical set of genetic information.
What happens to chromosomes during the active phases of cell division ?
During the active phases of cell division, chromosomes become very coiled and condensed.
What is a karyotype?
A karyotype is a special display or photograph of all the chromosomes of a cell, taken when the chromosomes are coiled and condensed during cell division.
What is the cell cycle?
The cell cycle is a sequence of events that a cell goes through to divide and bring about growth or asexual reproduction.
What are the main phases of the cell cycle?
The main phases are Interphase (which includes G1, S, and G2 phases), Mitosis (M phase), and Cytokinesis.
What happens during Interphase?
Interphase consists of three stages:
G1 (Gap 1): Cell growth and preparation for DNA replication.
S (Synthesis): DNA replication occurs.
G2 (Gap 2): Final preparations for mitosis, including the synthesis of proteins necessary for cell division.
What happens during the Mitotic phase?
The Mitotic phase includes two main processes:
Mitosis: The process where the cell’s nucleus divides into two identical nuclei.
Cytokinesis: The division of the cytoplasm to form two daughter cells.
How does the length of the cell cycle vary among different cells?
Some cells, like skin cells, divide rapidly (every 24 hours), while others, like nerve cells, can remain in a resting phase (G0) for years or may never divide.
What is cytokinesis?
Cytokinesis is the process where the cytoplasm of the parent cell is divided between the two daughter cells, completing cell division.
What is the significance of the G1 phase
During G1, the cell grows in size, carries out normal metabolic activities, and prepares for DNA replication in the next phase.
What happens during G1 (Gap 1)?
G1 is the phase between the end of the previous mitotic division and the start of chromosome replication. The cell grows, develops, and takes in materials. The length of G1 is variable, being short in actively dividing cells and long in some cells (even months or years). During G1, the cell grows and carries out its normal functions, including protein synthesis and metabolism.
What occurs during the S phase?
During the S phase, DNA replication occurs, and the chromosomes are duplicated to prepare for cell division.
What is the role of the G2 (Gap 2) phase?
During G2, the cell synthesizes organelles and other materials needed for cell division, ensuring that the cell has two of everything before division. In G2, the cell continues to grow, and more proteins and organelles are produced. The cell also checks for any DNA errors to ensure proper division.
What happens during Mitosis?
Mitosis is the stage when the nucleus actively divides, ensuring the genetic material is evenly distributed between two daughter cells.
What is Cytokinesis?
Cytokinesis is the final step of cell division, where the cytoplasm divides and the new cells separate into two distinct daughter cells.
How does the cell cycle differ during development versus in mature organisms?
In developing organisms, the cell cycle is repeated frequently, especially in actively dividing cells. In mature organisms, the cell cycle may slow down or stop completely in certain tissues.
What controls the progression of the cell cycle?
The cell cycle is controlled by chemical signals, including cyclins, which are proteins that regulate the cycle by activating cyclin-dependent kinases (CDKs). These complexes phosphorylate proteins to trigger the next phase of the cycle.
What is the role of cyclins in the cell cycle?
cyclins are small proteins that build up during the cell cycle and activate cyclin-dependent kinases (CDKs). Together, they phosphorylate target proteins to drive the cell cycle forward.
What is the effect of cyclin-CDK complexes on proteins in the cell?
Cyclin-CDK complexes phosphorylate proteins, which changes their shape and activates processes required for the next phase of the cell cycle. Examples include the phosphorylation of chromatin, making chromosomes denser, and the breakdown of the nuclear membrane during cell division.
What are checkpoints in the cell cycle?
Checkpoints are regulatory points where the cell cycle is assessed to ensure that each phase has been correctly completed before moving on to the next phase. Chemical signals and cyclin-CDK complexes help control progression through these checkpoints.
What is interphase in the cell cycle?
Interphase is the stage in the cell cycle where the cell performs normal metabolic functions, grows, and prepares for division. It consists of three phases: G1, S, and G2.
Why is ATP production increased during interphase?
ATP production is increased to provide the extra energy needed for processes like DNA replication, protein synthesis, and other metabolic activities necessary for cell division.
What marks the end of interphase?
Interphase ends when the cell has sufficient size, all necessary components, and ready DNA, and it proceeds into mitosis.
what are the stages of mitosis ?
Mitosis is the process of cell division that results in two genetically identical daughter cells. It involves stages: prophase, metaphase, anaphase, telophase, and cytokinesis.
How does interphase prepare a cell for mitosis?
Interphase prepares the cell by growing, duplicating its DNA, synthesizing proteins and organelles, and accumulating energy needed for cell division.
What is the "dance of the chromosomes"?
The "dance of the chromosomes" describes the dynamic series of movements during mitosis as chromosomes align in the center and then move to opposite sides of the cell. The "dance of the chromosomes" illustrates the precise movements required to ensure accurate segregation of genetic material during cell division, which is critical for the formation of two identical daughter cells.
What are the four main phases of mitosis?
The four main phases of mitosis are:
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase?
During prophase:
Chromosomes condense and become visible.
The nuclear membrane starts to break down.
The mitotic spindle begins to form.
What happens during metaphase?
During metaphase:
Chromosomes align at the center of the cell (metaphase plate).
Spindle fibers attach to the centromeres of the chromosomes.
What happens during anaphase?
During anaphase:
The sister chromatids are pulled apart toward opposite poles of the cell.
Spindle fibers shorten, separating the chromatids
What happens during telophase?
During telophase:
Chromatids (now individual chromosomes) reach opposite poles.
The nuclear membrane starts to reform around each set of chromosomes.
The chromosomes begin to de-condense back into chromatin.
Why is mitosis considered a continuous process?
Mitosis is continuous because the events flow into each other without distinct breaks, but for clarity, it is broken down into phases: prophase, metaphase, anaphase, and telophase.
What role do the chromosomes play in mitosis?
Chromosomes carry the genetic information that is evenly divided during mitosis, ensuring that each daughter cell receives an identical set.
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