Cell Structure and Functions
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Questions and Answers

What did Robert Hooke observe when he first discovered cells?

  • Bacteria from a water sample
  • Living cells in blood
  • Empty cell walls of dead plant tissue (correct)
  • Sperm cells in a microscope

What limitation did Antonie van Leeuwenhoek face despite his advancements?

  • He could not observe single-celled organisms
  • He could only observe dead cells
  • He had difficulty with low magnification
  • His lenses had low resolution (correct)

Which scientist concluded that all plant tissues are composed of cells?

  • Robert Brown
  • Theodor Schwann
  • Rudolf Virchow
  • Matthias Schleiden (correct)

According to the cell theory, which statement is NOT considered true?

<p>Cells can arise from non-living matter (A)</p> Signup and view all the answers

What is one key characteristic of living things mentioned?

<p>Ability to reproduce (A)</p> Signup and view all the answers

Which limitation did Robert Hooke have with his microscope?

<p>He could only enlarge objects to 30X their normal size (D)</p> Signup and view all the answers

What is the maximum resolution power of a light microscope?

<p>200 nm (A)</p> Signup and view all the answers

Which component of the cell was discovered by Robert Brown?

<p>Nucleus (C)</p> Signup and view all the answers

What discovery is Rudolf Virchow noted for in cell biology?

<p>All cells arise only from pre-existing cells (A)</p> Signup and view all the answers

Which type of microscope provides a three-dimensional view of the specimen's surface?

<p>Scanning electron microscope (B)</p> Signup and view all the answers

Why must specimens be dead when viewed using a transmission electron microscope (TEM)?

<p>Because it operates in a vacuum (B)</p> Signup and view all the answers

What is a significant limitation of light microscopes regarding resolution?

<p>Cannot resolve details finer than 0.2 µm (A)</p> Signup and view all the answers

What must often be used to enhance contrast when observing specimens with a light microscope?

<p>Staining (D)</p> Signup and view all the answers

What was one of the major advancements made by Max Knoll and Ernst Ruska?

<p>The creation of the transmission electron microscope (C)</p> Signup and view all the answers

Which of the following is a disadvantage of the transmission electron microscope?

<p>Produces two-dimensional images (D)</p> Signup and view all the answers

What is the resolving power of an electron microscope?

<p>0.2 nm (B)</p> Signup and view all the answers

What is a primary advantage of using a scanning electron microscope (SEM)?

<p>It displays the surface of structures clearly. (B)</p> Signup and view all the answers

Which statement accurately describes the process of homogenization in cell fractionation?

<p>It uses mechanical disruption to prepare cell samples. (C)</p> Signup and view all the answers

Why is the solution used during homogenization kept cold?

<p>To reduce enzyme activity and prevent autolysis. (A)</p> Signup and view all the answers

During differential centrifugation, what happens to larger and denser particles?

<p>They form a pellet at lower centrifugal forces. (D)</p> Signup and view all the answers

What is the function of the supernatant in the context of differential centrifugation?

<p>It is the fluid that remains above the pellet. (A)</p> Signup and view all the answers

What is the primary purpose of cell fractionation?

<p>To isolate cell components for study of their composition and functions. (A)</p> Signup and view all the answers

What determines the speed and duration of centrifugation in differential centrifugation?

<p>The size and density of the organelles. (B)</p> Signup and view all the answers

Which characteristic makes ultracentrifuges unique compared to regular centrifuges?

<p>They can spin samples at very high speeds. (A)</p> Signup and view all the answers

Which statement about modern cell theory is accurate?

<p>Cells contain DNA passed during cell division. (C)</p> Signup and view all the answers

What distinguishes eukaryotic cells from prokaryotic cells?

<p>Eukaryotic cells are generally larger and more complex. (A)</p> Signup and view all the answers

Which is a method used for studying cells?

<p>Microscopy. (B)</p> Signup and view all the answers

What is the maximum practical magnification of a light microscope?

<p>1000X (C)</p> Signup and view all the answers

What does resolution in microscopy refer to?

<p>The ability to distinguish two close points as separate. (A)</p> Signup and view all the answers

What formula is used to calculate resolution in microscopy?

<p>$R = 0.61 \frac{\lambda}{NA}$ (D)</p> Signup and view all the answers

How does the wavelength of light affect resolution in microscopy?

<p>Shorter wavelengths enhance resolution. (B)</p> Signup and view all the answers

What is the significance of the numerical aperture in microscopy?

<p>It indicates the ability to gather light and resolve detail. (B)</p> Signup and view all the answers

Flashcards

What is biology?

Biology is the study of life and living organisms.

What are the characteristics of living things?

Living things have organized structures, need energy, reproduce, grow, metabolize, respond to stimuli, adapt, move, and respire.

Who discovered cells?

Robert Hooke discovered cells in 1665.

Antonie van Leeuwenhoek's contribution

Leeuwenhoek improved microscopes and observed living cells like blood cells, sperm cells, bacteria, and single-celled organisms.

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What is the nucleus?

Robert Brown discovered the nucleus, a rounded structure found in every cell.

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Cell Theory (1st part)

The first part of the cell theory states that all organisms consist of one or more cells.

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Cell Theory (2nd part)

The second part of the cell theory states that the cell is the basic unit of structure for all organisms.

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What is the Cell Theory?

The Cell Theory explains that all living things are made of cells, and cells are the basic units of structure and function in living organisms.

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Cell Theory

A fundamental theory in biology stating that all living organisms are composed of cells, and that all cells arise from pre-existing cells.

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Prokaryotic Cells

Simple cells lacking a membrane-bound nucleus and other organelles. Examples include bacteria and archaea.

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Eukaryotic Cells

Complex cells containing a membrane-bound nucleus and other organelles. Examples include plants, animals, fungi, algae, and protozoa.

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Cell Fractionation

A technique used to separate different components of a cell, such as organelles, based on their size and density.

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Light Microscope

A microscope that uses visible light to illuminate and magnify a specimen.

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Magnification

The ratio of an object's image size compared to its actual size.

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Resolution

The ability of a microscope to distinguish two adjacent points as separate entities.

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Numerical Aperture (NA)

A measure of a microscope objective's ability to gather light and resolve fine details at a fixed distance.

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Resolution Power

The ability of a microscope to distinguish between two closely spaced objects. The smaller the distance between two objects that can be distinguished, the higher the resolution.

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Light Microscope Limitation

Light microscopes cannot resolve objects smaller than 0.2 micrometers (200 nanometers) due to the wavelength of visible light.

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Electron Microscope

A microscope that uses a beam of electrons to illuminate and magnify a specimen. It has a much higher resolution than a light microscope, allowing for visualization of fine cellular structures.

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Transmission Electron Microscope (TEM)

A type of electron microscope that transmits a beam of electrons through a thin specimen, creating a two-dimensional image. Used to study the internal structure of cells.

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Scanning Electron Microscope (SEM)

A type of electron microscope that scans a beam of electrons across the surface of a specimen to form a three-dimensional image. Used to study the external surface features of cells.

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TEM Advantages

Transmission Electron Microscopes offer high resolution (0.2 nm) for detailed visualization of internal cellular structures.

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TEM Disadvantages

Transmission Electron Microscopes require dead specimens, involve time-consuming and complex preparation, and can be expensive.

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Homogenization

The first step in cell fractionation where cells are mechanically disrupted, usually in a blender, to break down the cell wall and plasma membrane, releasing the organelles.

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Differential Centrifugation

The second step in cell fractionation where the homogenized mixture is spun at different speeds and durations, separating organelles based on their size and density.

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Ultracentrifuge

A very powerful centrifuge used in cell fractionation that spins at very high speeds, enabling the separation of the homogenized mixture into a pellet (heavier components) and a supernatant (lighter components).

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Pellet vs. Supernatant

After centrifugation, the pellet consists of heavier components that settle at the bottom of the centrifuge tube, while the supernatant is the lighter fluid above the pellet.

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Study Notes

Cell Structure and Functions

  • Cells are the basic unit of life.
  • Biology is the study of life and living organisms.
  • Living things exhibit characteristics, including an organized structure, requiring energy for existence, reproduction, growth, metabolism, response to stimuli, adaptation to the environment, movement, and respiration.
  • Cells are made up of organelles.

Discovery of Cells

  • 1665: Robert Hooke observed cork slices using a microscope and coined the term "cells". He only saw empty cell walls of dead plant tissue. His microscope could only magnify 30X.
  • 1650-1700: Antonie van Leeuwenhoek improved microscopes, achieving magnification up to 300X and observed living cells (blood cells, sperm, bacteria, protozoa, algae). His microscopes had limitations in resolution.
  • 1830: Robert Brown discovered the nucleus in cells.
  • 1838: Matthias Schleiden concluded that all plant tissues were made of cells.
  • 1839: Theodor Schwann concluded that all animal tissues are made of cells.
  • 1855: Rudolf Virchow discovered that all cells come from pre-existing cells.

Cell Theory

  • All organisms are composed of one or more cells.
  • The cell is the basic unit of structure and function in all organisms.
  • All cells arise from pre-existing cells.

Modern Cell Theory

  • Cells are the basic units of life.
  • All living things are made up of cells.
  • New cells arise from pre-existing cells.
  • Cells contain DNA, passed during cell division.
  • All cells are similar in chemical composition and metabolic activity.
  • All energy flow occurs within cells.

Cellular Organization

  • Simple: Prokaryotes (bacteria, archaebacteria).
  • Complex: Eukaryotes (plants, animals, fungi, algae, protozoa).
  • Eukaryotes have membrane-bound organelles.
  • Prokaryotes lack membrane-bound organelles.

The Study of Cells

  • Microscopy: The use of microscopes to study cells (with both light and electron microscopes).
  • Light Microscopy: Uses visible light to view specimens, provides magnification and resolution.
    • Resolution is the minimum distance between two points that can still be perceived as separate points (measured in nanometers).
    • Magnification is the measure of the enlargement of an image (using objective lenses and ocular lenses).
    • A lower resolution implies the images will appear blurry.
    • Smaller wavelengths of light provide enhanced resolution. Blue light is often used because its wavelength is shorter than other colors in the visible spectrum.
  • Electron Microscopy: Uses beams of electrons, vastly increasing resolution.
    • Transmission Electron Microscopy (TEM): Transmits electrons through thin tissue sections; produces 2-D images and uses a fluorescent screen or photographic plates (electron micrographs).
    • Scanning Electron Microscopy (SEM): Scans the surface of a specimen, forming a 3-D view of its contours and surface features.
    • The resolving power of a light microscope is about 200nm. The resolving power of an electron microscope is only about 0.2nm.
  • Limitations of the light microscope: The resolving power is limited by the wavelength of light used, and hence, the light microscope can't resolve finer details.
  • Limitations of the electron microscope: Specimens must be dead (for vacuum) and sample preparation can alter the tissue.

Cell Fractionation

  • Homogenization: Mechanical disruption of cells to break the cell wall and plasma membrane, is carried out in a cold, isotonic, buffered solution.

    • Cold temperatures help to reduce enzymatic activity to prevent cell damage.
    • An isotonic solution prevents osmotic damage.
    • A buffered solution helps maintain a stable pH.

  • Differential Centrifugation: Homogenate is centrifuged at different speeds; cellular components are separated based on size and density.

    • Larger and denser particles form pellets at lower speeds, lower centrifugal forces and shorter time duration.

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Description

Explore the fundamental concepts of cell structure and their functions in the living organism in this quiz. Learn about the historical discoveries of cells by scientists like Robert Hooke and Antonie van Leeuwenhoek. Test your knowledge on the characteristics and components of cells.

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