Evolution of Cell Theory: From Aristotle to Microscopy Advancements

1. Unit 3 Cycling of Matter in Living Systems

2. 1.0 The Cell Enduring Understanding: Our current understanding of the cell is due in part to developments in imaging technology • A Window on a New World • Development of the Cell Theory • Development in Imaging Technology and Staining Techniques • Cell Research at the Molecular Level

3. 1.1 A Window on a New World • Our understanding of life processes is the result of developments that date back to the time of Aristotle • Although early Greeks chose to propose answers to questions, but never test them, Aristotle followed a pathway of accurate observation and record making • He classified more than 500 animal species based on his scientific methods • It wasn’t until the development of the microscope that we were able to understand and see the building blocks of life

4. Early Microscopes • Hans and Zacharias Jensen, Dutch lens makers, invented the first compound microscope in 1595 • They used a two lens system, with an eye lens and an objective lens • It had a magnifying power of about 20x • By 1665, Robert Hooke was using a microscope with a three lens system with light illumination • Although he studied lots of items under the microscope, he is most famous for his observations of cork • When he observed cork under the microscope, he saw empty chambers that he called “cells”, which later became the name for the building blocks of life

5. At about the same time, a Dutch business man, Antoine van Leeuwenhoek, was observing single celled organisms under a single lens microscope • He was the first to observe cells living as free, independent systems, and named them “animalcules” • His microscope, although small, was able to view organisms at 250x their original size

6. Improvements in Technology • Early microscopes were often blurry and had a halo of light around the object being viewed • During the 18th century, scientists had discovered a way to correct the lens and develop views that were clear, with better detail than the predecessors

7. 1.2 Development of the Cell Theory • Many scientists helped develop our current understanding of cells • Many had to discredit theories that were long held by people of their time

8. Spontaneous Generation • Spontaneous generation proposes that life could emerge spontaneously from non-living matter • Widely accepted by Greeks and Romans through the 19th century • Ex. Mice developed from underwear and husks of wheat • Ex. Maggots appear spontaneously from meat

9. Contributions of Louis Pasteur • Louis Pasteur disproved the theory of spontaneous generation using the scientific method • Was one of the first scientists to develop the concept of controlled, manipulated and responding variables

10. Scientists Who Contributed to the Development of Cell Theory • It wasn’t until the 1830’s that the importance of the cell was identified • Robert Brown was the first to identify the importance of the nucleus • M.J. Schleiden was the first to identify plant cells, and also proposed that the nucleus was responsible for the development of the rest of the cell • Theodor Schwann believed that there must be similarities between animal and plant cells, and observed similar structures in animal cells, as Schleiden has seen in plant cells

11. The Cell Theory • Together they proposed that all living things were made of cells and that the cell was the basic structure of all living organisms • Rudolf Virchow extended this statement to propose that all existing cells came from pre-existing cells • The Cell Theory States: • All living things are made up of one or more cells • All life functions take place in cells, thus the cell is the smallest unit of life • All cells are produced from pre-existing cells through a process of cell division

12. 1.3 Development in Imaging Technology and Staining Techniques • Light microscope depends on a series of curved lenses to magnify objects with a light source • But they are limited; can only magnify 1000-2000x • Compound microscopes are also limiting because of their contrast and resolution

13. Contrast • Contrast refers to the differences between the organism being viewed and the surrounding of the object being viewed • Most cells are colourless when light passes directly through them under the microscope • Manipulating the light source can alter the contrast between structures in the cell • Scientists also experimented with various stains and colouring agents to improve contrast between the cells and their background • Ex. Methylene Blue or Iodine

14. Resolution • It’s not enough to simply magnify an object • Resolution is an important factor in determining how much can be seen under a microscope • Resolution or resolving power refers to the microscope’s ability to distinguish between two structures that are very close together • It is how much detail can be seen under the microscope

15. Contrast Enhancing Techniques and Fluorescence • Staining is not the only method for developing clear images • Darkfield, phase contrast and differential interference contrast (DIC) illumination are other techniques to help clarify images under the microscope • These techniques all alter the light passing through the specimen • Fluorescence microscopy helps scientists study different parts within the cells by attaching fluorescent substances to molecules within the cell • When viewed under UV light, the molecules fluoresce and individual parts are able to be studied

16. Confocal Technology • The use of laser beams and computers have made it possible to view living, transparent cells in 3-dimension using the compound light microscope • In the confocal microscope, a laser concentrates light into a specimen • The reflection is passed through a tiny opening called the confocal pinhole and reaches an electron detector • Only the light returning from an exact plane of focus can pass through the pinhole to the detector, because out of focus, the light is blocked by the pinhole • Thus, every image formed is of a very thin section through the specimen • This image is stored on a computer to be combined with other images to form a three dimensional image of the object

17. Electron Microscopy • In the first half of the 20th century, as scientists struggled to improve the light microscope, the electron microscope was developed by James Hillier and Albert Prebus • An electron microscope uses a beam of electrons, instead of light waves, producing images with finer detail • The image is formed by the absorption or scattering of the electron beam because electron –dense materials do not let electrons pass through • These microscopes are focused by adjusting the electromagnets, rather than a glass lens

18. Transmission Electron Microscopes (TEM) • Depend on a beam of electrons passed through a very thin section of fixed and stained tissue embedded in plastic • The electrons that pass through fall onto a fluorescent screen/photographic film and black and white photographs are produced • Magnifies up to 1 500 000x and has a much higher resolution than compound microscopes

19. Scanning Electron Microscope (SEM) • The SEM was developed in the 1940’s • This microscope gives views of the surface features of specimens • The specimens are fixed and covered with an electron dense material, like gold which reflects the beam of electrons • The scientist will scan the surface of the specimen, the electrons which are reflected back form a 3-dimensional image of the specimen • Magnifies up to 300 000x

20. 1.4 Cell Research at the Molecular Level • As a result of new technology and technological development, research on cells has made incredible breakthroughs in medicine and industry • The Scanning Tunnelling Microscope (STM) and the Atomic Force Microscope (AFM) allow scientists to produce images of molecules

21. Gene Mapping • Refers to understanding gene placement within the genome of an organism • Scientists have begun to map the genome of many plant and animal species • Helps scientists to understand how genes may work together, and may one day allow scientists to cure genetic-based disease • Gene mapping may also help insert foreign genes into organisms to help benefit the species

22. Cell Communication • Cells are considered open systems, ones which can exchange matter and energy with their environments • To function efficiently, cells need to communicate with neighbouring cells and interpret their environment • For cell-to-cell communication, messenger molecules, known as receptors, travel through the organism and attach at target sites on different cells • The binding of these molecules cause change in shape and trigger a chain reaction to carry the message within the cell • Scientists have found a way to attach fluorescent molecules to the messengers, and thus study cellular process, function and infections of cells

23. Three Dimensional Structure of Molecules • Molecules inside the cell or on its surface act as switches to control cell activity • The structure of the molecule determines the effect that it has on the functioning of the cell • X-ray crystallography uses x-ray and computer technology to allow scientists to study the structure of messenger molecules • Also allows scientists to study normal and defective protein structures within cells

24. GFP Technology and Genetics • Green Fluorescent Protein (GFP) technology has allowed scientists to tag molecules and study their function at a cellular level • It allows scientists to compare normal proteins with abnormal proteins in cell tissues, and may lead to treatment of degenerative diseases, such as Huntington's, Alzheimer’s and Parkinson’s

25. 2.0 The Function of Cell Structures and Organelles Enduring Understanding: Living systems are dependent upon the functioning of cell structures and organelles • The Cell as an Efficient, Open System • The Role of the Cell Membrane in Transport • Applications of Cellular Transport in Industry and Medicine • Is Bigger Better?

26. 2.1 The Cell as an Efficient, Open System • Cells carry on all life processes including: • Intake of Nutrients • Movement • Growth • Response to Stimuli • Exchange of Gases • Waste Removal • Reproduction • Cells work constantly to maintain a balance, while being efficient and conserving energy • Organelles are sub-structures within cells to help meet life processes

27. The Chemical Composition of Cell Structures • Organelles of the cell include: • The cell membrane • The nucleus • The cytoplasm • Cell Wall • Chloroplasts • Vacuoles • Endoplasmic Reticulum • Ribosomes • Lysosomes • Golgi Complex • Mitochondrion

28. Cell Membrane • A protective barrier • Semi-permeable • Useful for cell-to-cell interaction and communication • Interacts with molecules, such as hormones

29. Nucleus • Contains the DNA • Directs cell activity

30. Cytoplasm • Gel – like substance within the cell membrane • Contains nutrients for cell in order to carry on life processes • Organelles are suspended in cytoplasm

31. Cell Wall • Provides structure and support • Found in plant cells, and some protists and fungi

32. Chloroplasts • Found in plants cells and some protists • Contain chlorophyll • Site for photosynthesis

33. Vacuoles • Large structures that store nutrients, secretion and fats • In plants, stores water

34. Endoplasmic Reticulum • Transports materials through a series of tubes • Rough ER has ribosomes attached, associated with protein production • Smooth ER, ribosomes are absent, associated with fat and oil production

35. Ribosomes • Where amino acids are made into proteins during protein synthesis

36. Lysosomes • Membrane bound sacs in which digestion occurs • Defend against invaders • Destruct damaged cell organelles • Digest tissues during development

37. Gogli Complex • Receives proteins from the ER, packages and helps transport them around the cell

38. Mitochondrion • Convert large sugars into usable forms of energy for the cell during the process of cellular respiration

39. What Are Organelles Made Of? • Cell organelles are made of four basic components: • Lipids, like fats and oils • Carbohydrates, such as sugars • Proteins, like muscle fiber • Nucleic Acids, such as DNA • Water is another major component of cell systems

40. Similarities Between Plant and Animal Cells • Both have a cell membrane, and a cytoskeleton – a network of fibers made of proteins and lipids • Both have DNA made of sugars,nitrogen base and phosphate

41. Differences Between Plant and Animal Cells • Animal cells have centrioles, which are involved in reproduction • Animal cells are generally smaller and smoother • Plant cells have a cell wall made of cellulose • Plant cells contain the chemical chlorophyll which makes photosynthesis possible • Plant cells have a large central vacuole • Plant cells are generally larger and more boxy

42. The Structure of the Cell Membrane • The cell membrane is composed of two major components: • Phosopholipids • Glycoproteins

43. Phospholipids • The phospholipids are organized into a lipid bi-layer, which is essentially a double layer of lipids with a phosphate group attached • Each phospholipid has a hydrophilic head made of phosphate and a hydrophobic tail made of lipid • A layer of phospholipid heads faces the inside of the cell, tails pointed inward, and a second layer of heads face the environment tails facing inward

44. Glycoproteins • The glycoproteins are suspended in the phospholipid bi-layer and serve as transport mechanisms for the cell • They also help anchor the cytoskeleton • Proteins may have sugar groups attached, and act as hormone and other chemical receptors

45. The Function of the Cell Membrane • Major Functions of the Cell Membrane: • Helps the cell maintain equilibrium • Allows materials to pass in and out of the cell • Protects the cell from foreign invaders • Holds the cell together • Binds to neighbouring cells • Communicates with neighbouring cells using chemical transmitters

46. 2.2 The Role of the Cell Membrane in Transport • The cell membrane is very important at transporting materials inside and outside of the cell • Two basic process that are controlled by the cell membrane: (1) Passive Transport (2) Active Transport • Cell membranes are selectively permeable in the type of substances that are permitted to pass through the cell membrane • This means that some substances are able to be transported, while other substances are not

47. The Particle Model of Matter • All matter is made of molecules; particles in different substances may vary in size and composition • Particles are constantly moving; particles in gases have more energy than in solids • The particles of matter are attracted to one another or are bonded together • Particles have spaces between them; spaces being smaller in solids than in gases

48. Passive Transport • Passive Transport is a form of cell transport that does not use additional energy to transfer substances across the cell membrane • The only energy required is kinetic molecular energy, or energy contained naturally in each atom • Three forms of passive transport include: • Diffusion • Facilitated Diffusion • Osmosis

49. Diffusion • Diffusion is the natural movement of particles from a region of high concentration to a region of low concentration • A concentration gradient is all that is required; an uneven distribution of concentrations • Molecules are small enough, and soluble in lipids, that they can slip easily through the phospholipid bi-layer of the cell • The charge of the particle, or how soluble the molecule is in lipids will also determine whether of not it will use this form of transport • Gases diffuse more quickly than liquids, which diffuse more quickly than solids • Ex. Oxygen, carbon dioxide, nitrogen, salts, potassium ions