2021 Ch 5. Teoría celular (Cell Theory).

 Período 1. Capítulo 3. Semana 7.

Ø    Preliminares

Tiempos

Desde (19-04-2021) hasta (25-04-2021). Nota de puntualidad 50.

Desde (26-04-2021) hasta (30-04-2021). Nota de puntualidad 40.

Desde (01-05-2021) hasta (02-05-2021). Nota de puntualidad 30.

Después del (21-05-2021) Nota de puntualidad 20, más penalización de 5 puntos en cada actividad.

Eje temático

- Bioelementos, biocompuestos y nutrición

Objetivos

- Reconocer las moléculas que constituyen a las células, tejidos, órganos, sistemas y organismos y lo indispensables que son ellas para el sostenimiento de la vida sobre la tierra.

Ø    Contents and activities

Encuesta correos electrónicos.

https://docs.google.com/forms/d/e/1FAIpQLSfKZBQDgKedazNVkU3EfLmYVXEThcHcKCDzefrnjxIRUmARqQ/viewform

           Engagement

(5.1) Draw the following pictures in your notebook.

(5.2) Look at the following pictures and write three ideas for each picture in English and Spanish that relate them to the ideas of (theory) and (cell).

        Exploration

(5.3) Write everything you know about cells, it can be data from previous courses, documentaries, or TV shows and movies. (You can give the answer in Spanish).

(5.4) Look up the word “cell” in an English-Spanish or English-English dictionary, and write each possible meaning with an example drawing.

Explanation

          (5.5) Read the following text

The cell was first discovered by Robert Hooke in 1665, which can be found to be described in his book Micrographia. In this book, he gave 60 ‘observations’ in detail of various objects under a coarse, compound microscope. One observation was from very thin slices of bottle cork. Hooke discovered a multitude of tiny pores that he named "cells". This came from the Latin word Cella, meaning ‘a small room’ like monks lived in and also Cellulae, which meant the six sided cell of a honeycomb.

However, Hooke did not know their real structure or function. What Hooke had thought were cells, were actually empty cell walls of plant tissues. With microscopes during this time having a low magnification, Hooke was unable to see that there were other internal components to the cells he was observing. Therefore, he did not think the "cellulae" were alive.

fig 5.1. Robert Hooke's microscope.

fig 5.2. A reproduction of Anton van Leeuwenhoek's microscope from the 17th century with a magnification of 300x

His cell observations gave no indication of the nucleus and other organelles found in most living cells. In Micrographia, Hooke also observed mould, bluish in color, found on leather. After studying it under his microscope, he was unable to observe “seeds” that would have indicated how the mould was multiplying in quantity. This led to Hooke suggesting that spontaneous generation, from either natural or artificial heat, was the cause. Since this was an old Aristotelian theory still accepted at the time, others did not reject it and was not disproved until Leeuwenhoek later discovered that generation was achieved otherwise.

Antonie Philips van Leeuwenhoek (1632-1723) was a Dutch businessman and scientist in the Golden Age of Dutch science and technology. A largely self-taught man in science, he is commonly known as "the Father of Microbiology", and one of the first microscopists and microbiologists.

While running his draper shop, van Leeuwenhoek wanted to see the quality of the thread better than what was possible using the magnifying lenses of the time. He developed an interest in lens making, although few records exist of his early activity. After developing his method for creating powerful lenses and applying them to the study of the microscopic world, van Leeuwenhoek introduced his work to his friend, the prominent Dutch physician Reinier de Graaf. When the Royal Society in London published the groundbreaking work of an Italian lensmaker in their journal Philosophical Transactions of the Royal Society, de Graaf wrote to the editor of the journal, Henry Oldenburg, with a ringing endorsement of van Leeuwenhoek's microscopes which, he claimed, "far surpass those which we have hitherto seen". In response, in 1673 the society published a letter from van Leeuwenhoek that included his microscopic observations on mold, bees, and lice.

Over time, he wrote many more papers in which described many specific forms of microorganisms. Leeuwenhoek named these “animalcules,” which included protozoa and other unicellular organisms, like bacteria. Though he did not have much formal education, he was able to identify the first accurate description of red blood cells and discovered bacteria after gaining interest in the sense of taste that resulted in Leeuwenhoek to observe the tongue of an ox, then leading him to study "pepper water" in 1676. He also found for the first time the sperm cells of animals and humans. Once discovering these types of cells, Leeuwenhoek saw that the fertilization process requires the sperm cell to enter the egg cell. This put an end to the previous theory of spontaneous generation. After reading letters by Leeuwenhoek, Hooke was the first to confirm his observations that were thought to be unlikely by other contemporaries.

The cells in animal tissues were observed after plants were because the tissues were so fragile and susceptible to tearing, it was difficult for such thin slices to be prepared for studying. Biologists believed that there was a fundamental unit to life, but were unsure what this was. It would not be until over a hundred years later that this fundamental unit was connected to cellular structure and existence of cells in animals or plants. This conclusion was not made until Henri Dutrochet. Besides stating “the cell is the fundamental element of organization”, Dutrochet also claimed that cells were not just a structural unit, but also a physiological unit. In 1804, Karl Rudolphi and J.H.F. Link were awarded the prize for "solving the problem of the nature of cells", meaning they were the first to prove that cells had independent cell walls by the Königliche Societät der Wissenschaft (Royal Society of Science), Göttingen. Before, it had been thought that cells shared walls and the fluid passed between them this way.

Credit for developing cell theory is usually given to two scientists: Theodor Schwann and Matthias Jakob Schleiden. While Rudolf Virchow contributed to the theory, he is not as credited for his attributions toward it. In 1839, Schleiden suggested that every structural part of a plant was made up of cells or the result of cells. He also suggested that cells were made by a crystallization process either within other cells or from the outside. However, this was not an original idea of Schleiden. He claimed this theory as his own, though Barthelemy Dumortier had stated it years before him. This crystallization process is no longer accepted with modern cell theory. In 1839, Theodor Schwann states that along with plants, animals are composed of cells or the product of cells in their structures. This was a major advancement in the field of biology since little was known about animal structure up to this point compared to plants. From these conclusions about plants and animals, two of the three tenets of cell theory were postulated.

1. All living organisms are composed of one or more cells

2. The cell is the most basic unit of life

Schleiden's theory of free cell formation through crystallization was refuted in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker. In 1855, Rudolf Virchow added the third tenet to cell theory. In Latin, this tenet states Omnis cellula e cellula. This translated to:

3. All cells arise only from pre-existing cells

However, the idea that all cells come from pre-existing cells had in fact already been proposed by Robert Remak; it has been suggested that Virchow plagiarized Remak and did not give him credit. Remak published observations in 1852 on cell division, claiming Schleiden and Schawnn were incorrect about generation schemes. He instead said that binary fission, which was first introduced by Dumortier, was how reproduction of new animal cells were made. Once this tenet was added, the classical cell theory was complete.

The generally accepted parts of modern cell theory include:

1-   All known living things are made up of one or more cells.

2-   All living cells arise from pre-existing cells by division.

3-   The cell is the fundamental unit of structure and function in all living organisms.

4-   The activity of an organism depends on the total activity of independent cells.

5-   Energy flow (metabolism and biochemistry) occurs within cells.

6-   Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm.

7-   All cells are basically the same in chemical composition in organisms of similar species.

Elaboration

(5.6) Translate the following ideas to Spanish: (draper shop); (quality of the thread); (magnifying lenses).

(5.7) Draw a cartoon of 6 or more pictures that describes the research process of Antonie Philips van Leeuwenhoek. (Use English in text boxes)

(5.8) Describe the importance of the first two microscopists and their names. (You can give the answer in Spanish).

(5.9) How was the relationship between the first microbiologists? did they reach harmonious agreements, or were they copied and faced in disputes for the recognition of scientific communities? (You can give the answer in Spanish).

(5.10) Translate the modern principles of cell theory into Spanish and draw a picture of each one.

Evaluation

The following exercise is based on analyzing a graph of bacterial growth in a medium with limited food. Originally the bacterium has a low population and therefore there is a lot of food, which allows it to reproduce. However, as the population grows and consumes its resources, it is more difficult to feed itself, so its reproductive rate stops, and with time it begins to die out.

fig 5.3.  Typical bacterial growth chart. The number of cells is represented on the y-axis, so the higher the point, the more cells are counted in units of (log₁₀ viable cells/ml). The x-axis represents time, so the more to the right the point is, the measurement of the number of cells was made later.

(5.11) Approximately how many (log₁₀ viable cells/ml) of bacteria are there before the t₀ mark?

(5.12) How does the growth rate differ after t₀ and before t?

(5.13) What happens to bacterial growth after t?

(5.14) If the above measurement was made in a growth medium with limited feed, how can you explain the growth rate between t0 and t?

(5.15) If the above measurement was made in a growth medium with limited feed, how can you explain the growth rate after t?

Impacto vital

(5.16) Como parte de las actividades del PROYECTO AMBIENTAL ESCOLAR PRAE, se realizará la actividad de sensibilización ecológica, que consiste en dibujar el ave dada en el siguiente tutorial (Turdus fuscater), junto con su descripción zoológica. Se proporciona enlace donde encuentra un tutorial de su dibujo y descripción de sus características. https://youtu.be/rx5o5v8M13E  Dado la naturaleza virtual de esto, solo lo realizarán los estudiantes de trabajo virtual, siendo una nota de bonificación.