UNIT 5: Cell Theory

Project Number: 2023-1-PL01-KA220-SCH-000164042

UNIT 5: Cell Theory

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Education and Culture Executive Agency (EACEA). Neither the European Union nor EACEA can be held responsible for them.

Introduction

In this activity you will explore different types of cells and the similarities and differences between them.

Learning Outcomes

Student:

• Compare animal and plant cells in terms of their basic parts and functions.
• Specifies the names and functions of cell organelles.

Source: freepik.com

CELL: Smallest Unit of Life

• The cell is the smallest unit of life. Every human, animal, or plant around you is referred to as an organism. Cells are the fundamental building blocks of all these organisms.
• In multicellular organisms, certain types of cells come together to form tissues like muscle tissue, connective tissue, and nerve tissue, working together to perform specific functions.
• Some of these tissues combine to create organs such as the stomach, heart, or brain.
• Furthermore, certain organs work together to form organ systems like the digestive system, circulatory system, or nervous system. Through the coordination of these systems, organisms are formed.

Now, let's take a little journey with you on how the wage was discovered.

Source: canva.com

What is Cell Theory?

• For centuries, the origins of life and the nature of living organisms have been subjects of great curiosity for humanity. This curiosity has driven people to ask questions about the beginning of life and how it emerged.
• Until the 1600s, researchers could only gather information about the types of living organisms they could observe and were unaware of the existence of microscopic life forms.

What is Cell Theory?

• Where did the disease-causing microbes and molds come from?
• How did they reproduce?
• What were the components of each of their parts?
• If there were smaller components, what did they look like?

These questions remained unanswered until the invention of the microscope.

Source: canva.com

What is Cell Theory?

• With the invention of the microscope, a whole new world previously hidden from view was suddenly revealed, and insights into this microscopic realm began to enter our lives at an astonishing rate.
• In 1674, the Dutch scientist Antonie van Leeuwenhoek examined a sample of sticky fluid from his teeth using a microscope he had built himself. He discovered tiny structures he referred to as "animalcules," meaning "little animals." Leeuwenhoek is celebrated as the "Father of Microbiology" for uncovering this previously invisible world of living organisms.

What is Cell Theory?

• Around the same time, English scientist Robert Hooke examined thin slices of cork under the microscope and noticed a series of small, box-like structures. He named these structures "cells" due to their resemblance to the small rooms or cells in a monastery. Hooke's discovery marked the first time that cells were observed and described.

This observation laid the groundwork for the first doctrine of Cell Theory: “Cells are the smallest building blocks of living things.”

What is Cell Theory?

• In 1831, approximately 200 years after the initial discovery of the cell, Robert Brown identified the cell nucleus. By 1838, zoologist Theodore Schwann and botanist Mathias Schleiden, through their examinations of plants and animals, discovered similarities between the cells of both organisms. Their experiments revealed that these cells shared the same nuclear structure.

This led to the formulation of the second doctrine of Cell Theory: "All living organisms are composed of one or more cells."

What is Cell Theory?

• As a result of all these experiments and research, scientists began to wonder: If animals arise from other animals and plants arise from other plants, then what are bacteria made of?
• At that time, the prevailing view on microorganism reproduction was still influenced by Aristotle's idea of "spontaneous generation.“
• However, in 1858, Rudolf Virchow examined the division of bacteria and described this process as "binary fission." His research led him to conclude that all cells arise from pre-existing cells, thus challenging the notion of spontaneous generation and further refining Cell Theory.

What is Cell Theory?

• Years before Virchow, Lazzaro Spallanzani had disproved the theory of spontaneous generation by demonstrating that microbes came from the air and could be killed through boiling.
• Despite his findings, he struggled to find support for his ideas at that time. Nearly a century later, Louis Pasteur conducted experiments that supported Spallanzani's work, ultimately disproving the theory of spontaneous generation and solidifying the concept that microorganisms arise from other microorganisms.

Thus, the third doctrine of Cell Theory was established: "Cells arise from pre-existing cells."

What is Cell Theory?

• Each subsequent scientific study has taken our understanding of the cell one step further. For example, Schultze noted that physical and chemical effects in animal and plant cells are similar.
• However, differences between the two types of cells were also observed, with Cohn being the first to discover the presence of a cellulosic membrane. In animal cells, this membrane allows for more flexible movement and interaction with the external environment, while in plant cells, the cellulosic membrane permits only internal movement.

Source: canva.com

What is Cell Theory?

• In 1853, Huxley introduced the concept of the cell membrane, emphasizing its significance both chemically and morphologically, as it lies beneath the cell wall. Huxley also highlighted that living organisms do not arise spontaneously but through a process involving the fusion of sperm and egg, suggesting that a new organism is produced through this combination rather than by asexual reproduction alone.

What is Cell Theory?

• By the late 19th century, the development of staining techniques for cells under the microscope allowed for a clearer observation of the cytoplasm.
• This led to the discovery of various specialized structures known as organelles. Initially, the endoplasmic reticulum was identified, followed by the discovery of mitochondria and the Golgi apparatus, revealing that the cytoplasm is not empty but composed of living structures.

What is Cell Theory?

• Subsequent discoveries included observations of how cells divide, the mechanisms of division, chromatin structure, and the stages of mitosis and metaphase. These advancements significantly enhanced our understanding of cellular processes and structures.

Now that we’ve learned about the basics of Cell Theory, let’s dive into the different parts of a cell. By getting to know the various organelles and what they do, we can better understand how a cell works and keeps everything running smoothly.

LEARNING ACTIVITY:

In this activity you will explore the similarities and differences between cell types of different organisms.

• An organelle is a small structure within a cell that has a specific job to do. Just like organs in our body have their own special functions, organelles have their own unique tasks inside the cell.

This is why they are called organelles—because they work like the organs of a cell.

• The shape and structure of a cell can differ depending on the type of tissue it is attached to. You may have noticed that the image of an animal cell and the image of a nerve cell in your textbooks are not very similar. This is because the cell has specialized functions according to the tissue to which it is attached.

Therefore, keep in mind that the number and shape of organelles may differ depending on the cell type.

Let's Explore Together

• The development of cells provides us with various clues about the level of development of the organism to which that cell belongs. For example, some cells had a nucleus while others did not. This difference is very important for the classification of cells.
• Cells are divided into two types according to whether they have nuclei or not: Cells with a nucleus are called prokaryotes and cells with a nucleus are called "eukaryotes".

Scan the QR code on the right to learn more.

Let's Explore Together

• This difference in level of development also affects the organelles. However, eukaryotic and prokaryotic cells can also differ in terms of organelle structure.
• For example, an organelle in a eukaryotic animal cell may not be present in a eukaryotic plant cell (or vice versa). However, there are also organelles that are common to all cell types, regardless of the cell type. It can be stated that these organelles are essential for the cell to maintain its vitality.

Scan the QR code on the right to learn more.

Let's Explore Together

• Discovering this is an important step in our understanding of how life on earth began at the most basic level, and how today's advanced complex organisms evolved from single-celled organisms.

During the activity you will observe that some organelles are found in all cell types, while others are found only in some cells. What were the differences you noticed during your observations? ……………………………………………………………………………………………………………………………………………………………………………………………………………………………............................................. What structures do you observe as common to all cell types? ……………………………………………………………………………………………………………………………………………………………………………………………………………………………….........................................