NCERT-CELL: STRUCTURE AND FUNCTIONS-Line-by-Line Explanation-Biology is the study of living organisms. The detailed description of their form and appearance only brought out their diversity

Sentence 1: Biology is the study of living organisms.

This introductory sentence establishes biology as the scientific discipline dedicated to investigating all living things, from the towering redwood trees (Sequoia sempervirens) to the microscopic bacteria thriving in our gut.

Sentence 2: The detailed description of their form and appearance only brought out their diversity.

Focusing solely on outward appearances highlights the incredible range of life on Earth. Consider the colossal blue whale (Balaenoptera musculus), the largest animal ever recorded, compared to the single-celled paramecium, barely visible to the naked eye.

Sentence 3: It is the cell theory that emphasised the unity underlying this diversity of forms, i.e., the cellular organisation of all life forms.

The concept of cell theory, proposed by scientists like Theodor Schwann and Matthias Jakob Schleiden in the mid-1800s, bridges this apparent gap. It reveals a unifying principle – all living organisms, from the majestic lion (Panthera leo) to the humble yeast cell (Saccharomyces cerevisiae), are composed of cells, the fundamental unit of life.

Sentence 4: A description of cell structure and cell growth by division is given in the chapters comprising this unit.

The upcoming chapters will likely delve deeper into the fascinating world of cells, exploring their intricate structures and the remarkable process of cell division (mitosis) that allows organisms to grow and reproduce.

Sentence 5: Cell theory also created a sense of mystery around living phenomena, i.e., physiological and behavioural processes.

Cell theory presented a fascinating puzzle. If all life is cellular, what makes each organism function and behave in unique ways? This “mystery” refers to the physiological processes (internal functions) like digestion and respiration, and behavioral patterns (how organisms interact with their environment) that distinguish living things.

Sentence 6: This mystery was the requirement of integrity of cellular organisation for living phenomena to be demonstrated or observed.

The “mystery” unfolds here. To understand how organisms function and behave, their cellular organization must be intact. Disrupting a cell’s structure would prevent us from observing these vital processes.

Sentence 7: In studying and understanding the physiological and behavioural processes, one can take a physico-chemical approach and use cell-free systems to investigate.

This introduces a powerful method for studying life – the physico-chemical approach. It involves applying the principles of physics and chemistry to elucidate biological processes. Interestingly, this approach can utilize “cell-free systems,” which means investigating these processes in extracts or purified components isolated from cells.

Sentence 8: This approach enables us to describe the various processes in molecular terms.

A significant benefit of the physico-chemical approach is the ability to explain various biological processes in terms of molecules, the building blocks of life. For instance, studying the enzyme pepsin in a cell-free extract helps us understand the process of protein digestion at the molecular level.

Example: Unveiling the Secrets of DNA with Reductionist Biology

Here, we can insert the example about DNA:

Physico-Chemical Techniques: Techniques like X-ray diffraction were crucial in determining the double-helix structure of DNA by Rosalind Franklin and Maurice Wilkins in 1953. This technique uses X-rays to analyze the arrangement of atoms within a molecule, providing insights into DNA’s structure.

Isolation and Purification: Applying reductionist principles, scientists like Friedrich Miescher isolated DNA in the 1860s from white blood cells. This isolation allowed for further characterization of DNA’s chemical properties separate from other cellular components.

Reduction of DNA to its Building Blocks: Reductionist biology breaks down DNA into its fundamental units – nucleotides. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, thymine, or cytosine). Understanding the chemical interactions between these building blocks helps explain how DNA stores and transmits genetic information.

DNA Sequencing: Techniques like Sanger sequencing, a landmark achievement in reductionist biology, allowed scientists to determine the order of these nitrogenous bases in a DNA molecule. This provided a way to “read” the genetic code and understand how DNA encodes instructions for building proteins and other essential molecules.

Sentence 9: The approach is established by analysis of living tissues for elements and compounds.

This explains the initial steps of the physico-chemical approach. Scientists analyze living tissues to identify the elements and compounds (molecules) present within them. Techniques like chromatography can be used to separate and identify these molecules.

Sentence 10: It will tell us what types of organic compounds are present in living organisms.

Analyzing tissues reveals the types of organic molecules (carbon-based molecules) that make up living things. These include carbohydrates, proteins, lipids, and nucleic acids, each playing essential roles in cellular functions.

Sentence 11: In the next stage, one can ask the question: What are these compounds doing inside a cell? And, in what way they carry out gross physiological processes like digestion, excretion, memory, defense, recognition, etc.

This delves deeper. Once we know the organic molecules present, the next step is to understand their function within cells. These molecules are the key players in essential life processes like digestion (enzymes like pepsin break down food molecules), excretion (transport proteins remove waste products), memory (proteins involved in signal transmission in the brain), and many more.

Sentence 12: In other words, we answer the question, what is the molecular basis of all physiological processes? It can also explain the abnormal processes that occur during any diseased condition.

This clarifies the ultimate goal – to understand the molecular basis of all life functions. By knowing how molecules work within cells, we can also explain why these processes go awry in diseases. For example, mutations

Biology and Cell Theory

Biology is the study of living organisms. The detailed description of their form and appearance only brought out their diversity. It is the cell theory that emphasized the unity underlying this diversity of forms, i.e., the cellular organization of all life forms. A description of cell structure and cell growth by division is given in the chapters comprising this unit.

Biology and Cell Theory (continued)

Cell theory also created a sense of mystery around living phenomena, i.e., physiological and behavioral processes. This mystery was the requirement of integrity of cellular organization for living phenomena to be demonstrated or observed. In studying and understanding the physiological and behavioral processes, one can take a physico-chemical approach and use cell-free systems to investigate.

Biology and Cell Theory (continued)

This approach enables us to describe the various processes in molecular terms. The approach is established by the analysis of living tissues for elements and compounds. It will tell us what types of organic compounds are present in living organisms. In the next stage, one can ask the question: What are these compounds doing inside a cell? And, in what way they carry out gross physiological processes like digestion, excretion, memory, defense, recognition, etc.

G.N. Ramachandran

G.N. RAMACHANDRAN, an outstanding figure in the field of protein structure, was the founder of the ‘Madras school’ of conformational analysis of biopolymers. His discovery of the triple helical structure of collagen published in Nature in 1954 and his analysis of the allowed conformations of proteins through the use of the ‘Ramachandran plot’ rank among the most outstanding contributions in structural biology. He was born on October 8, 1922, in a small town, not far from Cochin on the southwestern coast of India. His father was a professor of mathematics at a local college and thus had considerable influence in shaping Ramachandran’s interest in mathematics. After completing his school years, Ramachandran graduated in 1942 as the top-ranking student in the B.Sc. (Honors) Physics course of the University of Madras. He received a Ph.D. from Cambridge University in 1949. While at Cambridge, Ramachandran met Linus Pauling and was deeply influenced by his publications on models of the α-helix and β-sheet structures that directed his attention to solving the structure of collagen. He passed away at the age of 78, on April 7, 2001.

G.N. Ramachandran (continued)

His discovery of the triple helical structure of collagen published in Nature in 1954 and his analysis of the allowed conformations of proteins through the use of the ‘Ramachandran plot’ rank among the most outstanding contributions in structural biology. He was born on October 8, 1922, in a small town, not far from Cochin on the southwestern coast of India. His father was a professor of mathematics at a local college and thus had considerable influence in shaping Ramachandran’s interest in mathematics.

G.N. Ramachandran (continued)

After completing his school years, Ramachandran graduated in 1942 as the top-ranking student in the B.Sc. (Honors) Physics course of the University of Madras. He received a Ph.D. from Cambridge University in 1949. While at Cambridge, Ramachandran met Linus Pauling and was deeply influenced by his publications on models of the α-helix and β-sheet structures that directed his attention to solving the structure of collagen.

G.N. Ramachandran (continued)

He passed away at the age of 78, on April 7, 2001.

Cell Theory

In 1838, Matthias Schleiden, a German botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. At about the same time, Theodore Schwann (1839), a British Zoologist, studied different types of animal cells and reported that cells had a thin outer layer which is today known as the ‘plasma membrane’. He also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character of the plant cells. On the basis of this, Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells. Schleiden and Schwann together formulated the cell theory. This theory however, did not explain as to how new cells were formed. Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape. Cell theory as understood today is: (i) all living organisms are composed of cells and products of cells. (ii) all cells arise from pre-existing cells.

Cell Theory (continued)

Cell theory has been one of the fundamental theories in biology, forming the basis for our understanding of life and living organisms. It highlights the significance of cells as the basic structural and functional units of all living organisms. The theory’s development over time, from its initial formulation by Schleiden and Schwann to its refinement by Rudolf Virchow, underscores the collaborative and cumulative nature of scientific progress.