Learn about the discovery of cells, their structure, organization, and the differences between prokaryotic and eukaryotic cells. Understand cell organelles, cell…
This chapter explores the fascinating world of cells, the basic units of life. You'll learn about the discovery of cells, their structure and organization, and the differences between prokaryotic and eukaryotic cells. The chapter also covers cell organelles and their functions, cell division processes like mitosis and meiosis, and the role of the plasma membrane in cell transport. Understanding cells is crucial as they are the foundation of all living organisms, from single-celled bacteria to complex multicellular humans.
This chapter introduces the concept of cells as the basic units of life. It covers the discovery of cells, their structure, organization, and the differences between prokaryotic and eukaryotic cells. The chapter also explores the functions of various cell organelles, the processes of cell division, and the role of the plasma membrane in cell transport. Understanding these concepts is essential as cells are the foundation of all living organisms.
The discovery of cells dates back to 1665 when Robert Hooke observed small box-like compartments in a thin slice of cork using a self-designed microscope. He named these compartments 'cells'. This discovery marked the beginning of cell biology. Over the years, scientists have improved microscopes, enhancing their resolution, contrast, and magnification, which has allowed us to study cells in greater detail. Light microscopes are commonly used in school laboratories to observe objects, while electron microscopes reveal fine details of cell structure.
Cells are organized into specialized tissues and organs, which collectively perform specific functions. For these cells to function as units, they must interact with one another and their surroundings. These interactions occur at the cell boundary, where substances move between the cells and their external environment. Even single-celled organisms exchange materials and respond to their environment through the cell membrane. The cell membrane is a thin boundary that surrounds a cell and protects its contents, defining the individuality of a cell.
Prokaryotic cells, such as bacteria, lack a well-defined nucleus and membrane-bound organelles. In these cells, most cellular activities take place directly in the cytoplasm. Eukaryotic cells, found in plants, animals, and fungi, have a well-defined nucleus and several membrane-bound organelles. These cells are larger and more complex than prokaryotic cells. The nucleus of eukaryotic cells contains chromosomes, which carry genetic information. Both prokaryotic and eukaryotic cells are surrounded by a cell membrane, but plant, fungal, and bacterial cells also have a cell wall outside the cell membrane.
Cell organelles are specialized structures within a cell that perform specific functions. The nucleus, often referred to as the 'control center' of the cell, contains the cell's genetic material and controls its activities. The endoplasmic reticulum (ER) is involved in the synthesis and transport of proteins and lipids. The Golgi apparatus modifies, sorts, and packages proteins and lipids for transport, secretion, or lysosome formation. Lysosomes are involved in the breakdown of unwanted materials and damaged organelles. Mitochondria, known as the 'powerhouses of the cell', supply the energy needed for most cellular activities. Plastids, found in plant cells, are involved in photosynthesis and the storage of food. Vacuoles store water, minerals, sugars, and waste materials, and help maintain pressure inside the cell.
Cell division is the process by which new cells are formed from pre-existing cells. It allows living organisms to grow, repair damaged tissues, and reproduce. There are two major types of cell division: mitosis and meiosis. Mitosis produces two genetically identical daughter cells from one parent cell and is important for normal growth, repair, maintenance, and asexual reproduction. Meiosis, on the other hand, is important for sexual reproduction and the creation of genetic diversity. It produces four daughter cells, each with half the number of chromosomes as the parent cell. Errors in mitosis or meiosis can lead to various problems in the body, such as the formation of tumours or genetic disorders.
The plasma membrane, also known as the cell membrane, is a thin boundary that surrounds a cell and protects its contents. It is selectively permeable, allowing some substances to pass through while blocking others. The structure of the cell membrane controls the movement of substances across it. The fluid-mosaic model explains the structure of the cell membrane, which consists of a lipid bilayer with proteins embedded in it. These proteins act like gatekeepers, helping substances pass through the membrane. The cell membrane allows water to move in and out of the cell but not sugar or salt molecules, a process known as osmosis. This movement of water is driven by a difference in concentration, also known as a concentration gradient.
Try each question first, then reveal the answer.
What is the smallest unit of life?
A cell is the basic building block of all living things and the smallest unit of life.
Which of the following is a characteristic feature of prokaryotic cells?
Prokaryotic cells lack a well-defined nucleus and membrane-bound organelles; their genetic material is present in a region called the nucleoid.
Which organelle is known as the powerhouse of the cell?
Mitochondria produces energy (ATP) for the cell, so it is called the powerhouse of the cell.
What is the primary purpose of mitosis in multicellular organisms?
Mitosis is important for normal growth, repair, maintenance, and asexual reproduction, producing genetically identical daughter cells.
What is the plasma membrane also known as?
The plasma membrane is the outer boundary of the cell and is also called the cell membrane. It controls what enters and leaves the cell.
Q1. Define a cell. Why is it called the fundamental unit of structure and function in all living organisms?
A cell is the basic structural and functional unit of all living organisms. It is called so because all living organisms are made up of cells, and the cell is the smallest unit that can carry out all life processes. Cells organize to form tissues, organs, and organ systems, yet the cell remains the fundamental unit of structure and function.
Q2. Who discovered the cell and how? What was the term 'cell' used for in that discovery?
Robert Hooke discovered the cell in 1665. He used a self-designed microscope with about 200–300X magnification to examine a thin slice of cork. He observed small box-like compartments and named them 'cells'. These were actually dead cork cells, and the term 'cell' referred to the empty compartments he saw.
Q3. Differentiate between prokaryotic and eukaryotic cells based on the presence of a nucleus and membrane-bound organelles. Give one example of each.
Prokaryotic cells lack a well-defined nucleus; their genetic material is present in a region called the nucleoid, and they do not have membrane-bound organelles. Eukaryotic cells have a well-defined nucleus enclosed by a nuclear membrane and contain membrane-bound organelles. Examples: prokaryotic – bacteria; eukaryotic – plant or animal cells.
Q4. Differentiate between prokaryotic and eukaryotic cells based on the presence of a nucleus and membrane-bound organelles. Give one example of each.
Prokaryotic cells lack a well-defined nucleus; their genetic material is present in a region called the nucleoid, which is not enclosed by a nuclear membrane. They also lack membrane-bound organelles. In contrast, eukaryotic cells have a well-defined nucleus enclosed by a nuclear membrane and contain several membrane-bound organelles. Examples: bacteria are prokaryotic, while plant and animal cells are eukaryotic.
Q5. Differentiate between rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) based on their structure and function.
RER has ribosomes attached to its surface, giving it a rough appearance, and is mainly involved in protein synthesis and secretion. SER lacks ribosomes, appears smooth, and is involved in the synthesis and storage of fats and hormones.
A cell is the basic unit of life and the foundation of all living organisms. It is the smallest unit that can perform all necessary functions of life.
Prokaryotic cells lack a well-defined nucleus and membrane-bound organelles, while eukaryotic cells have a well-defined nucleus and several membrane-bound organelles. Eukaryotic cells are larger and more complex than prokaryotic cells.
The nucleus, often referred to as the 'control center' of the cell, contains the cell's genetic material and controls its activities. It is involved in the synthesis of ribosomal subunits and the regulation of gene expression.
Mitochondria, known as the 'powerhouses of the cell', supply the energy needed for most cellular activities. They break down glucose and other molecules to release energy during a process called cellular respiration.
Mitosis produces two genetically identical daughter cells from one parent cell and is important for normal growth, repair, maintenance, and asexual reproduction. Meiosis, on the other hand, is important for sexual reproduction and the creation of genetic diversity. It produces four daughter cells, each with half the number of chromosomes as the parent cell.
The plasma membrane, also known as the cell membrane, is a thin boundary that surrounds a cell and protects its contents. It is selectively permeable, allowing some substances to pass through while blocking others. The structure of the cell membrane controls the movement of substances across it.
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