Define Negative Correlation

A cell is the fundamental unit of life, and the study of cells, from their basic structure to the functions of each cell organelle, is known as Cell Biology. Robert Hooke was the first biologist to discover cells.

All living organisms are composed of cells, which can be either single-celled (unicellular) or multicellular. Mycoplasmas are the smallest known cells. Cells serve as the foundational building blocks of all life forms, providing structural support and converting nutrients into energy.

Cells exhibit diversity in terms of shape and size, much like the bricks used in constructing buildings. The human body, for example, consists of cells of various shapes and sizes.

Cells represent the most basic level of organization in any living organism, and the number of cells varies from one organism to another. Humans, for instance, have more cells than bacteria.

Within cells, various organelles perform specialized functions crucial for life processes, each with a specific structure. Additionally, the genetic material of organisms is located within cells.

Discovery of Cells:-

The discovery of cells represents a significant milestone in the field of science, enhancing our understanding of life processes and the fundamental building blocks of all organisms.

The credit for discovering cells goes to Robert Hooke, who made this groundbreaking observation in 1665. Hooke used a compound microscope to examine a piece of cork from a bottle and noticed tiny structures resembling small rooms. These structures were subsequently named "cells" by Hooke. However, his microscope had limited magnification, preventing him from observing detailed cell structure. Consequently, Hooke initially believed that these cells were non-living entities.

Later, Anton Van Leeuwenhoek examined cells using another compound microscope with higher magnification. During his observations, Leeuwenhoek observed that these cells exhibited some form of movement, leading him to conclude that they were indeed "alive." Eventually, these microscopic entities were referred to as "animalcules" following a series of further observations.

In 1833, Robert Brown, a Scottish botanist, made a significant contribution by providing the first insights into cell structure. He described the presence of a nucleus in the cells of orchids.

These discoveries, from Hooke's initial observation of cells to Leeuwenhoek's recognition of their vitality and Brown's insights into cell structure, have played a pivotal role in advancing our understanding of life and its fundamental units.

Characteristics of Cells:-

1. Structural Support: Cells provide structural support to an organism's body.

2. Organelles: The interior of a cell is organized into distinct organelles, each enclosed by its own membrane.

3. Nucleus: The nucleus, a major organelle, contains genetic information crucial for cell growth and reproduction.

4. One Nucleus: Each cell typically contains a single nucleus and various membrane-bound organelles within its cytoplasm.

5. Mitochondria: Mitochondria, a double membrane-bound organelle, is primarily responsible for energy production, which is vital for the cell's survival.

6. Lysosomes: Lysosomes function to digest and break down unwanted materials within the cell.

7. Endoplasmic Reticulum: The endoplasmic reticulum plays a key role in organizing the cell's internal processes by synthesizing specific molecules and processing, directing, and sorting them to their designated locations.

Types of Cells:-

Cells are similar to factories with different labourers and departments that work towards a common objective. Various types of cells perform different functions. Based on cellular structure, there are two types of cells:

• Prokaryotes
• Eukaryotes

Prokaryotic Cells:

• Lack a true nucleus; genetic material is freely suspended in a region called the nucleoid.
• Generally, single-celled microorganisms such as archaea, bacteria, and cyanobacteria.
• Smaller in size, typically ranging from 0.1 to 0.5 µm in diameter.
• Hereditary material can be DNA or RNA.
• Reproduction primarily occurs through binary fission, a form of asexual reproduction, although they can engage in conjugation (not considered sexual reproduction).
• Examples include bacteria.

Eukaryotic Cells:

• Have a true nucleus that houses genetic material.
• Larger in size, with cells ranging from 10 to 100 µm in diameter.
• Include a wide range of organisms such as plants, fungi, protozoans, and animals.
• Plasma membrane is responsible for nutrient and electrolyte transport and cell-to-cell communication.
• Reproduction occurs both sexually and asexually.
• Plant cells contain chloroplasts, central vacuoles, and other plastids, whereas animal cells do not have these structures.

Cell Structure:-

Cell Membrane (Plasma Membrane):

• Supports and protects the cell.
• Controls the movement of substances in and out of the cell.
• Separates the cell from its external environment.
• Present in all types of cells.
• It is a porous membrane that allows the selective movement of substances.
• Also referred to as the plasma membrane.
• Protects cellular components from damage and leakage.
• Forms a boundary between adjacent cells and the cell's surroundings.
• In plants, it works in conjunction with the cell wall.

Cell Wall (Present in Plant Cells):

• Composed of cellulose, hemicellulose, and pectin.
• Exclusive to plant cells.
• Provides rigid support and protection to the cell membrane and other cellular components.
• Outermost layer of plant cells.
• Offers shape and protection against mechanical damage.

Cytoplasm:

• A thick, clear, jelly-like substance located inside the cell membrane.
• Where most of the cell's chemical reactions occur.
• Houses cell organelles like the endoplasmic reticulum, vacuoles, mitochondria, and ribosomes.
• Essential for various cellular processes.

Nucleus:

• Contains the cell's hereditary material, DNA.
• Controls cell growth, maturation, division, and death through signaling.
• Surrounded by the nuclear envelope, which separates DNA from the rest of the cell.
• Protects and houses the DNA.
• Integral component of a plant's cell structure.

Cell Organelles:-

Cells are composed of various cell organelles that perform certain specific functions to carry out life’s processes. The different cell organelles, along with its principal functions, are as follows:

Cell Organelles and their Functions:-

Nucleolus:

• Site of ribosome synthesis.
• Involved in controlling cellular activities and reproduction.

Nuclear Membrane:

• Forms a protective boundary around the nucleus, separating it from other cell organelles.

Chromosomes:

• Contain genetic information and play a role in determining an individual's sex.
• Human cells typically have 23 pairs of chromosomes.

Endoplasmic Reticulum:

• Involved in intracellular transportation.
• Plays a key role in carbohydrate metabolism, lipid, steroid, and protein synthesis.

Golgi Bodies:

• Responsible for the intracellular transportation of materials within the cell.

Ribosomes:

• Responsible for protein synthesis.

Mitochondria:

• Known as the "powerhouse of the cell" because they produce ATP (cell's energy currency).

Lysosomes:

• Engulf foreign bodies entering the cell.
• Assist in cell renewal.
• Sometimes referred to as the "cell's suicide bags."

Chloroplasts (Present in Plant Cells):

• Primary organelles for photosynthesis.
• Contain the pigment chlorophyll, which is essential for capturing light energy.

Vacuoles (Larger in Plant Cells):

• Store food, water, and waste materials within the cell.

Cell Theory:-

The Cell Theory, initially proposed by German scientists Theodor Schwann, Matthias Schleiden, and Rudolf Virchow, forms the foundation of modern biology. It states:

1. All living organisms on Earth are composed of cells.
2. The cell is the basic unit of life.
3. All cells arise from pre-existing cells.

A modern version of the cell theory includes additional postulates:

1. Energy flows within cells.
2. Genetic information is passed on from one cell to another.
3. The chemical composition of all cells is essentially the same.

Functions of cells:-

1. Provides Support and Structure: Cells form the structural basis of all organisms. Components like the cell wall and cell membrane provide support and structure. For example, skin cells provide support to the human body, and plant cells in the xylem offer structural support to plants.

2. Facilitates Growth and Mitosis: Cells play a critical role in growth. Through processes like mitosis, parent cells divide into daughter cells, allowing organisms to grow and develop.

3. Allows Transport of Substances: Cells import nutrients and export waste products through processes like diffusion (passive transport) and active transport. These processes are crucial for maintaining the cell's internal environment.

4. Energy Production: Cells require energy for various chemical processes. Energy is produced through photosynthesis in plants and respiration in animals and other organisms.

5. Aids in Reproduction: Cells are involved in reproduction through mitosis (asexual reproduction) and meiosis (sexual reproduction). Mitosis results in daughter cells identical to the parent cell, while meiosis produces genetically diverse offspring.