Introduction
A cell is chemical system that can maintain its structure and reproduce. Cells are the fundamental unit of life. All living things are cells or composed of cells. A cell is the basic unit of life, much like the smallest brick in a building. Without cells, life as we know it wouldn't exist. They work tirelessly, keeping everything alive and functional, whether it's a single-celled organism like bacteria or a multicellular giant like a human. Each cell is like a miniature factory, carrying out specialized tasks to ensure the organism's survival.
The story of cells began in 1665 when Robert Hooke observed a slice of cork under a microscope. He described the tiny compartments he saw as "cells," a term inspired by the small rooms in monasteries.
However, what Hooke saw were the empty walls of dead plant cells.
In the 1830s, Matthias Schleiden and Theodor Schwann proposed that plants and animals are made up of cells, laying the foundation for cell theory.
Later, Rudolf Virchow famously added, "Omnis cellula e cellula," meaning all cells arise from pre-existing cells. This discovery revolutionized biology, helping scientists understand that cells are the building blocks of all life.
1. Microscopic: Most cells are too small to see with the naked eye, but their impact is immense.
2. Dynamic Cells are always busy, converting energy, building proteins, and replicating themselves.
3. Self-sufficient: Cells can perform essential life processes like digestion, respiration, and repair.
4. Diverse: Cells come in different shapes and sizes, tailored to specific roles like nerve cells for
communication or muscle cells for movement.
5. Genetic Blueprint: Each cell carries DNA, which acts as the instruction manual for life.
On the basis of type of organization, cells are two types:
(i) These are primitive and incomplete cells.
(ii) They have less developed nucleus without nuclear membrane & nucleolus.
(iii) some prokaryotes such as bacteria have a region within the cell where the genetic material is freely suspended. This region is called the nucleoid.
(iv) They all are single-celled microorganisms.
(v) The cell size ranges from 0.1 to 0.5 µm in diameter.
(vi) The hereditary material can either be DNA or RNA.
(vii) Prokaryotes reproduce by binary fission, a form of sexual reproduction.
e.g. Bacteria, archaea bacteria and cyanobacteria.
I. These are well developed cells. They have advanced nucleus with unclear membrane and nucleolus.
II. Eukaryotic cells are characterised by a true nucleus.
III. The size of the cells ranges between 10–100 µm in diameter.
IV. This broad category involves plants, fungi, protozoans, and animals.
V. The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in and out of the cells. It is also responsible for cell to cell communication.
VI. They reproduce sexually as well as asexually.
e.g. Plants & animal
1. Cell Membrane: A flexible boundary that protects the cell and controls what goes in and out. Act as a security gate. The cell membrane is a protective barrier that surrounds the cell, regulating the movement of substances inside and outside. It is composed of a phospholipid bilayer with embedded proteins, providing structural support and facilitating communication between cells.
2. Cytoplasm: A jelly-like substance that fills the cell, holding all organelles in place. The plasma membrane is followed by the colloidal organic fluid called matrix or cytosol. The cytosol is the aqueous portion of the cytoplasm (the extranuclear protoplasm) and of the nucleoplasm (the nuclear protoplasm).
3. Nucleus: The brain of the cell where DNA is stored, dictating the cell's activities. The largest and most obvious membrane bound compartment - controls cell activities contains the nucleolus synthesized contains chromosomes- a darkened region where ribosomal RNA is consist of DNA
Mitochondria: The powerhouse, producing energy from nutrients. It is the powerhouses of the cell where energy is produced, they have double membrane structure inner membrane folded into inward projections called cristae- two spaces within the mitochondrion the matrix and the intermembrane space.
Mitochondria is the site of oxygen consumption within cells.
Have their own DNA that is similar to prokaryotic DNA.
Have their own ribosomes that are similar in construction to prokaryotic ribosomes.
Ribosomes: Protein factories. They are one of the smallest organelles of the cell. In prokaryotes, the ribosomes are free in the cytoplasm. In eukaryotes, they are either free in the cytoplasmic matrix or attached to the membranes of endoplasmic reticulum by glycoproteins called ribophorins. In eukaryotes, ribosomes are also found in mitochondria and chloroplasts. Ribosomes are the site for protein synthesis in the cell.
Endoplasmic Reticulum (ER): a web-like series of membranes within the cytoplasm in the form of flattened sheets, sacs, tubes, creates many membranes enclosed spaces - spreads throughout the cytoplasm – has connections with the outer membrane of the nucleus and the plasma membrane. Rough ER-studded with ribosomes site of synthesis of many proteins all ribosomes on rER are actively involved in protein synthesis. Smooth ER-site for synthesis of steroids and other lipids Ca++ storage in muscles detoxification of drugs, toxins, alcohol (especially in liver). The highly convoluted surface provides a large surface area for enzymatic activities. Many enzymes are imbedded in the membranes.
Golgi Apparatus: The packaging and delivery centre for proteins and lipids. Golgi apparatus is a differentiated portion of the endomembrane system found in both animal and plant cells. This membranous component is spatially and temporally related to the endoplasmic reticulum (ER) on one side and by way of secretory vesicles, may fuse with specific portions of the plasma membrane.
Golgi vesicles are often, referred to as the "traffic police" of the cell. They play important role in sorting many of cell's proteins and membrane constituents.
Lysosomes: The cytoplasm of animal cells contains many tiny, spheroid or irregular-shaped, membrane-bounded vesicles known as lysosomes. The lysosomes are originated from Golgi apparatus and contain numerous (about 50) hydrolytic enzymes for intracellular and extracellular digestion.
Chloroplasts: Found only in plant cells, converting sunlight into energy (photosynthesis). sites of photosynthesis - in nearly all plants and some protists trap light energy and convert it into chemical energy have double membrane structure - inner space is the stroma Within the stroma have a series of stacks of flattened membrane structures called thylakoids- the stacks are called grana. The light energy trapping molecules of photosynthesis are found in the membranes of the thylakoids
Cytoplasmic vacuoles: The cytoplasm of many plant and some animal cells (i.e., ciliate protozoans) contains numerous small or large-sized, hollow, liquid-filled structures, the vacuoles. These vacuoles are supposed to be greatly expanded endoplasmic reticulum or Golgi apparatus. The vacuoles of animal cells are bounded by a lipoproteinous membrane and their function is the storage, transmission of the materials and the maintenance of internal pressure of the cell.
The cell theory are as follows:
1. All living organisms are made of one or more cells- From the smallest bacterium to the largest blue whale, everything alive starts with cells.
2. The cell is the basic unit of structure and function in living organisms- Cells are like tiny factories performing all the necessary tasks for life.
3. All cells arise from pre-existing cells- This means life continues through cell division. Cells are the fundamental unit of life - nothing less than a cell is alive.
All organisms are constructed of and by cells.
* All cells arise from preexisting cells.
* Cells contain the information necessary for their own reproduction.
. No new cells are originating spontaneously on earth today.
Cells are multitaskers, responsible for keeping an organism alive and healthy.
1. Energy Production: Cells convert food into usable energy through processes like cellular respiration. Mitochondria play a key role in this process, earning them the title "powerhouses of the cell."
2. Growth and Repair: Cells divide and multiply, helping organisms grow and replace damaged tissues.
3. Reproduction: Cells reproduce through mitosis (for growth and repair) and meiosis (to produce reproductive cells).
4. Défense Mechanism: White blood cells fight infections and protect the body from harmful invaders.
5. Communication: Nerve cells send and receive signals, allowing organisms to respond to stimuli.
6. Transport: Cells transport nutrients, gases, and waste, maintaining a stable internal environment (homeostasis).
