Introduction
- In 1665, Robert Hooke observed cork under a microscope and noted its honeycomb-like structure composed of small compartments.
- Cork is derived from tree bark, and Hooke referred to these compartments as "cells," with the term "cell" originating from the Latin word for "a little room."
- This observation marked the first instance of recognizing that living organisms are made up of distinct units.
- The term "cell" continues to be used in biology to describe these fundamental units.
- Robert Hooke's discovery of cells in cork was a significant milestone in the history of science.
Cells can have different Shaped and Sizes
What are Living Organisms Made Up of?
- Living organisms are composed of structures that resemble each other and together form larger structures, akin to an onion bulb.
- Cells are the basic building units of living organisms, visible as small structures under a microscope.
- All organisms, including onions, are made up of cells, which can exist singly or in groups.
- Unicellular organisms like Amoeba and bacteria consist of a single cell forming the entire organism.
- Multicellular organisms, like some fungi, plants, and animals, are made up of many cells that perform different functions in various body parts.
- Cells divide to produce cells of their own kind, indicating that all cells come from pre-existing cells.
- Cells can vary in shape and size based on the specific functions they perform.
- Each living cell has the ability to carry out basic functions characteristic of all living forms.
- Within multicellular organisms, as with human beings, there is a division of labor among different body parts.
- Cells contain specialized components called cell organelles that perform specific functions necessary for the cell's survival and operation.
- All cells have the same organelles, regardless of their function or the organism they belong to.
Question for Short Notes: The The Fundamental Unit of Life
Try yourself:
What did Robert Hooke observe in cork under a microscope?Explanation
- Robert Hooke observed a honeycomb-like structure in cork under a microscope.
- This structure was composed of small compartments, which Hooke referred to as "cells".
- The observation of cells in cork was a significant milestone in the history of science.
- The term "cell" continues to be used in biology to describe the fundamental units of living organisms.
- Hooke's discovery laid the foundation for the understanding that living organisms are made up of distinct units.
Report a problem
Discovery of Cell & Cell Theory
- Cells were first identified by Robert Hooke in 1665 when he observed them in a cork slice using a basic microscope.
- Leeuwenhoek, in 1674, using an improved microscope, discovered free-living cells in pond water.
- In 1831, Robert Brown identified the nucleus within cells.
- In 1839, Purkinje introduced the term 'protoplasm' for the cell's fluid substance.
- The cell theory, proposed by Schleiden (1838) and Schwann (1839), states that all plants and animals are made up of cells, with the cell being the fundamental unit of life.
- Virchow (1855) expanded the cell theory by suggesting that all cells come from pre-existing cells.
- The electron microscope, invented in 1940, allowed for the observation and comprehension of the intricate structure of cells and their organelles.
What is a Cell Made Up Of?
Cells consist of organelles like plasma membrane, nucleus, and cytoplasm which allow cell activities and interactions.
The Structure of Cells in Plants and Animals
Plasma Membrane or Cell Membrane
- The plasma membrane is the outermost layer of a cell, controlling material entry and exit.
- Substances like CO2 and O2 move in and out of cells through diffusion.
- Osmosis is the movement of water across a selectively permeable membrane based on solute concentration.
- Cells in hypotonic solutions gain water, isotonic solutions have no net water movement, and hypertonic solutions cause water loss.
- Diffusion and osmosis are vital for gas and water exchange in cells.
- Cells also obtain nutrients through energy-requiring transport processes.
- The plasma membrane, made of lipids and proteins, is observed with an electron microscope and enables processes like endocytosis.
The Plasma Membrane
Question for Short Notes: The The Fundamental Unit of Life
Try yourself:
What is the function of the plasma membrane in a cell?Explanation
- The plasma membrane, also known as the cell membrane, is the outermost covering of a cell.
- Its primary function is to separate the contents of the cell from its external environment.
- The plasma membrane acts as a barrier, controlling the entry and exit of materials into and out of the cell.
- It is a selectively permeable membrane, allowing some substances to pass through while restricting others.
- Gases like CO2 or O2 can move across the cell membrane through a process called diffusion.
- The movement of water molecules through the plasma membrane is called osmosis, which helps maintain the water balance inside the cell.
- The plasma membrane is made up of lipids and proteins, providing flexibility to the cell membrane.
- Additionally, the flexibility of the cell membrane enables the cell to engulf food and other materials from its external environment through a process called endocytosis.
Therefore, the correct answer is Option B: It separates the contents of the cell from its external environment.
Report a problem
Cell Wall
- Plant cells have a rigid outer covering called the cell wall, composed mainly of cellulose.
- Plasmolysis is the shrinkage of living plant cell contents away from the cell wall due to water loss.
- Cell walls allow cells to withstand hypotonic conditions by preventing bursting and maintaining structural integrity.
Nucleus
- The nucleus, with a double-layered covering, contains chromosomes carrying genetic information.
Nucleus of a Cell
- Chromosomes are composed of DNA and protein, with genes as functional segments of DNA.
- The nucleus plays a central role in cellular reproduction and directs the cell's chemical activities.
- Prokaryotes lack a nuclear membrane and well-defined organelles, unlike eukaryotes.
Eukaryotic and Prokaryotic Cells
Cytoplasm
- Cytoplasm is the fluid content inside the plasma membrane, containing specialised cell organelles.
- Cell organelles have specific functions and are membrane-enclosed in eukaryotic cells.
- Viruses lack membranes and exhibit life characteristics only when inside a living host cell.
Question for Short Notes: The The Fundamental Unit of Life
Try yourself:
What is the outermost layer of a cell called?Explanation
- The outermost layer of a cell is called the plasma membrane or cell membrane.
- It controls the entry and exit of materials in the cell.
- The plasma membrane is made up of lipids and proteins.
- It is observed with an electron microscope and enables processes like diffusion and endocytosis.
- The cell wall, on the other hand, is a rigid outer covering found in plant cells, composed mainly of cellulose.
Report a problem
Cell Organelles
- Cells use membrane-bound organelles to separate different chemical activities.
- Organelles like endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, and plastids are crucial for cell functions.
Different Cell Organelles
Endoplasmic Reticulum (ER)
- Large network of membrane-bound tubes and sheets.
- Consists of rough ER (RER) with ribosomes for protein synthesis and smooth ER (SER) for lipid production.
- Functions include material transport within the cell and detoxification in liver cells.
Endoplasmic Reticulum
Golgi Apparatus
- System of membrane-bound vesicles involved in packaging and modifying products.
- Participates in sugar synthesis and formation of lysosomes.
Golgi Apparatus
Question for Short Notes: The The Fundamental Unit of Life
Try yourself:
What is the function of the Golgi apparatus in a cell?Explanation
- The Golgi apparatus is responsible for packaging and dispatching materials synthesized near the endoplasmic reticulum (ER) to various targets inside and outside the cell.
- It consists of a system of membrane-bound vesicles arranged in stacks called cisterns.
- The Golgi apparatus modifies and packages products in vesicles before sending them to their designated locations.
- It also plays a role in the formation of lysosomes, which are responsible for digestion and disposal of waste materials in the cell.
- The Golgi apparatus may also be involved in the synthesis of complex sugars from simple sugars.
- Overall, the Golgi apparatus acts as a packaging and distribution center within the cell, ensuring that materials are properly sorted and sent to their intended destinations.
Report a problem
Lysosomes
- Membrane-bound sacs with digestive enzymes for waste disposal.
- Break down foreign material and worn-out organelles, known as the "suicide bags" of cells.
Lysosome
Mitochondria
- Considered the powerhouses of the cell, producing ATP for energy.
- Contain their own DNA and ribosomes, aiding in protein synthesis.
Mitochondria
Plastids
- Present in plant cells, including chloroplasts for photosynthesis and leucoplasts for storage.
- Similar to mitochondria in structure, have their own DNA and ribosomes.
Types of Plastids
Vacuoles
- Storage sacs in cells, crucial for maintaining cell rigidity and storing various substances.
- Plant cells have large vacuoles, while animal cells have smaller ones.
Vacuoles in plant cells
Question for Short Notes: The The Fundamental Unit of Life
Try yourself:
Which organelle is responsible for producing ATP for energy in the cell?Explanation
- Mitochondria are considered the powerhouses of the cell and are responsible for producing ATP, which is the main source of energy for cellular activities.
- They have their own DNA and ribosomes, which aid in protein synthesis.
- The endoplasmic reticulum (Option A) is involved in material transport and protein synthesis, but it is not responsible for ATP production.
- The Golgi apparatus (Option B) is involved in packaging and modifying products, and the lysosomes (Option C) are responsible for waste disposal and breaking down foreign material.
- Therefore, the correct answer is Option D: Mitochondria.
Report a problem
Cell Division
- Process of cell division includes mitosis for growth and repair, and meiosis for gamete formation.
- Mitosis results in two identical daughter cells with the same chromosome number as the mother cell.
- Meiosis produces four cells with half the number of chromosomes, important for sexual reproduction.