Cell Structure and Function Short Notes PDF: Find below the important notes for the chapter, Cell Structure and Function as per the NEET Biology syllabus. This is helpful for aspirants of NEET and other exams during last-minute revision. Important notes for NEET Biology- Cell Structure and Function Short Notes PDF cover all the important topics and concepts useful for the exam.
Cell Structure and Function Short Notes PDF
The cell is the smallest, basic structural, and functional unit of living things; hence it is generally referred to as ‘building blocks of life. Cells are capable of independent existence and performing essential functions of life. All organisms including plants, animals are made up of one or more cells and all that cells come from pre-existing cells. Robert Hooke was the scientist who first discovered cells in a piece of cork.
- Study of form, structure, and composition of cell is called cytology.
- Cell is the structural and functional unit of life.
- In unicellular organism (amoeba, paramecium, yeast, bacteria) single cell performs all the essential functions of life.
- In multicellular organism, different kinds of tissues perform different function and have division of labour.
- Anton Von Leeuwenhoek first saw and described a live cell. Robert Brown later discovered the nucleus.
- Metthias Schleiden and Theodore Schwann ( 1938) proposed the cell theory which was later modified by Rudolf Virchow (1855)-
Characteristics of Cells
- Cells provide structure and support to the body of an organism.
- The cell interior is organised into different individual organelles surrounded by a separate membrane.
- The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.
- Every cell has one nucleus and membrane-bound organelles in the cytoplasm.
- Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions vital for the survival of the cell.
- Lysosomes digest unwanted materials in the cell.
- Endoplasmic reticulum plays a significant role in the internal organisation of the cell by synthesising selective molecules and processing, directing and sorting them to their appropriate locations.
Functions of Cell
- Provides Support and Structure
- Facilitate Growth Mitosis
- Allow Passive and Active Transport
- Produce Energy
- Create Metabolic Reactions
- Aids in Reproduction
Size of a Cell
The cells exhibit an endless variation in size, life span and cellular activities, e.g., Mycoplasma (smallest cell) or PPLOs (Pleuro-Pneumonia Like Organisms) is only 0.3 Jim in length and bacteria are approx. 3-5 Jim in size. An ostrich egg, which is known to be the largest isolated single cell measures about 170 X 135 mm. Human Red Blood Cells (RBCs) are about 7 Jim in diameter and the nerve cell of human being is the longest cell having length of 90-100 cm.
Types of Cell
Cells are similar to factories with different workers 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:
- Prokaryotic cells are represented by Bacteria, Blue-green algae, Mycoplasma and PPLO.
- They multiply rapidly and vary in size greatly.
- Bacterial cells may be Bacillus (rod-shaped), Coccus (spherical), Vibrio (comma-shaped) and Spirillum (spiral).
- All prokaryotic cells have cell wall surrounding the cell membrane except in Mycoplasma.
- Genetic material is naked.
- Cell organelles like Mitochondria, Golgi bodies etc. are absent in prokaryotes.
- A specialized differentiated cell membrane called Mesosome is the characteristic of prokaryotes.
- Presence of cell wall surrounding the cell membrane except in Mycoplasma.
- Ribosomes are attached to the cell membrane having two subunits 50s and 30s that form the 70s ribosomes together and act as protein synthesis sites.
- Polyribosomes are those ribosomes that attach to RNA to form a chain.
- Reserved materials in prokaryotic cells are present in cytoplasm as cell inclusion bodies, which may contain phosphate, granules, glycogen granules etc.
Characteristics of Prokaryotic Cell
- They lack a nuclear membrane.
- Mitochondria, Golgi bodies, chloroplast, and lysosomes are absent.
- The genetic material is present on a single chromosome.
- The cell wall is made up of carbohydrates and amino acids.
- The plasma membrane acts as the mitochondrial membrane carrying respiratory enzymes.
- They divide asexually by binary fission. The sexual mode of reproduction involves conjugation.
- The histone proteins, the important constituents of eukaryotic chromosomes, are lacking in them.
Structure of Prokaryotic Cell
- Capsule: It is an outer protective covering found in the bacterial cells, in addition to the cell wall.
- Cell Wall: It is the outermost layer of the cell which gives shape to the cell.
- Cytoplasm: The cytoplasm is mainly composed of enzymes, salts, cell organelles and is a gel-like component.
- Cell Membrane: This layer surrounds the cytoplasm and regulates the entry and exit of substances in the cells.
- Pili: These are hair-like outgrowths that attach to the surface of other bacterial cells.
- Flagella: These are long structures in the form of a whip, that help in the locomotion of a cell.
- Ribosomes: These are involved in protein synthesis.
- Plasmids: Plasmids are non-chromosomal DNA structures. These are not involved in reproduction.
- Nucleoid Region: It is the region in the cytoplasm where the genetic material is present.
Components of Prokaryotic Cell
- Plasma Membrane: It is an outer protective covering of phospholipid molecules which separates the cell from the surrounding environment.
- Cytoplasm: It is a jelly-like substance present inside the cell. All the cell organelles are suspended in it.
- DNA: It is the genetic material of the cell. All the prokaryotes possess a circular DNA. It directs what proteins the cell creates. It also regulates the actions of the cell.
- Ribosomes: Protein synthesis occurs here.
- Some prokaryotic cells possess cilia and flagella which helps in locomotion.
Examples of Prokaryotic Cell
- Bacterial Cells: These are unicellular organisms found everywhere on earth from soil to the human body. They have different shapes and structures. The cell wall is composed of peptidoglycan that provides structure to the cell wall.
- Archaeal Cells: Archaebacteria are unicellular organisms similar to bacteria in shape and size. They are found in extreme environments such as hot springs and other places such as soil, marshes, and even inside humans. They have a cell wall and flagella. The cell wall of archaea does not contain peptidoglycan.
- Eukaryotic Cells are found in Fungi, Protista, Plants and Animals.
- The cytoplasm is divided into compartments because of the presence of membrane-bound organelles.
- Presence of a well-organised nucleus bound by a nuclear membrane.
- Genetic material arranged in chromosomes.
- Plant cells have a cell wall in addition to the membrane. They have a large central vacuole, which is absent in animal cells.
- Characteristic presence of centrioles in animal cells.
Characteristics of Eukaryotic Cell
- Eukaryotic cells have the nucleus enclosed within the nuclear membrane.
- Eukaryotic cells have mitochondria.
- Flagella and cilia are the locomotory organs in a eukaryotic cell.
- A cell wall is the outermost layer of the eukaryotic cells.
- The cells divide by a process called mitosis.
- The eukaryotic cells contain a cytoskeletal structure.
- The nucleus contains a single, linear DNA, which carries all the genetic information.
Structure of Eukaryotic Cell
- Plasma Membrane: The plasma membrane separates the cell from the outside environment. It comprises specific embedded proteins, which help in the exchange of substances in and out of the cell.
- Cell Wall: A cell wall is a rigid structure present outside the plant cell. It is, however, absent in animal cells. It provides shape to the cell and helps in cell-to-cell interaction. It is a protective layer that protects the cell from any injury or pathogen attacks. It is composed of cellulose, hemicellulose, pectins, proteins, etc.
- Cytoskeleton: The cytoskeleton is present inside the cytoplasm, which consists of microfilaments, microtubules, and fibres to provide perfect shape to the cell, anchor the organelles, and stimulate the cell movement.
- Endoplasmic Reticulum: It is a network of small, tubular structures that divides the cell surface into two parts: luminal and extraluminal.
- Nucleus: The nucleoplasm enclosed within the nucleus contains DNA and proteins. The nuclear envelop consists of two layers- the outer membrane and the inner membrane. Both the membranes are permeable to ions, molecules, and RNA material. Ribosome production also takes place inside the nucleus.
- Golgi Apparatus: It is made up of flat disc-shaped structures called cisternae. It is absent in red blood cells of humans and sieve cells of plants. They are arranged parallel and concentrically near the nucleus. It is an important site for the formation of glycoproteins and glycolipids.
- Ribosomes: These are the main site for protein synthesis and are composed of proteins and ribonucleic acids.
- Mitochondria: These are also known as “powerhouse of cells” because they produce energy. It consists of an outer membrane and an inner membrane. The inner membrane is divided into folds called cristae. They help in the regulation of cell metabolism.
- Lysosomes: They are known as “suicidal bags” because they possess hydrolytic enzymes to digest protein, lipids, carbohydrates, and nucleic acids.
- Plastids: These are double-membraned structures and are found only in plant cells.
Examples of Eukaryotic Cell
- Plant Cells: The cell wall is made up of cellulose, which provides support to the plant. It has a large vacuole which maintains the turgor pressure. The plant cell contains chloroplast, which aids in the process of photosynthesis.
- Fungal Cells: The cell wall is made of chitin. Some fungi have holes known as septa which allow the organelles and cytoplasm to pass through them.
- Animal Cells: These do not have cell walls. Instead, they have a cell membrane. That is why animals have varied shapes. They have the ability to perform phagocytosis and pinocytosis.
- Protozoa: Protozoans are unicellular organisms. Some protozoa have cilia for locomotion. A thin layer called pellicle provides supports to the cell.
Difference between Prokaryote Cells and Eukaryotic Cell
Structure of a Cell
The cells also vary in their shapes. They may be polygonal, disc-like amoeboid, thread-like, cuboid or irregular. The cell shape is always related and vary with the function they perform.
- Cell Membrane
- Composed of lipids that are made up of phosphoglycerides and arranged in a bilayer. Protein compounds were also discovered later on.
- Proteins are present as – integral protein that remains buried in the membrane and peripheral protein that lies on the surface.
- The protein movement across the bilipid layer is possible because of the quasi-fluid nature of the membrane, as proposed by Singer and Nicholson.
- The primary function of the plasma membrane is to ensure transport of substances.
- Cell Wall
- Present in plants and algae.
- The cell wall in plants is made up of cellulose, hemicellulose and pectin.
- The algal cell wall is composed of cellulose, galectins and minerals.
- The primary cell wall in plants is incapable of growth, it soon transforms into a secondary cell wall in mature plants.
- The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane.
- Most of the chemical reactions within a cell take place in this cytoplasm.
- The cell organelles such as endoplasmic reticulum, vacuoles, mitochondria, ribosomes, are suspended in this cytoplasm.
- Endoplasmic Reticulum
- Smooth Endoplasmic Reticulum – Involved in lipid synthesis and does not bear ribosomes on the surface.
- Rough Endoplasmic Reticulum – Performs protein synthesis and secretion and bears ribosomes on the surface.
- Membrane bound structures.
- Contains sap, excretory products and water.
- Present as food vacuole or contractile vacuole.
- Found in sites of aerobic respirations.
- Produce cellular energy in the form of ATP.
- The matrix contains circular DNA molecules, RNA molecules, ribosomes and components of protein synthesis.
- Plastids are found in plant cells and in Euglenoids.
- Plastids are of three types: Leucoplasts, Chromoplasts and Chloroplasts
- Leucoplasts are colourless plastids of varied shape with stored nutrients.
- Chromoplasts are yellowish or reddish in appearance because of the presence of soluble fats.
- Chloroplasts are double membranous structures. The inner membrane is known as the stroma. Thylakoids present in the stroma as stacks known as grana. The stroma contains enzymes for protein synthesis.
- It has highly extended nucleoprotein fibres called chromatin, nuclear matrix and nucleoli.
- Chromatin material rearranges into chromosomes during cell division.
- Consist of histone and proteins.
- The centromere or the primary constriction of each chromosome on the discs of which kinetochores are present.
- On the basis of the position of the centromere, chromosomes can be divided into – metacentric, submetacentric, telocentric and acrocentric.
- Some chromosomes have non-staining secondary constriction, that gives a small fragment called a satellite.
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