Cell Biology Introduction

The Fundamental Unit of Life

• The cell is the basic unit of structure and function in living organisms.

Cytology

• Cytology is the branch of biology that deals with the study of structure and function of plant and animal cells.

Invention of Microscope

• The simplest microscope was constructed in 1600.
• Galileo and Anton van Leeuwenhoek later used the microscope.
• In 1665, Robert Hooke observed a thin slice of cork (dead cell) under the microscope and saw like structures, which he called cells.
• These "cells" were actually seed cells of the outer cover of the plant called periderm bark.

Microscope Sections

• A thin slice of any part is called a section.
• A longitudinal section is a cut along the length of a structure.
• A transverse section is a cut across a structure.

Working of a Microscope

• A microscope uses light reflected by a mirror, directed through the specimen into the lenses.
• The lenses produce a greatly magnified image of the specimen, which can be studied directly or photographed.
• The object is placed on a glass slide on a stage with a central hole under an objective lens.
• Light is reflected through the specimen with the help of a mirror and condenser below the stage.
• The magnified image is seen through an eyepiece at the top of the microscope.
• Focusing is done by adjusting coarse and fine adjustors.
• Various lenses are available, including:
  • Eyepiece lenses with magnifications of 5X, 10X, and 15X.
  • Objective lenses with magnifications of 40X, 100X (high power), and 10X (low power).

Magnification

• Magnification is calculated as observed size divided by actual size.
• Under a microscope, cells become magnified, making them easier to observe.

The Fundamental Unit of Life

• The cell is the basic unit of structure and function in living organisms.

Cytology

• Cytology is the branch of biology that deals with the study of structure and function of plant and animal cells.

Invention of Microscope

• The simplest microscope was constructed in 1600.
• Galileo and Anton van Leeuwenhoek later used the microscope.
• In 1665, Robert Hooke observed a thin slice of cork (dead cell) under the microscope and saw like structures, which he called cells.
• These "cells" were actually seed cells of the outer cover of the plant called periderm bark.

Microscope Sections

• A thin slice of any part is called a section.
• A longitudinal section is a cut along the length of a structure.
• A transverse section is a cut across a structure.

Working of a Microscope

• A microscope uses light reflected by a mirror, directed through the specimen into the lenses.
• The lenses produce a greatly magnified image of the specimen, which can be studied directly or photographed.
• The object is placed on a glass slide on a stage with a central hole under an objective lens.
• Light is reflected through the specimen with the help of a mirror and condenser below the stage.
• The magnified image is seen through an eyepiece at the top of the microscope.
• Focusing is done by adjusting coarse and fine adjustors.
• Various lenses are available, including:
  • Eyepiece lenses with magnifications of 5X, 10X, and 15X.
  • Objective lenses with magnifications of 40X, 100X (high power), and 10X (low power).

Magnification

• Magnification is calculated as observed size divided by actual size.
• Under a microscope, cells become magnified, making them easier to observe.

The Fundamental Unit of Life

• The cell is the basic unit of structure and function in living organisms.

Cytology

• Cytology is the branch of biology that deals with the study of structure and function of plant and animal cells.

Invention of Microscope

• The simplest microscope was constructed in 1600.
• Galileo and Anton van Leeuwenhoek later used the microscope.
• In 1665, Robert Hooke observed a thin slice of cork (dead cell) under the microscope and saw like structures, which he called cells.
• These "cells" were actually seed cells of the outer cover of the plant called periderm bark.

Microscope Sections

• A thin slice of any part is called a section.
• A longitudinal section is a cut along the length of a structure.
• A transverse section is a cut across a structure.

Working of a Microscope

• A microscope uses light reflected by a mirror, directed through the specimen into the lenses.
• The lenses produce a greatly magnified image of the specimen, which can be studied directly or photographed.
• The object is placed on a glass slide on a stage with a central hole under an objective lens.
• Light is reflected through the specimen with the help of a mirror and condenser below the stage.
• The magnified image is seen through an eyepiece at the top of the microscope.
• Focusing is done by adjusting coarse and fine adjustors.
• Various lenses are available, including:
  • Eyepiece lenses with magnifications of 5X, 10X, and 15X.
  • Objective lenses with magnifications of 40X, 100X (high power), and 10X (low power).

Magnification

• Magnification is calculated as observed size divided by actual size.
• Under a microscope, cells become magnified, making them easier to observe.

Microscope Magnification

• Light microscopes use 10X or 40X objective lenses and 10X or higher eyepiece lenses, resulting in total magnification ranges of 100X to 450X.
• The best light microscopes can magnify structures up to 1500 times their original size.

Cell Theory

• Formulated by Matthias Schleiden in 1838 and Theodor Schwann in 1839.
• States that:
  • All living organisms are composed of cells and products of cells.
  • All cells arise from pre-existing cells.

Cell Characteristics

• Size: Ranges from 10 to 100 microns; examples include:
  • The ostrich egg, which has the largest animal cell.
  • PPLO (Pleuropneumonia-like organism), which is the smallest cell, measuring 0.1 to 0.5 microns.
• Shape: Depends on specific cell function; examples include:
  • Elongated and branched: Nerve cells.
  • Discoidal/saucer-shaped: Red blood cells.
  • Spindle-shaped: Muscle cells.
  • Spherical: Eggs.
  • Branched: Pigment cells of the skin.
  • Slipper-shaped: Paramecium.
  • Cuboidal: Germ cells of gonads.
  • Polygonal: Liver cells.

Microscope Magnification

• Light microscopes use 10X or 40X objective lenses and 10X or higher eyepiece lenses, resulting in total magnification ranges of 100X to 450X.
• The best light microscopes can magnify structures up to 1500 times their original size.

Cell Theory

• Formulated by Matthias Schleiden in 1838 and Theodor Schwann in 1839.
• States that:
  • All living organisms are composed of cells and products of cells.
  • All cells arise from pre-existing cells.

Cell Characteristics

• Size: Ranges from 10 to 100 microns; examples include:
  • The ostrich egg, which has the largest animal cell.
  • PPLO (Pleuropneumonia-like organism), which is the smallest cell, measuring 0.1 to 0.5 microns.
• Shape: Depends on specific cell function; examples include:
  • Elongated and branched: Nerve cells.
  • Discoidal/saucer-shaped: Red blood cells.
  • Spindle-shaped: Muscle cells.
  • Spherical: Eggs.
  • Branched: Pigment cells of the skin.
  • Slipper-shaped: Paramecium.
  • Cuboidal: Germ cells of gonads.
  • Polygonal: Liver cells.

Microscope Magnification

• Light microscopes use 10X or 40X objective lenses and 10X or higher eyepiece lenses, resulting in total magnification ranges of 100X to 450X.
• The best light microscopes can magnify structures up to 1500 times their original size.

Cell Theory

• Formulated by Matthias Schleiden in 1838 and Theodor Schwann in 1839.
• States that:
  • All living organisms are composed of cells and products of cells.
  • All cells arise from pre-existing cells.

Cell Characteristics

• Size: Ranges from 10 to 100 microns; examples include:
  • The ostrich egg, which has the largest animal cell.
  • PPLO (Pleuropneumonia-like organism), which is the smallest cell, measuring 0.1 to 0.5 microns.
• Shape: Depends on specific cell function; examples include:
  • Elongated and branched: Nerve cells.
  • Discoidal/saucer-shaped: Red blood cells.
  • Spindle-shaped: Muscle cells.
  • Spherical: Eggs.
  • Branched: Pigment cells of the skin.
  • Slipper-shaped: Paramecium.
  • Cuboidal: Germ cells of gonads.
  • Polygonal: Liver cells.

Microscope Magnification

• Light microscopes use 10X or 40X objective lenses and 10X or higher eyepiece lenses, resulting in total magnification ranges of 100X to 450X.
• The best light microscopes can magnify structures up to 1500 times their original size.

Cell Theory

• Formulated by Matthias Schleiden in 1838 and Theodor Schwann in 1839.
• States that:
  • All living organisms are composed of cells and products of cells.
  • All cells arise from pre-existing cells.

Cell Characteristics

• Size: Ranges from 10 to 100 microns; examples include:
  • The ostrich egg, which has the largest animal cell.
  • PPLO (Pleuropneumonia-like organism), which is the smallest cell, measuring 0.1 to 0.5 microns.
• Shape: Depends on specific cell function; examples include:
  • Elongated and branched: Nerve cells.
  • Discoidal/saucer-shaped: Red blood cells.
  • Spindle-shaped: Muscle cells.
  • Spherical: Eggs.
  • Branched: Pigment cells of the skin.
  • Slipper-shaped: Paramecium.
  • Cuboidal: Germ cells of gonads.
  • Polygonal: Liver cells.

Unicellular and Multicellular Organisms

• Unicellular organisms are made up of a single cell, examples include Bacteria, Amoeba, Paramecium, and Chlamydomonas.
• Multicellular organisms are made up of multiple cells, examples include Fungi (except yeast), plants, and animals.

Viruses

• Viruses are the only living beings that do not have cells.
• Viruses are composed of genetic material (DNA or RNA) wrapped in a protein capsule.

Cell Organization

• All cells have three major functional regions: plasma membrane, cytoplasm, and nucleus.
• Cytoplasm and nucleus together are known as protoplasm.

Plasma Membrane

• The plasma membrane is a membrane that bounds all cells, enclosing the protoplasm.
• Characteristics of the plasma membrane:
• Made up of proteins and phospholipids
• Selectively permeable, allowing only specific solutes to pass through
• Thickness is less than 1/10,000 mm (70A)
• Best explained by the fluid mosaic model proposed by Singer and Nicolson (1972)
• Enables functions such as diffusion, osmosis, and ion movement.

Unicellular and Multicellular Organisms

• Unicellular organisms are made up of a single cell, examples include Bacteria, Amoeba, Paramecium, and Chlamydomonas.
• Multicellular organisms are made up of multiple cells, examples include Fungi (except yeast), plants, and animals.

Viruses

• Viruses are the only living beings that do not have cells.
• Viruses are composed of genetic material (DNA or RNA) wrapped in a protein capsule.

Cell Organization

• All cells have three major functional regions: plasma membrane, cytoplasm, and nucleus.
• Cytoplasm and nucleus together are known as protoplasm.

Plasma Membrane

• The plasma membrane is a membrane that bounds all cells, enclosing the protoplasm.
• Characteristics of the plasma membrane:
• Made up of proteins and phospholipids
• Selectively permeable, allowing only specific solutes to pass through
• Thickness is less than 1/10,000 mm (70A)
• Best explained by the fluid mosaic model proposed by Singer and Nicolson (1972)
• Enables functions such as diffusion, osmosis, and ion movement.

Cell Membrane Structure and Function

• Polysaccharides attached to membrane proteins or lipids are involved in cell-to-cell recognition mechanisms, such as fertilization.
• The lipid bilayer is a barrier to water and water-soluble substances.
• Protein molecules in the membrane act as hydrophilic pores, allowing water-soluble chemicals to pass through.
• Pores are small and highly selective, allowing only specific molecules or ions to pass through.

Polar and Non-Polar Substances

• Water is a polar molecule with regions of positive and negative charge, allowing it to dissolve polar substances like sugars, ions (Na+, Cl-, Ca2+, K+), B and C vitamins, and amino acids.
• Polar substances do not dissolve in lipids and must cross the cell surface membrane through pores.
• Non-polar molecules like fats, oils, and lipids lack charged regions and do not dissolve in water.
• Non-polar substances like vitamins A, D, E, and K can dissolve in lipids and cross the cell surface membrane without passing through pores.

Transport Across the Plasma Membrane

Passive Transport

• A type of membrane transport that does not require energy to move substances across the cell membrane.

Diffusion

• The movement of substances from higher concentration to lower concentration, such as oxygen diffusing from alveoli into the blood in capillaries.

Osmosis

• The net diffusion of water across a selectively permeable membrane towards a higher solute concentration, such as the absorption of water from soil by roots.
• Osmosis results in hydrostatic pressure within the cell, known as turgor pressure.
• There are two types of osmosis: endosmosis and exosmosis.

Cell Membrane Structure and Function

• Polysaccharides attached to membrane proteins or lipids are involved in cell-to-cell recognition mechanisms, such as fertilization.
• The lipid bilayer is a barrier to water and water-soluble substances.
• Protein molecules in the membrane act as hydrophilic pores, allowing water-soluble chemicals to pass through.
• Pores are small and highly selective, allowing only specific molecules or ions to pass through.

Polar and Non-Polar Substances

• Water is a polar molecule with regions of positive and negative charge, allowing it to dissolve polar substances like sugars, ions (Na+, Cl-, Ca2+, K+), B and C vitamins, and amino acids.
• Polar substances do not dissolve in lipids and must cross the cell surface membrane through pores.
• Non-polar molecules like fats, oils, and lipids lack charged regions and do not dissolve in water.
• Non-polar substances like vitamins A, D, E, and K can dissolve in lipids and cross the cell surface membrane without passing through pores.

Transport Across the Plasma Membrane

Passive Transport

• A type of membrane transport that does not require energy to move substances across the cell membrane.

Diffusion

• The movement of substances from higher concentration to lower concentration, such as oxygen diffusing from alveoli into the blood in capillaries.

Osmosis

• The net diffusion of water across a selectively permeable membrane towards a higher solute concentration, such as the absorption of water from soil by roots.
• Osmosis results in hydrostatic pressure within the cell, known as turgor pressure.
• There are two types of osmosis: endosmosis and exosmosis.

Osmosis and Cell Response

• When a cell is placed in an isotonic solution, there is no net movement of water molecules, and the cell size remains the same.
• In a hypotonic solution, water molecules flow into the cell, causing the cell to swell, a process known as endosmosis.
• In a hypertonic solution, water molecules flow out of the cell, causing the cell to shrink, a process known as exosmosis.

Active Transport

• Active transport is the movement of substances through the cell membrane that requires energy, provided by adenosine triphosphate (ATP) produced by aerobic respiration in the mitochondria.
• This process is rapid, unidirectional, and involves transport proteins that help move substances into and out of the cell.

Cell Membrane Permeability

• Cell membranes can be permeable (allowing solvents and solutes to pass), semipermeable (only allowing solvents to pass), selectively permeable (allowing solvents and selected solutes to pass), or impermeable (not allowing anything to pass).

Cell Wall

• The cell wall is an additional protective covering outside the cell membrane, found in plants, fungi, bacterial cells, and certain protists.
• It provides mechanical strength, shape, and rigidity to the cell.
• In plants, the cell wall is made up of cellulose, a type of carbohydrate.
• The cell wall consists of three layers: middle lamella (cementing layer), primary wall (thinner, elastic layer), and secondary wall (thicker layer in mature, non-dividing cells).

Cell Organelles

• Cytoplasm is the fluid content/protoplasmic mass of the cell, excluding the nucleus, and consists of cytosol (aqueous, transparent, structureless ground substance) and cell organelles (subcellular structures with characteristic form, structure, and function).

Plasmolysis

• When a plant cell is placed in a hypertonic solution, exosmosis occurs from the central vacuole, causing the protoplasm to separate from the cell wall, a process known as plasmolysis.

Osmosis and Cell Response

• When a cell is placed in an isotonic solution, there is no net movement of water molecules, and the cell size remains the same.
• In a hypotonic solution, water molecules flow into the cell, causing the cell to swell, a process known as endosmosis.
• In a hypertonic solution, water molecules flow out of the cell, causing the cell to shrink, a process known as exosmosis.

Active Transport

• Active transport is the movement of substances through the cell membrane that requires energy, provided by adenosine triphosphate (ATP) produced by aerobic respiration in the mitochondria.
• This process is rapid, unidirectional, and involves transport proteins that help move substances into and out of the cell.

Cell Membrane Permeability

• Cell membranes can be permeable (allowing solvents and solutes to pass), semipermeable (only allowing solvents to pass), selectively permeable (allowing solvents and selected solutes to pass), or impermeable (not allowing anything to pass).

Cell Wall

• The cell wall is an additional protective covering outside the cell membrane, found in plants, fungi, bacterial cells, and certain protists.
• It provides mechanical strength, shape, and rigidity to the cell.
• In plants, the cell wall is made up of cellulose, a type of carbohydrate.
• The cell wall consists of three layers: middle lamella (cementing layer), primary wall (thinner, elastic layer), and secondary wall (thicker layer in mature, non-dividing cells).

Cell Organelles

• Cytoplasm is the fluid content/protoplasmic mass of the cell, excluding the nucleus, and consists of cytosol (aqueous, transparent, structureless ground substance) and cell organelles (subcellular structures with characteristic form, structure, and function).

Plasmolysis

• When a plant cell is placed in a hypertonic solution, exosmosis occurs from the central vacuole, causing the protoplasm to separate from the cell wall, a process known as plasmolysis.

Ribosomes

• Ribosomes are also called "organelle within an organelle" and the protein factory of the cell
• Each ribosome is made up of two unequal subunits that join together during protein synthesis in the presence of Mg2+ ions
• Ribosomes are small, sub-spherical, granular organelles not enclosed by a membrane
• They are composed of r-RNA and proteins and attach to m-RNA to form polyribosomes during protein synthesis
• In prokaryotes, the two subunits are 30S and 50S (together 70S), and in eukaryotes, they are 40S and 60S (together 80S)
• In mammals, 55S type of ribosomes are present in the mitochondrial matrix

Endoplasmic Reticulum (ER)

• ER is a three-dimensional, complicated, interconnecting system of membrane-lined channels that run through the cytoplasm
• ER remains continuous with the plasma membrane, nuclear envelope, and Golgi body
• ER is composed of cisternae, vesicles, and tubules
• There are two types of ER: smooth ER and rough ER
• Smooth ER is engaged in the synthesis and storage of glycogen, fat, and steroids, and detoxification of drugs and poisons
• Rough ER is associated with protein synthesis due to the presence of ribosomes on its surface

Golgi Body

• The Golgi body was discovered by Camillo Golgi in 1898 in nerve cells of owls and cats
• In animal cells, it is localized near the nucleus, but in plant cells, it is in the form of unconnected units called dictyosomes
• The Golgi body is composed of cisternae, vesicles, tubules, and vacuoles
• It is a single membrane-bound organelle
• Functions of the Golgi body include secretion, formation of carbohydrates, glycoproteins, cell wall, cell membrane, lysosomes, acrosome of sperm, and cell plate formation

Lysosomes

• Lysosomes were first reported by Christian de Duve in 1955
• They occur in most animal cells but are absent in prokaryotes
• Lysosomes are tiny, membrane-bound, vesicular structures that perform intracellular digestion
• They are polymorphic, with four types: primary lysosomes, secondary lysosomes, residual bodies, and autophagic vacuoles
• Lysosomes regularly engulf bits of cytosol containing waste, foreign material, and worn-out cell organelles, which are digested there
• They contain digestive enzymes capable of digesting proteins, carbohydrates, lipids, and nucleic acids
• Lysosomes are involved in the digestion of microorganisms such as bacteria entering the cell by phagocytosis
• In certain conditions, lysosomes start to digest old or dead cell organelles, a process known as autophagy
• Lysosomes are sometimes called "suicide bags" because the enzymes they contain could digest the whole cell if they burst

Ribosomes

• Ribosomes are also called "organelle within an organelle" and the protein factory of the cell
• Each ribosome is made up of two unequal subunits that join together during protein synthesis in the presence of Mg2+ ions
• Ribosomes are small, sub-spherical, granular organelles not enclosed by a membrane
• They are composed of r-RNA and proteins and attach to m-RNA to form polyribosomes during protein synthesis
• In prokaryotes, the two subunits are 30S and 50S (together 70S), and in eukaryotes, they are 40S and 60S (together 80S)
• In mammals, 55S type of ribosomes are present in the mitochondrial matrix

Endoplasmic Reticulum (ER)

• ER is a three-dimensional, complicated, interconnecting system of membrane-lined channels that run through the cytoplasm
• ER remains continuous with the plasma membrane, nuclear envelope, and Golgi body
• ER is composed of cisternae, vesicles, and tubules
• There are two types of ER: smooth ER and rough ER
• Smooth ER is engaged in the synthesis and storage of glycogen, fat, and steroids, and detoxification of drugs and poisons
• Rough ER is associated with protein synthesis due to the presence of ribosomes on its surface

Golgi Body

• The Golgi body was discovered by Camillo Golgi in 1898 in nerve cells of owls and cats
• In animal cells, it is localized near the nucleus, but in plant cells, it is in the form of unconnected units called dictyosomes
• The Golgi body is composed of cisternae, vesicles, tubules, and vacuoles
• It is a single membrane-bound organelle
• Functions of the Golgi body include secretion, formation of carbohydrates, glycoproteins, cell wall, cell membrane, lysosomes, acrosome of sperm, and cell plate formation

Lysosomes

• Lysosomes were first reported by Christian de Duve in 1955
• They occur in most animal cells but are absent in prokaryotes
• Lysosomes are tiny, membrane-bound, vesicular structures that perform intracellular digestion
• They are polymorphic, with four types: primary lysosomes, secondary lysosomes, residual bodies, and autophagic vacuoles
• Lysosomes regularly engulf bits of cytosol containing waste, foreign material, and worn-out cell organelles, which are digested there
• They contain digestive enzymes capable of digesting proteins, carbohydrates, lipids, and nucleic acids
• Lysosomes are involved in the digestion of microorganisms such as bacteria entering the cell by phagocytosis
• In certain conditions, lysosomes start to digest old or dead cell organelles, a process known as autophagy
• Lysosomes are sometimes called "suicide bags" because the enzymes they contain could digest the whole cell if they burst

Mitochondria

• Mitochondria are known as the powerhouse of the cell or ATP generation site.
• They are enclosed in a double membrane envelop, with a smooth outer membrane and an inner membrane that surrounds a fluid-filled central cavity called the matrix.
• The inner membrane is infolded into the matrix as incomplete partitions called cristae, which increase the surface area.
• Cristae bear small tennis racket-like particles called elementary particles, Fo-F1 particles, or oxysomes, which are associated with respiration and the formation of energy in the form of ATP.
• Mitochondria have their own DNA and ribosome and can self-replicate, making them semi-autonomous bodies.
• ATP synthetase enzyme is responsible for the formation of ATP.
• In the absence of mitochondria, a cell's energy metabolism would be severely reduced.

Plastids

• Plastids are semi-autonomous organelles with DNA and a double membrane envelope.
• There are three types of plastids: leucoplasts, chromoplasts, and chloroplasts.
• Leucoplasts are colorless and used to store proteins, oil, and starch.
• Chromoplasts are colored and contain pigments other than green.
• Chloroplasts are green and participate in the synthesis of organic food through photosynthesis.
• Chloroplasts have a ground substance called stroma, with membranous structures called thylakoids that contain chlorophyll and are arranged in stacks to form grana.
• The main functions of plastids are photosynthesis, storage of fats, proteins, and starch.

Vacuoles

• Vacuoles are membrane-bound non-cytoplasmic sacs that contain non-living liquid or solid contents.
• They are common in both plant and animal cells.
• In animal and young plant cells, sap vacuoles are small.
• In mature plant cells, there is a large central vacuole that occupies 50-90% of the cell volume.
• The covering membrane of the vacuole is called tonoplast.
• The fluid content of the vacuole is called cell sap.
• Vacuoles store salts, sugars, amino acids, organic acids, and some proteins.
• They also act as a dump for waste products in plant cells and help maintain turgidity and rigidity of the cell.

Mitochondria

• Mitochondria are known as the powerhouse of the cell or ATP generation site.
• They are enclosed in a double membrane envelop, with a smooth outer membrane and an inner membrane that surrounds a fluid-filled central cavity called the matrix.
• The inner membrane is infolded into the matrix as incomplete partitions called cristae, which increase the surface area.
• Cristae bear small tennis racket-like particles called elementary particles, Fo-F1 particles, or oxysomes, which are associated with respiration and the formation of energy in the form of ATP.
• Mitochondria have their own DNA and ribosome and can self-replicate, making them semi-autonomous bodies.
• ATP synthetase enzyme is responsible for the formation of ATP.
• In the absence of mitochondria, a cell's energy metabolism would be severely reduced.

Plastids

• Plastids are semi-autonomous organelles with DNA and a double membrane envelope.
• There are three types of plastids: leucoplasts, chromoplasts, and chloroplasts.
• Leucoplasts are colorless and used to store proteins, oil, and starch.
• Chromoplasts are colored and contain pigments other than green.
• Chloroplasts are green and participate in the synthesis of organic food through photosynthesis.
• Chloroplasts have a ground substance called stroma, with membranous structures called thylakoids that contain chlorophyll and are arranged in stacks to form grana.
• The main functions of plastids are photosynthesis, storage of fats, proteins, and starch.

Vacuoles

• Vacuoles are membrane-bound non-cytoplasmic sacs that contain non-living liquid or solid contents.
• They are common in both plant and animal cells.
• In animal and young plant cells, sap vacuoles are small.
• In mature plant cells, there is a large central vacuole that occupies 50-90% of the cell volume.
• The covering membrane of the vacuole is called tonoplast.
• The fluid content of the vacuole is called cell sap.
• Vacuoles store salts, sugars, amino acids, organic acids, and some proteins.
• They also act as a dump for waste products in plant cells and help maintain turgidity and rigidity of the cell.

Organelles in Plant Cells

• Glyoxysomes are organelles found only in plant cells, especially in fatty seeds and unripe fruits.
• They are highly specialized peroxisomes that convert fats into carbohydrates.
• Glyoxysomes are related to the metabolism of fats.

Sphaerosomes

• Sphaerosomes are small, single-membrane organelles found only in plant cells.
• They are the major site of lipid storage and synthesis in plants.
• Sphaerosomes also have lysosome-like activity, earning them the term "plant lysosomes".

Peroxisomes or Uricosomes

• In animal cells, peroxisomes are involved in peroxide (H2O2) metabolism.
• They contain enzymes like urate oxidase, amino acid oxidase, and peroxidase.
• Peroxidase induces the oxidation of amino acids to produce H2O2.
• Catalase degrades H2O2 into water and oxygen.
• In plant cells, peroxisomes occur in cells of green tissues and are involved in photorespiration.
• They also detoxify alcohol in liver cells.

Cytoskeleton

• The cytoskeleton is an elaborate network of filamentous proteinaceous structures present in the cytoplasm.
• It provides mechanical support, motility, and maintains the shape of the cell.
• The cytoskeleton consists of microtubules, microfilaments, and intermediate filaments.

Microtubules

• Microtubules are composed of protein tubulin.
• In plant cells, microtubules are often found associated with the cell wall.
• They probably transport cell wall material from the Golgi body to the outside of the cell.
• During cell division, microtubules form spindle fibers.

Microfilaments

• Microfilaments are composed of contractile protein actin.
• Actin is concerned with muscle contraction.

Intermediate Filaments

• Intermediate filaments have a size/diameter between microfilaments and microtubules.
• They form basket-like structures around the nucleus.

Organelles in Plant Cells

• Glyoxysomes are organelles found only in plant cells, especially in fatty seeds and unripe fruits.
• They are highly specialized peroxisomes that convert fats into carbohydrates.
• Glyoxysomes are related to the metabolism of fats.

Sphaerosomes

• Sphaerosomes are small, single-membrane organelles found only in plant cells.
• They are the major site of lipid storage and synthesis in plants.
• Sphaerosomes also have lysosome-like activity, earning them the term "plant lysosomes".

Peroxisomes or Uricosomes

• In animal cells, peroxisomes are involved in peroxide (H2O2) metabolism.
• They contain enzymes like urate oxidase, amino acid oxidase, and peroxidase.
• Peroxidase induces the oxidation of amino acids to produce H2O2.
• Catalase degrades H2O2 into water and oxygen.
• In plant cells, peroxisomes occur in cells of green tissues and are involved in photorespiration.
• They also detoxify alcohol in liver cells.

Cytoskeleton

• The cytoskeleton is an elaborate network of filamentous proteinaceous structures present in the cytoplasm.
• It provides mechanical support, motility, and maintains the shape of the cell.
• The cytoskeleton consists of microtubules, microfilaments, and intermediate filaments.

Microtubules

• Microtubules are composed of protein tubulin.
• In plant cells, microtubules are often found associated with the cell wall.
• They probably transport cell wall material from the Golgi body to the outside of the cell.
• During cell division, microtubules form spindle fibers.

Microfilaments

• Microfilaments are composed of contractile protein actin.
• Actin is concerned with muscle contraction.

Intermediate Filaments

• Intermediate filaments have a size/diameter between microfilaments and microtubules.
• They form basket-like structures around the nucleus.

Cilia and Flagella

• Cilia are small, hair-like structures that work like oars, causing movement of either the cell or surrounding fluid.
• Cilia are small in size, with a large number per cell, beating in a coordinated manner to facilitate locomotion, attachment, and feeding.
• Flagella are longer than cilia, fewer in number, and beat independently in a non-coordinated manner, responsible only for locomotion.

Centrioles

• Centrioles are short, cylindrical structures with a 9 + 0 pattern of microtubule triplets, found in pairs near the nucleus in animal cells, except mature mammalian RBCs.
• Centrioles move to the poles and form asters during cell division, organizing spindle fibers.
• The region surrounding the centriole pair is known as the centrosphere, and together they form the centrosome.

Nucleic Acids

• Nucleic acids are long-chain macromolecules, comprising Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA).
• Nucleotides are the basic units of nucleic acids, consisting of a pentose sugar, phosphoric acid, and a nitrogen base.

Nucleotides

• Nucleotides contain one of two types of pentose sugars: ribose or deoxyribose.
• Nitrogen bases are heterocyclic compounds, classified as purines (Adenine, Guanine) and pyrimidines (Cytosine, Thymine, Uracil).
• A combination of a nitrogen base with a pentose sugar is known as a nucleoside.

Cilia and Flagella

• Cilia are small, hair-like structures that work like oars, causing movement of either the cell or surrounding fluid.
• Cilia are small in size, with a large number per cell, beating in a coordinated manner to facilitate locomotion, attachment, and feeding.
• Flagella are longer than cilia, fewer in number, and beat independently in a non-coordinated manner, responsible only for locomotion.

Centrioles

• Centrioles are short, cylindrical structures with a 9 + 0 pattern of microtubule triplets, found in pairs near the nucleus in animal cells, except mature mammalian RBCs.
• Centrioles move to the poles and form asters during cell division, organizing spindle fibers.
• The region surrounding the centriole pair is known as the centrosphere, and together they form the centrosome.

Nucleic Acids

• Nucleic acids are long-chain macromolecules, comprising Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA).
• Nucleotides are the basic units of nucleic acids, consisting of a pentose sugar, phosphoric acid, and a nitrogen base.

Nucleotides

• Nucleotides contain one of two types of pentose sugars: ribose or deoxyribose.
• Nitrogen bases are heterocyclic compounds, classified as purines (Adenine, Guanine) and pyrimidines (Cytosine, Thymine, Uracil).
• A combination of a nitrogen base with a pentose sugar is known as a nucleoside.

Cilia and Flagella

• Cilia are small, hair-like structures that work like oars, causing movement of either the cell or surrounding fluid.
• Cilia are small in size, with a large number per cell, beating in a coordinated manner to facilitate locomotion, attachment, and feeding.
• Flagella are longer than cilia, fewer in number, and beat independently in a non-coordinated manner, responsible only for locomotion.

Centrioles

• Centrioles are short, cylindrical structures with a 9 + 0 pattern of microtubule triplets, found in pairs near the nucleus in animal cells, except mature mammalian RBCs.
• Centrioles move to the poles and form asters during cell division, organizing spindle fibers.
• The region surrounding the centriole pair is known as the centrosphere, and together they form the centrosome.

Nucleic Acids

• Nucleic acids are long-chain macromolecules, comprising Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA).
• Nucleotides are the basic units of nucleic acids, consisting of a pentose sugar, phosphoric acid, and a nitrogen base.

Nucleotides

• Nucleotides contain one of two types of pentose sugars: ribose or deoxyribose.
• Nitrogen bases are heterocyclic compounds, classified as purines (Adenine, Guanine) and pyrimidines (Cytosine, Thymine, Uracil).
• A combination of a nitrogen base with a pentose sugar is known as a nucleoside.

Deoxyribonucleic Acid (DNA)

• DNA model was given by Watson and Crick
• Consists of two polynucleotide chains that form a double helical staircase
• Chains are joined together by weak hydrogen bonds between nitrogen bases

Nitrogen Bases in DNA

• Purines: Adenine (A) and Guanine (G)
• Pyrimidines: Cytosine (C) and Thymine (T)
• Base pairing: Adenine (A) pairs with Thymine (T) with two hydrogen bonds, and Cytosine (C) pairs with Guanine (G) with three hydrogen bonds
• A + G = C + T, establishing Chargaff's rule of base equivalence

Structure of DNA

• Double helix is twisted, taking a complete turn after every 34 A
• 10 nitrogen base pairs in a complete turn
• Width of DNA molecule is 20 A
• DNA found in mitochondria, plastids, and prokaryotes is generally circular, uncovered with protein (naked)

Ribonucleic Acid (RNA)

• Occurs in all living cells and viruses
• Found in cytoplasm and nucleus of eukaryotic cells
• Can be genetic material in some viruses (genetic RNA)
• Non-genetic RNA found in nucleus, cytoplasm, ribosomes, chloroplasts, and mitochondria

Structure of RNA

• Single-stranded molecule, shorter than DNA
• Uracil replaces thymine as nitrogen base
• Pentose sugar is ribose
• Occurs in three forms: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)

Significance of DNA

• Controls all cell activities directly and indirectly
• Unique feature: ability to duplicate itself during cell division (replication)
• Genetic material, containing information for protein synthesis
• Can undergo mutations and recombination, leading to variations and speciation

Deoxyribonucleic Acid (DNA)

• DNA model was given by Watson and Crick
• Consists of two polynucleotide chains that form a double helical staircase
• Chains are joined together by weak hydrogen bonds between nitrogen bases

Nitrogen Bases in DNA

• Purines: Adenine (A) and Guanine (G)
• Pyrimidines: Cytosine (C) and Thymine (T)
• Base pairing: Adenine (A) pairs with Thymine (T) with two hydrogen bonds, and Cytosine (C) pairs with Guanine (G) with three hydrogen bonds
• A + G = C + T, establishing Chargaff's rule of base equivalence

Structure of DNA

• Double helix is twisted, taking a complete turn after every 34 A
• 10 nitrogen base pairs in a complete turn
• Width of DNA molecule is 20 A
• DNA found in mitochondria, plastids, and prokaryotes is generally circular, uncovered with protein (naked)

Ribonucleic Acid (RNA)

• Occurs in all living cells and viruses
• Found in cytoplasm and nucleus of eukaryotic cells
• Can be genetic material in some viruses (genetic RNA)
• Non-genetic RNA found in nucleus, cytoplasm, ribosomes, chloroplasts, and mitochondria