Introduction to Cells for Class 9

Introduction to Cells

• Introduction to the cell, fundamental unit of life, for Class 9 students.

The Cell: Fundamental Unit of Life

• The cell is the basic building block of all living organisms.
• All living organisms are composed of cells.
• Cells are the fundamental units of life because all functions of a living organism begin at the cellular level.

Cell Theory

• Cells are the basic structural and functional units of all living organisms.
• All organisms are made up of one or more cells.
• All cells arise from pre-existing cells.
• This theory was developed by Schleiden, Schwann, and Virchow.

Types of Organisms Based on their Cellular Structure

• Unicellular Organisms: Organisms made up of a single cell.
  • Examples: Bacteria, Amoeba, Paramecium
• Multicellular Organisms: Organisms made up of multiple cells.
  • Examples: Humans, animals, plants

History of Cell Discovery

• Robert Hooke: Discovered the cell in 1665.
  • Observed dead cells in a thin slice of cork using a microscope.
  • The cells observed were from a plant (cork).
• Antonie van Leeuwenhoek: First to observe living cells under a microscope.
• Robert Brown: Discovered the nucleus of the cell in 1831.
• Purkinje: Discovered the protoplasm of the cell in 1839.

Components of the Cell

• Plasma Membrane (Cell Membrane): Outer boundary of the cell.
  • Acts as a gatekeeper, controlling what enters and exits the cell.
• Cytoplasm: Jelly-like substance inside the cell, containing cell organelles.
  • Site of many chemical reactions.
• Nucleus: Control center of the cell.
  • Contains the cell's genetic material (DNA), controlling all cell activities.
• Cell Organelles: Specialized structures within the cell performing specific functions.
  • Like tiny organs within the cell.
• Cell Wall: Rigid outer layer in plant cells.
  • Provides structural support and protection.
  • Made of cellulose.

Importance of Cell Organelles

• Cell organelles perform specific functions, essential for the cell's survival and function.

The Cell: A Building Block of our Body

• Cells combine to form tissues.
• Tissues combine to form organs.
• Organs combine to form organ systems.
• Organ systems combine to form a complete organism.

Cell Size and Shape

• Cell size and shape vary based on species and function.
• Largest cell: Ostrich egg
• Smallest cell: Mycoplasma (type of bacteria).

Key Fact

• The importance of studying science is emphasized in the text, with a focus on engaging teaching methods.

Cell Membrane

• Outermost covering of the cell.
• Separates the cell from its surroundings.
• Controls what enters and exits the cell.
• Also known as the plasma membrane.
• Selective permeable membrane; selectively allows substances in and out of the cell.
• Made of lipids and proteins.

Membrane Transport

• Movement of substances across the cell membrane.
• Two types:
  • Passive transport: Movement from high to low concentration, no energy required.
  • Active transport: Movement from low to high concentration, requires energy (ATP).

Passive Transport

• Two types:
  • Diffusion: Movement of substances from high to low concentration.
  • Osmosis: Movement of water from high to low concentration across a semi-permeable membrane.

Osmosis

• Two types:
  • Endosmosis: Water enters the cell, causing it to swell.
  • Exosmosis: Water exits the cell, causing it to shrink (shrivel).

Types of Solutions

• Hypertonic solution: Higher solute concentration than the cell.
• Hypotonic solution: Lower solute concentration than the cell.
• Isotonic solution: Same solute concentration as the cell.

Cell Wall

• Rigid outer layer in plant, fungi, and bacteria cells.
• Provides structural support and rigidity.
• Prevents cells from bursting during osmosis.
• Composition:
  • Plant cells: Cellulose
  • Bacteria cells: Peptidoglycan
  • Fungi cells: Chitin

Plasmolysis

• Shrinkage of the living cell content in hypertonic solutions.
• Cell membrane pulls away from the cell wall as water exits the cell.
• Cell wall remains intact.

Functions of the Cell Wall

• Provides rigidity and strength to the cell, preventing bursting.
• Maintains cell shape.
• Protects from pathogens and environmental stress.

Differences Between Plant and Animal Cells

• Plants have rigid cell walls for structural support.
• Animals lack cell walls due to mobility requirements.

Cell Wall (updated)

• Provides structural support and rigidity to plant cells.
• Plant cells are immobile, needing a rigid, tough outer layer for support.

Nucleus

• Control center of the cell.
• Enclosed by a double-layered nuclear membrane with pores for material exchange.
• Houses DNA, the genetic material defining organism traits.
• DNA is a thread-like structure.
• DNA controls eye color and hair type.
• Controls cell reproduction and development.

Chromatin & Chromosomes

• Chromatin: Thread-like, uncoiled DNA in the nucleus.
• Chromosomes: Condensed, coiled DNA during cell division.
• Chromosomes are paired DNA.

Prokaryotic & Eukaryotic Cells

• Prokaryotic: Smaller, lack a defined nucleus, nucleoid region for DNA, single chromosome, lack membrane-bound organelles.
• Eukaryotic: Larger, defined nucleus containing multiple chromosomes, membrane-bound organelles.

Ribosomes

• Protein synthesis factories in the cell.
• Found in both prokaryotic and eukaryotic cells.
• Lack a membrane.

Endoplasmic Reticulum (ER)

• Network of membranes in the cytoplasm.
• Involved in lipid and protein synthesis, transport and modification.
  • Rough ER: Protein production
  • Smooth ER: Lipid production, detoxification of harmful substances.

Golgi Apparatus

• Processes, packages, and transports cellular products in vesicles.
• Involved in protein modification, storage, and packaging.
• Assists in lysosome formation.

Lysosomes

• "Suicide bags" of the cell.
• Contain digestive enzymes to break down waste and cellular debris.
• Formed from the Golgi apparatus.
• Break down worn-out cell parts and ingested food.
• Can digest the entire cell if needed.

Cytoplasm

• Fluid content of the cell, enclosed by the cell membrane.
• Essential for cell processes and movements.
• Contains organelles.

Cell Organelles (updated)

• Endoplasmic Reticulum (ER): A network of membranes involved in lipid and protein synthesis.
  • Rough ER: Protein production
  • Smooth ER: Lipid production, detoxification.
• Golgi Apparatus: Packages and modifies cellular products in vesicles.
• Lysosomes: Digest waste and cellular debris, "suicide bags."
• Vacuoles: Store excess materials and water, maintaining turgor pressure in plant cells.
• Mitochondria: Energy production (ATP) through cellular respiration, contain their own DNA and ribosomes.
• Plastids: Found only in plant cells.
  • Chloroplasts: Photosynthesis.
  • Chromoplasts: Color to flowers/fruits.
  • Leucoplasts: Store starch, oil, and proteins.

Cell Organelle Membranes

• Double-membrane bound organelles: Nucleus, Mitochondria, Plastids
• Single-membrane bound organelles: Vacuole, Lysosomes, Golgi apparatus, Endoplasmic reticulum
• Membrane-less organelles: Ribosomes, centrosomes

Cell Division

• Cell division: Process for producing new cells.
  • Parent cell: Original cell
  • Daughter cells: Cells produced from parent cell division.
  • Mitosis: Division resulting in two daughter cells with the same chromosome number (growth and repair)
  • Meiosis: Division creating four daughter cells with half the chromosome number (reproduction).

Table of Key Differences Between Plant and Animal Cells

(Table provided previously)

Osmosis Demo

• Dry apricots in pure water, then transferred to sugar solution.
• Water moves into apricots when in water, making them swell (endosmosis).
• Transferring to a sugar solution (hypertonic) causes water to move out, shrinking the apricots (exosmosis).

This quiz serves as an introduction to cells, the fundamental unit of life, specifically designed for Class 9 students. It covers the structure of cells, types of organisms, cell theory, and notable discoveries in cell history. Test your understanding of these essential concepts in biology!