🧬 Class 9 Biology Flashcards – Chapter: The Fundamental Unit of Life

Cell

The structural and functional unit of life

Robert Hooke

Discovered cells in cork in 1665 using a microscope

Unicellular organism

Single-celled organism like Amoeba or Paramecium

Multicellular organism

Organism made up of many cells performing specific functions

Cell theory

All living organisms are made of cells and all cells come from pre-existing cells

Schleiden and Schwann

Proposed the cell theory in 1838-1839

Rudolf Virchow

Added that all cells arise from pre-existing cells in 1855

Prokaryotic cell

Cell without a true nucleus (e.g., bacteria)

Eukaryotic cell

Cell with a well-defined nucleus and organelles (e.g., plant and animal cells)

Plasma membrane

Outer layer of cell; selectively permeable membrane

Selectively permeable membrane

Allows only certain substances to pass through

Diffusion

Movement of molecules from high to low concentration

Osmosis

Diffusion of water through a selectively permeable membrane

Hypotonic solution

Lower solute concentration outside; cell swells

Isotonic solution

Equal solute concentration; cell stays same

Hypertonic solution

Higher solute outside; cell shrinks

Endocytosis

Process of engulfing materials through membrane (e.g., Amoeba feeding)

Cell wall

Rigid outer layer in plant cells; provides support; made of cellulose

Plasmolysis

Shrinkage of cytoplasm in hypertonic solution

Nucleus

Control center of the cell containing genetic material

Nuclear membrane

Double-layered membrane with pores

Chromosomes

Rod-like structures made of DNA and proteins

Chromatin

Thread-like mass of DNA in non-dividing cells

Gene

Functional unit of DNA that carries genetic information

Nucleoid

Undefined nuclear region in prokaryotic cells

Cytoplasm

Fluid part of cell that contains organelles

Endoplasmic reticulum (ER)

Network of membranes for transport

Rough ER

ER with ribosomes; helps in protein synthesis

Smooth ER

ER without ribosomes; helps in lipid synthesis and detoxification

Golgi apparatus

Packs and transports proteins and lipids; forms lysosomes

Lysosomes

Digestive sacs; destroy waste and worn-out organelles

Mitochondria

Powerhouse of the cell; site of ATP production

ATP

Adenosine triphosphate; energy currency of cell

Plastids

Organelles found in plant cells; includes chloroplasts and leucoplasts

Chloroplasts

Plastids with chlorophyll; site of photosynthesis

Leucoplasts

Plastids for storage of starch, protein, and lipids

Vacuole

Storage sac; large in plant cells; provides turgidity

Food vacuole

Stores food in unicellular organisms like Amoeba

Mitosis

Cell division for growth and repair; produces 2 identical cells

Meiosis

Cell division for gamete formation; produces 4 cells with half the chromosomes