Cell: THE Unit OF Life flash cards

1. 1.Who first discovered and named the cell?

   Robert Hooke (1665) observed dead cork cells in a self-designed microscope and named them 'cells'.

   Hint: Cork, 1665

2. 2.Who was the first to see living cells?

   Anton von Leeuwenhoek first saw and described living cells (e.g. bacteria, protozoa).

   Hint: 'Father of microbiology'

3. 3.Who discovered the nucleus?

   Robert Brown (1831) discovered the nucleus.

   Hint: Botanist, Brownian motion

4. 4.State the two components of the Cell Theory given by Schleiden and Schwann.

   (1) All plants and animals are composed of cells. (2) The cell is the basic unit of life.

   Hint: Schleiden = plants, Schwann = animals

5. 5.What did Rudolf Virchow add to the cell theory?

   Omnis cellula-e cellula — all cells arise from pre-existing cells (cell division).

   Hint: Cells from cells

6. 6.Who proposed the cell theory and in which year?

   Matthias Schleiden (1838) and Theodore Schwann (1839) proposed the cell theory.

   Hint: Botanist + zoologist

7. 7.State the modern cell theory in full.

   (1) All living organisms are composed of cells and products of cells. (2) All cells arise from pre-existing cells.

   Hint: Two statements

8. 8.What is the smallest cell known?

   Mycoplasma (PPLO), about $0.3\,\mu m$ in length.

   Hint: Also lacks a cell wall

9. 9.Which is the largest isolated single cell?

   The egg of an ostrich.

   Hint: Bird egg

10. 10.Which are the longest cells in the human body?

    Nerve cells (neurons) are among the longest cells.

    Hint: Can be over a metre long

11. 11.What is the size range of bacterial cells?

    Bacteria range from $3$ to $5\,\mu m$ in length.

    Hint: Microns

12. 12.How big are human RBCs?

    Human red blood cells are about $7\,\mu m$ in diameter.

    Hint: About 7 micrometres

13. 13.Name the two broad categories of cells based on nuclear organisation.

    Prokaryotic cells and eukaryotic cells.

    Hint: No true nucleus vs true nucleus

14. 14.Which organisms have prokaryotic cells?

    Bacteria, blue-green algae (cyanobacteria), mycoplasma and PPLO.

    Hint: Kingdom Monera

15. 15.What is the defining feature of a prokaryotic cell?

    Absence of a nuclear membrane (no true membrane-bound nucleus); genetic material lies naked in the cytoplasm.

    Hint: No nuclear envelope

16. 16.Do prokaryotes have membrane-bound organelles?

    No — prokaryotes lack membrane-bound organelles (no ER, Golgi, mitochondria, plastids, etc.).

    Hint: Only ribosomes present

17. 17.What is the nucleoid?

    The region of a prokaryotic cell where the genomic (naked, coiled) DNA is located, not bound by a membrane.

    Hint: Prokaryotic 'nucleus'

18. 18.What are plasmids?

    Small circular extra-chromosomal DNA present in bacteria; confer traits like antibiotic resistance and are used as vectors.

    Hint: Extra-chromosomal DNA

19. 19.List the three basic shapes of bacteria.

    Bacillus (rod-shaped), Coccus (spherical), Vibrio (comma-shaped) and Spirillum (spiral).

    Hint: Rod, sphere, comma, spiral

20. 20.Describe the three-layered envelope of a bacterial cell.

    Glycocalyx (outermost) → cell wall → plasma membrane. Together they act as a single protective unit.

    Hint: Outer to inner

21. 21.What is glycocalyx? Differentiate slime layer and capsule.

    Glycocalyx is the outer sticky coat. A loose sheath = slime layer; a thick, tough coat = capsule.

    Hint: Loose vs thick

22. 22.On what basis are bacteria classified as Gram-positive or Gram-negative?

    On their response to Gram's staining, which depends on cell-wall structure.

    Hint: Christian Gram's stain

23. 23.What is a mesosome and its functions?

    An infolding of the plasma membrane (vesicles, tubules, lamellae). Functions: cell wall formation, DNA replication and distribution, respiration, secretion, increasing surface area for enzymes.

    Hint: Plasma membrane infolding

24. 24.What are chromatophores in cyanobacteria?

    Membranous extensions into the cytoplasm containing pigments; sites of photosynthesis.

    Hint: Photosynthetic in prokaryotes

25. 25.What is the size of prokaryotic (70S) ribosomes and their subunits?

    70S ribosomes made of 50S (large) and 30S (small) subunits.

    Hint: 70S = 50S + 30S

26. 26.What is a polysome (polyribosome)?

    Several ribosomes attached to a single mRNA forming a chain; they translate the mRNA to form a protein.

    Hint: Ribosomes on one mRNA

27. 27.What are inclusion bodies in prokaryotes?

    Reserve material stored freely (not membrane-bound) in cytoplasm — e.g. phosphate granules, cyanophycean granules, glycogen granules, gas vacuoles.

    Hint: Stored, not membrane-bound

28. 28.What is the structure and function of bacterial flagella?

    Thin filamentous extensions for motility, made of three parts — filament, hook, and basal body.

    Hint: Filament-hook-basal body

29. 29.Differentiate pili and fimbriae.

    Pili: elongated tubular structures (made of pilin), aid in conjugation. Fimbriae: small bristle-like fibres that help attachment to surfaces/host.

    Hint: Conjugation vs attachment

30. 30.What are the two main components common to all cells?

    Plasma membrane and cytoplasm (all cells contain genetic material as well).

    Hint: Membrane + cytoplasm

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