Cell Biology: History, Properties, Sizes, and Shapes

Comprehensive practice flashcards covering milestones in cell biology, cell size extremes, surface area constraints, and diverse cell morphologies and functions.

What is the primary focus of cell biology (cytology)?

It is the branch of biology that studies the structure, function, and behavior of cells as the basic unit of life.

What did Robert Hooke observe under a compound microscope in 1665 when he first coined the term "cells"?

He observed thin slices of cork, identifying tiny box-like compartments (cellulae) which were actually dead plant cell walls.

What is the name of Robert Hooke's landmark 1665 book on microscopy?

Micrographia.

What term did Antonie van Leeuwenhoek use to describe the living microscopic organisms he discovered between 1674 and 1683?

Animalcules.

What foundational concept did Matthias Schleiden and Theodor Schwann propose in 1838–1839?

They formulated the original Cell Theory, stating that all living organisms are composed of cells and that the cell is the basic structural and functional unit of life.

What Latin phrase did Rudolf Virchow contribute to the Cell Theory in 1855, and what does it mean?

"Omnis cellula e cellula," meaning that new cells arise only from pre-existing cells.

Who invented the Transmission Electron Microscope (TEM) in 1931, and what did it enable scientists to see?

Ernst Ruska; it allowed visualization of subcellular ultrastructures such as mitochondria, ribosomes, and membranes.

Which scientist is credited with describing the cell nucleus in 1831?

Robert Brown.

Who discovered lysosomes in 1955, and who visualized ribosomes using electron microscopy in the 1950s?

Christian de Duve discovered lysosomes, and George Palade visualized ribosomes.

What did Frederick Griffith discover in 1928 using Streptococcus pneumoniae?

The process of transformation.

Which 1952 experiment definitively confirmed that DNA, and not protein, is the genetic material?

The Hershey-Chase experiment using bacteriophages.

Who proposed the double helix model of DNA in 1953, and whose X-ray diffraction data did they use?

James Watson and Francis Crick, using X-ray diffraction data produced by Rosalind Franklin and Maurice Wilkins.

Who was the first scientist to describe mitosis in 1879?

Walther Flemming.

Who discovered meiosis, the specialized cell division involved in gamete formation?

Edouard van Beneden.

What is the typical average size range of prokaryotic cells compared to eukaryotic cells?

Prokaryotic cells are approximately $0.1 \text{ to } 5\,\mu\text{m}$, while eukaryotic cells are approximately $10 \text{ to } 100\,\mu\text{m}$.

What is the smallest known free-living cell and organism, and what is its approximate size?

Mycoplasma gallisepticum, with a size of $\sim 0.1\,\mu\text{m}$.

What is the smallest human cell, and what is its approximate size?

The sperm cell, with an approximate size of $\sim 5\,\mu\text{m}$.

What is identified as the largest animal cell, and what is its approximate dimension?

The ostrich egg, measuring approximately $\sim 15\,\text{cm}$ in diameter.

What is the longest cell cited in the notes, and what is an example?

The neuron (nerve cell), which can measure $>1\,\text{meter}$ (e.g., the human sciatic nerve).

What is the largest plant cell listed in the notes, and what is its approximate size?

Acetabularia (a giant unicellular green alga), measuring approximately $\sim 10\,\text{cm}$.

What is the approximate size of duckweed (Wolffia spp.), cited as the smallest flowering plant?

$\sim 0.1 \text{ to } 0.2\,\text{mm}$ ($100\text{--}200\,\mu\text{m}$).

Why must cells maintain a high surface area to volume (SA:V) ratio?

Because as cell size increases, volume grows faster than surface area; a high SA:V ratio allows efficient exchange of nutrients, oxygen, and waste.

How does the nuclear-cytoplasmic ratio constrain maximum cell size?

The nucleus controls cellular activities; if the cytoplasm becomes too large, nuclear control efficiency decreases, prompting the cell to divide or become multinucleated.

What are the four primary factors that influence cell shape?

1. Cell wall or cell membrane, 2. Cytoskeleton, 3. Functional demands, and 4. Physical environment (pressure, fluid flow, surrounding tissues).

What is the functional advantage of the biconcave, disc-shaped structure of red blood cells (RBCs)?

It increases the surface area for efficient gas exchange.

What is the description, example, and function of polygonal cells?

Tightly packed cells with many sides (usually 4–6), exemplified by liver cells (hepatocytes), which fit tightly for compact tissue organization.

What is the description, example, and function of columnar cells?

Tall and rectangular cells found in the lining of the intestine, functioning to increase surface area for absorption.

What is the structure and role of stellate (star-shaped) cells in the brain?

Cells with multiple radiating processes (such as astrocytes) that provide structural and metabolic support to neurons.

What cell shape is characterized as spindle-shaped (fusiform) with tapered ends, and what is its role?

Muscle cells, which facilitate contraction and relaxation.

How do parenchyma, collenchyma, and sclerenchyma cells differ in plant support and morphology?

Parenchyma cells are round or oval for general storage and support; collenchyma cells are elongated with uneven walls for flexible support; sclerenchyma cells are thick-walled with varied shapes for rigid support.