Study sheet: Cell Biology

📋 Course Outline

1. Cell Definition and Cell Theory
2. Cell Organization and Genetic Material
3. Cell Biology and Cell-Type Classification
4. Unicellular and Multicellular Organization
5. Classical Eukaryotic Classification
6. Comparative Cell Sizes

📅 Key Dates

1. 19th centuryMatthias Schleiden showed that plants are made of cells and Theodor Schwann showed that animals are made of cells — Schleiden and Schwann, 19th century
2. 1665Robert Hooke observed regularly spaced compartments in thin slices of cork and named them “cells”
3. 1855Rudolf Virchow proposed that every cell comes from a pre-existing cell

📖 1. Cell Definition and Cell Theory

🔑 Key Concepts & Definitions

• Cell : the basic structural and functional unit of life, carrying out nutrition, growth, reproduction, and responses to its environment
• Cell theory : states that life is organized at the cellular level and that organismal functions are ultimately explained through cells

📝 Essential Points

• The main principles of cell theory are:
  • All living organisms are composed of one or more cells
  • The cell is the basic structural and functional unit of life
  • Every cell arises from a pre-existing cell

💡 Memory Hook

Cells organize life → organisms grow, reproduce, and respond

📖 2. Cell Organization and Genetic Material

★ Must-know

📌 Prokaryotic cells have DNA that is not enclosed within a true nucleus, whereas eukaryotic cells have DNA enclosed within a membrane-bound nucleus.

Further detail

• Modern cell biology adds that DNA stores genetic information and directs cellular activities.

💡 Memory Hook

Prokaryote: no true nucleus; eukaryote: true nucleus

📖 3. Cell Biology and Cell-Type Classification

🔑 Key Concepts & Definitions

• Cell biology : the branch of biology that studies cell structure, organelles, cellular functions, cell division, cell death, and interactions between cellular components
• Prokaryotic organism : A prokaryotic organism lacks a true nucleus and membrane-bound organelles, has DNA concentrated in a nucleoid region, and has relatively simple cellular organization.
• Eukaryotic organism : A eukaryotic organism has a true nucleus containing its DNA, membrane-bound organelles, and a more complex cellular organization.

★ Must-know

📌 Viruses belong to neither the prokaryotic nor the eukaryotic group because they are not cells.

Further detail

• Bacteria and archaea are examples of prokaryotic organisms, while animals, plants, fungi, and many unicellular organisms are eukaryotic.

💡 Memory Hook

Simple prokaryotic organization contrasts with complex eukaryotic organization

📖 4. Unicellular and Multicellular Organization

🔑 Key Concepts & Definitions

• Unicellular organism : consists of a single cell that performs all essential functions, including feeding, growth, and reproduction
• Multicellular organism : consists of many cooperating cells that can specialize and organize into tissues and organs

📝 Essential Points

• Many protozoa and yeasts are unicellular organisms, whereas animals and plants are multicellular organisms.

💡 Memory Hook

One cell performs all functions; many cells specialize into tissues and organs

📖 5. Classical Eukaryotic Classification

📝 Essential Points

• The four broad classical groups are:
  • Protozoa
  • Fungi
  • Metazoa (animals)
  • Plants

📌 Plants are autotrophic and can make their own food, for example by photosynthesis, whereas protozoa, fungi, and metazoa depend on organic matter produced by other organisms.

📌 Classical classification groups organisms by general characteristics and level of organization, whereas modern classification uses phylogenetic evidence to trace common ancestry.

💡 Memory Hook

PFMP: protozoa, fungi, metazoa, plants

📖 6. Comparative Cell Sizes

★ Must-know

📐 Formula — One micrometer equals $1\,\mu\mathrm{m}=10^{-6}\,\mathrm{m}$, or one millionth of a meter.

• Approximate sizes are:
  • Bacteria: 1–5 μm
  • Yeast: 5–10 μm
  • Protozoa: 10–200 μm
  • Animal cells: 10–50 μm
  • Plant cells: 50–100 μm

Further detail

📌 A plant cell can be up to about one hundred times wider than a bacterium.

💡 Memory Hook

Bacteria → yeast → animal cells → protozoa → plant cells

📊 Synthesis Tables

Prokaryotic and Eukaryotic Organisms

Feature	Prokaryotic organisms	Eukaryotic organisms
True nucleus	Absent	Present
DNA location	Nucleoid region	Inside the nucleus
Membrane-bound organelles	Absent	Present
Organization	Relatively simple	More complex

Unicellular and Multicellular Organisms

Feature	Unicellular organisms	Multicellular organisms
Number of cells	One	Many
Cell functions	One cell performs all essential functions	Cells cooperate and specialize
Organization	No tissues or organs	Cells organize into tissues and organs
Examples	Many protozoa and yeasts	Animals and plants