Study sheet: Organization of Living Things

📋 Course Outline

1. Classifying Living Organisms
2. Microscopes and Cellular Observation
3. Unicellular Organisms
4. Eukaryotic and Prokaryotic Cells
5. Organization of Multicellular Organisms
6. Extracellular Matrix and Tissues
7. Discovery and Role of the Nucleus
8. DNA Structure and Information

📅 Key Dates

1. 1831Robert Brown discovered a spherical organelle at the center of plant cells using a microscope.
2. 1835Rudolf F. J. Wagner observed the nucleus of animal cells. — Rudolf F.J.H. Wagner, 1835
3. 25 April 1953Francis Crick and James Watson first described the structure of DNA based on Rosalind Franklin's research.

📖 1. Classifying Living Organisms

📝 Essential Points

📌 Living organisms may be classified by size or by number of cells; this course uses the distinction between unicellular organisms, made of one cell, and multicellular organisms, made of several cells.

• Yeasts and euglenas are unicellular organisms, whereas trees, humans, and zebrafish are multicellular organisms.

• The vital functions are:

  • grow
  • obtain nutrients
  • reproduce
  • defend themselves

💡 Memory Hook

One cell versus many cells

📖 2. Microscopes and Cellular Observation

🔑 Key Concepts & Definitions

• Transmission electron microscope : provides nanometric resolution and is suited to observing thin sections, internal cell structures, and large molecules.
• Scanning electron microscope : has lower resolution than a TEM but produces detailed three-dimensional images of object surfaces.
• Optical microscope : uses an objective and an eyepiece to magnify small objects and separate image details so that they can be seen by the human eye.

💡 Memory Hook

MET sees inside, MEB sees surfaces, MO magnifies for the eye

📖 3. Unicellular Organisms

🔑 Key Concepts & Definitions

• Escherichia coli : Escherichia coli is a unicellular prokaryotic bacterium that absorbs nutrients through its wall, reproduces asexually by cell division, moves with flagella, adheres using pili, and produces toxic molecules against some pathogenic bacteria.
• Plasmodium : a unicellular eukaryotic human parasite responsible for malaria, a potentially fatal infectious disease transmitted by bites from the Anopheles mosquito.
• Microbiota : the set of microorganisms living on and inside the human body, including bacteria, viruses, parasites, and non-pathogenic fungi.

★ Must-know

• Euglena reproduces asexually by cell division, and its population increases from 400 to 1000 cells per microlitre in six days when water contains mineral salts and light is available.

Further detail

• The intestinal microbiota contains between 10¹² and 10¹⁴ microorganisms and is qualitatively and quantitatively specific to each individual.

💡 Memory Hook

One cell → all vital functions

📖 4. Eukaryotic and Prokaryotic Cells

🔑 Key Concepts & Definitions

• Organelle : a cell compartment bounded by one or more membranes that performs a specific function, such as storing genetic information or producing energy.

★ Must-know

📌 Eukaryotic organisms have cells containing organelles, whereas prokaryotic organisms have cells lacking a nucleus and other organelles.

Further detail

📌 A unicellular organism may be pathogenic and cause an infection or disease, or non-pathogenic and not cause disease.

💡 Memory Hook

Eukaryotes have organelles; prokaryotes lack them

📖 5. Organization of Multicellular Organisms

🔑 Key Concepts & Definitions

• Specialized cell : possesses structures that enable it to perform a particular function within a multicellular organism.
• Tissue : a group of specialized cells that perform the same function.

★ Must-know

• Chloroplasts enable photosynthesis in Elodea leaf cells, amyloplasts store starch in potato tuber cells, chromoplasts contain pigments in tomato cells, and stomata enable gas exchange in leaves.

Further detail

• Muscle tissue is made of cells able to contract and produce movement, while neurons respond to stimulation by transmitting an electrical nerve message.

💡 Memory Hook

Cells → tissues → organs → organism

📖 6. Extracellular Matrix and Tissues

🔑 Key Concepts & Definitions

• Extracellular matrix : a set of macromolecules surrounding cells, linking them together, organizing them into tissues, and forming an essential framework for tissue integrity.

★ Must-know

• The extracellular matrix contributes to:

  • cell adhesion and tissue cohesion
  • resistance to compression and stretching
  • communication between cells
  • protection
  • maintenance of cell shape
  • cell form, development, and proliferation

• In plants, the extracellular matrix is the cell wall, composed mainly of cellulose secreted by plant cells into the extracellular space, and it allows cells to adhere to one another.

Further detail

• In humans, the extracellular matrix allows the existence of connective, epithelial, muscle, and nervous tissues.

💡 Memory Hook

Matrix molecules → cell adhesion → tissue cohesion

📖 7. Discovery and Role of the Nucleus

🔑 Key Concepts & Definitions

• Nucleus : a cell organelle that contains DNA, the molecule forming the genetic heritage of living organisms.

💡 Memory Hook

1831: plant cells; 1835: animal cells

📖 8. DNA Structure and Information

🔑 Key Concepts & Definitions

• DNA : or deoxyribonucleic acid, is a molecule that contains the genetic heritage of every form of life and has the shape of a double helix made of two strands.

★ Must-know

• The four DNA nucleotides are:
  • adenine
  • thymine
  • cytosine
  • guanine

📌 DNA nucleotides pair complementarily: adenine is always opposite thymine, and cytosine is always opposite guanine.

Further detail

• In the example given for a bacterium, adenine represents 16% of the nucleotides, thymine 16%, cytosine 34%, and guanine 34%.

💡 Memory Hook

A double helix with paired bases: A–T and C–G

📊 Synthesis Tables

Unicellular and multicellular organization

Feature	Unicellular organism	Multicellular organism
Number of cells	One	Several
Organization	One cell performs all vital functions	Specialized cells form tissues and organs
Example	Euglena or Escherichia coli	Human, tree, or zebrafish