Ciencias Naturales Study Notes

Comparison of Animal and Plant Cells

Membrane and Cell Wall

Both plant and animal cells possess a cell membrane, but plant cells also have a cellulose cell wall which provides rigidity.

Chloroplasts and Photosynthesis

Plant cells contain chloroplasts, organelles capable of performing photosynthesis, making them autotrophic organisms.

Vacuoles

Plant cells have a single large vacuole filled with liquid that occupies most of the cell's interior.

Type of Reproduction

Plant cells can reproduce through a process resulting in cells identical to the parent cells, known as asexual reproduction.

Animal Cells

Animal cells possess a cell membrane but lack a cellulose cell wall.
They do not contain chloroplasts and thus cannot perform photosynthesis.
Animal cells may have several small vacuoles or none at all.
Animal cells can reproduce through sexual reproduction, where offspring exhibit characteristics from both parents but are not identical to them.

Cellular Biology Fundamentals

Microorganisms and Pathogens

Definition

Pathogenic microorganisms are referred to as pathogens or germ pathogens.

Prokaryotes

Prokaryotes are considered the oldest group of organisms on Earth from an evolutionary perspective.

Environments for Prokaryotes

Prokaryotes can survive in many extreme environments, including the icy expanses of Antarctica, the dark depths of the ocean, and even in nearly boiling waters of natural hot springs.

Eukaryotic vs. Prokaryotic Cells

Main Difference

Eukaryotic Cells: Have a defined cell nucleus encased by a membrane.
Prokaryotic Cells: Do not have a defined nucleus and lack a nuclear membrane.

Definition of Cell

The cell is the basic and indispensable unit present in all living beings, being the smallest unit of life. All three vital functions of an organism (nutrition, reproduction, interaction) are carried out by the cells composing it.

Definition of Eukaryotic Cells

Eukaryotic cells are termed from Greek origin; "eukaryota," combining "eu-" (true) and "karyon" (nut, nucleus) meaning true nucleus. Eukaryotic cells date back 1.4 to 1.6 billion years according to fossil records, whereas prokaryotic cells emerged 3.45 to 3.7 billion years ago.

Organisms with Eukaryotic Cells

Eukaryotic cells, having a defined nucleus, have chromosomes that store the organism's genetic information. All organisms in the kingdoms of Animalia, Plantae, Fungi, and Protista are composed of eukaryotic cells, with examples including the protist Plasmodium, animal cells in a grasshopper, and plant cells in a jacaranda.

Definition of Prokaryotic Cells

Prokaryotic cells do not have a defined nucleus and their genetic material is dispersed within the cytoplasm in an area called the nucleoid. Bacteria and archaea are the two types of organisms with prokaryotic cells; for example, methanogenic archaea and Pseudomonas bacteria.

Biomolecules and Organic Life

Organic Precursors Experiment

A historical experiment demonstrated that the precursors of organic life could have arisen from a chemical reaction.

Biomolecules

Biomolecules are molecules that occur naturally in living organisms, primarily composed of carbon and hydrogen, along with nitrogen, oxygen, phosphorus, and sulfur. All known forms of life are exclusively made up of biomolecules.

Microscopy and Cellular Organization

The use of the microscope advanced the study of cellular origins by allowing biologists to differentiate between two cell types: eukaryotic and prokaryotic.

Differences and Commonalities

Despite the significant structural differences, eukaryotic and prokaryotic cells share the basic molecular mechanisms that govern life.

Microbes

Microbes, or microorganisms, are living beings that are too small to be seen with the naked eye. A microscope is necessary to observe these organisms, which can survive in a variety of environments.

Anton van Leeuwenhoek

In 1674, Anton van Leeuwenhoek discovered tiny moving creatures in stagnant water, which he called "animalcules."

Microbial Characteristics

The general characteristic shared by all microbes or microorganisms, except viruses, is that they are unicellular; viruses are not cells but rather possess a biomolecular organization lacking nuclear or cellular membranes.

Types of Microorganisms

Microorganisms can be categorized based on their cellular organization:

Organisms with Cellular Organization: These are living beings composed of cells, possessing a cell membrane and nucleic acids (DNA and RNA).
Prokaryotic Microorganisms: Unicellular organisms without a nucleus, such as bacteria.
Eukaryotic Unicellular Microorganisms: Unicellular organisms with a nucleus, including protozoa, algae, and microscopic fungi.

Bacteria

Bacteria are prokaryotic microorganisms that are a few micrometers in size and come in diverse shapes, including:

Cocci (spherical)
Bacilli (rod-shaped)
Spirilla (spiral)

Evolutionary Importance of Bacteria

Bacteria are considered the first living beings on the planet. Many bacteria have flagella or other locomotion systems, making them mobile.

Diseases Caused by Bacteria

Koch's Bacillus: Causes tuberculosis.
Pneumococci: Cause pneumonia and meningitis.

Protozoa

Protozoa are unicellular microscopic organisms with eukaryotic cellular structures; they are motile, heterotrophic, do not photosynthesize, and lack a rigid cell wall. They thrive in moist environments or water (both saltwater and freshwater). Protozoa represent the most primitive and simplest known animals, with Toxoplasma causing toxoplasmosis, an infectious disease spread from animals to humans.

Eukaryotic and Prokaryotic Cells

Characteristics of Eukaryotic Cells

Eukaryotic cells integrate both multicellular (many cells) and unicellular (one cell) organisms, varying in structural characteristics. They are generally larger than prokaryotic cells, are aerobic (require oxygen to survive), and reproduce via mitosis (producing two genetically identical daughter cells) and meiosis (producing four genetically distinct haploid cells).

Characteristics of Prokaryotic Cells

Prokaryotic cells exist only in unicellular organisms, are smaller in size, and less complex than eukaryotic cells. Their genetic material is dispersed in the cytoplasm in an irregular area called the nucleoid. They can be aerobes or anaerobes (do not need oxygen to survive) and reproduce both asexually and sexually. Their nutrition can be autotrophic (photosynthesis or chemosynthesis) or heterotrophic (dependent on autotrophs for nourishment). Prokaryotic cells include cytoplasm, a plasma membrane, a cell wall, nucleoid, and ribosomes.

Eukaryotic Cell Structures

All eukaryotic cells are composed of three fundamental structures:

Plasma Membrane: Also known as the cell membrane, this structure consists of a phospholipid bilayer (composed of one alcohol molecule bonded to two fatty acids and a phosphate group) and proteins.
Cytoplasm: This is the basic or fundamental substance made up of proteins in an aqueous medium, containing cellular structures and organelles.
Nucleus: This is the most prominent structure of the cell, typically oval or spherical in shape, serving to control cellular activities and transmit cellular characteristics from one generation to another during cell division.

Parts of the Nucleus

Nuclear Membrane: A well-defined membrane that encases the nucleus and isolates it from the surrounding cytoplasm; it is double-layered and porous.
Nuclear Sap: The internal medium of the nucleus, also known as nucleoplasm, with a chemical composition similar to cytosol and where the nucleolus and chromatin are suspended.
Nucleolus: A compact, spherical structure rich in ribonucleic acid (RNA) with potential to have multiple instances based on cell type and organism species; it synthesizes ribosomal RNA.
Chromatin: A crucial material consisting of fine intertwined filaments termed chromosomes that contain hereditary material (genes), mainly composed of DNA.

Organelle Function Summary

Organelle	Description	Function
Mitochondria	Small oval cellular structure with double membranes.	Principal function is energy production via oxygen consumption, resulting in carbon dioxide and water as cellular respiration byproducts.
Lysosome	Spherical or oval sac enclosed by a simple irregular membrane.	Contains vital enzymes for digesting particles ingested by the cell.
Golgi Apparatus	Differentiated part of the intracellular membrane system.	Involved in secretion processes, recycling of the cell membrane, and formation of lysosomes and vacuoles.
Endoplasmic Reticulum	A complex system of interrelated flat sacs and tubules.	Transports proteins manufactured by ribosomes.
Vacuoles	Bubble-like structures filled with cell sap.	Store food, pigments, wastes, and regulate the amount of water in the cell.
Cell Wall	A rigid and resistant layer external to the cell membrane.	Protects the cell's contents, providing rigidity and mediating all interactions of the cell with its environment, establishing structure and support for tissues and parts of the cell.

Protozoa, Fungi, and Viruses

Protozoan Diseases

Malaria

The organisms that cause malaria (paludism) are Plasmodium malariae and P. falciparum.

Fungi

Fungi are a group of eukaryotic organisms that differ from plants and animals, and are classified in a separate kingdom called Fungi. The science of studying fungi is referred to as Mycology.

Importance of Fungi

Fungi serve various important roles:

They act as a food source.
They can be used in medicine.
They are decomposers.
They are utilized in food production.
Some can cause diseases.

Viruses

Viruses are infectious agents distinguished by their small size and obligatory intracellular parasitism to reproduce. They do not eat, do not have metabolism, and do not reproduce independently. Viruses consist of nucleic acid (DNA) and proteins and are about 100 times smaller than bacteria.

Diseases Caused by Viruses

There are approximately 1000 to 1500 viruses capable of infecting humans with examples including influenza, measles, rabies, poliomyelitis, yellow fever, mumps, chickenpox, herpes, HIV, HPV, COVID-19, etc.

Beneficial Bacteria

Lactobacillus bacteria, often referred to as beneficial, useful, or probiotic bacteria, aid in digesting food.

Foods Produced by Microbial Growth

Microbial growth is responsible for producing foods such as cheese, bread, yogurt, chocolate, vinegar, and alcohol.

Fermentation

Fermentation is a chemical change initiated by microbes wherein complex sugars are broken down into simpler compounds, like carbon dioxide or alcohol.

The Origin of Life in Biology

Humanity’s Question

Humanity has long sought to understand its origin and that of life, posing one of the toughest questions for modern biology.

Historical Explanations

Various historical explanations for the origin of life have been proposed, some discarded while others like the panspermia theory are still considered today.

Categories of Explanations

The explanations for the origin of life are categorized into three:

Creationism
Spontaneous Generation
Cosmic Origin

Creationism

For Catholic believers, creationism accepts the Bible explicitly, holding the Genesis account of the creation of the world and humanity as true.

Spontaneous Generation

In ancient Greece, it was believed that living beings could arise from mud, water, decomposing meat, and other elements without the need for prior organisms.

Disproof of Spontaneous Generation

Francesco Redi's experiments and particularly Louis Pasteur's work disproved the possibility of spontaneous generation, establishing that there always had to be precursor organisms for descendant formation.

Cosmic Origin or Panspermia

This theory, proposed by Svante Arrhenius in 1908, posits that life initiated in space and traveled between worlds via comets and meteorites carrying organic materials like hydrocarbons, fatty acids, and amino acids.

Current Theories

The current theory regarding the origin of life involves experimentally verifying each necessary step leading to life as we know it.

Explanation Steps of Life’s Origin

The elucidation of life's origin consists of the steps:

Origin of organic precursors
Origin of biomolecules
Origin of cellular organization.