Notes, summaries, assignments, exams, and problems for Biology

The Immune System and Disease Prevention

The immune system is a set of organs, cells, and molecules whose primary function is to defend the body against infectious agents and abnormal cells within the organism.

It is responsible for defense once infectious agents have crossed the skin or mucous membranes, and it acts through:

Nonspecific Defenses

Nonspecific defenses, such as inflammation, are not dependent on the nature of the pathogen.

Specific Defenses

Specific defenses are based on the specific recognition of foreign substances, known as antigens, against which an immune response is triggered. This response has the following characteristics:

• Specificity: Lymphocytes, which are cells of the immune system, distinguish specific antigens from others

Vegetative Reproduction in Plants

Vegetative reproduction is a form of asexual reproduction in plants. A part of a single individual, a cell (e.g., spores), or a group of cells (fragmentation) develops into a duplicate of the progenitor. The offspring are identical to each other and identical to their preserved vegetative progenitor. Plants always have embryonic tissues, the meristems, which consist of totipotent cells. Therefore, they have a great capacity for regeneration, and asexual reproduction is common.

Structures Involved in Asexual Reproduction

• Stolons: Stems that run parallel to the ground, which occasionally produce roots and new stems and leaves. Example: Strawberries.
• Rhizomes: Underground stems that occasionally produce roots and

Immunology

By removing serum from pustules of the udder of a cow and injecting it into human skin, an individual suffered from a mild illness but never acquired smallpox. It was the first experiment of active immunization.

1. The Body's Defenses

All organisms have developed mechanisms of defense against the invasion of pathogens. These mechanisms may be nonspecific, preventing entry into the body or destroying them quickly, or very specific, which is known as the immune response.

1.1 Nonspecific Defense Mechanisms

These act against any organism or foreign substance. They are of three types:

a) Natural Barriers: Skin and secretions from the mucosal surfaces.

• Skin is a mechanical barrier because its outermost stratum corneum is fully keratinized.
• It

The Miller-Urey Experiment: Origin of Life

The Miller-Urey experiment represents the first demonstration that organic molecules can form spontaneously from simple inorganic substances under simulated early Earth conditions. This groundbreaking experiment provided crucial insights into the chemical origins of life.

In the experiment, a gaseous mixture (simulating Earth's early atmosphere) was introduced into a sealed flask, where water was kept boiling to mimic the primordial ocean. The resulting vapor then underwent condensation. Substances were circulated continuously through the experimental setup, while two electrodes consistently produced electric shocks, simulating lightning.

Crucially, samples were extracted from the apparatus for analysis.... Continue reading "Evolutionary Biology: Miller-Urey, Lamarck, and Natural Selection" »

Levels of Biological Organization

Living matter is organized into distinct levels, categorized as abiotic or biotic:

• Abiotic: Components that do not conform to living matter, such as inert substances.
• Biotic: Components exclusive to living organisms.

Hierarchy of Living Matter

• Subatomic: Particles and atoms.
• Atom: The smallest portion of a chemical element.
• Molecular: Molecules formed by the joining of two or more atoms.
• Macromolecules: Resulting from the binding of many molecules to form a polymer.
• Supramolecular Complexes: Aggregations of macromolecules.
• Subcellular Structures: Union of different supramolecular complexes, resulting in the cell's structure with characteristic functions.
• Cells: Comprised of various organelles and structures. (Biotic Level)

Proteins and Amino Acids

Proteins are formed by a union of linear amino acids (NH2-COOH). There are 20 amino acids that are part of proteins. Nucleobases form a triplet or codon, which determines a particular amino acid. There are 4x4x4 = 64 different triplets; this implies that there are different triplets that encode the same amino acid. The code is degenerate because the combination of 3 letters adds up to 64 possible triplets.

The Genetic Code

The genetic code is the relationship between the sequence of bases in DNA and the ratio of amino acids in protein. There are three special triplets coding for a stop sign:

• TAA
• TAG
• TGA

There is also a triplet (ATG) determining a beginning.

Functions of Proteins

Proteins perform various essential functions:

• Transport

DNA Structure and Function

DNA is a large molecule formed by the union of simpler molecules called nucleotides. They are composed of phosphoric acid, deoxyribose, and a nitrogenous base (adenine (A), guanine (G), cytosine (C), or thymine (T)).

DNA consists of two long chains of nucleotides twisted into a double helix. Adenine joins with Thymine (with double hydrogen bonds), and Guanine joins with Cytosine (with triple hydrogen bonds).

Molecular Tools in Genetics

Cellular enzymes are used to cut and join fragments of DNA within cells. Restriction enzymes are responsible for "cutting" the DNA, and ligases unite the fragments.

Cloning DNA Technology

DNA Cloning Process

Cloning a DNA fragment consists of obtaining billions of identical copies of that... Continue reading "DNA Structure, Genetic Engineering, and Stem Cell Applications" »

The Nervous System

The nervous system is a biological system that enables very complex beings to interact with what surrounds us. We can say that it is a huge network responsible for the collection of internal and external stimuli. It processes these stimuli to generate the response that the decision center (brain) considers optimal.

There are two main divisions:

• Central Nervous System: Consists of the brain and spinal cord.
• Peripheral Nervous System: Includes all the nerves of the body that connect internal and external stimuli to the central nervous system.

Peripheral Nervous System

The peripheral nervous system includes different types of nerves:

• Sensory Nerves: Transmit information from sensory receptors (like those for touch, pain, temperature)

Advances in Stem Cells and Regenerative Medicine

Recent breakthroughs in stem cell research offer immense potential for tissue regeneration, curing diseases like cancer, and even slowing the aging process.

Key Concepts in Cellular Biology and Genetics

• Cloning: The process of creating an exact genetic copy of an organism or cell.
• Embryonic Stem Cells: These remarkable cells possess the ability to reproduce and differentiate into various specialized cells and organs.
• Therapeutic Cloning: A technique where the development of an individual is intentionally halted to obtain stem cells from a very early-stage embryo, known as a blastocyst.
• Totipotent Stem Cells: Cells capable of dividing and differentiating into any cell type required by an organism.
• Pluripotent

Core Terminology in Classical Genetics

• Character (Trait): An inherited attribute of an individual.
• Gene: The fundamental unit of heredity responsible for a character.
• Alleles: The different variations or forms that a gene can take.
• Homozygous: An individual possessing two identical alleles for a specific gene.
• Heterozygous: An individual possessing two different alleles for a specific gene.
• Genotype: The specific set of genes an individual possesses.
• Phenotype: The set of observable, hereditary traits expressed by an individual.

Allelic Expression and Inheritance Patterns

• Dominant Factor (Allele): The allele that is phenotypically expressed in both homozygous and heterozygous individuals.
• Recessive Factor (Allele): The allele whose phenotypic expression