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

Creationism

The origin of each species was due to a specific act of creation.

Fixism

Species remain unchanged over time.

Catastrophism

During the course of Earth's history, catastrophes happened, causing the extinction of certain species.

Biological Evolution

The process of transformation from one species into another by the accumulation of differences that appear between one generation and the next.

Lamarckism

Lamarck argued that God creates nature and this gives rise to species because of its tendency toward complexity and adaptations caused by environmental variations.

Darwinism

• High reproductive capacity: Since food resources are limited, it does not increase indefinitely.
• Variation in offspring: The descendants of sexually reproducing organisms are

Humoral Immune Response Dynamics

Primary Antibody Response

The primary humoral response involves the amount of antibody secreted by plasma cells and the clonal expansion of these cells upon first contact with an antigen. This response typically peaks around 7 days (ranging from 5-10 days) after the initial infection. The maximum antibody response is primarily of the IgM isotype, although IgG is also induced by various immunogens. Immunization generally requires a relatively high antigen dose, optimally in the presence of adjuvants for protein antigens.

Secondary Antibody Response

A secondary antibody response occurs upon repeated infection by the same antigen, activating memory cells created following the primary humoral response. This response... Continue reading "Immune Response Dynamics: Humoral Immunity & Acquired Protection" »

Cell Membrane Transport

Diffusion

Some substances move through diffusion inside and outside cells. Diffusion is a physical process based on random movement. The kinetic energy associated with the random motion causes diffusion, the net movement of particles (atoms, ions, and molecules) from a region of high concentration to a region of low concentration, resulting in a uniform distribution.

Conveyor-Mediated Transport

For the transport of ions and nutrients, conveyor systems (permease proteins) evolved early in the origin of cells. This transfer of solutes by membrane proteins is called carrier-mediated transport. There are two variants: facilitated diffusion (along the concentration gradient or electrochemical-chemical-concentration difference,... Continue reading "Cell Membrane Transport and Hormonal Regulation" »

Cell Types

The most primitive cells are called prokaryotes. Bacteria are unicellular prokaryotes. All other living things are composed of eukaryotic cells, which are more complex; in them, the nucleus is well-differentiated.

Eukaryotic organisms, in turn, may include:

• Unicellular organisms such as some fungi, some algae, and protozoa.
• Multicellular organisms such as animals, plants, some fungi, and some algae.

Not all eukaryotic cells are equal. Plant eukaryotic cells differ from animal eukaryotic cells because they present a rigid cellulose wall outside the cell membrane that provides high resistance, and they also contain chloroplasts, where photosynthesis takes place.

The cells of the same organism are not equal. This is because they specialize... Continue reading "Cell Types and Nutrition: Prokaryotes, Eukaryotes, Autotrophs, Heterotrophs" »

Infectious Diseases

Infectious diseases are caused by microorganisms such as bacteria, viruses, and parasitic organisms, or certain infectious proteins. These diseases are transmitted from one individual to another, accounting for about one-third of all deaths worldwide.

Zoonotic Diseases

Zoonotic infections are diseases that are initially passed from animals to humans.

Antibiotics

Antibiotics are drugs that destroy infection-causing bacteria without harming the organism's cells. They are not effective against viral infections and should not be administered in such cases.

AIDS

AIDS is an infectious disease caused by the human immunodeficiency virus (HIV), a retrovirus characterized by its small size and RNA-based genetic material. HIV can be transmitted... Continue reading "Understanding Diseases and Illnesses" »

Limiting Factors in Aquatic Ecosystems

In aquatic ecosystems, the following are the limiting factors:

Salinity

• Freshwater, as in rivers.
• Seawater, as in seas and oceans.
• Brackish water, as in marshes.

Living things are adapted to the salinity value of their aquatic environment. Very few species, such as salmon, can live in all of them.

Light Penetration

Filtered light entering the water decreases in intensity with depth. There are three zones:

• Photic zone: Sufficient light for photosynthesis.
• Oligophotic zone: Low light levels.
• Aphotic zone: Total darkness.

Temperature

Temperature determines the amount of dissolved oxygen; less oxygen at higher temperatures. Changes in ocean temperature are responsible for ocean currents that distribute nutrients.

Biotic

Hypotheses on the Origin of Life

Panspermia Hypothesis

The Panspermia Hypothesis suggests that life originated in space and traveled in spore form from one planetary system to another.

Prebiotic Synthesis Hypothesis

The Prebiotic Synthesis Hypothesis posits that life arose from organic molecules on Earth, which in turn originated from inorganic matter. This hypothesis was defended by Haldane and Oparin. In 1953, Stanley Miller experimentally tested the hypothesis of Oparin and Haldane. Miller designed an experiment that reproduced the alleged conditions of early Earth in specific areas: one section simulated the primitive atmosphere's composition, while another simulated solar radiation and lightning.

Fixity of Species

Fixity, or the theory of fixed... Continue reading "Theories of Life's Origin and Species Evolution" »

The Male Reproductive System

Components

The male reproductive system produces sperm, sex hormones, and semen. Its key components include:

• Testicles: Two glands housed in the scrotum that produce sperm and testosterone.
• Genital Tracts: The epididymis and vas deferens collect and transport sperm from the testicles to the urethra.
• Attached Glands: The prostate and seminal vesicles produce secretions that enable sperm maturation and create semen.
• Penis: The external organ that deposits sperm into the female vagina. Erectile tissue expands during sexual excitement, causing an erection. The glans is protected by the foreskin.

Sperm Production

Sperm production occurs in the seminiferous tubules of the testicles. Sperm travel from the seminiferous tubules... Continue reading "Human Reproductive System: Male and Female Anatomy" »

The Cell: A Fundamental Unit of Life

The cell is the structural unit of all organisms, both animals and plants, as they are composed of cells and cellular products. It is also the functional unit, since in all cell types, chemical composition and metabolic processes are similar. The cell can develop its activity individually (single-celled organisms) or associate with other cells, interacting and complementing each other to build multicellular organisms. It is the unit of origin because every cell originates from another cell. Finally, it is the biochemistry unit, for the cell has the biochemical machinery that allows it to copy itself and its genetic information. Through this, it controls the biosynthesis of macromolecules involved in its structure... Continue reading "Cellular Biology: Structure, Functions, and Organelles" »

Vertebrates vs. Invertebrates

Vertebrates: are generally larger than invertebrates and possess a bony or cartilaginous internal skeleton. This skeleton includes a spine composed of bones or cartilages called vertebrae.

Invertebrates: lack a spine and internal skeleton. They exhibit either radial or bilateral symmetry, undergo metamorphosis to reach adulthood, and their bodies are formed by true tissues.

Mammals: Key Characteristics

Mammals are characterized by:

• The presence of hair on their bodies.
• The ability to regulate their body heat (homeothermy), making them warm-blooded animals.
• Internal fertilization and viviparous reproduction (live birth).
• Pulmonary respiration.
• Double-loop blood circulation with a heart divided into four chambers.
• A skeleton