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

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

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

Types of Digestion

Digestion is the process by which complex molecules are broken down into simpler ones. There are two methods of digestion:

• Intracellular Digestion: This takes place inside cells. Each cell functions as a complete digestive system:
  • Food capture (pseudopodia, cilia, or flagella)
  • Food inclusion (endocytosis)
  • Food digestion (lysosomes)
  • Expulsion of undigested material (exocytosis)
  Typical of sponges.
• Extracellular Digestion: This is performed inside the digestive systems consisting of one tract and specialized glands. The nutrients pass into the bloodstream and are distributed to reach all cells. Typical of most animals.

Some animals combine both types of assimilation:

• The food comes in the form of large fragments.
• The inner wall of the

Protein Definition

A protein consists of amino acids linked together. Each amino acid has a central carbon atom attached to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable radical group (side chain).

Protein Classification

Proteins can be classified based on their composition:

• Holoprotein: Composed solely of amino acids.
• Heteroprotein: Composed of amino acids along with other non-amino acid molecules (prosthetic groups).

Amino Acids

Amino acids are organic compounds characterized by having both a carboxyl group (-COOH) and an amino group (-NH2). They are typically solid, crystalline substances with high melting points, soluble in water, and possess optical activity. Their chemical behavior is amphoteric, meaning they... Continue reading "Protein Essentials: Structure, Properties, and Functions" »

Non-Infectious Diseases

Cardiovascular Diseases

Cardiovascular diseases affect the heart and blood vessels, and their incidence is higher in adults and the elderly.

• Atherosclerosis: An enlargement of the walls of the arteries due to the deposition of cholesterol, platelets, and fibrous tissue. The arteries can become calcified and hardened, resulting in a loss of elasticity.
• Thrombus: A blood clot that occurs in an artery or vein, leading to its obstruction (thrombosis). When the clot forms in a vein, it can be released and easily move to another place (embolism).
• Aneurysm: A weakening of the arterial wall, which promotes dilation of the artery. This can rupture and form a hemorrhage.
• Stroke: Interruption of blood supply to the brain.
• Coronary Artery