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

Biological Life Cycle: Different Stages in a Living Being

Any biological life cycle can be divided into three parts:

• Early Stage: In most organisms, this begins with a single-cell stage.
• Development: This is the stage at which changes in size occur, as well as the differentiation of internal structures. Development ends when the new body has reached the characteristics of an adult.
• Reproduction: This is the phase in which organisms produce "breeding units" that will give rise to new individuals with the characteristics of the parent.

Cell Cycle

A set of phenomena of variable duration that occurs in the period that begins after cell division:

• Interphase: The period between two consecutive divisions.
• Division Phase: In which cell multiplication occurs,

Plasma Membrane: Structure and Function

Key Functions of the Plasma Membrane

• Protects cell shape and provides rigidity.
• Regulates the entry and exit of substances.

Models of the Plasma Membrane

The Daniel-Davson Model

In this model, proteins are found in blocks or internal/external layers, separated by a lipid bilayer. This bilayer is predominantly composed of phospholipids, which are bipolar.

The Singer-Nicholson Fluid Mosaic Model

In this model, proteins are internalized within the phospholipid bilayer. Some smaller proteins are located on the outer and inner sides. The membrane also contains a small proportion of carbohydrates that tend to form complexes with proteins and lipids. Among the proteins that span the membrane, defined pores allow the... Continue reading "Cell Membrane Dynamics: Models, Roles, and Molecular Transport" »

Habitat and Environmental Conditions

A habitat is the environmental conditions in the place where a species lives.

Environmental Factors

Abiotic factors are the biotype and temperature. Biotic factors define the biocoenosis.

Each species is accustomed to living under certain environmental conditions. The term tolerance refers to the range of a factor that a species can withstand.

Limiting Factors in Terrestrial Environments

In the terrestrial environment, the main limiting factors for life are temperature and humidity.

Temperature

The air is cooled or heated quickly, according to the solar radiation it receives. This depends on latitude, altitude, seasons, and day and night.

Terrestrial beings adapt to temperature changes by following habits and adapting... Continue reading "Terrestrial Environment: Factors, Adaptations, and Soil" »

Achalasia: Esophageal Motility Disorder

Achalasia is a disorder of esophageal motility characterized by decreased peristalsis and a failure of the lower esophageal sphincter (LES) to relax. The etiology is unknown. As the sphincter fails to relax, food accumulates in the lower esophagus within the thoracic cavity. The esophagus becomes dilated, its walls hypertrophied, and food does not pass until it accumulates enough to force its way through.

Clinical Manifestations of Achalasia

Symptoms result from the difficulty of food passing through the esophagus into the stomach. These may include:

• Food regurgitation
• Burning and retrosternal pain after meals, which may increase or decrease with movement

Diagnostic Procedures for Achalasia

Diagnosis is typically... Continue reading "Achalasia, Esophageal Diverticula, and Gastritis: Symptoms and Treatments" »

The Human Ear and Hearing Process

The ear consists of three main parts:

• Outer Ear: Formed by the auricle (pinna) and the ear canal. The canal is protected by auditory wax and ends at the eardrum (tympanic membrane).
• Middle Ear: Contains three tiny bones called ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup).
• Inner Ear: The deepest part, formed by the membranous labyrinth, which is contained within the bony labyrinth. Between these two labyrinths is perilymph, and within the membranous labyrinth is endolymph. The membranous labyrinth includes the cochlea (a snail-shaped structure responsible for detecting sounds) and the vestibular apparatus (involved in balance).

How Sound Perception Occurs

When sound waves reach the eardrum,... Continue reading "Human Body Systems: Hearing, Touch, Bones, and Joints Explained" »

The menstrual cycle is the process by which people develop female gametes (oocytes, ova) and produce a series of changes designed to establish a possible pregnancy. The beginning of the cycle is defined as the first day of menstruation, and the end of the cycle is the day before the start of the next menstruation. The mean cycle length is 28 days, although this may be longer or shorter.

The first menstruation is termed menarche, and the last is known as menopause. Depending on the changes in the ovary and uterus, the menstrual cycle is divided into two phases:

• Follicular phase: From the first day of menstruation until ovulation, which consists of menstruation and the proliferative phase.
• Luteal phase: From ovulation until the first day of menstruation,

The Respiratory System

The respiratory system is responsible for ensuring the supply of oxygen to body cells and removing carbon dioxide. Blood oxygenation is a process that occurs through gas exchange between the blood vessels and the pulmonary alveoli. The respiratory system also prevents the entry of unwanted elements and the development of infections.

Anatomy of the Respiratory System

The respiratory system consists of various organs, which are divided into:

Upper Airways

Located outside the thoracic cavity, including the nose, nares, pharynx, and larynx.

Lower Airways

Located inside the chest cavity, including the trachea, bronchi, bronchioles, alveoli, lungs, and pleura.

Upper Respiratory Tract

1. Nose

   The air enters through the nostrils, right and

Operation of the Nephron

Filtration of blood occurs as it passes through the glomerulus. Substances pass into the renal tubule, small molecules but not large molecules or cells. This process forms the primary urine.

Reabsorption of useful substances, such as glucose, amino acids, and over 90% of the water, takes place along the renal tubule.

Secretion of noxious substances, such as urea or some mineral salts, from the capillaries into the renal tubule, continues along the entire duct, so that inside it, concentrated urine is formed. This is drained into a collecting duct, common to many nephrons, which flows into the renal pelvis. As a result of the process, blood from the kidneys, via the renal veins, is cleansed of waste products.

Average Domestic

Interstitial

Chemistry of Life

The universe is mainly composed of Hydrogen (H) and Helium (He). The Earth's crust is composed of Silicon (Si), Iron (Fe), Magnesium (Mg), and carbon (C). Living organisms form organic macromolecules. Oxygen and Hydrogen constitute 68-70% of living matter (Water = H₂O). Nitrogen (N) is part of proteins.

Properties of Living Beings

Living beings are complex materials that can interact with the world around them and reproduce.

Features

• Made mostly of Carbon and H₂O
• Their reactions inside cells are governed by the laws of physics and chemistry.
• They reproduce

Interaction with the Environment

Living beings evolve and react to external or internal stimuli, creating responses through the nervous and endocrine systems (hormones).

Nutrition

Living... Continue reading "Chemical Composition and Functions of Living Beings" »

Skeletons: Types and Functions

Exoskeletons

External systems support proportionally less weight than endoskeletons of the same size, which is why larger animals such as vertebrates have internal skeletal systems.

Key developments in exoskeletons are found among arthropods and some invertebrates, where the exoskeleton forms a shell or outer structure that protects the internal organs.

Given the limitations on animal growth imposed by exoskeletons, species with this feature have evolved various solutions. Most molluscs have calcareous shells that grow along with the animal, maintaining a consistent growth morphology. Other animals, such as arthropods, shed their old exoskeleton to grow, a process known as "molting." The new... Continue reading "Skeletons: Exoskeletons, Endoskeletons, and Hydrostatic Systems" »