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

Central Dogma

The Central Dogma concept illustrates the mechanisms and expression of genetic inheritance. The DNA molecule contains useful biological information that is stably transmitted. The process involves DNA replication without variation from cell to cell and generation to generation, with simple mechanisms for the translation of messages. Occasional variations may occur, reflecting the biological needs of organic evolution, leading to the production of new genotypes on which natural selection can act. DNA structure allows for mutation and recombination.

Cloning

Cloning is the process of obtaining one or more individuals from a somatic cell or a nucleus from another individual, so that the cloned individuals are identical or nearly identical... Continue reading "Central Dogma, Cloning, Stem Cells, and Genetic Engineering" »

Endoplasmic Reticulum

In all eukaryotes (animals and plants), a complex system of sacs and tanks exists in the cytoplasm, separated by a membrane. This system, the endoplasmic reticulum (ER), covers the entire cell and delimits two non-interconnected spaces: the inside of the ducts and the hyaloplasm. It is part of the cytoplasmic vacuolar system, which also includes the nuclear envelope and the Golgi apparatus.

The ER consists of a series of tubular cavities or tanks, isolated from the cytosol by a membrane. This membrane may or may not be covered with ribosomes, which are responsible for protein and phospholipid biosynthesis. The ER is composed of flattened, stacked vesicles. The rough endoplasmic reticulum (RER) has ribosomes attached to its... Continue reading "Endoplasmic Reticulum: Structure, Function, and Composition" »

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" »

Skin Vascularization: Blood Supply

The skin is nourished by blood vessels found in the dermis and hypodermis, which transport oxygen and other essential nutrients.

These vessels form two main networks (plexuses):

• Subpapillary (Superficial) Plexus: Located in the deep dermis.
• Subdermal Plexus: Located in the hypodermis.

Skin Innervation: Nerve Endings

The skin is one of the body's most richly innervated sensory organs. There are two main types of nerve endings in the skin:

1. Receiving (Sensory) Endings

   These perceive external environmental stimuli and transmit them to the brain. They allow us to appreciate the sensations of touch, cold, heat, and pain.

2. Effector Endings

   These innervate the blood vessels, perspiration glands, and arrector pili muscles (erector

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