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

Glycolysis and the Krebs Cycle

The Krebs cycle (also known as the citric acid cycle or tricarboxylic acid cycle) is named after its discoverer, Hans Krebs, who proposed the key elements of O₂ consumption in an amount disproportionate to the amounts added. Based on experimental observations, Hans Krebs proposed a cyclic pathway and cell reactions. The sequence, being a functional unit of all organisms, has a very coordinated and specific operation of all its organelles. However, within all this perfect machine, it is paramount that it takes energy for all this machinery to work to perfection. Cells use energy in the form of ATP (adenosine triphosphate). This is a molecule consisting of one molecule of adenine, a ribose, and three phosphate groups.... Continue reading "Glycolysis and Krebs Cycle: Energy Production in Cells" »

Neurons: The Building Blocks of the Nervous System

Neurons are fundamental cells of the nervous system, representing the anatomical and functional unit of the human brain. They are specialized cells designed to receive, carry, and transmit electrochemical signals called nerve impulses.

Neurons are irreplaceable. Once they age, are injured, or die, they cannot be replaced. This is because these cells are primarily formed during the prenatal period of gestation. A child is born with the largest number of neurons, approximately 100 billion, which immediately begin to decrease in number.

Glial Cells: Supporting the Neurons

The name 'glial' comes from the Greek root 'glia,' meaning concrete. These cells lack axons and are not essential for directly... Continue reading "Understanding Neurons, Glial Cells, Axons, Dendrites, and Synapses" »

Anatomy Q&A

Respiratory System

Bronchioles

1. Lack of cartilage

Alveoli

2. Gas exchange (hematosis) occurs in the lung alveoli.

Pleura

3. Plural recesses provide more space for lung expansion during inspiration.

Bronchi

4. The right main bronchus has a larger diameter than the left.

Larynx

5. The glottic cleft is the space between the vocal cords.

Digestive System

Duodenum

6. The hepatopancreatic ampulla is located in the descending portion of the duodenum.

Esophagus

7. The muscular layer of the esophagus transports the food bolus via peristalsis.

Stomach

15. The lesser curvature of the stomach is supplied by the left and right gastric arteries.

Hepatic Portal System

16. The splenic vein opens into the portal vein.

17. The superior mesenteric vein and splenic... Continue reading "Anatomy Q&A: Respiratory, Digestive, Circulatory, and Nervous Systems" »

Genetic Material

Genetic information is stored in the DNA molecule and is composed of three elements:

• Silica
• A sugar phosphate group
• A nitrogenous base

Chromosome

Hereditary information for each individual is stored in the DNA. This is called the genome, and the protein formed by it is called chromatin.

Genes

A gene is the unit of living legacy and consists of a linear sequence of nucleotides in the DNA molecule.

Homologous Chromosome

In somatic cells, each chromosome has a companion, which constitutes a pair of homologous chromosomes.

Mutation

A mutation is an alteration or change of genetic information in a living being. Therefore, it will produce a change of features spontaneously and can be transmitted or inherited by the offspring.

Genetic Mutation

A... Continue reading "Understanding Genetic Material and Mutations" »

Photosynthesis

It is a unique process of plants containing chlorophyll, transforming simple substances such as water and carbon dioxide into more complex substances like carbohydrates.

Chlorophyll

It is a green pigment that absorbs radiation reflected in colors like blue, purple, and red. There are four types of chlorophyll (a, b, c, and d), with slight chemical variations in their formulas.

Chloroplasts

These are cytoplasmic organelles formed by polymembranous structures containing areas called grana, where light-phase reactions occur. There are other areas called stroma, where enzymatic reactions take place.

Factors Affecting Photosynthesis

1. Light: A decisive factor in this process because it can accelerate or retard the reaction. This energy is

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,

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" »