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

The Stages of Evolution and Speciation

The evolution of changes in living things that occur over time, leading to new species, can be distinguished in four stages:

1. Production of Evolutionary Change

   Natural selection favors certain individuals while harming others. Both still belong to the same species.

2. Genetic Isolation of the New Population

   To constitute a new species, it's imperative that members of the new species do not reproduce with the originals. This occurs when the new settlement becomes genetically independent. Various types of barriers include:

   • Geographical Barriers

     Prevent physical contact between populations (among individuals).

   • Sexual Barriers

     Due to anatomical differences that prevent mating or lack of synchrony in the fertile period,

Plant Waste Products

Gaseous substances: These include carbon dioxide and ethylene. Carbon dioxide is removed via stomata and lenticels, while ethylene is found in ripe fruits.

Liquid substances:

• Essential oils are expelled to the outside (ciliary ganglion) or stored (oleifera bags).
• Resins accumulate in the resin canals.
• Latex is stored within laticiferous channels.

Solid substances: Calcium oxalate accumulates as crystals in cell vacuoles.

Plant Respiration

Plants, like most living organisms, require oxygen for cellular respiration. As photosynthetic organisms, they also require carbon dioxide to synthesize their own organic matter. The addition of these gases does not require a respiratory apparatus as in animals, due to the following peculiarities:... Continue reading "Plant Waste, Respiration, and Vertebrate Urine Formation" »

The Anatomy of Human Phonation

The process of human voice production, known as phonation, involves a complex set of anatomical structures. These can be broadly divided into three distinct zones:

• Subglottic Cavity
• Larynx (Glottic Cavity)
• Supraglottic Cavity

Subglottic Cavity: The Powerhouse of Voice Production

The subglottic cavity comprises the diaphragm, lungs, bronchi, and trachea. This region is crucial for generating the airflow necessary for phonation.

The diaphragm is a muscular septum, shaped like a dome, that separates the chest and abdominal cavities. Its movement drives the respiratory cycle:

• Inspiration: When the diaphragm contracts and the ribs rise, the volume of the chest cavity increases. This draws outside air through the nose or mouth,

Proteins

Proteins are polymers of amino acids, also known as polypeptides. They are essential biomolecules, as nearly all life depends on them.

Protein Structural Levels

Proteins can have thousands of amino acids, and therefore, their thousands of atoms can adopt a wide variety of positions. Importantly, a protein consists of thousands of amino acids linked one after another through peptide bonds, forming long linear chains. However, the final spatial structure of a protein is not a linear chain; it adopts a specific three-dimensional form in space, which is essential for its function.

Primary Structure

Consists of the amino acid sequence of a protein. It is the most basic and arguably the most important level of structural organization.

Secondary

Sexual Reproduction in Plants

Understanding the Process

Sexual reproduction is typical of plants with seeds. The reproductive organs are inside the flower, where gametes are produced. After pollination, fertilization and the formation of embryos and seeds take place. Pollination is the transfer of pollen grains from the anther of the stamen to the stigma of the pistil.

Flower Structure

A flower is the reproductive unit of a plant. It consists of the following parts:

• Calyx: Green sepals which protect the developing flower.
• Corolla: Brightly colored petals.
• Stamen: The male reproductive organ of the flower. It consists of a stalk (filament) and sacs (anthers), where pollen is stored.
• Pistil: The female reproductive organ of the flower. It consists of

Stem cells (or stem cells) are cells that have not completed their differentiation, either by being part of an embryo a few days old, or by being part of nature's reserves of immature cells in the adult organism.

Characteristics of Stem Cells

The key characteristics of stem cells are:

1. Self-renewal: The ability to produce more stem cells.
2. Differentiation: The origination of daughter cells of various types, which are converted by differentiation into specialized cell types.

Different Types of Stem Cells

Stem cells can be classified into the following types:

Totipotent Cells

There are about two hundred types of specialized cells, and all of them originate from unspecialized stem cells or differentiated cells. The first cell of every living thing, the... Continue reading "Stem Cells: Types, Characteristics, and Applications" »

Cellular Respiration: Energy Production in Cells

Understanding Cellular Respiration

Cellular respiration is often associated with the exchange of gases. The utilization and disposal of gases occur within the confines of individual cells in animal or plant bodies, or within the single cell of unicellular organisms. This process is known as cellular respiration. During cellular respiration, the breaking of chemical bonds follows a sequence of steps catalyzed by various enzymes, allowing for a gradual release of energy. This energy is not transformed into light; instead, it is partly "packaged" into ATP molecules, while the remainder is dissipated as heat.

Stages of Cellular Respiration

The first stage, Glycolysis, occurs in the cytoplasm's matrix,... Continue reading "Cellular Respiration and Cell Cycle: Fundamental Biological Processes" »

The endosymbiotic theory explains the process of moving from a prokaryotic cell, which lacks most organelles, through symbiogenetic additions.

The Three Stages of Endosymbiosis

1. A bacterium that uses sulfur as an energy source merges with a swimming bacterium to form a new entity. The result was the first eukaryotic cell. The nucleoplasm of animal cells, plants, and fungi would be the result of the union of these two bacteria. A baseline characteristic of both cells was added: a new, more complex morphology. DNA remained confined to an inner core separated from the rest of the cell by a membrane.
2. This new organization was still anaerobic, unable to metabolize oxygen, as this gas was poisonous to it. Therefore, they lived in environments where oxygen,

Understanding Fertilization

Fertilization is the union of an egg and sperm, occurring within the female genital tract, specifically in a fallopian tube. The immediate result of this union is the formation of a single-celled organism called the zygote. The fallopian tube connects the ovaries, where ova (eggs) are produced, to the uterus, the structure within which the development of the zygote begins.

Stages of Human Embryonic Development

Embryonic development is the set of profound changes that occur in any living being throughout its early life. In humans, as in many other living beings, it commences with the formation of the zygote. This initial development, often referred to as prenatal development, concludes at the time of birth. Postnatal

Digestive System Components

Salivary Glands

These glands help moisten the food bolus. Saliva moistens food to aid swallowing and begins the process of food degradation. The main salivary glands are:

• Parotid
• Submandibular (formerly Submaxillary)
• Sublingual

Pharynx

Located just after the mouth, the pharynx serves as a junction for both the respiratory and digestive systems.

Esophagus

The esophagus is a long, muscular tube connecting the pharynx to the stomach. It ends at the cardia, regulated by the lower esophageal sphincter.

Stomach

A thick-walled muscular sac located on the left side of the upper abdomen, below the ribs. It churns food and mixes it with digestive juices.

Small Intestine

A long, coiled tube (approximately 6-7 meters) where most nutrient... Continue reading "Human Digestive & Circulatory System Anatomy" »