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

Key Terms in Phonetics

Accent: This is the way a language is pronounced, varying according to geographical location, social class, age, and other factors.

Dialect: A variety of a language that differs from others not only in pronunciation but also in vocabulary, grammar, and word order.

Allophone: A predictable phonetic variant of a phoneme.

RP (Received Pronunciation): The standard form of pronunciation, often used as a reference point.

Vowels

Vowels are produced with no obstruction to the airflow; the air passes freely through the vocal tract from the larynx (voiced).

Types of Diphthongs

• Falling Diphthongs: The first element is more prominent.
• Rising Diphthongs: The second element is more prominent.
• Closing Diphthongs: Characterized by a reduced aperture

Understanding Viruses: Structure, Infection, and Immunity

A virus is a biological entity that needs a cell host to reproduce. Each virus particle, or virion, is a potentially infective agent consisting of a capsid (or protein coat) of protein surrounding the nucleic acid, which can be DNA or RNA. The shape of the capsid may be straightforward or helical, typically icosahedral (polyhedral or near-spherical), or complex, typically comprising a head and a tail. This structure can, in turn, be surrounded by the viral envelope, a lipid layer with different proteins, depending on the virus.

The life cycle of a virus always requires the metabolic machinery of the invaded cell to replicate its genetic material, producing many copies of the original virus.... Continue reading "Viruses Explained: From Structure to Treatment" »

Population Dynamics

Expanding Populations

In expanding populations, there is a high birth rate. The growth of these populations follows an exponential model.

Stable Populations

In stable populations, the number of individuals stabilizes after passing a phase of exponential growth. This occurs because factors limit population growth, such as competition between individuals for space and food, or pressure from predators. This growth limit imposed by the ecosystem is called the carrying capacity (K). In this case, the model that represents the stable population is a logistic or sigmoidal function.

Declining Populations

In declining populations, the number of older individuals predominates. The decline may be due to a low birth rate or a decrease... Continue reading "Population Dynamics and Ecosystem Relationships" »

Genetic Disorders

A genetic disorder is a disease caused by an alteration of a gene, called a mutation. These mutations can occur randomly or as a consequence of exposure to some environmental risk factors.

Amniocentesis

Amniocentesis is a test used to determine whether a fetus has a genetic disease.

Environmental Factors

• Exposure to carcinogens: Components of cigarette smoke may induce gene expression, provoking different types of cancer.
• Water and food: In some rural areas, water could be contaminated with pesticides or substances from farms and industries. In developing countries, contaminated water is responsible for many (often fatal) diseases.
• Pollution: Cities with high levels of pollution and areas close to nuclear power plants may increase

Human Cell Structure

Cell Components

Human cells consist of three main structures:

• Plasma Membrane: The outer membrane protecting the cell, regulating nutrient intake and waste removal.
• Cytoplasm: A water-based solution containing dissolved substances and protein fibers forming the cytoskeleton. Organelles within the cytoplasm include ribosomes, mitochondria, endoplasmic reticulum, Golgi apparatus, vacuoles, and lysosomes.
• Nucleus: The spherical control center containing:
  • Nuclear Membrane: Separates the nucleus from the cytoplasm.
  • Nucleoplasm: The watery solution inside the nucleus.
  • Chromatin: Genetic material (DNA) responsible for cell control, organized into chromosomes.
  • Nucleolus: Composed of RNA and proteins, responsible for ribosome organization.

DNA: The Molecule of Life

DNA (Deoxyribonucleic Acid) is the biomolecule responsible for carrying genetic information. A core component of chromosomes and found within the nuclei of eukaryotic cells, DNA belongs to the nucleic acid family. DNA is formed from nucleotides, each composed of a monosaccharide, a phosphoric acid, and a nucleobase. DNA consists of four types of nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). DNA comprises two chains of nucleotides coiled together, forming the double helix. Adenine pairs with thymine, and cytosine pairs with guanine. The sequence refers to the order in which nucleotides are arranged. DNA duplication or replication is the process where a cell makes an exact copy of its DNA to share... Continue reading "Fundamentals of DNA, Genetic Concepts, and Biotechnology" »

The Origin of the Oceans

When edges diverge from the same continent, rift valleys form.

If the gap in these valleys continues to widen and connects to an ocean, it floods, creating a new ocean.

The ocean floor will have a dorsal ridge where the lithosphere is created, producing intense volcanism.

Borders with Lateral Movement

Edges with lateral movements separate plates that slide laterally with respect to each other. These are broken, called transform faults, which are usually interspersed along the different edges, allowing the accommodation of plate fragments that move at different speeds.

As these borders neither create nor destroy lithosphere, they are called passive. They are highly unstable areas, with frequent and strong earthquakes.

Endosymbiosis

Adaptation to Parasitism

Normally, endoparasites are animals that have undergone major structural changes regarding their architectural pattern, such as the disappearance of unnecessary structures. Locking mechanisms are another common characteristic in parasitic animals. Reproduction and life cycle are significantly affected in animal parasites. Populations often maintain very low levels, so finding a partner can be a problem. The appearance of hermaphroditism ensures reproduction despite the cost of producing two reproductive systems. The production of a high number of eggs compensates for the low probability of one completing the life cycle. The cyst is one of the more developed structures in these animals. Finally, to complete the life cycle,... Continue reading "Parasitism, Coral Reefs, Oligochaeta, and Biological Concepts" »

The Vital Role of Blood in Circulation

Blood is a red liquid that circulates through the blood vessels. It transports nutrients and oxygen to cells and collects carbon dioxide and other wastes.

Blood Composition: Plasma and Cells

Blood is made up of plasma and blood cells.

Blood Plasma Explained

Blood plasma is a yellowish liquid that carries nutrients, hormones, enzymes, and waste products from cells.

Types of Blood Cells

• Red blood cells (RBCs or erythrocytes): These contain hemoglobin, which binds oxygen in the lungs and transports it through the bloodstream to the capillaries, where it is released to reach all cells.
• White blood cells (leukocytes): These defend us from infectious agents like bacteria, viruses, and various parasites that enter through

Cerebral Palsy (CP): An Overview