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

Charles Darwin and the Discovery of Natural Selection

Charles Darwin made the groundbreaking discovery of natural selection. He observed that organisms with favorable traits are more likely to survive and reproduce, passing on those traits to future generations.

Artificial Selection: Shaping Outcomes through Human Intervention

Artificial selection involves deliberately pairing two organisms to produce desired traits in their offspring.

Gene Flow: The Transfer of Genes between Populations

Gene flow occurs when genes are transferred from one population to another through migration and mating.

Genetic Drift: Changes in Gene Frequency within a Population

Genetic drift refers to the random change in the frequency of a gene within a population. Over time,... Continue reading "Understanding the Mechanisms of Evolution: Natural Selection and More" »

Understanding Plague: Causes, Forms, and Treatment

The Gram-negative bacterium Yersinia pestis is the causative agent of the systemic invasive infectious disease known as plague.

Historical Impact of Yersinia pestis

• Yersinia pestis has been responsible for three devastating pandemics: the Justinian Plague, the Black Death, and modern plague.
• The Black Death, in the 14th century, is estimated to have reduced the total world population from 450 million down to 350–375 million.

Transmission and Symptoms

Yersinia pestis is primarily a rodent pathogen, with humans being an accidental host. Infection typically occurs when a human is bitten by an infected rat flea. The flea draws viable Y. pestis organisms into its intestinal tract, where they multiply.... Continue reading "Plague Disease: Causes, Forms, Symptoms, and Treatment" »

Mendelian Principles of Inheritance

Gregor Mendel

• In the 19th century, he studied inheritance: the passing of characteristics from parents to offspring.
• His work was based on the study of the crossing of different varieties of plants.
• The species chosen was the pea (Pisum sativum).

Method

• Characteristic selection
• Obtaining pure-bred individuals for those characteristics

Parental generation (P)

• Crossing two different pure breeds to obtain descendants

First filial generation (F1)

• Crossing F1 individuals and studying their descendants

Second filial generation (F2)

Complete Inheritance

In the heterozygote, the dominant phenotype is manifested.

Special Cases in Genetics

Complete Inheritance

In the heterozygote, the dominant phenotype is manifested.

Intermediate Inheritance

The... Continue reading "Mendelian Genetics: Principles of Inheritance" »

Early Chordates and the Rise of Tetrapods

The earliest known chordate, Myllokunmingia, is found in the Chengjiang fauna. One of the major challenges for early tetrapods was supporting their bodies on land, along with reproductive and sensory adaptations. Tetrapod limbs consist of three segments: the stylopod (humerus/femur), zeugopod (ulna/radius, tibia/fibula), and autopod (wrist/fingers, ankle/toes). Tiktaalik represents a key transitional fossil between fish and tetrapods.

Amphibians and Amniotes

Amphibians, with over 4,000 living species, represent a halfway point in the transition to land. They still rely on water for breeding and maintaining water balance. Amniotes, including reptiles, birds, and mammals, evolved a semipermeable shell made... Continue reading "Evolution of Life: From Early Chordates to Modern Biodiversity" »

The Human Heart: Structure and Function

The heart is a muscular organ situated between the lungs, slightly to the left. Its walls, known as the myocardium, are responsible for pumping blood.

It is made up of four chambers:

• Two atria (upper chambers)
• Two ventricles (lower chambers)

The heart also contains valves that regulate blood flow:

• The tricuspid valve connects the right atrium and the right ventricle.
• The mitral valve connects the left atrium and the left ventricle.

Understanding the Cardiac Cycle

The cardiac cycle is the sequence of events that occurs with each heartbeat. As the heart beats, it circulates blood through the body's pulmonary and systemic circuits.

There are two main phases of the cardiac cycle:

• Diastole Phase: The heart ventricles

The structural organization of eukaryotic cells is remarkably complex and compartmentalized, reflecting the diverse functions these cells perform. Eukaryotes encompass a wide array of organisms, including plants, animals, fungi, and protists. Below is a detailed exploration of the structural components of eukaryotic cells:

1. Cell Membrane (Plasma Membrane)

• Composition: The cell's outer boundary is formed by a phospholipid bilayer with embedded proteins and other molecules.
• Function: It regulates the passage of substances into and out of the cell, acting as a selective barrier.

2. Cell Wall (in some cells)

• Present in: Plant cells, fungal cells, and some protists.
• Composition: A rigid structure made of cellulose in plants and chitin in fungi.
• Function:

Histogenesis of Blood Tissue

Histogenesis refers to the origin and development of cells.

Development of Granulocytes (Myelopoiesis)

Granulocytes are cells with granular cytoplasm, including neutrophils, eosinophils, basophils (cells ending in -phil), and mast cells.

Stages of Granulocyte Development:

• Myeloblast
• Promyelocyte
• Myelocyte (stage when granules appear)
• Metamyelocyte

Origin of Blood Cells

All blood cells originate from the Hematopoietic Stem Cell. These cells differentiate after being stimulated by hormones or interleukins. For example, B-lymphocytes become plasma cells after being stimulated by IL-2 in order to fight infections.

Characteristics and Composition of Blood

General Characteristics of Blood

• Consists of blood plasma and matured blood

Understanding Kidney Function

As capillaries exit organs, they converge into larger blood vessels, veins, which eventually return the blood to the heart at the right atrium.

Abnormal Kidney Function:

An individual's kidneys are unable to remove waste, the medical treatment known as hemodialysis. Use a dialysis machine 'artificial kidney' is only temporary, until the patient recovers normal kidney function or receives a kidney transplant. Blood is put in close contact with a special solution similar to blood plasma. The semipermeable membrane allows urea and other waste materials to exit the blood and prevents the escape of blood cells.

Painful Stones:

The substances transported in the urine can trigger the formation of crystals, commonly referred... Continue reading "Understanding Kidney Function, Stones, and Blood Disorders" »

Brain Anatomy and Functions

The human brain is a complex organ, the control center of the nervous system. Below are key parts and their vital roles:

Cerebral Cortex

The outermost layer of neural tissue that covers the brain, responsible for higher-level functions like thought, language, and memory.

Corpus Callosum

A large bundle of nerve fibers connecting the two cerebral hemispheres, facilitating communication and influencing logic and creativity.

Hypothalamus

A crucial part of the brain that links the nervous system to the endocrine system via the pituitary gland, regulating essential bodily functions.

Thalamus

A major relay station for sensory information, also regulating sleep, alertness, and consciousness.

Midbrain

Involved in motor movement, particularly

The Central Dogma of Molecular Biology

Replication - General Characteristics:

• DNA replication is semiconservative: each strand in the DNA double helix acts as a template for the synthesis of a new, complementary strand. The new two daughter molecules of DNA have a new strand and an old one.
• DNA polymerase III: is the enzyme that adds nucleotides to the growing DNA chain, incorporating only those that are complementary to the template. DNA polymerase III has the following characteristics:
  • It can only read a template in 3’-----5’ direction so the new strand grows in 5’----3’ direction.
  • It needs a pre-existing strand of nucleotides called a primer which provides a 3’-OH end to bind new nucleotides.
  • It is able to repair the mistakes by removing