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

Differential Diagnosis of Oral Ulcers and Vesiculobullous Lesions

Classification by Number and Etiology

• Single Ulcers: Traumatic, Tuberculosis (TB), Primary Syphilis.
• Multiple Ulcers: Recurrent Aphthous Stomatitis, Herpetic Stomatitis, Erythema Multiforme, Pemphigus Vulgaris.

Classification by Location

• Keratinized Mucosa: Recurrent Intraoral Herpes, Mucous Membrane Pemphigoid, Major Aphthous Ulcers.
• Non-Keratinized Mucosa: Minor Aphthous Ulcers, Herpetiform Ulcers.

Classification by Clinical Features

• Ulcers Causing Scarring: Major Aphthous Ulcers, Mucous Membrane Pemphigoid Ulcers, Tertiary Syphilis.
• Painless Ulcers: Tuberculosis (TB), Primary Syphilis, Tertiary Syphilis.
• Painful Ulcers: Primary Herpetic Gingivostomatitis, Recurrent Intraoral Herpes,

Anatomy and Physiology Fundamentals

Anatomical Terminology

• Anatomical Descriptors
  • Anterior — at or near the front of the body
  • Posterior — at or near the back of the body
  • Midline — imaginary vertical line dividing the body equally
  • Lateral — farther from the midline
  • Medial — nearer to the midline
  • Superior — toward the head or upper part of a structure
  • Inferior — away from the head or lower part of a structure
  • Superficial — close to the surface of the body
  • Deep — away from the surface of the body
  • Proximal — near the origination of a structure
  • Distal — farther from the origination of a structure
  • Contralateral — on the opposite side
• Anatomical Planes
  • Sagittal — body divided into left and right halves by a vertical plane passing through

Circulatory System

Deoxygenated blood from the body returns to the right atrium of the heart through the superior and inferior vena cavae. The right atrium contracts, pushing the blood through the tricuspid valve into the right ventricle. The right ventricle contracts, pumping the deoxygenated blood through the pulmonary valve into the pulmonary artery. The pulmonary artery carries the deoxygenated blood to the lungs, where it picks up oxygen and releases carbon dioxide through the process of gas exchange. Oxygenated blood returns from the lungs to the left atrium of the heart via the pulmonary veins. The left atrium contracts, pushing the oxygenated blood through the mitral valve into the left ventricle. The left ventricle contracts, pumping... Continue reading "Understanding the Circulatory and Reproductive Systems" »

DNA Replication: Definition and Mechanism

Definition: DNA replication is the process of producing two identical copies of DNA from one original DNA molecule. It is bidirectional and semiconservative—each daughter DNA contains one parental (old) strand and one new strand.

Steps of DNA Replication

1. Unwinding of DNA: Hydrogen bonds between base pairs break.
   • Two antiparallel strands separate, starting at the origin of replication.
   • The enzyme Helicase unwinds DNA, forming a replication fork.
2. Nucleotide Activation: Deoxyribonucleotides are activated using energy and the enzyme phosphorylase.
3. Strand Cutting and Stabilization: Endonuclease cuts the DNA at A-T rich regions (fewer hydrogen bonds).
   • Topoisomerase and helix destabilizing proteins stabilize the

The Human Heart: Structure and Function

The human heart, like other mammalian hearts, is a muscular pump with four chambers. The upper two chambers are the right atrium and the left atrium. The lower chambers are the right ventricle and the left ventricle. Both sides of the heart work simultaneously.

The walls of the atria are thinner than those of the ventricles. The right atrium receives deoxygenated blood from the body via the superior vena cava (collecting from the head, neck, arms, and chest) and the inferior vena cava (collecting from the lower parts of the body). The left atrium receives oxygenated blood from the lungs via the pulmonary veins.

After the blood enters both ventricles from the corresponding atrium, the deoxygenated blood in... Continue reading "Biological Systems: Heart Function, Genetics, and Plant Disease Management" »

Chromosomes and DNA

Genes are contained within chromosomes, which are made of DNA and located in the cell nucleus. A chromosome contains thousands of genes. Every normal human contains 23 pairs of chromosomes, a total of 46 chromosomes.

Traits and Alleles

A trait is any gene-determined characteristic, often determined by more than one gene. Gene: A segment of DNA that controls a hereditary trait. Alleles are different versions of a gene that produce distinguishable traits in offspring. Two alleles must be present in order for a trait to appear in the offspring. One allele is provided by each parent to the offspring. When fertilization of sperm and eggs occurs, the new offspring will have 2 alleles for each gene.

Gregor Mendel's Contributions

Gregor... Continue reading "Genetics: The Basics of Heredity and Traits" »

Prokaryotic Cells: Bacteria

• Bacteria capsule: The outer jelly-like layer.
• Bacteria wall: The rigid structure that maintains cell shape.
• Fimbriae: Multiple short appendages used to attach to surfaces.
• Flagellum: A long appendage used for movement.
• Plasmid: A small ring of DNA.
• Ribosomes: Organelles that synthesize proteins.
• Nucleoid: The area where genetic material is concentrated.
• Cell membrane: A selective barrier.
• Cytoplasm: Everything inside the cell excluding the nucleus.

Eukaryotic Cells: Animal Cells

• Mitochondrion: Produces energy for the cell.
• Cell membrane: A selective barrier.
• Cytoplasm: Everything inside the cell excluding the nucleus.
• Nucleus: The site where ribosomes are made.
• Cytoskeleton: A network of protein filaments in the cytoplasm.
• Ribosomes:

The Human Eye: Structure and Function

• A spherical organ (approx. 2.3 cm) that allows us to perceive light, color, and depth.
• Key Parts:
  • Sclera: Outer white protective layer.
  • Cornea: Transparent front part that allows light entry.
  • Iris: Colored muscular part controlling pupil size.
  • Pupil: Opening through which light enters.
  • Lens: Flexible structure that focuses light onto the retina.
  • Retina: Light-sensitive layer converting light to electrical impulses.
    • Cones: Detect bright light and color.
    • Rods: Detect dim light and are responsible for night vision.
  • Optic Nerve: Transmits signals to the brain.
  • Blind Spot: Point where the optic nerve leaves the retina; no photoreceptors.

The Camera: Components and Operation

• An optical device that captures and stores images