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

Lymphocyte Migration and Immune Response

Lymphocytes constantly migrate through the blood and lymph, moving from one lymphoid organ to another. This process:

• Enhances the chance that an antibody will encounter its specific antigen.
• The spleen filters blood, while other lymphoid organs filter lymph.

Phagocytosis: A Non-Specific Innate Immune Response

Phagocytosis is the ingestion of microorganisms or particulate matter by a cell. It is performed by phagocytes, which are certain types of white blood cells or their derivatives.

Actions of Phagocytic Cells

1. Among the granulocytes, neutrophils are the most important phagocytes.
2. Enlarged monocytes transform into wandering macrophages and fixed macrophages.
3. Fixed macrophages are located in selected tissues

Local Inflammation

1. Occurs when bacteria enter a break in the skin.
2. Inflammatory reaction is initiated by nonspecific mechanisms of phagocytosis and complement activation.
3. Complement activation attracts phagocytes to the area.
4. As inflammation progresses, B cells produce antibodies against bacterial antigens.
5. Attachment of antibodies to antigens amplifies nonspecific responses because of complement activation.
6. Promotes phagocytic activity of neutrophils, macrophages, and monocytes (through opsonization).
7. In the inflamed area, leukocytes attach to the surface of endothelial cells.
8. Move by chemotaxis to the inflamed site.

• Neutrophils arrive first, then monocytes, then T cells.
  • Undergo extravasation (the entire process of movement of leukocytes from the bloodstream

Nervous and Endocrine Systems

The nervous system receives external and internal stimuli, interprets them, and decides an appropriate response. The response is executed by the effector organ or tissue. Nervous tissue is made up of cells called neurons.

Stimulus → Nervous System → Effectors → Muscles, Glands

Neuron Structure

• Cell body: The central part of the neuron.
• Dendrites: Extensions of the cell body. They receive the nerve impulse and transmit it to the cell body.
• Axon: A long fiber extending from the cell body. It transmits the nerve impulse to other neurons or effector cells.
• Myelin sheath: This layer protects the axon and increases the speed of the nerve impulse.
• Axon terminals: These are located at the end of the axon. They contain neurotransmitters,

Anatomy, Pathology, and Lab Essentials

Bones: Rigid organs that make up the skeletal system of vertebrates, providing support and protection for the body’s organs.

Cranium: The part of the skull that protects the brain.

Backbone: Also known as the spine or vertebral column, a flexible and strong structure running along the center of the back, made up of small bones called vertebrae.

Skull: A bony framework enclosing the brain of a vertebrate.

Joints: The points where two or more bones, or a bone and cartilage, are attached in the body.

Ligaments: Short bands of tough, flexible fibrous connective tissues that connect two bones or cartilages, or hold joints together.

Cartilage: Firm, flexible connective tissue found in various forms, from which the... Continue reading "Anatomy, Pathology, and Lab Essentials: A Comprehensive Glossary" »

The Human Respiratory System

By Marco Rios

Ventilation: Air Movement in the Lungs

Pulmonary Ventilation

The total volume of air breathed in and out per minute.

Alveolar Ventilation

The volume of air exchanged between the atmosphere and the alveoli per minute.

The Lungs: Core Organs of Respiration

A pair of organs consisting of the lower part of the respiratory airways, pulmonary circulation, and connective tissue.

Pleural Sacs and Cavity

Thin, fluid-filled membranes that enclose the lungs. The space between the pair is known as the pleural cavity.

Alveolar Cell Types

Type I Cells

Form the walls of the alveoli, facilitating gas exchange.

Type II Cells

Secrete pulmonary surfactant.

Pulmonary Surfactant

A substance that reduces the surface tension of water inside... Continue reading "Human Respiratory System Functions" »

Carbohydrates: Structure and Classification

Classification

• Monosaccharides: Single sugar unit (e.g., glucose, fructose).
• Disaccharides: Two sugar units joined (e.g., sucrose = glucose + fructose).
• Polysaccharides: Many sugar units linked (e.g., starch, glycogen).

Aldose vs. Ketose

• Aldose: Contains an aldehyde (-CHO) group (e.g., glucose).
• Ketose: Contains a ketone (>C=O) group (e.g., fructose).
• Number of Carbons: Triose (3C), Tetrose (4C), Pentose (5C), Hexose (6C).

Structural vs. Stereoisomers

• Structural Isomers: Same molecular formula, different bonding patterns or structure.
• Stereoisomers: Same connectivity, different spatial arrangement of atoms.

Chiral Carbons

• Chiral Carbon: A carbon atom bonded to four different groups, creating an asymmetric center.

Most living things obtain their energy either directly or indirectly from the energy of sunlight captured through photosynthesis.

Photosynthesis in 2 Stages

1. Pigments in the leaves' cells (chlorophyll) capture or absorb the sun's energy, which is used to power the second stage. The leaf cells also need water (absorbed through roots) and carbon dioxide (that enters through small openings on the undersides of leaves called stomata).
2. Inside the chloroplasts, water and carbon dioxide are transformed into glucose and oxygen. Plants use glucose for food and store what they don't need as starch (energy for later use) and cellulose (that makes up the cell walls). Oxygen and water exit the leaf through the stomata.

Stomata

Carbon dioxide enters the plant... Continue reading "Photosynthesis and Cellular Respiration in Plants" »

Understanding DNA Analysis Techniques

Restriction Enzymes: Cutting DNA with Precision

Role: Restriction enzymes cut foreign DNA into pieces to prevent infection.

Mechanism: Special proteins recognize specific DNA sequences (restriction sites) and cut at those locations. Bacteria protect their own DNA from self-cleavage using methylation.

Example: EcoRI

EcoRI recognizes the sequence GAATTC and cuts between G and A. This creates "sticky ends" (overhangs) like G- and AATT, which help join DNA fragments.

DNA Fragmentation and Gel Electrophoresis

DNA is cut into fragments using restriction enzymes. These fragments are then sorted by size using gel electrophoresis.

• Shorter fragments travel farther and faster in the gel.
• DNA fragments are stained for visibility,

Echinoderms

Phylum: Echinodermata

• Sea stars (starfish)
• Sea urchins
• Sand dollars
• Sea cucumbers
• Brittle stars

Key Features:

• Symmetry: Larvae: Bilateral; Adults: Pentaradial
• Body Covering: Spiny skin, endoskeleton made of calcium carbonate
• Movement: Tube feet powered by water vascular system
• Nervous System: No brain; nerve ring with radial nerves
• Circulation: Water vascular system (no true circulatory system)
• Respiration: Diffusion via tube feet or skin gills
• Reproduction: Mostly external fertilization; can regenerate lost parts
• Habitat: Marine only (no freshwater/terrestrial species)

Water Vascular System

A hydraulic system for movement, feeding, and respiration.

Frequently Asked Questions

1. What type of symmetry do adult echinoderms have? Pentaradial symmetry
2. Which

Frog Embryology: Developmental Stages

Frogs reproduce through external fertilization, where the female lays eggs in water, and the male releases sperm over them. Fertilization occurs in the animal hemisphere of the egg. This process forms a diploid zygote. The point of sperm entry determines the gray crescent, which helps in the later development of the body axis.

1. Cleavage: Early Cell Division

The zygote undergoes holoblastic, unequal, and radial cleavage. The first two cleavages are vertical, forming four equal blastomeres. The third cleavage is horizontal but displaced towards the animal pole, resulting in smaller cells (micromeres) in the animal pole and larger cells (macromeres) in the vegetal pole. These divisions continue to form a morula,... Continue reading "Key Biological Systems & Mechanisms Explained" »