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

The Human Digestive System: An Introduction

The digestive system transfers organic nutrients, vitamins, minerals, and water from the foods we eat to the internal environment. Upon entering the body, food moves through the gastrointestinal (GI) tract, and the nutrients are absorbed and transported to the circulatory system where they are utilized.

Net Gain to the Body

Food and air are the primary sources of net gain to the body.

Distribution within the Body

Nutrients and substances are distributed throughout the body via the GI tract, lungs, storage deposits, and metabolism.

Net Loss from the Body

Excretion from the body occurs via the lungs, GI tract, kidneys, and skin.

Epithelial Cells

Epithelial cells separate compartments and are crucial in the digestive... Continue reading "Human Digestion and Metabolic Regulation" »

Introduction to Biomolecules

Living organisms are made up of thousands of biomolecules—molecules produced by living systems with distinct properties and functions favored through evolution. Small, simple molecules called micromolecules (or monomers), such as water, minerals, simple sugars, and nucleotides, serve as building blocks for larger macromolecules (or polymers) like proteins, lipids, carbohydrates, and nucleic acids. Biomolecules are classified into inorganic types (e.g., water, minerals, gases) and organic types (e.g., lipids, carbohydrates, proteins, nucleic acids). While biomolecules alone do not exhibit life, they organize into cells and are continuously synthesized and broken down to maintain and perpetuate life.

Water: The Essential

c) Antigen Processing and Presentation

• Engulf protein antigens, partially digest them, and display polypeptide fragments on the surface for T cells to "see."
• Fragments are associated on the surface with Major Histocompatibility Antigens (MHC II), which are necessary to activate T cells.

d) Dendritic Cell Migration

To increase the chance of interacting with the correct T cells, dendritic cells migrate to secondary lymphoid organs (chemokines are secreted to attract T cells).

VII. Extracellular Killing by the Immune System

A. Natural Killer (NK) Cells

NK cells lyse virus-infected cells, tumor cells, and parasites. They kill cells that do not express MHC class I antigens.

B. Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

1. In ADCC, NK cells and macrophages

Lab 8: Temperature and Microbial Growth

Key Concepts

• Psychrophiles grow best between 0–20°C. Often found in cold environments like glaciers.
• Mesophiles prefer 20–45°C. These include human pathogens like E. coli.
• Thermophiles thrive at 55°C or higher. They are often found in hot springs.

Materials and Their Functions

• Tryptic Soy Broth (TSB): A nutrient-rich medium that supports bacterial growth.
• Incubators set to different temperatures (4°C, 25°C, 37°C, 55°C): Used to simulate environmental conditions.
• Spectrophotometer (OD600): Measures turbidity (cloudiness) of a culture to estimate cell density.
• Classification by growth: “+++” indicates heavy growth; “0” means no growth.

In this lab, students investigated how temperature affects... Continue reading "Microbiology Lab Fundamentals: Growth, Metabolism, Genetics" »

Essential Biological Macromolecules

Properties: Hydrophilic vs. Hydrophobic

• Hydrophilic (water-loving): Nucleic Acids, Carbohydrates, Starch, Chitin. Glucose is hydrophilic because it contains many hydroxyl functional groups.
• Hydrophobic (water-fearing): Lipids.

Key Molecules and Building Blocks

• Organic Molecules: Examples include Methane (CH4) and Glucose.
• Creating Polymers: Polymers are created from monomers through a Dehydration Reaction.

Types of Macromolecules

Carbohydrates

• Monosaccharides: Simple sugars like glucose, fructose, and galactose.
• Disaccharides: Maltose is formed from two glucose molecules.

Lipids

• Unsaturated Fats & Oils: These contain carbon-carbon double bonds in their fatty acids.

Proteins

• Proteins are unique in that they contain

Microbiology Lab Practice Questions

What is the optimal temperature range for Bacillus stearothermophilus?

Answer: 55°C (a thermophile)

Which organism produces red pigment at 25°C?

Answer: Serratia marcescens

What does no pigment but visible turbidity in S. marcescens at 37°C suggest?

Answer: Growth occurred, but pigment production is temperature-sensitive.

What is the term for bacteria that grow best at cold temperatures but also at room temperature?

Answer: Psychrotroph (e.g., Pseudomonas fluorescens)

What color does E. coli appear on MacConkey agar?

Answer: Pink (lactose fermenter)

Which test detects mixed acid fermentation?

Answer: Methyl Red (MR) test

What does a black precipitate on HE agar indicate?

Answer: H₂S production (e.g., Salmonella)

Which

Sex Determination and Genetic Inheritance

Offspring formed from the union of a sperm and an egg develop as females, while unfertilized eggs develop as males.

Environmental Sex Determination

In this case, the sex is not determined by genes or chromosomes but by environmental factors:

• In some reptiles, like crocodiles and turtles, the temperature of the eggs during a certain period of development is the deciding factor in determining sex.
• Some young fish are male and may become female as they get older.

Sex-Linked Inheritance

Sex-linkage appears when genes are located on sex chromosomes. Since males and females have different sex chromosomes, sex-linked genes show different phenotypic ratios depending on the sex.

X-Linked Inheritance

X-linked inheritance... Continue reading "Sex Determination and Genetic Mutations" »

Insect Defenses Against Predators

Three Plant Mechanisms to Defend Against Insects

• Physical: Thick walls
• Chemical: Phytochemicals that kill insects
• Entrapment: Pitcher plants

How Insects Overcome Physical Defenses

• Specialized mandibles
• Evolution
• Immunity to phytochemicals
• Specialization to survive the digestive liquid of pitcher plants

Insect Parasitism

Endoparasites

Approximately 20% of insect orders include endoparasites. Some orders that include endoparasites are:

• Hymenoptera
• Diptera
• Strepsiptera

Ectoparasites

Some orders that include ectoparasites are:

• Anoplura
• Mallophaga
• Siphonaptera

Three Challenges Faced by Endoparasites

• Respiration
• Excretion/getting rid of toxic nitrogenous waste without killing the host
• Avoiding the host's endocrine system

Insect Social Behavior

Subsocial

Endocrine Pharmacology Study Roadmap

🔹 1. Thyroid Physiology & Pathophysiology

🔸 Physiology

• TRH (hypothalamus) → stimulates TSH (anterior pituitary) → stimulates T3/T4 release (thyroid)

• T3 = active, T4 = prohormone

• Feedback loop: T3/T4 inhibit TRH and TSH

• T3/T4 actions:

  • ↑ Metabolic rate, heart rate, cardiac output

  • ↑ Oxygen consumption, lipolysis, glucose metabolism

  • CNS effects (mood), reproductive effects

🔸 Synthesis

• Iodide uptake → oxidation to iodine → binds to thyroglobulin → forms MIT/DIT → forms T3/T4

🔸 Disorders

• Hypothyroidism: Hashimoto's thyroiditis, iodine deficiency, thyroidectomy, myxedema coma

• Hyperthyroidism: Graves' disease, toxic adenoma, thyroid storm

🔹 2. Thyroid Pharmacology

🔸 For Hypothyroidism

• Levothyroxine

Animal Eukaryotic Cells and Organelles

• Nucleus: Holds genetic material. Protected by a double membrane that separates it from the cytoplasm.

• Vacuoles: Small sacs that store different substances.

• Lysosomes: Made by the Golgi apparatus; digest materials inside the cell.

• SER (Smooth Endoplasmic Reticulum): Produces lipids and helps remove toxic substances.

• Mitochondria: Have two membranes; break down glucose to release energy (cellular respiration).

• Cytoplasm: Jelly-like fluid with the cytoskeleton that supports and gives shape to the cell.

• RER (Rough Endoplasmic Reticulum): Stores and transports proteins made by ribosomes attached to it.

• Ribosomes: Smallest organelles, no membrane; make proteins, free or attached to RER.

• Cell membrane: Made of lipids