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

Cell Structure and Function

Key Components of the Cell

The cell is the basic unit of life, and it is composed of several essential components:

• Cell Membrane: A thin layer surrounding the cell, forming the boundary between the cell and its surrounding environment, the extracellular medium.
• Cytoplasm: The substance of the cell, excluding the nucleus. It is formed by a water-rich solution in which a variety of structures, called organelles, are dispersed. These organelles are responsible for carrying out the different functions of the cell.
• Cellular Nucleus: A structure that is usually spherical and located in the center of the cell. It contains the genetic material with the necessary information to direct and control cellular functions.
• Mitochondria:

Organism Response to Stimuli

Organisms have systems that allow them to collect information from within and outside their bodies and respond to changes that occur.

Key Concepts

• Stimulus: Any factor capable of triggering a response in an organism. This can be physical or chemical.
• Response: The action an organism performs as a reaction to the stimulus received.
• Sensation: The ability to receive stimuli (e.g., sight, hearing, touch, smell, and taste).
• Perception: A function that requires the interpretation of a stimulus by the brain and the elaboration of complex responses.

Sense Organs and Receptors

Sense organs are responsible for receiving environmental stimuli. Receptors are cells within these organs that capture and transmit the stimulus to the brain... Continue reading "Organism Response to Stimuli & Coordination" »

Basic Concepts of Genetics

Genetics studies the transmission of hereditary traits.

• Gene: A fragment of DNA containing the information needed to make proteins or to determine a specific characteristic.
• Genome: The complete set of genes from an organism.
• Genotype: The genetic makeup of an organism (e.g., represented by letters like AA, Aa, aa).
• Phenotype: The observable traits or characteristics resulting from the genotype and its interaction with the environment.

Mendelian Genetics Principles

Mendelian genetics applies the methodology practiced by Gregor Mendel, which involves making crosses between individuals with known phenotypes to infer their genotypes.

Mendel's Laws of Inheritance

Mendel formulated three fundamental laws governing the transmission... Continue reading "Genetics Fundamentals: Mendelian Laws & Human Conditions" »

1. Functions of the Digestive System

Digestion and absorption of nutrients.

2. Elements Forming the Small Intestine

Duodenum, jejunum, and ileum.

3. Valves of the Stomach

The stomach has the pyloric valve, and the duodenum connects with the esophagus via the cardia.

4. Portions of the Large Intestine

The large intestine is divided into the following parts:

• The first portion consists of a blind sac.
• The second part is called the ascending colon.
• The third portion is the transverse colon.
• The fourth part is the descending colon.
• Finally, the sigmoid colon, rectum, and anus.

5. Intestinal Loops

Intestinal loops are folds that form the small intestine to adapt to the available space in the abdomen.

6. Gastrointestinal Annexes

These include the parotid salivary... Continue reading "Digestive System: Functions, Organs, and Common Conditions" »

Vertebrate Circulatory Systems

Simple Closed Circulation (Single Circuit)

Fishes

The heart in fishes has one atrium and one ventricle. From the ventricle, deoxygenated blood is pumped to the branchial artery, which branches into arteries supplying the gill lamellae. In the gills, blood becomes oxygenated. This oxygenated blood is then collected by efferent gill arteries that converge into the aortic root and then the dorsal aorta, which distributes it to the body tissues. This is a single-circuit system.

Closed Double Incomplete Circulation

Amphibians

The heart is composed of two atria and one ventricle. The two atria are separated by an interatrial septum. The right atrium receives deoxygenated blood from the body, and the left atrium receives oxygenated... Continue reading "Animal Circulatory Systems: Vertebrates & Invertebrates" »

DNA and Chromosomes

DNA (deoxyribonucleic acid) is the biomolecule containing the genetic instructions for building proteins. Proteins, especially enzymes, regulate all life processes, including growth, tissue repair, and reproduction. DNA resides in the nucleus of eukaryotic cells as part of the chromosomes.

Chromosomes are composed of chromatin, a complex of DNA and proteins. When a cell is at rest, chromatin is dispersed within the nucleus, making chromosomes invisible. Before cell division, DNA replicates, and chromatin condenses into shorter, thicker fibers, forming visible chromosomes. Due to DNA replication, each chromosome comprises two identical arms called chromatids, joined by a centromere.

Karyotype

The number, shape, and size of chromosomes... Continue reading "DNA, Chromosomes, Genes, and Cell Division" »

Nutrition Basics

Nutrition involves how our bodies obtain, process, and utilize essential nutrients from food. These nutrients, vital for cell function and survival, include:

Types of Nutrients

• Carbohydrates: The primary energy source. Glucose provides quick energy, while complex carbohydrates (starch, glycogen) require longer digestion. Cellulose, a plant fiber, aids digestion.
• Lipids (Fats): Store energy and form reserves in adipose tissue. Phospholipids are crucial components of cell membranes.
• Proteins: Essential for cell structure and regulatory functions.
• Water: The most abundant component, vital for cooling, transporting substances, waste elimination, and facilitating chemical reactions.
• Minerals: Play structural and regulatory roles in various

Arteriosclerosis vs. Atherosclerosis

These terms are similar, but distinct. Arteriosclerosis is a general term for hardening and loss of arterial elasticity. Atherosclerosis is hardening specifically caused by atherosclerotic plaques.

Heart Conditions

Heart Murmurs

Heart murmurs are pathological noises heard during auscultation, caused by increased flow through normal valves, valve alterations, intracardiac abnormalities, or extracardiac issues. They can be systolic, diastolic, or continuous.

Tachycardia

Tachycardia is an increased heart rate, specifically above one hundred beats per minute at rest.

Leukemia

Leukemia is a group of malignant bone marrow diseases causing an uncontrolled increase in white blood cells (WBC), often appearing in peripheral... Continue reading "Understanding Cardiovascular Diseases and Related Conditions" »

Gregor Mendel's Contributions to Genetics

Note: This section details the scientific method applied to the study of inheritance.

Mendel's Scientific Method in Inheritance

Formulation of the Problem:

How are characteristics passed down from parents to offspring?

Hypothesis:

Sex cells contain structures responsible for the transmission of characters.

Experiment (Proof):

Crosses were made with purebred pea plants. In Cross 1, one character varied while six others remained constant.

Results and Conclusions:

Cross 1: All F1 generation individuals expressed the dominant character. In the F2 generation, the phenotypic ratio was 3:1.

Conclusions: Gametes contain factors responsible for character transmission, and each character is determined by two factors.

Key

Meiosis: Cell Division for Genetic Diversity

Meiosis is a specialized process of cell division that reduces the amount of DNA to maintain a constant number of chromosomes across generations. In advanced organisms, specialized tissues called gonads are responsible for reproduction, producing reproductive cells or gametes.

Therefore, gametes must contain half the number of chromosomes as their parent cells. Without this reduction, the amount of DNA would double with each successive generation. Meiosis ensures that the four resulting haploid cells are genetically distinct from one another and from the parent cell.

Meiotic First Division (Meiosis I)

Prophase I: Homologous Chromosome Pairing

Chromosomes pair together to form homologous pairs. This is... Continue reading "Meiosis Explained: Cell Division for Genetic Diversity" »