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

The Human Digestive System

The digestive system is responsible for processing food and transforming it so nutrients can be absorbed and distributed to every cell in the body.

The Respiratory System

The respiratory system captures the oxygen needed by cells and removes the carbon dioxide (CO2) produced during cellular metabolism.

The Circulatory System

The circulatory system transports nutrients and oxygen to cells and removes waste substances.

The Urinary System

The urinary system handles debris and waste products ejected from cell metabolism, which are carried by the circulatory system to be filtered and expelled.

Key Components of the Digestive System

• Digestive Tract: Measures about 8 meters and varies in diameter along its length. It begins in the

Evolutionary Theories and the Nature of Life

Early Concepts: Creationism and Fixism

Two early concepts attempted to explain the origin of species:

• Creationism: A conception rooted in religious beliefs, which posits that the universe and the various beings within it were created by a divine being or God.
• Fixism: The belief that living creatures of different species possess unchanging characteristics, meaning each individual is biologically identical to its parents.

Lamarck's Theory of Evolution

In his work, Philosophie Zoologique, Jean-Baptiste Lamarck laid out an evolutionary explanation for nature and life based on two core principles.

Core Principles of Lamarckism

1. The Function Creates the Organ: An organism's organs change based on use or disuse.

Water Properties

• Water behaves like a dipole: OH bonds shift to oxygen, creating partial charges.
• Hydrogen bonds form between water molecules.
• Water is a great solvent due to hydration atmospheres.

Osmotic Pressure

• Hypertonic: Increased osmotic pressure, higher concentration.
• Hypotonic: Lower osmotic pressure, lower concentration.

Disaccharide Characteristics

1. Hydrolyzable into subunits.
2. Sweet taste.
3. Crystallizable.
4. Water-soluble.
5. No reducing power loss.

Hemiacetal Linkage

Cellulose

Cellulose consists of parallel chains joined by hydrogen bonds, forming microfibrils and fibers. This structure makes cellulose water-insoluble and rigid, providing structural support in plants. Humans and animals lack enzymes to break down cellulose, but some organisms (e.g.,... Continue reading "Water, Lipids, and Carbohydrates: Essential Biochemicals" »

Understanding Genetics: Key Concepts

Genetics is the branch of biology that studies the laws governing the transmission of traits.

Basic Genetic Terms

• Gene: The unit of genetic transmission.
• Genotype: The complete set of genes of an individual.
• Phenotype: The observable characteristics of an individual.
• Allele: A variant form of a gene.
• Dominant Allele: An allele that prevents the manifestation of the alternative allele for the same trait.
• Recessive Allele: An allele that is only manifested when the dominant allele is not present.

Mendel's Laws of Inheritance

1. 1st Law (Law of Segregation): When two heterozygous individuals are crossed, all descendants of the first filial generation are equal in both genotype and phenotype.
2. 2nd Law (Law of Independent Assortment)

Theories on the Origin of Life

Panspermia

Panspermia suggests that life forms originated elsewhere in the universe and were transported to Earth.

Oparin and Miller's Hypothesis (Abiogenesis)

The Oparin-Miller hypothesis posits that under the conditions of the primitive Earth, simple biomolecules could spontaneously generate simple organic molecules.

Historical Views and Evolutionary Dating

Fixism and the Static Universe

The ideas of Aristotle and Plato, often incorporated into Christian thought, supported a fixed, static universe (Fixism).

Molecular Clocks

Molecular clocks are used to calculate the evolutionary proximity of species. This method is based on the principle that the genetic difference between two species depends on the time elapsed since... Continue reading "Evolutionary Theories and the Origin of Life on Earth" »

Digestive Systems in Animals

Models of the Digestive Apparatus

• A stomach cavity with one opening, e.g., Porifera.
• A digestive tract with two openings (mouth and anus), i.e., vertebrates.

Digestive Systems in Invertebrates

• Platyhelminthes: Flatworms have a blind tube with a single hole.
• Nematodes: A mouth and an anus appear.
• Annelids: In the digestive tract with a mouth and an anus, specialized structures like the esophagus, crop, and gizzard appear.
• Molluscs: The digestive tract has specialized regions and displays a body attached to the hepatopancreas.
• Echinoderms: The digestive tract has specialized regions in which Aristotle's lantern stands out among the sea urchins.
• Arthropods: They all possess a digestive tract with specialized regions and also

Understanding Autoimmunity

An animal's immunological system can typically recognize its own body's molecules and distinguish them from foreign ones, producing antibodies against foreign substances. However, in rare cases, it produces antibodies against the body's own components. This phenomenon is called autoimmunity.

The consequence of this error is the development of serious diseases. Autoimmunity can be caused by genetic factors and may be inherited.

The body's own molecules that trigger autoimmunity are called autoantigens. Certain proteins can act as autoantigens. An autoimmune response occurs when these proteins are released into the bloodstream due to tissue injury.

Biochemical analysis has revealed that many microbes have evolved a strategy... Continue reading "Immune System Disorders: Autoimmunity & Allergies" »

Postovulatory Phase and Fertilization

The postovulatory phase comprises days 15 to 28 of the menstrual cycle. After the expulsion of the ovum, the follicle degenerates, fat accumulates, and it becomes the corpus luteum. The innermost layer of the uterus gradually thickens and acquires a spongy appearance with numerous glands and blood vessels to nourish a future embryo. If fertilization does not occur, around the 28th day, the thickened layer of the uterus, the endometrium, is destroyed and expelled, along with the remains of the unfertilized egg. This process produces a hemorrhage known as menstruation or a period.

If fertilization occurs, the innermost layer of the uterus remains swollen during pregnancy. The corpus luteum in the ovary continues... Continue reading "Understanding Postovulatory Phase, Fertilization, and Childbirth" »

Male Reproductive System

• The Testes

  The testes are the gonads that produce male gametes. These two bodies consist of seminiferous tubules, which give rise to sperm. The testes are covered by a fold of skin called the scrotum.

• The Reproductive Tract

  These tubes carry collected sperm out of the body. They include:

  • Epididymis: Where sperm complete the maturation process that makes them capable of fertilization.
  • Vas Deferens: A continuation of the epididymis that ascends into the abdomen. It is used to store sperm until ejaculation.
  • Urethra: This tube also belongs to the urinary tract, and its final section is housed within the penis.

• The Penis

  The penis is the male copulatory organ. It widens at its end, forming the glans, which is covered with a fold

Heart: Function

The heart is responsible for carrying oxygen in the blood and nutrients to all body cells for proper functioning. It is also in charge of collecting and transporting waste material for disposal.

Heart: Structure

The heart is a hollow organ the size of a fist, located in the center of the left chest between the lungs. It consists of a heart wall and four cavities.

Heart Wall

The heart wall has three parts:

• The endocardium is the innermost layer and is in contact with blood.
• The myocardium is the middle layer, composed of cardiac muscle tissue, and it is thick.
• The pericardium is the outer layer containing liquid, and it also absorbs the friction of the heart.

Cardiac Cavities

The heart is divided into two halves, which in turn are divided... Continue reading "Heart Anatomy and Physiology: Structure and Function" »