Notes, abstracts, papers, exams and problems of Biology

The Circulatory System

The circulatory system is the anatomical structure that includes both the cardiovascular system (which carries and circulates blood) and the lymphatic system (which carries lymph).

Its main function is to transport nutrients, gases, hormones, and blood cells to the body's cells. It also helps fight disease, stabilize body temperature and pH, and maintain homeostasis.

Basic Structures of the Circulatory System

• Arteries
• Veins
• Blood
• Heart
• Capillaries

The Nervous System

The nervous system is a network of ectodermal tissues found in animals. Its basic unit is the neuron. Its main function is to quickly capture and process signals, exerting control and coordination over other body systems to achieve timely and effective interaction with... Continue reading "Understanding Human Body Systems: Circulatory, Nervous, Locomotor, and Digestive" »

Sperm and Egg Characteristics

Sperm are male gametes, representing highly specialized cells. These cells are small and mobile and consist of three parts:

• Head: The most voluminous part of the sperm. It contains the nucleus, with 23 chromosomes, and the acrosome, a cellular organelle that secretes substances that participate in the fertilization of the egg.
• Tail: Consists of a flagellum, a protein structure that allows the movement of the sperm.
• Neck: Lies between the head and tail. It contains numerous mitochondria around the base of the flagellum; these cellular organelles provide the energy needed to travel to the egg. It also contains a centriole, an organelle responsible for controlling movement.

Eggs have 23 chromosomes and have a very different... Continue reading "Sperm, Egg, Ovaries, and Spermatogenesis" »

Part II: The Endocrine System

Endocrine System Function

The endocrine, or hormonal, system is another system of coordination within the body. This system is closely related to the nervous system, and they are dependent on each other. In some cases, the nervous system stimulates or inhibits the secretion of hormones, and in others, the hormones stimulate or inhibit the action of the nervous system.

The endocrine system consists of a series of glands located throughout the body. These glands, called endocrine glands, are not anatomically connected to each other. They pour their secretions directly into the bloodstream.

Endocrine glands are formed by specialized secretory cells that synthesize chemicals called hormones. Once produced, hormones are... Continue reading "Endocrine System: Function, Hormones, and Diseases" »

Mitosis: is a dynamic, continuous and very complex whereby the nuclear material is duplicated and then divided and shared equally between the daughter cells.
Phases of mitosis: interphase, prophase, prometaphase, metaphase, anaphase, telophase.
Chromatic chromosome is a newly formed, still attached by the centromere.
Equatorial plate: the formation is taken as linear chromosomes in the center of the spindle in the metaphase stage of mitosis and meiosis.
Spindle fibers: attract the respective chromosomes toward the centrioles.
Meiosis is a type of reduction division and multiple it is performed by two successive divisions during which four daughter cells are formed, the chromosomes are duplicated so that the number of chromosomes that appear... Continue reading "Mitosis and Meiosis" »

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)

... Continue reading "Understanding Genetics: Genes, Alleles, and Inheritance" »

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

... Continue reading "Digestive and Circulatory Systems in Animals" »

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" »

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" »