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

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)

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" »

Tendon Structure

Tendon: A structure composed of collagen fibers arranged parallel to the tendon's axis. These fibers are designed for low flexibility and resistance to extension. Within the tendon, we find loose connective tissue and cells called tenocytes.

The entire structure is termed the endotendon, enclosed within a sheath called the peritenon. The peritenon's extension is continuous with the periosteum at one end and the perimysium at the other.

Some tendinous fibers, known as Sharpey's fibers, penetrate the bone and calcify, forming a strong union between tendon and bone.

The tendon is protected by an outer sleeve consisting of a parietal layer and an inner visceral synovial layer. A space filled with synovial fluid separates these layers.... Continue reading "Tendon, Fascia, and Cranial Bones: Structure and Function" »

NADP⁺ acts as a powerful reducing agent, carrying hydrogen atoms essential for reducing carbon compounds and facilitating the formation of ATP and carbohydrates. NADP⁺ and ATP are also crucial for nitrogen assimilation during photosynthesis, leading to the synthesis of amino acids. Nitrogen, assimilated as nitrates and nitrites dissolved in the crude sap, is transported to plant tissues. Similarly, sulfur, obtained from sulfates and sulfites, is fixed to form the sulfhydryl (-SH) group of amino acids like cysteine. This process of incorporating bioelements, including phosphorus, into organic molecules is fundamental for plant life.

Carbon Fixation in the Dark Phase (Fig. 12, p. 184)

The fixation of carbon from CO₂ follows a cyclic pathway known... Continue reading "Photosynthesis Dark Reactions: Carbon & Nitrogen Assimilation" »

Nervous vs. Endocrine System Coordination

Living organisms utilize different systems for coordination. These include:

• Nervous System: Receives information and processes it for a fast response. It utilizes nerve impulses, and its effects are generally short-lasting.
• Endocrine System: Elaborates hormones for communication. Its response is typically very slow but durable.

Nervous System Response Pathway

The nervous system's response to stimuli involves several key components:

Receptor, Center, and Effector

• Receptor: The organ or structure responsible for perceiving stimuli from the internal or external environment.
• Nervous Center: Receives information from receptors and transmits processed information, producing a series of organized responses.
• Effector: