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

DNA Structure and Function

DNA is a large molecule formed by the union of simpler molecules called nucleotides. The nucleotides correspond to the links of a long chain and consist of:

• A molecule of phosphoric acid
• A carbohydrate called deoxyribose
• A nitrogenous base (adenine (A), guanine (G), cytosine (C), or thymine (T))

The DNA sequence is the order of DNA nucleotides. Each DNA molecule is composed of two long chains of nucleotides coiled up in a double helix. The two strands are chemically complementary. This is because the nitrogenous bases are joined and locked inside the double helix, with specific pairings: (A = T), (T = A), (C = G), and (G = C).

DNA Replication

The DNA molecule is the only molecule in living beings that can make an exact copy... Continue reading "DNA Structure, Replication, and Biotechnology" »

The Human Digestive System: Key Organs and Functions

The Small Intestine

The small intestine is a vital part of the digestive system, measuring approximately 6.5 meters in length with a diameter of about 3 cm. It is highly convoluted and its interior walls are covered with numerous folds and microscopic projections called villi, significantly increasing its surface area for absorption. There are approximately 3,000 villi per square centimeter. The inner layer of the small intestine also contains intestinal glands that secrete digestive enzymes.

The small intestine is divided into three main sections:

• Duodenum: The first and shortest section, where most chemical digestion occurs as it receives digestive fluids from the pancreas and liver.
• Jejunum:

The Human Digestive System

The digestive process begins in the **mouth**. The first processes are chewing, conducted by teeth (*incisors, canines, molars, and premolars*), and salivation, managed by a muscular organ called the tongue. The **tongue** moves food during chewing and contains **taste buds** for sensing flavor. During salivation, food is broken down by teeth and moistened by **saliva**, a watery secretion produced by the **salivary glands**. Saliva production can be triggered by the sight or smell of food. Saliva contains **mucin**, which gives it viscosity, and enzymes such as **salivary amylase** and **lingual lipase** (which hydrolyzes milk fat).

The ground food and saliva form the **bolus**, which is pushed into the **esophagus*... Continue reading "Human Digestive and Respiratory Systems: A Detailed Look" »

The Male Reproductive System and Gametes

• Testicles: Glands in the scrotum that produce sperm.
• Prostate Gland: A walnut-sized gland surrounding the urethra. It produces a prostatic fluid that protects the sperm against the acidity of the urethra and vagina.
• Ductus Deferens (Vas Deferens): Tubes that are a continuation of the epididymis and converge in the urethra.
• Seminal Vesicles: Glands that produce seminal fluid, in which sperm swim. This fluid empties into the ductus deferens.
• Urethra: Duct that communicates with the outside. Its muscular walls contract rhythmically during ejaculation, propelling the sperm.
• Epididymis: A long, very thin, coiled tube located on each testicle. Sperm mature inside it.
• Penis: A cylindrical organ, whose widened end,

The Female Reproductive Cycle

The reproductive cycle in girls begins at puberty and ends at menopause, which is when reproductive capacity ceases. In this cycle, two main phases are distinguished: the ovarian cycle and the uterine or menstrual cycle.

The Ovarian Cycle

The ovarian cycle typically lasts 28 days. It develops in two stages and is only interrupted by pregnancy.

• Follicular Growth and Maturation

  This stage is characterized by the maturation of a follicle containing an egg. In the middle of the cycle, the Graafian follicle ruptures on the ovary wall, releasing the egg into the fallopian tube in a process known as ovulation. The oocyte is then conveyed towards the uterus.

• Corpus Luteum Formation

  After ovulation, the ruptured follicle fills

Phases of Infectious Diseases

All infectious illnesses typically follow three phases:

• Incubation: The time that elapses between infection and the appearance of disease symptoms.
• Overt Disease: Symptoms and signs of the disease are clear.
• Convalescence: The phase when the pathogens are completely eliminated. The body recovers lost health and repairs damage.

Prevention of Infectious Diseases

Prevention involves two main approaches:

• Following healthy lifestyle habits.
• Vaccination: The introduction of killed or weakened microorganisms into a healthy person's body, prompting the immune system to produce antibodies against the specific disease.

Treating Infectious Diseases

Treatment often involves chemotherapy, which is the use of chemical substances. There... Continue reading "Infectious & Non-Infectious Diseases: Phases & Treatments" »

Ecological Factors

Characteristics of the environment that affect all living things, can be abiotic or biotic. Abiotic are the physical and chemical conditions that influence living beings. Biotic are those who share the same environment.

Limiting Factor

The factor closest to the value at which an organism cannot thrive.

Adaptation

The evolutionary adaptation of organisms to a given environment.

Eurioic Organisms

Organisms that have a wide tolerance to changes in their environment.

Stenoic Organisms

Organisms that have a narrow margin of tolerance to changes in their environment.

Adaptations to Water Scarcity

• Water stored in tissues
• Drought-resistant seeds
• Large and deep roots
• Small plants with hard leaves born in spring
• Resistant structures to desiccation
• Low

Immunological Terms

• Vector Transmission: A DNA molecule used to transfer a particular gene or a specific DNA sequence to another cell.
• Reservoir: A deposit, such as a straight one developed by surgeons, once the rectum has been removed due to disease.
• Phagocyte: A cell capable of surrounding, engulfing, and digesting microorganisms, foreign matter, old cells, and cellular debris, which it covers with its pseudopodia and then digests in the cytoplasm.
• Lymphocyte: A type of leukocyte (white blood cell) included within the agranulocytes.
• Antigen: Antigens are usually proteins or polysaccharides.
• Antibody: Antibodies are glycoproteins of the gamma globulin type. The soluble form can be found in the blood or other bodily fluids of vertebrates.

Infectious

Action Potential: Cellular Electrical Signals

An action potential is a rapid, transient electrical potential change that occurs exclusively in excitable cells, such as neurons and muscle cells. It is fundamental for transmitting information throughout the nervous system and initiating muscle contraction.

Neuron Operation and Signal Transmission

In neurons, excitation typically originates in the dendrites or soma (cell body), and this electrical information is then transmitted along the axon. Many axons are covered with Schwann cells, forming a myelin sheath that allows for faster signal propagation (myelination). It's important to distinguish that when referring to nerve fibers, we mean axons, whereas muscle fibers refer to muscle cells.

Schwann... Continue reading "The Physiology of Excitable Cells: Action Potentials and Muscle Structure" »

Reproduction and Growth

The hypothalamus is responsible for synthesizing sex steroids. The whole process is triggered by environmental sexual stimuli. Hormones are similar. There are invertebrate males and females.

Growth in vertebrates is dependent on growth hormone released by the adenohypophysis.

The exoskeleton of crustaceans limits their growth. In this case, the juvenile hormone (JH) is synthesized at a low rate to allow the organ to synthesize molting hormone (ecdysone) at higher concentrations for the molt to take place. This happens when they reach sexual maturity and to allow copulation, once the old exoskeleton is clear (allows gonadal development). Once removed, large amounts of JH are re-synthesized to build a new exoskeleton. Regeneration... Continue reading "Animal Reproduction, Growth, and Activity: Key Factors" »