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

The Building Blocks of Life: DNA and Nucleic Acids

DNA (Deoxyribonucleic Acid) is the main component of genetic material in most organisms. Together with RNA (Ribonucleic Acid), it forms the genetic material for some viruses. Both DNA and RNA belong to a group of molecules called nucleic acids.

Nucleotides: The Basic Units

Nucleotides are the smaller molecules that, when linked together in a repeating pattern, form the structure of nucleic acids like DNA.

The Structure of DNA

DNA has a super-compact, coiled form that allows it to fit inside cells. This coiled structure is organized into bodies called chromosomes.

Location of DNA in Cells

• Prokaryotes: The DNA is located in the cytoplasm.
• Eukaryotes: The DNA is found within the cell nucleus.

The Core

Asexual Reproduction in Cormophytes

Asexual reproduction in cormophytes involves specific vegetative organs such as stolons, rhizomes, tubers, and bulbs.

• Runners: These are side branches emerging from the base of the stems with horizontal growth. Roots emit buds, giving rise to new independent individuals.
• Rhizomes: Underground stems that grow horizontally in the soil and accumulate reserve substances. Ground stems can emerge from buds, eventually taking root and separating from the main rhizome.
• Tubers: Very enlarged underground stems that store food. They can be separated from the main plant to form separate plants.
• Bulbs: Underground stems that are more or less spherical, with fleshy, layered storage. Smaller bulbs are often formed with buds

Charles Darwin and the Theory of Evolution

Charles Robert Darwin (February 12, 1809 - April 19, 1882) was an English naturalist who postulated that all species of life have evolved over time from a common ancestor through a process called natural selection. The outcome was accepted as fact by the scientific community and much of the public in his lifetime, while his theory of evolution by natural selection was not seen as the primary explanation of the evolutionary process until 1930 and now forms the basis of modern evolutionary synthesis. In modified form, the scientific discoveries of Darwin are still the foundational pillar of biology as a science, since they constitute a logical explanation that unifies the observations on the diversity... Continue reading "Darwin's Evolutionary Theory: Core Concepts and Principles" »

Cellular Metabolism and Aerobic Respiration ATP Yield

The metabolism includes all chemical transformations and energy changes that occur in living beings. Each of these transformations requires the participation of an enzyme; enzymes themselves may be modified as products of other reactions, including protein synthesis.

Enzymes biological catalysts

Enzyme classes include:

• Hydrolases
• Lyases
• Transferases
• Isomerases
• Oxidoreductases
• Synthetases

Vitamins essential for metabolism

Vitamins are essential biomolecules for metabolism. They include:

• Water-soluble: complex B and vitamin C
• Fat-soluble: vitamins A, D, E, K

Aerobic respiration: stages

Stage 1: Glucose to acetyl-CoA

Glucose to acetyl-CoA. Glucose is converted to pyruvate and then to acetyl-CoA.

Stage 2: Krebs

As a result of cephalocaudal and lateral folding, a portion of the yolk sac lined by endoderm is incorporated into the embryo to form the primitive gut. The primitive gut is divided into three parts: foregut, midgut, and hindgut. The midgut communicates with the yolk sac through the temporary omphalomesenteric duct.

Foregut Development

It extends from the oropharyngeal membrane to the second portion of the duodenum (ampulla of Vater).

Esophagus Formation

Its primordium arises from the tracheoesophageal septum around the 4th week. The endoderm proliferates to temporarily occlude the lumen. At the end of the embryonic period, the lumen recanalizes, and the endoderm differentiates into stratified squamous epithelium. The muscle of the upper 1/3 is... Continue reading "Digestive System Embryology" »

Understanding Plant Biology: Structure, Function, and Diversity

Autotrophs and Photosynthesis

Plants are autotrophic organisms, meaning they produce their own food. They are typically fixed in place and do not move actively. Their characteristic green color is due to a vital substance called chlorophyll.

Photosynthesis: This fundamental process allows plants to harness sunlight as energy. Chlorophyll captures this solar energy, enabling plants to produce organic substances from inorganic compounds absorbed from their environment (like water and minerals).

Plant Anatomy: Vegetative and Reproductive Organs

Vegetative Organs

The vegetative body of plants consists of specialized organs essential for growth and survival:

• Root: This part grows into the

Prenatal development is divided into two main periods: the embryonic period, which occurs during the first 2 months, and the fetal period, which follows. The embryonic period begins in the oviduct with the segmentation of the zygote. This involves successive mitotic divisions that produce 2 cells, called blastomeres, approximately 36 hours after fertilization. These cells then divide into 4, then 8, then 16, and so on, forming a morula.

About 5 days after fertilization, the morula transforms into a hollow, spherical structure called the blastocyst. The blastocyst consists of a cavity and two sets of cells: trophoblast cells (or the outer cell mass) and the embryoblast (the inner cell mass). After 7 days, the trophoblast attaches to the endometrium... Continue reading "Prenatal Development: Embryonic and Fetal Stages" »

Desenvolvemento Embrionario Inicial

Implantación e Primeiras Etapas

A implantación no endometrio ocorre de forma temperá. Unha vez implantado, o embrión continúa crecendo e desenvolvéndose.

Formación do Sistema Nervioso e Órganos

Prodúcese a formación inicial do sistema nervioso. Arredor dos tres meses, o embrión convértese nun feto e os seus órganos comezan a funcionar.

Reprodución Humana Asistida: Técnicas

Inseminación Artificial

A inseminación artificial consiste en introducir artificialmente o esperma no tracto reprodutor feminino.

Fecundación In Vitro (FIV)

A fecundación in vitro (FIV) consiste en fecundar o óvulo co esperma fóra do corpo, no laboratorio. O termo in vitro fai referencia ao uso de material de laboratorio, como... Continue reading "Embrións, Reprodución Asistida e Células Nai" »

Adrenal Cortex Secretion Control

Control of secretion by the adrenal cortex is regulated by the hypothalamic-pituitary axis. Various other mechanisms also influence the release of adrenal cortical hormones.

Negative Feedback and ACTH Regulation

The regulation of ACTH secretion involves a negative feedback mechanism centered on cortisol and its derivative, cortisone. An increase in cortisol levels inhibits ACTH secretion, while a drop stimulates it. Furthermore, an excess of cortisol leads to a decrease in Corticotropin-Releasing Factor (CRF).

Circadian Rhythm of Cortical Hormones

The levels of adrenal cortical hormones depend on circadian rhythms and can be influenced by certain drugs. Cortisol exhibits a marked circadian rhythm, reaching its highest

The Digestive System

Role of Digestion

During the process of digestion, food is broken down. The broken molecules can then be used by cells.

Digestive Tract Structure

The digestive tract is a duct, a 9-meter long pipe through which food passes, extending from the mouth to the anus.

Glands: Glands pour their juices into the tube. The main glands are the salivary glands, liver, and pancreas.

Food is transported by a wave of contraction and relaxation called peristaltic movements.

Layers of the Digestive System

Internal or Mucosal Layer: This layer secretes digestive juices and mucus, protecting the surface. Nutrients are absorbed through this layer.

Muscularis: This layer consists of involuntary muscle fibers that contract. The anal sphincter muscles... Continue reading "How Your Body Processes Food and Air" »