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

Cellular Biology

Synthesis of Cell Theory

• Each living organism is made up of one or more cells (structural unit).
• The smallest living organisms are single cells, and cells are structural units of multicellular organisms.
• All cells come from preexisting cells (the source drive).

Forms of bacteria:

• Bacilli
• Coccobacilli
• Vibrio
• Spirochetes / Spirilla

Prokaryotic and Eukaryotic Cells

Prokaryotic Cells: Are those that have no internal membranes or an organized nucleus (bacteria).

Eukaryotic Cells: They have internal membranes and an organized nucleus.

Difference Between Animal and Plant Cells

Plasma membrane: Structure that separates the intracellular from the extracellular... Continue reading "Cellular Biology: Prokaryotic and Eukaryotic Cells" »

Microbiology: The Science of Microorganisms

Microbiology, derived from the Greek words mikros ("small"), bios ("life"), and logos ("study"), is the scientific discipline dedicated to the study of microorganisms. These are living things too small to be seen with the naked eye. Microorganisms, often called germs, were discovered over 300 years ago. Their only common characteristic is their small size.

Microscopy depends on factors such as contrast, resolution, and magnification.

Taxonomy involves the study of nomenclature, classification, and identification of microorganisms.

Factors Influencing Microbial Growth

The number and types of microorganisms in an environment depend on factors like humidity, heat, nutrient availability, aeration, and pH.

• Soil

Genetic Transcription Process

TRANSCRIPTION: The process of copying a part of the genetic message from its original form (DNA) to another (RNA) that can be used directly for protein synthesis.

Transcription forms a strand of RNA whose sequence is complementary to the DNA template strand. Consequently, its sequence is the same as the non-template DNA strand (with uracil replacing thymine).

Transcription requires:

• A DNA strand serving as template
• Ribonucleotide triphosphates
• Enzymes (primarily RNA polymerase)

Stages of Transcription

Initiation

The RNA polymerase recognizes specific short sequences of nitrogenous bases (promoter) to which it binds. RNA polymerase opens the DNA double helix to allow incorporation of ribonucleotides.

Elongation

Addition of... Continue reading "Understanding Genetic Transcription & Code" »

Plant Anatomy: Roots, Stems, and Leaves

Root Structure

The root has a simple structure with no central bone. It contains vascular tissue in the phloem and wood beams, along with fundamental bark tissue. The endodermis clearly demarcates these areas. Two meristems are present: the cambium, which forms a ring of dividing cells between the phloem and wood, and the phellogen, which develops in the cortical parenchyma. The phellogen produces corky tissue layers for protection and cortical parenchyma internally.

Stem Structure

Stem structure differs between dicotyledonous and monocotyledonous plants. In dicots, vascular tissue forms a cylinder with the xylem inside and phloem outside. Fundamental tissue is located between the epidermis and vascular tissue... Continue reading "Plant Root, Stem, and Leaf Anatomy: Structure and Function" »

Internal Environment: The Body's Inner Sea

The internal environment refers to the set of fluids that surround the cells of an organism. From these fluids, cells extract the nutrients and oxygen they need.

Key Components of the Internal Environment

• Interstitial Fluid: This fluid, also known as tissue fluid, performs defensive and nutritive functions, remaining between the cells.
• Blood: Responsible for the transport of substances, blood circulates through blood vessels.
• Lymph: A fluid formed from plasma and interstitial fluid, lymph flows through lymphatic vessels.

The Blood Circulatory System

The blood circulatory system distributes nutrients and oxygen throughout the body while collecting waste products of cell metabolism.

Blood Vessels: Pathways of

Meiosis: The Key to Genetic Diversity

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four daughter cells with unique genetic information. This genetic diversity arises from the exchange of genetic material between homologous chromatids. Meiosis occurs in two successive divisions, meiosis I and meiosis II, separated by interphases. Importantly, DNA replication does not occur during the interphase between meiosis I and meiosis II.

Meiosis I: Reduction Division and Genetic Recombination

The first meiotic division is characterized by genetic recombination and a reduction in chromosome number. It consists of four stages:

Prophase I: The Longest and Most Complex Stage

Prophase I is the longest stage... Continue reading "Understanding Meiosis: Stages, Processes, and Genetic Diversity" »

Optics: Lenses, Mirrors, and the Eye

An optical lens is a system comprising two or more refractive surfaces, of which at least one is curved.

Types of Lenses

• Convex or Converging Lenses: Thicker in the center, causing rays to converge.
• Concave or Diverging Lenses: Thinner in the central part, causing rays to diverge.

Specific Lens Shapes

• Convex Lenses: Convex, plano-convex, meniscus-convex
• Concave Lenses: Concave, plano-concave, concave meniscus

Image Formation by Convex Lenses

• If s0 > 2f: Real, inverted, smaller image.
• If s0 = 2f: Real, inverted, same size image.
• If 2f > s0 > f: Real, inverted, larger image.
• If s0 = f: No sharp image formed (image at infinity).
• If s0 < f: Virtual, upright, magnified image (magnifying glass).

Image Formation

Reproduction of Human Beings

It is comprised of the following processes:

• The production of gametes: In specialized reproductive organs.
• Fertilization: Is the union of two gametes within the female reproductive system, forming a single cell, the zygote.
• Zygote development: Inside the female reproductive system.
• Birth: A fully formed baby is born.

Development to Sexual Maturity

Changes from infancy to sexual maturity:

• Primary sexual characters: Are present at birth. These are the sexual organs: the penis in boys, and the vulva and excretory system in girls.
• Secondary sexual characters (Puberty):
  • In children: Deep voice, beard, pubic and underarm hair, increased bone and muscle mass.
  • In girls: High voice, growth of breasts and hips, and pubic and underarm

Siphonaptera (Fleas)

Fleas have three pairs of legs, a segmented body, and are 0.5 to 4 mm in size. They can jump 33 times their size. Ctenidia are hairs on their body. The female spermatheca is where the eggs are stored. They have a complete or holometabolous life cycle. The adult lays eggs, and in three weeks, the larvae emerge. In 9-15 days, the pupa stage is reached, and then the adult. Males and females feed on blood. The larvae feed on the feces of the adult fleas. The pupa is covered with earth and is motionless until the temperature changes.

• Pulex irritans (Human flea)
• Ctenocephalides canis (Dog flea)
• Ctenocephalides felis (Cat flea)
• Xenopsylla cheopis (Rat flea)
• Tunga penetrans: The female introduces itself inside the skin, producing a wound

Electron Transport Chain

Cytochrome P-450 - NADH cytochrome reductase: This enzyme facilitates the hydroxylation of many substrates. Therefore, it is important in the synthesis of steroid hormones and detoxification processes. Cytochrome b5 - cytochrome b5 reductase NADF4: These endoplasmic reticulum (ER) membrane proteins exhibit asymmetry, with one face oriented towards the hyaloplasm and the other towards the lumen. Carbohydrates are attached to lipids and proteins facing the luminal side.

Synthesis of Exportable Proteins (Rough Endoplasmic Reticulum)

The cell synthesizes proteins that either remain within the cell or are exported to other locations. These locations can be extracellular, as products of secretion, or intracellular. Protein synthesis... Continue reading "Endoplasmic Reticulum: Protein and Lipid Synthesis" »