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

Vision Development in Infants

The visual system is designed to capture light effects. The apparatus of global vision allows us to perceive images based on the amount of light reflected. Light enters through the cornea, passes through the pupil to the lens, and is then sent to the retina.

Developmental Milestones

• Newborn: Distinguishes between light and dark (chiaroscuro).
• 1 Month: Can stare at a large object.
• 2 Months: Can accommodate and converge their vision.
• 3 Months: Can follow a moving object by turning their head.
• 4 Months: Has a vertical and horizontal visual field of 180 degrees.
• 6 Months: Acquires eye-hand coordination.
• 8 Months: Examines objects with more detail.
• 12 Months: Acquires adult-like visual acuity.

Vision Disorders

Refractive Errors

• Myopia

1.2. Carbohydrates and Lipids: Concept, Classification, and Functions

Carbohydrates

Carbohydrates are biomolecules formed fundamentally by C, H, and O in the proportion C_nH_2nO_n. Hence, H and O are in the same proportion as in water (H₂O), also called hydrates of carbon. Carbohydrate molecules are chains formed by carbon atoms attached to radical groups and hydroxyl (OH) groups. There may be an alcoholic or a carbonyl group; this group may be an aldehyde (gluc aldose) or a ketone (gluc ketonic). For this reason, they are defined as polyhydroxyaldehydes or polyhydroxyketones.

Classification:

Carbohydrates are classified in two forms:

1. According to the functional group they possess:
   • Ketoses: if they have ketone groups.
   • Aldoses: if they have aldehyde groups.

Mitosis and Cytokinesis

Mitosis

Mitosis (discovered by botanist Eduard Strasburger) is a process of nuclear division exclusive to eukaryotes, ensuring the segregation and equal distribution of sister chromatids between the daughter cells during cell division.

Mitosis is an equational division that ensures the conservation of the genetic and chromosomal makeup of the species. Thus, mitosis of a parent cell yields two daughter cells with the same number of chromosomes and genetic information as the parent cell.

Mitosis can be structured into five phases: prophase, prometaphase, metaphase, anaphase, and telophase.

Prophase

During prophase, the following key changes occur:

• Chromatin Condensation: Chromatin condenses into visible chromosomes, each composed

Plant Parts & Functions

• Roots: Anchorage & Absorption

  Roots provide anchorage for the plant and are responsible for the absorption of water and nutrients from the soil.

• Stems: Support & Transport

  Stems hold the leaves, flowers, and fruits, providing structural support. They also transport fluids (water, nutrients, and sugars) throughout the plant.

• Leaves: Gas Exchange & Vital Processes

  Leaves are the primary sites for gas exchange, which is essential for processes like photosynthesis, transpiration, and respiration.

• Flowers: Reproduction

  Flowers are modified leaves specialized for reproduction. They contain the reproductive organs of the plant.

• Fruits: Seed Protection & Dispersal

  Fruits protect the seeds and facilitate their dissemination

Nutrient Transport and the Circulatory System

Once nutrients have been absorbed, the circulatory system is responsible for transporting them to the rest of the body's cells. In animals, the circulatory system varies from poorly developed to highly complex. In more developed animals, the system is composed of transport liquids, vessels, and a heart.

Transport Liquids (Connective Tissue)

The transport liquid is a connective tissue that circulates through the circulatory system. It is formed by water, minerals, proteins, cells, and various pigments, primarily responsible for transporting gases and nutrients. Types include:

• Hydrolymph (Echinoderms)

  Its composition is very similar to that of seawater. It transports nutrients and waste substances.

• Hemolymph

2. Genetic Engineering: Genetic engineering is defined as the set of technologies to manipulate the genetic material of a living being, i.e., modifying genes. This manipulation consists basically of: introducing new genes into a genome, removing existing genes from a genome, and modifying the information in a particular gene. The new genetic combinations are introduced into organisms capable of transmission to subsequent generations. It is also called recombinant DNA technology because most techniques rely on DNA fragments that recombine.

2.1. Genetic Engineering Tools To obtain new combinations of heritable material, you must use:

• 1. Restriction Enzymes: They are a type of protein that can recognize a specific DNA fragment and cut it. Using

Levels of Organization: These correspond to degrees of complexity in organized matter. The levels are: subatomic, atomic, molecular, cellular, tissue, system, organelle, and body.

Cell Structure: Eukaryotic cells possess several key elements:

• Plasma Membrane: A thin layer surrounding the cell, composed of proteins and lipids.
• Cytoplasm: An aqueous solution containing organelles.
• Nucleus: A spherical structure containing genetic material, formed by the nuclear membrane, nucleoplasm, chromatin, and the nucleolus.

The major organelles of eukaryotic cells include: mitochondria, endoplasmic reticulum, ribosomes, Golgi complex, vacuoles, lysosomes, and the centrosome.

Tissues: A tissue is a collection of similar cells with a very similar structure that... Continue reading "Biological Organization and Nutrition Fundamentals" »

Eukaryotes

The term Eukaryote comes from the Latin eu (good or true) and karyon (nucleus).

• These are cells possessing a true nucleus and a cell membrane. The DNA is contained within chromosomes inside the nucleus.
• They are generally large cells, ranging from 10 to 100 microns. While a few are unicellular or colonial, most form multicellular tissues.
• Reproduction is either asexual or sexual, with cell division occurring via mitosis. They possess a mitotic spindle or some form of microtubule-based organization.
• Eukaryotes are strictly aerobic for gas exchange with the environment, although some, like yeast, perform anaerobic fermentation.
• They feature cytoplasmic organelles, such as vacuoles, mitochondria, endoplasmic reticulum, and the Golgi apparatus.

Elements Involved

In order to perform the transcription of DNA into cells, the following elements are required:

• Original DNA to serve as a template to be copied.
• RNA polymerase: synthesizes RNA from a DNA template.
• Ribonucleotide triphosphates to perform the copy.
• Poly-A polymerase, small nuclear ribonucleoprotein, RNA ligase.

Transcription Mechanism

As in replication, there are differences between prokaryotes and eukaryotes. The main differences are the existence of multiple RNA polymerases in eukaryotes and, above all, the need to produce a "mature" form of some RNAs due to the existence of introns. The process is divided into three stages:

• Initiation: The RNA polymerase binds to a region of DNA prior to the DNA that is to be transcribed. It then

The Journey of Childbirth and Lactation

Understanding Childbirth

Stages of Labor and Delivery

Childbirth begins with labor, typically lasting around 12 hours, characterized by frequent uterine contractions that move the fetus towards the dilating cervix. If the amniotic sac ruptures, amniotic fluid exits through the vagina. The baby then passes through the cervix and vagina during birth, after which the umbilical cord is cut. The process concludes with the expulsion of the placenta and other membranes.

Hormonal Regulation of Childbirth

• Progesterone: This hormone remains in the uterus, maintaining pregnancy conditions, particularly by relaxing uterine walls and keeping the cervix closed.
• Estrogens: During pregnancy, estrogens stimulate the growth