Notes, summaries, assignments, exams, and exercises for Biology for Secondary education

The Cell: Fundamental Unit of Life

All living organisms are formed by cells, which remain the functional and structural unit of life. Cells are capable of performing three vital functions: relationship, nutrition, and reproduction. Every cell contains three basic structures: the plasma membrane, the nucleus, and the cytoplasm.

Cellular Morphology

• Disc-shaped: Such as red blood cells.
• Binocular: Prism-shaped.
• Spindle: Spindle-shaped.
• Stellate: Star-shaped.
• Irregular: Various distinct shapes.

When many cells unite, they form a tissue, such as skin.

Biological Tissues

• Integumentary: Protective tissue on the outside of the body.
• Mucous: Tissue protecting internal cavities.
• Adipose: Reserve tissue that stores fat.
• Bone: Supporting tissue.
• Glandular: Secretory

Vital Functions of Living Things

Living things eat, breathe, and release waste products. We perceive and respond to changes in the environment, grow, and reproduce. These are known as vital functions.

Nutrition and Respiration

• Food and nutrition: We incorporate substances from the environment through feeding. Upon reaching the cells, substances are transformed by chemical reactions into energy and matter; this process is called nutrition.
• Breathing: We obtain the energy contained in ingested food through respiration.
• Release of waste products: As a result of respiration and food processing, toxic substances occur if they accumulate. Excretion is the process by which these waste substances are expelled to the exterior. The main products are carbon

Understanding Sensory Receptors

Receptors are specialized structures that convert environmental stimuli into nerve impulses. They are crucial for our interaction with the world, translating various forms of energy into signals our brain can interpret.

What are Receptors?

Receptors are categorized based on their location and the type of energy they react to:

• Location-based Classification:
  • Exteroceptors: Located on the body surface, they detect external stimuli (e.g., touch, temperature, light, sound).
  • Interoceptors: Located internally, they detect internal stimuli (e.g., blood pressure, body temperature, pain).
• Energy-based Classification:
  • Mechanoreceptors: Respond to mechanical stimuli like pressure, touch, vibration, and stretch.
  • Chemoreceptors: Detect

Cellular Organelles

• Mitochondria: Oval-shaped organelles with a double membrane. They provide the energy necessary for cell function.
• Vacuoles: Membranous vesicles that store water, reserve substances, or waste products.
• Lysosomes: Membranous vesicles that break down complex substances into simpler molecules for cellular use.
• Cytoskeleton: A network of filaments distributed throughout the cytoplasm. It forms the cell's skeleton and facilitates movement.
• Centrioles: Two hollow cylinders formed by filaments that direct the movement of the cytoskeleton.
• Golgi Apparatus: Stacks of flattened membranous sacs surrounded by vesicles. It packages substances manufactured in the reticulum and manages cellular secretion.
• Endoplasmic Reticulum: A network of sacs

The Structure and Function of DNA

DNA is a molecule that stores information about all the features inherited from parent to offspring and, therefore, is hereditary or genetic material. DNA is formed by the union of several smaller units called nucleotides. Nucleotides are joined one after the other, forming a chain. DNA is made up of two opposing lines joined together by nitrogenous bases that are paired. The string is wound in the form of a spiral, forming a double helix.

The sequence or order in which the nucleotides are arranged in the DNA chain constitutes the genetic information. DNA has a unique property among the molecules of living things: it can duplicate itself, i.e., generate identical copies of itself. This allows the transmission...

Fundamental Genetics Terminology

• Homologous Chromosomes: The two members of a pair of chromosomes that are physically identical in shape, length, and centromere position. In organisms that reproduce sexually, each parent contributes a member of the pair; the counterpart is called the homolog.
• Gene: The unit of inheritance. Gene pairs are located in corresponding positions on homologous chromosomes, with each member of the pair known as an allele.
• Alleles: Genes located at the same locus on a pair of homologous chromosomes. Alleles interact to determine a particular trait and are usually designated by pairs of letters, where each letter represents a particular character.
• Recessive: Refers to a character that is expressed only in its homozygous state.

Understanding Human Sexuality

Human sexuality encompasses three fundamental aspects:

• Biological: The physiological and anatomical differences between sexes.
• Spiritual: The emotional and relational dimensions of sexuality.
• Socio-cultural: How society and culture shape sexual norms and behaviors.

Biological Foundations of Sex

The differentiation between the two sexes begins at the cellular level. In a zygote, if the 23rd pair of chromosomes has the characteristics XY, the individual is male; if XX, the individual is female. From that moment, primary sexual characteristics (reproductive organs) begin to form. At puberty, secondary sexual characteristics develop due to hormone production, leading to changes in body shape, voice tone, and hair growth....

Annexes to the Eye

• Eyebrows: Folds of skin covered in hair that direct sweat away from the eyes and protect them from direct sunlight.
• Eyelids: Skin folds that move reflexively to protect the eye from small foreign bodies. At the edges of the two eyelids are Meibomian glands, which prevent the eyelids from sticking together.
• Eyelashes: Associated with small sebaceous glands, they act jointly with the eyelids for protection.
• Stye: An infection of the eyelashes.
• Conjunctiva: A very thin and transparent membrane located below the eyelid and above the eyeball.
• Conjunctivitis: Inflammation of the conjunctiva.
• Lacrimal gland: Produces and sheds tears into the conjunctiva.
• Tear ducts: These remove excess liquid and carry it to the nostrils.
• Lacrimal secretion:

Understanding Nutrients and Cellular Energy

Food consists of a mixture of organic and inorganic molecules called nutrients, which provide energy and matter to our cells.

Essential Nutrient Categories

• Carbohydrates: Sugar, pasta, bread, rice.
• Lipids: Vegetable and animal fats, butter, peanuts, walnuts.
• Proteins: Meats, legumes, milk.
• Vitamins: Fruits, vegetables, milk.
• Minerals: Table salt, fruits, vegetables, milk.
• Water: Primarily found in fruits and vegetables.

Nutrient Functions

• Carbohydrates: Provide immediate energy to the cell.
• Lipids: Serve as energy reserves for the cell.
• Proteins: Form cellular structures and participate in immune defense.
• Vitamins: Regulate enzyme functioning.
• Minerals: Participate in physiological activities like bone and tooth

Metabolic Pathways in Biology

Glycolysis

Consists of a series of chemical reactions in the process of respiration that leads to the transformation of glucose into pyruvic acid.

Krebs Cycle

Includes a series of reactions starting from when acetyl groups are converted into citric acid, and then, by a sequence of reactions, water originates.

Electron Transport Chain

Includes a series of reactions between various substances, during which the electrons are gradually losing energy, so that upon reaching the last element of the chain, they are at a low energy level.

Calvin Cycle

It operates in the dark phase of photosynthesis, specifically in the stroma of chloroplasts. It is named after Dr. Melvin Calvin, who won a Nobel Prize in 1962 for determining the...