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

The Cell Theory

Cells were observed for the first time by Robert Hooke in 1665, in a slide of cork, where, by means of a microscope, he saw something similar to a hive. That's why he called these structures cells (cellula is a Latin word meaning "small room").

In 1838, two German scientists, botanist Matthias Schleiden and zoologist Theodor Schwann, stated the Cell Theory, which can be synthesized in the following tenets:

• All living things are made up of one or more cells.
• A cell is the smallest and simplest living thing.
• In a multicellular organism, cells keep their own activity, although a coordination among them occurs.
• All cells can only arise from pre-existing cells. (That idea was added later on by Rudolf Virchow. Originally, Schleiden and

Reproduction and the Biological Life Cycle

Reproduction is the biological function through which progenitor individuals give rise to new individuals similar to them, known as descendants.

Types of Reproduction

There are two primary types of reproduction:

• Asexual Reproduction: Involves a single individual or parent, from which new individuals are formed that are identical to them. This is present in algae, protozoa, fungi, and some plants.
• Sexual Reproduction: Usually involves two parents: one male and one female. The resulting individuals possess characteristics from both parents. This is present in multicellular organisms.

The Biological Life Cycle

The life cycle or biological cycle is the set of stages that an organism goes through during its life,...

Properties of Enzymes as Biological Catalysts

An enzyme is a biocatalyst biologically synthesized by the body whose chemical composition is wholly or partially composed of protein. These biocatalysts are substances that are not consumed in the chemical reactions they facilitate; they work by lowering the activation energy, thus increasing the speed of the reaction.

The Mechanism of Enzyme Action

In general, the mechanism of enzyme action always takes place with the substrate binding, forming an intermediate enzyme complex (or enzyme-substrate complex) between them, without which the chemical reaction cannot take place. The enzymatic reaction can be symbolized as follows:

The substrate is any substance or molecule that acts as a reagent in the enzymatic...

The Internal Environment and Homeostasis

The internal environment is the set of fluids surrounding the cells of the body. From this environment, cells extract nutrients and oxygen, and into it, they discharge metabolic waste and CO₂.

Components of the Internal Environment

In humans, the internal environment consists of:

• Blood: A fluid that acts as a transport for various substances and travels through the blood vessels.
• Interstitial Fluid: A fluid with defensive and nutritive functions that lies between the cells. It arises from blood filtered by the capillaries.
• Lymph: The fluid found in the lymphatic vessels, which originates from interstitial plasma.

System Organization and Regulation

The operation and organization of the body depend on homeostasis,...

Function and Response Relationship

Allows beings to perceive changes in the external or internal cause of responses. This process consists of:

• Perception of the stimulus
• Analysis of the information
• Production of a response

The Sense of Sight (Vision)

Through this sense, we perceive shapes, colors, sizes, and distances. The organ is the eye. To work, light enters the eye through the pupil, which is controlled by the iris. From there, it reaches the lens, which acts like a focusing mechanism, projecting the image onto the retina. The retina contains photoreceptors called rods and cones. These translate the light into a nerve impulse that passes through the optic nerve to the brain.

The Sense of Hearing (Audition)

Through this sense, we perceive the intensity,...

Cellular Division

• Cellular Division: A mother cell produces two daughter cells.
• Cellular Interphase: The time period between the end of cell division and the beginning of the next.
• Cell Division Stages: Meiosis, mitosis, and cytokinesis.
• Meiosis: A process where the nucleus divides through two successive stages, resulting in four cells with half the chromosomes of the original cell. This process is used to form eggs and sperm.
• Cytokinesis: The division of the cytoplasm and organelles.

Mitosis Phases

• Prophase: Centrioles duplicate and move toward the poles of the cell; mitotic spindle fibers appear.
• Metaphase: Chromosomes align at the equatorial plate, attached to spindle fibers.
• Anaphase: Spindle fibers shorten, pulling chromosomes toward the cell poles.

Cellular Nutrition and Energy Transformation

Cellular nutrition is the set of processes by which cells incorporate and transform matter and energy from their environment. This function includes the exchange of substances through the membrane, the chemical transformations of molecules, and the excretion of waste products. Nutrition builds new structures or repairs existing ones, providing the energy required for all cellular activities.

Transport Without Membrane Deformation

Substances are exchanged in two primary ways. In transport without membrane deformation, gases like oxygen and small molecules like water pass through the membrane via simple diffusion. This is the movement of particles from an area of higher concentration to an area of lower...

Human Excretory System and Kidney Function

Excretion is the process of eliminating waste substances resulting from cell metabolism from the blood.

Components of the Urinary System

• Kidneys: Two organs located in the rear of the abdominal cavity on both sides of the spine.
• Urinary tract: The ducts that carry urine from the kidneys to the outside of the body.

Other Excretory Organs

Besides the urinary system, other organs involved in excretion include the lungs, liver, and sweat glands.

The Nephron and Urine Formation

Nephrons are the functional units responsible for filtering and purifying blood to produce urine. The parts of a nephron include:

• Malpighian glomerulus
• Bowman's capsule
• Renal tubule
• Collecting duct

Urine is formed in two main stages: filtration

Arthropod Characteristics and Classification

Arthropods live in all environments, and there are more than a million different species. They exhibit bilateral symmetry, and their bodies are divided into the head, abdomen, and thorax. In some cases, the head and thorax are united to form a cephalothorax.

• Anatomy: They possess two antennae, eyes (which can be simple ocelli or compound), and buccal mouthparts.
• Appendages: They have jointed appendages.
• Exoskeleton: Their body is made of jointed exoskeleton parts composed of a substance called chitin. The exoskeleton protects them and prevents the dehydration of their bodies.
• Diet: They can be carnivores, herbivores, or scavengers.
• Reproduction: They are usually oviparous with internal fertilization and

Understanding Mutation Rates

Gene mutations are linked to changes in the genes themselves. They originate at the DNA level, and changes can occur through the loss of a nucleotide, the disappearance of a nucleotide, or duplication.

Chromosomal Mutations

Also known as interchromosomal changes, these occur during cellular division. Types include:

• Deletion: The loss of one or more segments of chromosomes.
• Translocation: The exchange of genetic material between chromosome segments, causing pairing complications and genotypic changes.
• Inversion: An alteration in the gene sequence of the chromosomes.
• Duplication: The repetition of a part of a chromosome.
• Changes in Chromosome Number: While humans typically have 46 chromosomes (44 autosomes and 2 sex chromosomes)