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

Plant Anatomy and Reproduction

The flower, which is responsible for reproduction, has a female part: the carpel, and a male part: the stamen. The female gametes (ovules) are produced in the ovary inside the carpel, while the male gametes are called pollen grains. Petals attract animals and protect the flower, while sepals cover and protect the other parts of the flower.

As a result of fertilization, a seed develops, which is responsible for the survival and dispersal of the plant.

3. Reproduction in Plants

Aquatic organisms often use water as a medium for transporting their gametes and for fertilization. On land, the vast majority of plants have developed mechanisms of reproduction that make their fertilization independent of water. Plants can...

Fundamentals of Genetics and Chromosomes

In humans, there are 46 chromosomes, occurring in 23 pairs. The diploid number refers to the total number of chromosomes in each body cell of a plant or animal.

Key Genetic Terms

• Gene: A length of DNA that is the code for making a specific protein molecule. Genes are always located in the same position on a chromosome.
• Allele: Different versions of the same gene.
  • A dominant allele is expressed and affects the appearance (phenotype) of the individual.
  • A recessive allele is only expressed if two copies are present or if the dominant allele is absent.
• Genotype: The specific combination of alleles an organism possesses for a trait.
  • Homozygous: Having two identical alleles for a trait (e.g., TT or tt).
  • Heterozygous:

1. Challenges in Human Genetic Studies

The study of human genetics entails specific challenges, including:

• Limited offspring: Human couples have very few offspring, making it difficult to apply statistical methods.
• Long biological cycle: The human life cycle is long (approximately 15 years), requiring several decades to track specific traits across generations.
• Ethical constraints: We cannot plan crosses for individuals to determine their genotype due to ethical reasons.

2. The Human Karyotype

• A karyotype is the complete set of chromosomes of a species, providing information about their number, type, and structure.
• Karyotypes are derived from karyograms, which are images of all chromosomes in an individual. By comparing a person's karyogram to the

DNA technology refers to laboratory techniques that allow combining DNA from different origins, even from different species, into a single DNA molecule. Typically, only a few genes are transferred to other cells.

Applications of DNA Technology

In Agriculture

DNA technology has already been applied to many plants, producing new varieties with improved characteristics:

Protection against certain pests: These plants manufacture proteins or substances that protect them from attack by insects, diseases, or viruses. Herbicide resistance: Crops are not affected by herbicides, allowing for easier weed removal. Improved food characteristics: Producing foods with better characteristics or that are healthier. Increased tolerance to adverse conditions: Obtaining...

Nervous System Information Processing

The nervous system receives, interprets, prepares a response, sends orders, and coordinates the functioning of the organs. It also performs mental and intellectual functions and is responsible for emotions and feelings.

Neurons and Synapses

Neurons are specialized cells throughout our bodies that have lost the ability to reproduce. The synapse generates and transmits impulses. When a neuron is stimulated, an electrical change occurs in the membrane, transmitting signals from the axon shaft to the dendrites.

Central Nervous System (CNS)

The CNS is composed of the brain (including the spinal bulb, brain stem, cerebrum, and cerebellum) and the spinal cord. It is protected by the meninges, cerebrospinal fluid, and...

The Epidermal Tissue System: Protective Layers

The epidermal tissue system consists of tegumentary tissues that provide protection. These include the epidermis of young plants and the periderm, found only in plants with secondary growth. This layer eventually forms the suber or cork.

1. Epidermis

In herbaceous plants, the protective tissue is reduced to the epidermis, which includes a single layer of cells. In stems and leaves, these cells secrete a protective cover called the cuticle. This waterproof layer protects these organs and defends against external agents. Some epidermal cells differentiate into trichomes or hairs.

2. Periderm

The periderm is a tissue composed of many layers of cells formed under the epidermis, which also serves a protective...

The Nervous System

The nervous system is responsible for processing information and coordinating responses throughout the body.

Nerve Centers

These centers process the information that reaches the sensory organs and elaborate answers.

The Brain

The brain is located in the head, protected by the skull bones. It has an oval shape. It consists of three main parts: the cerebrum, the cerebellum, and the brainstem.

The Spinal Cord

The spinal cord is a long cord that runs inside the backbone. It is connected directly to the brain.

The Cerebellum

The cerebellum is one of the parts of the encephalon, along with the cerebrum and brainstem. One of its most representative functions is to coordinate voluntary movements of the human body. The cerebellum integrates...

Theories on the Origin of Life

Panspermia Hypothesis

Life originated from spores traveling through space from one planetary system to another.

Prebiotic Synthesis Hypothesis

Life emerged from organic molecules on Earth, which in turn formed from inorganic matter.

Oparin-Haldane Hypothesis (Prebiotic Synthesis)

In 1923, Oparin and Haldane proposed that simple organic molecules could form from gases present in the early atmosphere. This hypothesis is based on several key points:

• Millions of years ago, the planet had an atmosphere without oxygen.
• When the Earth's temperature decreased, water vapor condensed into clouds, resulting in rain and the formation of oceans.
• The energy from the sun and electric discharges caused inorganic compounds present in the

Cell Tissues: Structure and Function

A tissue is a group of embryonic cells that share a similar structure and are specialized to perform a specific function. There are four primary types of tissues in the human body:

Epithelial Tissues

Epithelial tissues line the outer surfaces and surround cavities and ducts inside the body. They are primarily categorized into two types:

Coating Epithelia

These epithelia protect outer surfaces and inner cavities and canals. Examples include the epidermis (the outermost layer of skin), mucous membranes that line internal cavities (such as the mouth), and the endothelium (which forms the innermost layer of blood vessels).

Glandular Epithelia

Consisting of cells grouped into structures called glands, these epithelia...

Levels of Biological Organization

Living matter is organized into distinct levels, categorized as abiotic or biotic:

• Abiotic: Components that do not conform to living matter, such as inert substances.
• Biotic: Components exclusive to living organisms.

Hierarchy of Living Matter

• Subatomic: Particles and atoms.
• Atom: The smallest portion of a chemical element.
• Molecular: Molecules formed by the joining of two or more atoms.
• Macromolecules: Resulting from the binding of many molecules to form a polymer.
• Supramolecular Complexes: Aggregations of macromolecules.
• Subcellular Structures: Union of different supramolecular complexes, resulting in the cell's structure with characteristic functions.
• Cells: Comprised of various organelles and structures. (Biotic Level)