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

Human Sexual Reproduction

Sexual reproduction involves the union of two specialized cells (gametes), each from a different individual.

Gonads

These are the primary reproductive organs responsible for producing gametes and sex hormones.

Testes

The male gonads, two glands located outside the body within a sac called the scrotum.

Ovaries

The female gonads, responsible for secreting sex hormones and producing ova (eggs).

Puberty

The developmental stage when individuals acquire the ability to reproduce.

Primary Sexual Characteristics

These are the reproductive organs themselves. They contain the gonads, the organs necessary for fertilization, and in females, structures that house the embryo until it develops and is born.

Spermatogenesis

The process of formation...

Fundamental Ecological Definitions

Ecosystem

An Ecosystem is a particular area where environmental conditions allow the development of specific entities.

Biotope

The Biotope is the physical environment in which an ecosystem is established.

Biocenosis

The Biocenosis is the set of living beings that inhabit the biotope.

Abiotic Factors

Abiotic factors are all the non-living environmental factors of an ecosystem.

Classification of Abiotic Factors

• Aquatic Factors: Light, salinity, and pressure.
• Terrestrial Factors: Soil type, temperature, humidity, and lighting.

Specific Abiotic Components

• Climatic Factors: These are the most important factors for any organism's growth, including temperature and precipitation.
• Physical and Chemical Factors:
  • Light: A crucial factor

The Digestive System

The digestive system converts food into nutrients, absorbs them, and expels waste. Key glands involved include:

• Salivary Glands: Three types (sublingual, submandibular, and parotid) that keep the mouth moist, clean teeth, enhance taste, dissolve food, lubricate, and initiate digestion.
• Pancreas: Produces pancreatic juice and controls glucose levels via insulin.
• Liver: Manufactures and excretes bile, stores glucose, and regulates metabolic processes.

Digestion of Food

Digestion transforms food into absorbable nutrients through two processes:

• Mechanical: Reduces the size of food particles.
• Chemical: Breaks down molecules for easy intestinal absorption.

Food enters the stomach through the cardias valve. The intestinal mucosa releases...

Evidence for Biological Evolution

Fossils are the preserved remains of organisms that lived on Earth in the past. They demonstrate that many organisms that once existed are now extinct. The study of fossils reveals the process of change in living things over time.

Key Biological Concepts

• Homology: Structural similarities inherited by organisms, observed in both skeletons and body structures (homologous traits).
• Molecular Genetics: A discipline developed in the mid-twentieth century following the discovery of the DNA double helix. It provides compelling evidence for biological evolution.
• Mutations: Heritable changes in genetic material. Most are harmless, and rarely are they beneficial. If a mutation provides neither benefits nor harm, it is considered

The Fundamental Characteristics of Bacteria

Bacteria are prokaryotes. The absence of compartments separated by membranes means metabolites are disseminated throughout the cytoplasm. Despite this structural simplicity, bacteria are complex and diverse creatures from a biochemical viewpoint, which has enabled them to adapt to varied conditions.

Size and Structure

Most bacterial cells are very small: their volume is about one thousandth the size of the smallest eukaryotic cells. They are typically about 1 micrometer ($\mu$m) in diameter and 0.2 to 3-4 $\mu$m long. Most bacteria are unicellular organisms, but some form colonies or filaments, sometimes exhibiting cell specialization.

Basic Bacterial Shapes

Although many species have irregular shapes,...

DNA Viral Life Cycles

Not all viral life cycles are identical; variations occur depending on the type of infected cell (prokaryotic or eukaryotic) and the genetic material contained within the virus (DNA or RNA). Below is the general life cycle of a DNA virus:

1. Binding: Specific viral surface glycoproteins bind to receptors on the surface of the infected cell.
2. Entry: Membrane fusion occurs, and the viral nucleocapsid enters the cell.
3. Disassembly: The nucleocapsid disassembles. The viral DNA remains in the cytoplasm, and viral capsid proteins are degraded.
4. Replication: The viral DNA is replicated.
5. Transcription: The viral genome is transcribed to synthesize messenger RNA (mRNA).
6. Translation: mRNA is translated to synthesize viral capsid proteins and

Neo-Darwinism: Principles of Variation and Selection

Variability of Offspring

Organisms exhibit reproducibility. Asexual reproduction relies solely on mutations. In sexually reproducing organisms, variation is primarily generated by sexual recombination, which occurs during meiosis.

Mutations arise randomly and can be favorable, unfavorable, or neutral. They are preadaptive, meaning they occur before selection acts upon them. This inherent variability is the raw material upon which natural selection operates.

Core Tenets of Neo-Darwinism (The Modern Synthesis)

1. The evolutionary process is based on the Darwinian principles of variation in offspring and natural selection.
2. Offspring variability is due to genetic mutation and recombination. Mutations

Plasma Membrane: Structure and Function

The plasma membrane is a semipermeable, fluid, flexible, and selective membranous structure that surrounds the entire cell. It consists of a phospholipid bilayer (semipermeable), proteins (transport and structural), carbohydrates (cell communication), and cholesterol (structural). Its functions are to:

• Protect the cell
• Contain the cytoplasm and its organelles
• Maintain cell shape
• Establish communication between the cell and its environment
• Limit the cell
• Manage transport within the cell

Types of Transport

Passive Transport

Passive transport is a type of transport that does not require energy expenditure. However, it does require certain conditions.

a) Diffusion

Diffusion is the transport of substances through a semipermeable...

Nutrient Transport Vessels

The transport of nutrients in plants is managed by a system of carrying vessels. These vessels are formed by:

• Xylem: Composed of raw sap, it moves from the root to the top of the plant.
• Phloem: Formed by elaborated sap, it ranges from the upper part to the root of the plant.

Root Functions and Structure

Root Functions

1. Supports and fixes the plant to the ground.
2. Absorbs the nutrients needed for plant growth.
3. Stores and transports water throughout the plant.

Parts of the Root

The root is the part of the plant that grows into the center of the earth and sustains the plant.

• Collar: The part of the root located on the land surface; it is the area that joins the root to the stem.
• Main root: The primary root which holds the plant.
• Secondary

Characteristics of Plants

Plants are living things and multicellular eukaryotes (cells with nuclei). Plants have tissues formed by clusters of specialized cells that perform the same function. These associated tissues form their bodies. They are autotrophs that perform photosynthesis, since they produce their own organic matter from inorganic substances using light as an energy source. They are green because they contain chlorophyll and live fixed to the soil.

Evolution and Adaptation

We classify plants into those without flowers or seeds (mosses and ferns) and flowering plants with seeds (gymnosperms and angiosperms). All samples appeared some 500 million years ago, evolving from certain species of algae. They spread across the continents thanks...