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

Chromosomes and the Cell Cycle

Chromosomes undergo distinct changes throughout the cell cycle. Here's a summary of their states:

• Invisible Chromosomes (Chromatin) with One Chromatid: Initially, chromosomes exist as invisible chromatin fibers, each with a single chromatid.
• Formation of a Second Chromatid: A second chromatid is formed, creating a mirror image.
• Invisible Chromosomes (Chromatin) with Two Chromatids: Chromosomes remain as invisible chromatin but now consist of two chromatids.
• Condensation and Visibility: Condensation of the chromatids occurs, making the chromosomes visible.
• Visible Chromosomes with Two Chromatids: Chromosomes are now clearly visible, each composed of two chromatids.
• Separation of Chromatids: The two chromatids separate

Choroid: is black and is the iris diaphragm that determines the color of the pupil. The retina is the innermost layer, which contains photoreceptors. The axons of these neurons form the optic nerve, which leads to the two types of photoreceptors in the brain. There are rods, which are involved in vision when the light intensity is low, and cones, which are responsible for vision in high light intensity.

MECHANISM OF VISION: Light enters the pupil, hits the lens, and the retina forms an image that is equal to the real one but inverted. It is here where the image is converted into nerve signals that travel through the optic nerve to the brain, where we recognize the image.

ANATOMY OF THE NERVOUS SYSTEM

The nervous system consists of the central...

Types of Sensory Receptors

According to their function, sensory receptors are classified as follows:

• Chemoreceptors: Sensitive to chemical stimuli.
• Mechanoreceptors: Sensitive to mechanical stimuli such as friction and pressure.
• Photoreceptors: Light-sensitive receptors.
• Thermoreceptors: Sensitive to temperature variations.
• Nociceptors: Sensitive to intense pressure and responsible for pain.

Anatomy of the Eye and Ear

The Pupil: It controls the amount of light entering the eye. It contracts when there is a lot of light and dilates in low light.

The Retina: The retina forms an inverted image that is smaller than the real object. This image is captured by the photoreceptors.

Eustachian Tube: It connects the ear to the airways.

Semicircular Canals: Their...

Animal Feeding and Digestion

Animals are heterotrophs. They need to capture food to transform it into nutrients and utilize the energy and nutrients they contain.

The food enters the mouth and travels along the digestive tract: mouth, stomach, small intestine, large intestine, and anus.

The Process of Digestion

Digestion is the process by which the food ingested by a living being is transformed into simple molecules or nutrients that can reach the cells and be utilized. This occurs in two ways:

• Intracellular digestion: Occurs within the cell.
• Extracellular digestion: Occurs outside the cell.

Intracellular Digestion

This occurs in single-celled creatures such as protozoa. These protists use phagocytosis to trap food particles and form digestive vacuoles...

Types of Neurons

Depending on the number of extensions, neurons are classified into:

• Monopolar: Possess only one axon.
• Bipolar: Possess one axon and dendrites.
• Multipolar: Possess more than one axon and dendrite.

Glia Cells

Glia cells are the most abundant cells in the nervous system. Their primary functions are to support, protect, and nourish neurons. There are five main types:

Central Nervous System (CNS) Glia

• Astrocytes: Provide structural support and nutrients to neurons.
• Microglia: Act as macrophages to remove dead cell debris.
• Oligodendrocytes: Produce myelin sheaths covering CNS axons.
• Ependymal cells: Line the brain ventricles and spinal canal; they produce cerebrospinal fluid.

Peripheral Nervous System (PNS) Glia

• Schwann cells: Produce the myelin

Charles Darwin and the Theory of Evolution

Charles Robert Darwin (February 12, 1809 - April 19, 1882) was an English naturalist who postulated that all species of life have evolved over time from a common ancestor through a process called natural selection. The outcome was accepted as fact by the scientific community and much of the public in his lifetime, while his theory of evolution by natural selection was not seen as the primary explanation of the evolutionary process until 1930 and now forms the basis of modern evolutionary synthesis. In modified form, the scientific discoveries of Darwin are still the foundational pillar of biology as a science, since they constitute a logical explanation that unifies the observations on the diversity...

The Cardiac Cycle and Heartbeat Phases

• Diastole: Blood enters the right atrium of the heart through the vena cava and the left atrium through the pulmonary veins. The atria dilate while the mitral and tricuspid valves remain closed.
• Atrial Systole: The atria contract, opening the mitral and tricuspid valves, allowing blood to pass into the ventricles.
• Ventricular Diastole: The ventricles swell to receive blood from the atria. The semilunar valves remain closed, preventing blood from entering the arteries from the ventricles.
• Ventricular Systole: The ventricles contract, and the mitral and tricuspid valves close to prevent blood from flowing back into the atria.

Dual Circulation in the Human Body

Circulation is described as double because, during...

The Human Circulatory System

The interstitial fluid is the liquid found in the spaces between cells.

Blood is a viscous, salty liquid that runs inside the ducts of the circulatory system.

Blood Plasma

Blood plasma is a yellow liquid composed of water and various dissolved molecules.

Blood Cells and Platelets

• Red Blood Cells (Erythrocytes): These are the most numerous blood cells, with about 5 million present. They are disc-shaped, lack a nucleus, and contain hemoglobin, a red pigment responsible for the color of blood. Hemoglobin contains iron and carries oxygen from the lung alveoli to all body cells.
• White Blood Cells (Leukocytes): Found in the blood in smaller numbers than red blood cells, they defend the body against microbes. Types include:
  • Granulocytes:

The Role of Nutrition and Digestion

The role of nutrition: food digests (breaks it down into nutrients and undigested residues (feces)) and absorbs nutrients (from the digestive tract into the blood).

Functions of the Mouth

The mouth prevents food from falling out during chewing and allows us to suckle. The palate separates the mouth from the nasal passages and allows us to breathe while eating. It consists of the hard palate (anterior, formed by bone) and the soft palate (posterior, a membranous muscle formed by the uvula or 'bell' ending).

The tongue is a muscle on whose surface gustatory papillae are located. It detects the taste of food and moves food during chewing and swallowing.

The Small Intestine

The small intestine is a long tube that begins...

Ecosystems: An Overview

Ecology is the science that studies the characteristics of living beings, their environment, and the relationships they build with each other and their surroundings.

What is an Ecosystem?

An ecosystem consists of a fragment of the biosphere where living organisms interact and form relationships.

Biotope

The biotope is the physical environment or place where living things develop, including the environmental conditions that characterize it.

Biocenosis

Biocenosis refers to the set of living organisms within a given ecosystem.

The Biotope: Terrestrial and Aquatic Environments

The terrestrial environment is located on the surface of the continents, while the aquatic environment is made up of water.

Abiotic Factors

Abiotic factors are...