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

The Origin of Life: Two Key Processes

1. Chemical Evolution

This process created the molecules that make up living things (biomolecules) and subsequently formed structures called protocells.

• Biomolecule Formation: Simple organic molecules originated from meteorites.
• Complexification: More complex biomolecules were created from simple molecules in the primordial soup (the first biomolecules on the planet).
• Protocell Formation: Protocells were formed when biomolecules became organized into hollow, spherical membranes containing proteins and nucleic acids.

2. Biological Evolution

This process led protocells to become different types of cells, resulting in all the organisms that have ever inhabited the Earth.

• Primitive Cells: Similar to prokaryotic cells,

Key Terms in Genetics

DNA: deoxyribonucleic acid, substance that carries genetic information in a cell.

Protein: organic compound that consists of long chains of molecules and is an essential part of living things.

Genetic code: set of instructions in a gene that tells a cell how to make a specific protein.

Genome: set of genes in an organism.

Genetic engineering: manipulation of genetic material to change the traits of an organism.

Biotechnology: biological techniques to create improved products for human consumption.

Genes and Their Role

Genes: are located in the chromosomes and are the basic unit of inheritance that carry genetic information. Genes consist of DNA, the molecule that gives cells and all organisms biological information.

Cell Cycle

The Human Respiratory System

Carbon dioxide production can be detected using an indicator, and the heat produced by respiration can be measured.

Thorax Anatomy

The lungs are located in the thorax, which is separated from the lower body by the diaphragm. These sponge-like organs are protected by the ribcage and surrounded by pleural membranes.

Breathing Mechanics

• Breathing in: Intercostal muscles and the diaphragm contract, increasing thorax volume. This decreases pressure, drawing air into the lungs.
• Breathing out: Intercostal muscles and the diaphragm relax, decreasing thorax volume, which forces air out.

Gas Exchange in Alveoli

Alveoli are specialized for gas exchange, facilitating the transfer of oxygen into the blood and carbon dioxide out of the...

Impulse Transmission in the Nervous System

Impulse / nervous system: The stimulus is received and a depolarization takes place in the neuron membrane. The impulse travels along the axon; many axons are insulated by a substance called myelin. When the impulse arrives at the end of the axon it has to cross a gap called the synaptic cleft. Synaptic vesicles fuse with the membrane and release neurotransmitters, which pass to the dendrite of the next neuron. The message then goes to the nervous system and finally to the effectors.

Protection of the Central Nervous System

Protection of the CNS: The brain and the spinal cord are surrounded by three membranes called the meninges and by a liquid called the cerebrospinal fluid (líquido encefalorraquídeo)...

Adaptation of the Alveoli

There are millions of alveoli (300-500 million in two lungs), providing a large surface area. There is a lot of blood around them. The wall is only one cell thick, so it is not difficult for gas to cross it.

Oxygen Transport and Destination

Oxygen travels through capillaries attached to the red blood cells to be transported to the respiring tissues. They form oxyhemoglobin by attaching to hemoglobin. It reaches all the body tissues.

Carbon Dioxide Production and Removal

It is produced in the respiring cells (in the mitochondria). It has to be removed. The carbon dioxide travels dissolved in the plasma.

Effects of Nicotine on the Body

Nicotine is a poisonous and addictive drug. It damages the heart, blood vessels, and nerves...

Human Body Structure: Classification and Composition

Firstly, human beings are classified within the animal kingdom, in the group of vertebrate animals because we have an internal skeleton and a spine. We are classified within the group of mammals because we are viviparous; we feed on our mother’s milk during the first stages of our lives.

Secondly, human beings are formed by cells; this is the most important characteristic of all living beings. Living things are classified into two different groups according to the number of cells that they have. These groups are unicellular beings and pluricellular beings.

Unicellular Organisms

They are formed by one single cell which performs all their vital functions. They are small, simple organisms such...

Heterotrophs and Nutrition

Heterotrophs are living beings which feed on organic matter produced by other living things. They transform this matter to obtain nutrients and energy.

The Process of Digestion

1. Ingestion: The intake of food into the body through the mouth.
2. Digestion: The transformation of food into nutrients which the body can absorb. There are two types:
   • Intracellular digestion: Takes place inside the cells of single and primitive multicellular organisms.
   • Extracellular digestion: Takes place inside the digestive tube and not in individual cells.
   The transformation of food is both mechanical and chemical.
3. Absorption: The passage of nutrients from the digestive system into the blood. The blood carries the nutrients to the cells.
4. Egestion: The

What Is Embryonic Development?

Embryonic development includes the processes from the formation of the zygote to the birth of the new individual. After fertilization, the zygote undergoes many cellular changes and becomes a developing organism, called an embryo. Depending on the species, embryonic development takes place in three main ways:

Viviparous Development

• The embryo develops inside the female body where it receives nourishment and protection.
• In this case, the embryo grows inside an organ in the abdomen, called the uterus.
• A special organ, called the placenta, feeds the embryo through the umbilical cord.
• Embryonic development ends with birth. This is typical of mammals.

Oviparous Development

• The embryo develops inside an egg, normally outside

Sperm and Egg Characteristics

Sperm are male gametes, representing highly specialized cells. These cells are small and mobile and consist of three parts:

• Head: The most voluminous part of the sperm. It contains the nucleus, with 23 chromosomes, and the acrosome, a cellular organelle that secretes substances that participate in the fertilization of the egg.
• Tail: Consists of a flagellum, a protein structure that allows the movement of the sperm.
• Neck: Lies between the head and tail. It contains numerous mitochondria around the base of the flagellum; these cellular organelles provide the energy needed to travel to the egg. It also contains a centriole, an organelle responsible for controlling movement.

Eggs have 23 chromosomes and have a very different...

Nervous System Actions: Reflexes and Voluntary Acts

Reflex acts are fast and automatic, and do not involve conscious brain processing. These acts occur when a quick response is needed.

Neurons Involved in Reflexes

• Sensory neurons: Come from the skin and their axons enter the spinal posterior roots.
• Interneurons: Synapse with sensory neurons and transmit nerve impulses to other neurons.
• Motor neurons: They leave the spinal cord by the anterior roots and reach muscles, causing contraction and reflex.

Voluntary acts are varied, changing, and more elaborate than reflexes, involving the cerebral cortex.

Autonomic Nervous System

Also called the involuntary nervous system, it is responsible for the proper regulation and coordination of internal organs.

Types