Notes, summaries, assignments, exams, and problems for Biology

The Immune System: Body's Defense Mechanisms

The body's defense mechanisms protect us against various pathogens such as viruses, bacteria, fungi, protozoa, extraneous cellular tissue introduced from outside (e.g., in transplantation), and cells transformed into malignant or cancerous forms. The set of biological structures that enable specific defense against these agents constitutes the immune system, and all such defense mechanisms provide immunity. The science of studying the immune system is called immunology.

Types of Immunity: The Body's Defense Lines

The body has three lines of defense against microbial attacks:

• First Line: External Barriers

  These prevent microorganisms from entering the body.

• Second Line: Non-Specific Internal Defenses

  These

Topic 2: Fruit Propagation Techniques

Importance of a Quality Plant Nursery

A good plant nursery is key to the success of an orchard, ensuring plants possess the desired characteristics of size, age, conformation, and health.

Nursery Establishment Criteria

A fruit nursery must be located in areas with good accessibility and suitable weather conditions. The soil must have abundant organic matter.

Fundamental Propagation Types

Sexual Reproduction (Seed Propagation)

This method uses seeds, which are zygotic embryos.

Advantages:

• Produces vigorous plants.
• Plants produced are generally free from viral diseases.

Disadvantages:

• Lack of uniformity in the produced plants.

Apomictic Reproduction

This involves asexual propagation using an asexual seed embryo (e.g.,... Continue reading "Effective Fruit Propagation Methods & Nursery Success" »

What are Plant Hormones?

Plants require light, carbon dioxide, water, and minerals, including nitrogen, for growth. Utilizing energy from the sun, they produce much of their own substance, transforming simple materials into complex organic compounds. Hormones play a crucial role in regulating plant growth and development by stimulating or inhibiting specific processes. Among the most important internal factors are plant hormones. By definition, hormones are substances produced in one tissue and transported to another, where they exert highly specific effects.

Types of Plant Hormones

Among the many plant hormones identified, the best known are auxins, cytokinins, gibberellins, abscisic acid, and ethylene.

Auxins

Auxins are a group of plant hormones... Continue reading "Plant Hormones: Types, Functions, and Effects on Growth" »

Cellular Biology: Functions, Nutrition, and Systems

All living things are composed of cells. In multicellular organisms, cells consist of a plasma membrane, nucleus, cytoplasm, and organelles. Cells perform vital functions necessary for life: nutrition, relationships, and reproduction. In multicellular beings, cells are grouped into tissues, tissues into organs, organs into systems, and finally, all these form a complete living being.

Internal Environment and Homeostasis

The internal environment is regulated by homeostatic mechanisms, which are controlled by the brain. Nutrients from the digestive tract are broken down into simpler substances that are absorbed into the animal's internal environment. Aquatic animals obtain oxygen dissolved in water,... Continue reading "Cellular Biology: Functions, Nutrition, and Systems Explained" »

Cytoplasm

The cytoplasm is located just after the plasma membrane. Its components are mostly water, which acts as a solvent, and proteins that function as enzymes.

Chloroplasts

Chloroplasts produce nutrients from the sun's radiant energy through photosynthesis. They have two membranes: an outer and an inner smooth one. The inner membrane has folds called lamellae, which are located in the grana.

Mitochondria

Mitochondria oxidize food through cellular respiration and store the released energy. They are surrounded by two membranes: a smooth external surface and internal folds or ridges.

Endoplasmic Reticulum

The endoplasmic reticulum has a membrane structure that connects easily with the membrane of the nucleus and has compartments called cisterns.... Continue reading "Cellular Components and Transport Mechanisms" »

How the Human Body Perceives and Reacts

Humans constantly interact with their environment. This interaction is facilitated by complex relational functions.

These functions are carried out through three main types of components:

• Receivers
• Controllers
• Effectors

Receivers: Our Sensory Organs

Receivers are our sensory organs. They capture what happens outside or inside the body and send this information to the control center.

Controllers: The Nervous System

Controllers are the organs of the nervous system.

The Brain (Cerebrum)

Located within the cranium, the brain receives information from receptors, interprets and relates it, prepares response commands, stores information in memory, and coordinates all the body's organs.

The Spinal Cord

Situated within the... Continue reading "The Human Body's Sensory and Response Systems" »

Blood

Blood is a viscous, red fluid that circulates inside the blood vessels.

An adult usually has about five liters of blood, representing 8% of their body mass. Blood volume varies with age, sex, height, and weight.

Functions of Blood

• Nutrition: Transports nutrients from the digestive system to all body cells.
• Respiration: Carries oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs.
• Excretion: Collects waste products produced by cells and transports them to the excretory system for elimination.
• Defense: Carries the body's defense cells.
• Thermoregulation: Participates in the regulation of body temperature, heating or cooling.

Composition of Blood

Plasma

Plasma is a yellowish liquid, up to 90% water. It contains a variety... Continue reading "Understanding the Circulatory System: Blood, Heart, and Components" »

Understanding Vision: How the Eye Works

Light enters the eye, passing through to the retina where it stimulates specialized photoreceptor cells: the rods and cones. The amount of light is regulated; the pupil adjusts its size, and blinking provides protection. Too much light can potentially damage cells, while insufficient light prevents stimulation.

Focusing is achieved by the lens, which changes shape (bulges or stretches) to project a clear image onto the retina. This image is actually formed inverted, but our brain interprets it correctly.

Human vision is stereoscopic, meaning we perceive depth and 3 dimensions. This is possible because our brain processes and combines the slightly different images captured by each of our two eyes.

The Human

Bright Cyclic Electron Flow

The electrons freed after reaching ferredoxin are passed to plastoquinone and follow the electron transport chain to return to the plastocyanin and photosystem I.

Nucleic Acids

Nucleic acids are macromolecules composed of repeating polymers of monomers called nucleotides linked by phosphodiester bonds.

Types of Nucleic Acids

• The sugar (pentose) present: deoxyribose in DNA and ribose in RNA.
• The nitrogen-containing bases: adenine, guanine, cytosine, and thymine in DNA; adenine, guanine, cytosine, and uracil in RNA.
• In eukaryotes, DNA has a double-stranded structure, while RNA is typically single-stranded. RNA can occur in extended form, such as mRNA, or in folded form, such as tRNA and rRNA.
• The molecular mass of DNA is generally

Photosynthesis: Energy from Sunlight

Photosynthesis is the process by which organisms, typically plants, create energy-rich organic substances from inorganic substances, using sunlight as an energy source.

Photosynthesis Reaction and Phases

It is an anabolic process that takes place in chloroplasts. In this process, water, carbon dioxide, and minerals are transformed into organic compounds (glucose).

For photosynthesis to occur, it requires an energy source from sunlight. This light energy is captured by a pigment present in chloroplasts, called chlorophyll. The general equation is:

CO₂ + H₂O + Light Energy + Minerals → Glucose + O₂

Photosynthesis has two main phases:

• Light-dependent phase: Energy captured from the sun is converted into chemical