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

Population Autoregulation

A population is constituted by a set of individuals of the same species living in a given location. Environmental resistance is a set of factors that prevent a population from reaching its maximum biotic potential. These factors include:

• External factors: These may be biotic (predators, parasites) or abiotic (climate change, food shortages, disasters, etc.).
• Internal factors: Increasing population density adversely affects individuals.

There are two forms of reproduction strategies:

• r strategists: These are simple organisms with very high biotic potential. They have many offspring with no parental care. Consequently, only a few manage to survive and reach adulthood. The population size remains relatively stationary (e.g.

Industrial Composting Processes

Compost is created through a biological process, relying on aerobic fermentation (with air). This technique ensures hygienic processing of organic waste into a homogeneous substance easily assimilated by the soil. The process involves a microbial population, including bacteria, actinomycetes, and fungi (responsible for 95% of the activity), as well as algae, protozoa, and cyanophytes.

Suitable Organic Materials for Composting

• Plants from the garden or orchard
• Adventitious herbs or "weeds" (before they seed)
• Poultry manure and bedding
• Lawn clippings (in thin, dried layers)
• Organic food remains
• Napkins and tissues (unprinted and uncolored)
• Haircuts (undyed)
• Raw wool or old mattresses (in small, mixed layers)
• Wine, vinegar,

The Human Ear: Structure and Function

The ear is the organ that allows us to capture sound, which consists of vibrations and waves. Audition has two essential characteristics: intensity and tone. Intensity depends on the amplitude of the sound waves, and tone depends on the number of waves received per second.

Parts of the Ear

• External Ear: Includes the pinna (or auricle) and the external auditory canal. The pinna captures sound vibrations, which are then transmitted to the middle ear. The auditory canal contains ceruminous glands that produce wax for protection, hygiene, and cleanliness.
• Middle Ear: Starts with the tympanic membrane (eardrum), which vibrates upon receiving sound waves. These vibrations are transmitted to the ossicles (three small

Mutated Acetylcholine Receptors and Muscle Function

If a child is born with a mutated acetylcholine receptor in a muscle cell, the depolarization of the muscle cell membrane will not be initiated, resulting in no intracellular calcium release.

Excitation-Contraction Coupling Mechanism

Excitation-contraction coupling occurs because intracellular calcium is released, allowing myosin to bind to actin, which in turn permits the shortening of myofibrils.

Impact of Spinal Cord Ventral Horn Damage

Damage to the medial ganglion of the ventral horns of the spinal cord primarily affects the movement of the limbs.

Effect of Intracellular Calcium Depletion in Muscle

If intracellular calcium is removed from a muscle fiber, it blocks the excitation-contraction... Continue reading "Neuroscience & Muscle Physiology: Core Concepts Explained" »

Proteins and Gene Expression

• Activator: A DNA-binding protein that positively regulates the expression of one or more genes, i.e., the rate of transcription increases when an activator is bound to DNA. It is a positive modulator.
• Aminoacyl-tRNA Synthetase: Allosteric enzymes that catalyze the synthesis of aminoacyl-tRNA at the expense of ATP energy.
• Attenuation/Attenuator: An RNA sequence involved in the regulation of the expression of certain genes. The terminator functions in transcription.
• Inductor: A signal molecule that, when coupled with a regulatory protein, produces an increase in the expression of a particular gene.
• Leucine Zipper: A structural protein motif involved in protein-protein interactions in many eukaryotic regulatory proteins.

Animal Coordination: Nervous and Endocrine Systems

Stimuli are transmitted to focal points. Animals have two systems for coordinating information received through sensory receptors: the nervous system, which transmits electrical signals through nerves, and the endocrine system, which sends chemical signals through the blood. Both systems produce responses to stimuli that are transmitted to effector organs (muscles or glands), thereby regulating the organism's activity at all times.

The Nervous System

The nervous system is the control center and coordinating agency.

Function: To gather information from various receptors, interpret it, generate responses, and transmit these responses to other parts of the body to inform them of what action to take.... Continue reading "Animal Nervous and Endocrine Systems: Coordination Explained" »

Understanding Cellular Genetic Information

The Genetic Code and Protein Synthesis

The information contained in messenger RNA (mRNA) must be read and translated in the ribosomes. This information is interpreted using the genetic code, which is determined by the sequence of nitrogenous bases. A sequence of three nucleotide bases, known as a codon, carries specific information for a particular amino acid.

DNA Packaging: Chromatin and Chromosomes

Chromatin is the functional form of DNA within the nucleus. In this uncondensed state, DNA's information can be read to produce messenger RNA copies, which are then transported to the cell's cytoplasm for ribosomes to translate into corresponding proteins. DNA in chromatin is found associated with proteins... Continue reading "Decoding DNA: Genetic Code, Chromosomes, and the Human Genome" »

Androecium

The androecium is the male reproductive part of a flower. It is composed of stamens, each consisting of a filament and a capsule called the anther. Inside the anther are a series of chambers called pollen sacs, where pollen grains (male gametes) are formed.

Gynoecium

The gynoecium is the female reproductive part of a plant. It consists of carpels, which are sets of fused leaves that form a cavity where the ovules reside. The carpels are called the pistil. The bottom part of the pistil is the ovary (containing the eggs), the middle part is the style, and the top part is the stigma.

Types of Pollination

• Self-Pollination

  Self-pollination occurs when pollen from the same flower or from different flowers on the same plant fertilizes the ovules.

Punctuated Equilibrium

The fossil record, while incomplete, reveals periods of stability punctuated by the sudden appearance of new species. These species often remain unchanged for extended periods before disappearing abruptly. In 1972, Gould and Eldredge proposed punctuated equilibrium to explain these sudden shifts, suggesting that not all evolutionary changes are gradual. Periods of stasis, where species remain unchanged, alternate with short bursts of rapid change (speciation), during which new species emerge from existing ones.

Gradualism vs. Punctuated Equilibrium

Gradualism

Species evolve along a single lineage, transforming slowly and continuously through small changes over long periods. The entire population transforms, not just isolated... Continue reading "Evolution: Gradualism vs. Punctuated Equilibrium" »