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

Bryophyte Nutrition

Bryophytes have no true tissues or organs such as roots, stems, or leaves. Nutrients pass directly from cell to cell by diffusion or active transport. Bryophytes require permanently moist environments for transport. Their structure is not equivalent to higher plants; mosses and liverworts have a false root, or rhizoid, which serves only for attachment, and leaf-like structures where photosynthesis occurs. They do not possess true stems, and their cells lack lignin, meaning the plant has no conducting or support systems. Nutrients move very slowly. Because they lack roots to absorb water and conducting tissues to transport it, they must absorb water directly from the air through their photosynthetic areas.

Cormophyte Nutrition

Cormophytes... Continue reading "Plant Nutrient Acquisition: Bryophyte and Cormophyte Strategies" »

Fundamentals of Genetics and Heredity

Deoxyribonucleic Acid (DNA)

DNA is the inherited material that carries genetic information in all living organisms, passed down from generation to generation. A DNA molecule is composed of nucleic acid nucleotides.

Nucleotides are formed by three essential components:

• A phosphate group.
• A pentagonal ring sugar (Deoxyribose).
• A nucleobase (nitrogenous base).

In DNA, there are four basic types of nitrogenous bases: Cytosine (C), Guanine (G), Thymine (T), and Adenine (A).

DNA Replication: Ensuring Genetic Continuity

The information contained within the sequence of DNA bases is the foundation of inheritance for every species. This information must be transmitted intact from cell to cell to ensure the continuity of that... Continue reading "DNA, Genes, and Chromosomes: Core Concepts of Heredity" »

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

Digestive Tract Diseases

Dental Health and Caries

Dental caries is an infectious disease caused by bacteria that affects the hard tissues of teeth. Bacteria feed on carbohydrates in the mouth and produce acids that cause cavities in teeth.

Constipation

Constipation is a disorder that hinders the evacuation of the stool. It is due to the excessive absorption of water by the intestine, which causes a dry, hard stool.

Ulcers

Ulcers are open sores on the inner walls of the digestive tract; they occur in the stomach and duodenum.

Gastroenteritis

Gastroenteritis is an inflammation of the membranes lining the inner stomach and intestine. It is due to an infection caused by viruses or bacteria.

Cirrhosis

Cirrhosis is a chronic disease that involves the progressive... Continue reading "Common Digestive and Respiratory System Disorders" »

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.

Invertebrate Chordates: Defining Characteristics

Invertebrate chordates possess several key features, including:

• A notochord
• A dorsal hollow nerve cord
• Gill slits (present at some point in development)
• Muscle blocks (present at some point in development)

They also exhibit fundamental characteristics shared by many complex animals:

• Bilateral symmetry
• A well-developed coelom
• Segmentation

The Notochord

The notochord is a long, semi-rigid, rod-like structure located between the digestive system and the dorsal hollow nerve cord.

• Invertebrate chordates retain this feature throughout life.
• In vertebrates, it is replaced by a backbone during development.
• It develops just after gastrulation from mesoderm tissue on what becomes the dorsal side of the embryo.
• The support

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" »