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

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" »

DNA Replication Process

DNA replicates just before cell division, ensuring daughter cells inherit the same genetic information as the stem cell. Genetic information is transmitted via genes. In general, each DNA strand serves as a template. Specific enzymes, known as DNA polymerases, join nucleotides one by one. A new chain is formed that is complementary to the template and identical to the chain that was previously attached to it. This process results in two double-stranded DNA molecules.

On occasion, errors occur during DNA replication that give rise to mutations. Some mutations can lead to certain types of diseases. The extraordinary importance of base complementarity allows DNA strands to be copied from a stem cell to a daughter cell, and... Continue reading "DNA Replication, Gene Expression, and Recombinant DNA" »

The Circulatory System: Heart, Blood, and Vessels

The circulatory system is a vital network responsible for transporting blood throughout the body, delivering essential substances to cells, and removing waste products. It primarily consists of the heart, blood vessels, and blood.

Blood Composition

Blood is a complex fluid composed of two main parts:

• Plasma: The liquid component, primarily water, containing dissolved salts, proteins, lipids, glucose, and urea.
• Blood Cells: Various types of cells suspended in the plasma.

Blood Cells

The main types of blood cells include:

• Red Blood Cells (Erythrocytes): The most abundant cells, non-nucleated, containing the red pigment hemoglobin, which is crucial for transporting oxygen (O2).
• White Blood Cells (Leukocytes)

Autoclave (Moist Heat Sterilization)

The autoclave is a device used in hospitals for moist heat sterilization. It effectively destroys spores, fungi, bacteria, and viruses. It maintains a temperature of 120 ºC for 15 to 30 minutes, depending on the size and nature of the load.

Autoclave Components and Operation

The autoclave features a reservoir with thick stainless steel walls and a tight-fitting lid. Key components include:

• A pressure gauge indicating the internal pressure and temperature.
• A safety valve that opens automatically if the pressure reaches a dangerous level, preventing explosion.
• A bleed valve (or purge valve) through which steam is released.
• A tank containing water up to a certain level, which is heated by electric heat, gas, or other

Infectious and Parasitic Diseases

Prion Diseases

Caused by infectious agents called prions (proteins with a configuration different from the normal protein). Prions are transmitted to other proteins, affecting adjacent organs. Example: Bovine Spongiform Encephalopathy (BSE), commonly known as Mad Cow Disease.

Viral Diseases

Caused by acellular virus particles. Viruses consist of a nucleic acid (DNA or RNA) surrounded by a protein envelope. They self-replicate using the machinery of the infected cell. Treatment is often complicated.

Examples include: Yellow fever, Influenza A, Hepatitis, Mumps, AIDS, and Measles.

Bacterial Diseases

Caused by bacteria, which are unicellular living beings classified as prokaryotes (lacking a defined nucleus). While many... Continue reading "Classification of Human Diseases: Etiology and Examples" »

Prokaryotes and Eukaryotes

Prokaryotes are small, simple cells with their genetic material dispersed throughout the cytoplasm. Eukaryotes are larger, more complex cells with their genetic material contained within a structure called the nucleus, separated from the cytoplasm by a membrane called the nuclear membrane.

• Animal Cell: Found in protozoa and animals.
• Plant Cell: Found in algae and plants.

Photosynthesis

Photosynthesis is the process by which organisms synthesize energy-rich organic molecules, such as glucose, from inorganic substances lacking energy. Sunlight provides the necessary energy. Photosynthesis occurs in leaves and green stems and takes place within chloroplasts.

Formula: H₂O + CO₂ + sunlight = Mineral salts = Glucose + O₂

Cellular

Cellular Digestion: Monomers, Polymers, and Enzymes

Cells may absorb simple molecules (monomers). Monomers are scarce in nature. Typically, there are large molecules (polymers), where hundreds or thousands of simple molecules are joined together, forming foods. Digestion is a process where digestive enzymes break down the bonds between monomers, releasing free monomers. Digestive enzymes are specific to each polymer.

For example, amylase breaks down the links between glucose molecules in starch. Lipase separates fatty acids from glycerol in fats. Proteases break the links between amino acids in proteins, releasing them. The digestive system is essentially a tube. Food undergoes a series of transformations during its journey.

These actions are... Continue reading "Cellular Digestion: Monomers, Polymers, and Digestive Enzymes" »

Regulation of Gene Expression

Cells do not continuously synthesize proteins, which could result in metabolic chaos. There must be a regulation. Jacob and Monod devised a model for gene regulation in bacteria called Operon. An operon is a set of genes on the chromosome, fairly close together, that encode proteins involved in related metabolic processes. In each operon, there are two classes of genes:

• Structural genes

  (z, A) that code for the synthesis of proteins in a given process.

• Regulator gene

  (I) that codes for the synthesis of a repressor protein, which controls the expression of structural genes.

There are also two regions close to these genes whose base sequences influence regulation:

• The promoter (P)

  Next to the structural genes, this is the

The Human Heart: Anatomy and Function

The heart is an organ about the size of a fist, located in the center of the chest, slightly to the left. It is comprised of two atria and two ventricles. Blood enters the atria through the veins and is driven out of the ventricles through the arteries. The heart has valves that force the blood to circulate in one direction.

The Heartbeat

The beating of the heart is the most noticeable manifestation of its activity. The frequency with which the heart beats varies according to the body's needs. Every heartbeat follows a set of phenomena that constitute a cardiac cycle:

• Atrial systole: The atria contract and push blood into the ventricles.
• Ventricular systole: The ventricles contract, and blood leaves through