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

Darwin’s Theory of Evolution

Darwin’s theory posits that the world is not static; it is constantly changing. The process of change is gradual and continuous, and similar organisms are related and descended from a common ancestor. Evolutionary change is the result of natural selection.

The Mechanism of Natural Selection

Darwin explained natural selection through the following principles:

• In any population, individuals have variations, which are produced randomly.
• In the fight for existence, only the fittest survive.

Darwin’s explanation for this fact is that, when resources are limited, individuals in a population must compete for them. In this fight for existence, only those with favourable variants survive, as they are best adapted to the... Continue reading "Principles of Evolutionary Biology and Natural Selection" »

Describe the sources, targets, and primary effects of the hormones of calcium metabolism

The parathyroid gland is the hormone that affects Ca2+ concentration. When Ca2+ concentration is too low in the plasma, the parathyroid hormone secretion is stimulated, and vice versa. This parathyroid hormone can have several effects. It can send a signal to the bones and the osteoblasts will break down and more Ca2+ enters the blood. It can also stimulate the formation of 1,25 (OH)₂D to reabsorb Ca2+ in the intestines and kidneys so less Ca2+ is excreted, it also increases the excretion of phosphate ions. It also stimulates the reabsorption of Ca2+ in the GI tract. Calcitonin is a peptide hormone secreted by parafollicular cells in the thyroid gland. Calcitonin... Continue reading "Hormones of Calcium Metabolism and Stress Response Pathways" »

Infectious Diseases

Pathogenic Bacteria and Associated Diseases

Compare and contrast the morphological characteristics of various pathogenic bacteria given below and explore their role in human diseases.

• Bacillus anthracis: Anthrax
• Clostridium botulinum: Botulism
• Clostridium tetani: Tetanus
• Corynebacterium diphtheriae: Diphtheria
• Haemophilus influenzae: Influenza (flu); Bacterial Meningitis
• Mycobacterium tuberculosis: TB (Tuberculosis)
• Neisseria gonorrhoeae: Gonorrhea
• Salmonella Typhi: Typhoid Fever
• Shigella Dysenteriae: Dysentery
• Staphylococcus aureus: Boils and Pimples
• Streptococcus pneumoniae: Pneumonia
• Streptococcus pyogenes: Strep Throat; Scarlet Fever; Rheumatic Fever

Microbiology Concepts and Tests

Hemolytic Activity

Describe how hemolytic activity is... Continue reading "Key Pathogenic Bacteria and Tests" »

The Endocrine System Explained

The endocrine system consists of a coordinated group of glands known as endocrine glands. They are termed endocrine (endo meaning internal) because they release hormones directly into the bloodstream.

Hormones are organic molecules responsible for the regulation, control, and coordination of organs to ensure they function correctly as a unified system. Although all hormones reach all body tissues, each hormone acts only on specific cells, known as target cells.

Nervous System vs. Endocrine System

• Nervous System: Information is transmitted via nerve impulses (electrical signals). The action is fast and short-lived.
• Endocrine System: Information is transmitted via chemical substances. The action is slower but lasts longer.

Pollination and Fertilization in Plants

Pollination is the mechanism to achieve the objective of transferring pollen grains, shed from the anther, to the stigma of a pistil. This transfer is termed pollination.

Kinds of Pollination

Depending on the source of pollen, pollination can be divided into three types:

• Autogamy
• Geitonogamy
• Xenogamy

Double Fertilization

After entering one of the synergids, the pollen tube releases two male gametes into the cytoplasm of the synergid. One of the male gametes moves towards the egg cell and fuses with its nucleus, thus completing the syngamy. This results in the formation of a diploid cell, the zygote. The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce... Continue reading "Pollination, Fertilization, and Reproduction in Plants and Humans" »

Biology Study Guide

Cellular Biology and Genetics

Cell Growth and Reproduction

Benign vs. Malignant Tumors

Benign tumors are characterized by slow growth, non-invasive behavior, and the absence of metastasis. Malignant tumors, on the other hand, exhibit rapid growth, invasiveness, and the ability to spread to other parts of the body through a process called metastasis.

Cancer Terminology

A carcinogen is a substance that can cause cancer. Genetics is the study of genes and their inheritance patterns. Inheritance refers to the transmission of genetic information from parents to offspring. Alleles are alternative versions of a gene. A homozygous individual has two identical alleles for a particular gene, while a heterozygous individual has two different... Continue reading "Biology Study Guide: Key Concepts and Definitions" »

Human Circulatory System: Double Circulation

The human circulatory system performs double circulation, meaning that the blood passes through the heart twice in order to complete a full circuit. The two loops are completely separate from one another, which prevents the mixing of deoxygenated blood.

• Blood passes through the lungs.
• All the organs receive blood that is equally rich in oxygen and nutrients.

Right Half of the Heart

• Vena cavae carry blood back to the heart.
• Blood enters through the right atrium and moves to the right ventricle.
• Blood exits through the pulmonary artery and goes to the lungs.

Left Half of the Heart

• Pulmonary veins bring blood from the lungs to the heart.
• Blood enters through the left atrium and moves to the left ventricle.
• Blood

Cell Structure and Function

1. Cytoplasm

   The cytoplasm is the internal "soup" of the bacterial cell, bounded on the outside by the cell envelope. It is mostly water, but contains bacterial inclusions.

2. Cell Membrane

   The cell membrane protects the cell from its surroundings. It controls the movement of substances in and out of cells and consists of the phospholipid bilayer with embedded proteins.

3. Nucleus

   The nucleus is located in the very center of the cell and serves as the control center. It is made up of the nucleolus, chromosomes, and is surrounded by the nuclear envelope.

4. Nuclear Envelope

   The nuclear envelope surrounds the nucleus with a double membrane and multiple pores. The pores regulate the passage of macromolecules but permit free passage of

MENDEL’S LAWS OF INHERITANCE

During the mid-nineteenth century, significant progress was made in understanding inheritance. Gregor Mendel conducted hybridization experiments on garden peas for seven years (1856-1863) and proposed the laws of inheritance in living organisms. Mendel's investigations marked the first time statistical analysis and mathematical logic were applied to problems in biology. His experiments involved large sample sizes, enhancing the credibility of his collected data. The confirmation of his inferences through successive generations of test plants demonstrated that his results reflected general rules of inheritance rather than mere speculation.

Mendel studied characters in garden pea plants that exhibited two contrasting... Continue reading "Mendel's Laws of Inheritance: Understanding Genetics" »