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

The Nephron

The nephron is the functional unit of the kidneys, responsible for filtering blood and producing urine. Each kidney contains over one million nephrons.

Parts of the Nephron

• Bowman's Capsule: Surrounds a tiny network of capillaries.
• Tubule: Shaped like a handle, the tubule of several nephrons empties into a larger tube called a collecting duct.
• Collecting Ducts: Move urine into the renal pelvis.

Kidney Function

1. Filtration: Molecules exit the bloodstream and enter the Bowman's capsule, forming filtrate.
2. Reabsorption: As filtrate travels through the tubule, some molecules are reabsorbed by the capillaries. Glucose, 99% of water, a small amount of urea, and salts return to the blood.
3. Excretion: The remaining filtrate forms urine, which is excreted

Degradation of Purine Nucleotides + 50. Synthesis of Uric Acid and Its Secretion. Hyperuricaemia (Gout) - p.298

Digestion of dietary NA (dietary nucleotides):

• Small intestine: Pancreatic enzymes hydrolyze the NAs to nucleotides
• Inside mucosal cells: Degradation of purine nucleotides to nucleosides, free bases, and uric acid as end product

Degradation of de novo nucleotides:

• In liver
• Free bases are sent out from the liver and sent to peripheral tissues for salvage

Degradation of Dietary Nucleic Acids in the Small Intestine:

a) Ribonucleases and deoxyribonucleases (secreted by pancreas) hydrolyze dietary RNA and DNA to oligonucleotides

b) Pancreatic Phosphodiesterases produce a mixture of mononucleotides

c) Intestinal mucosal cells: Nucleotidases remove... Continue reading "Purine Nucleotide Degradation and Uric Acid Synthesis" »

Abiogenesis

Process through which life appeared from non-living matter, such as simple organic molecules.

Cyanobacteria

Photosynthetic organisms responsible for the existence of oxygen in the atmosphere.

Homologous Organs

Organs that share an evolutionary origin and structure, but may have different functions. They evidence divergent evolution. Examples: whale and bat extremities.

Analogous Organs

Organs with the same function but different evolutionary origins. They evidence convergent evolution. Examples: insect and bird wings.

Vestigial Organs

Organs that are disappearing because they are no longer useful. Examples: kiwi and cassowary wings.

Evolutionary Lineage

Fossils show progressive transformations, providing evidence of evolution and allowing... Continue reading "Key Concepts in Evolutionary Biology" »

Lymph Nodes and Nephrons

Lymph Nodes

Lymph nodes are made of lymphatic tissue located in specific areas of some lymphatic vessels. They make lymphocytes and release lymph plasma.

Nephrons

Nephrons are the structural and functional units of the kidneys. They are tubes with one closed end and are surrounded by blood capillaries. Nephrons are responsible for filtering blood and forming urine, regulating water and mineral content.

• Bowman's Capsule: Initial zone
• Convoluted Tube: Long twisted tube with two main parts, proximal and distal
• Loop of Henle: Section located between the proximal convoluted tube and the distal zone

Urinary System

Ureters

Ureters are thin tubes that start from each kidney and end in the bladder, an elastic bag in which urine accumulates.... Continue reading "Human Body Systems and Health" »

Su,Aalo Iyo Jawabo biology 

• 1. a) i) Define transport

• Movement of substances from one part of the body to another

  ii) Explain the necessity of transport in plants and animals

• make nutrients move from one point to another

• movement of respiratory gases i.e. oxygen and carbon IV oxide

• elimination of metabolic wastes

• movement of hormones

• movement of water

• movement of salts

• movement of enzymes

  b) i) Describe the structure and function of root hair

• root hairs are found near the root tip

• they are cells with elongated finger-like projections which are in contact with soil particles

• they are permeable to water and mineral salts hence are used to absorb Water and mineral salts

• There large number offers a large surface area for absorption of water and mineral salts.

Classification of Cell Organelles

Organelles without membrane: The cell wall, ribosomes, and cytoskeleton are non-membrane-bound cell organelles. They are present both in the prokaryotic cell and the eukaryotic cell.

Single membrane-bound organelles: Vacuole, lysosome, Golgi apparatus, and endoplasmic reticulum are single membrane-bound organelles present only in a eukaryotic cell.

Double membrane-bound organelles: Nucleus, mitochondria, and chloroplast are double membrane-bound organelles present only in a eukaryotic cell.

Let us learn more in detail about the different cell organelles in brief.

Key Cell Organelles and Their Functions

Plasma Membrane

The plasma membrane, also called the cell membrane, is the membrane found in all cells that... Continue reading "Cell Organelles and Membrane Transport Mechanisms" »

Charles Darwin and the Discovery of Natural Selection

Charles Darwin made the groundbreaking discovery of natural selection. He observed that organisms with favorable traits are more likely to survive and reproduce, passing on those traits to future generations.

Artificial Selection: Shaping Outcomes through Human Intervention

Artificial selection involves deliberately pairing two organisms to produce desired traits in their offspring.

Gene Flow: The Transfer of Genes between Populations

Gene flow occurs when genes are transferred from one population to another through migration and mating.

Genetic Drift: Changes in Gene Frequency within a Population

Genetic drift refers to the random change in the frequency of a gene within a population. Over time,... Continue reading "Understanding the Mechanisms of Evolution: Natural Selection and More" »

Understanding Plague: Causes, Forms, and Treatment

The Gram-negative bacterium Yersinia pestis is the causative agent of the systemic invasive infectious disease known as plague.

Historical Impact of Yersinia pestis

• Yersinia pestis has been responsible for three devastating pandemics: the Justinian Plague, the Black Death, and modern plague.
• The Black Death, in the 14th century, is estimated to have reduced the total world population from 450 million down to 350–375 million.

Transmission and Symptoms

Yersinia pestis is primarily a rodent pathogen, with humans being an accidental host. Infection typically occurs when a human is bitten by an infected rat flea. The flea draws viable Y. pestis organisms into its intestinal tract, where they multiply.... Continue reading "Plague Disease: Causes, Forms, Symptoms, and Treatment" »

Mendelian Principles of Inheritance

Gregor Mendel

• In the 19th century, he studied inheritance: the passing of characteristics from parents to offspring.
• His work was based on the study of the crossing of different varieties of plants.
• The species chosen was the pea (Pisum sativum).

Method

• Characteristic selection
• Obtaining pure-bred individuals for those characteristics

Parental generation (P)

• Crossing two different pure breeds to obtain descendants

First filial generation (F1)

• Crossing F1 individuals and studying their descendants

Second filial generation (F2)

Complete Inheritance

In the heterozygote, the dominant phenotype is manifested.

Special Cases in Genetics

Complete Inheritance

In the heterozygote, the dominant phenotype is manifested.

Intermediate Inheritance

The... Continue reading "Mendelian Genetics: Principles of Inheritance" »

Early Chordates and the Rise of Tetrapods

The earliest known chordate, Myllokunmingia, is found in the Chengjiang fauna. One of the major challenges for early tetrapods was supporting their bodies on land, along with reproductive and sensory adaptations. Tetrapod limbs consist of three segments: the stylopod (humerus/femur), zeugopod (ulna/radius, tibia/fibula), and autopod (wrist/fingers, ankle/toes). Tiktaalik represents a key transitional fossil between fish and tetrapods.

Amphibians and Amniotes

Amphibians, with over 4,000 living species, represent a halfway point in the transition to land. They still rely on water for breeding and maintaining water balance. Amniotes, including reptiles, birds, and mammals, evolved a semipermeable shell made... Continue reading "Evolution of Life: From Early Chordates to Modern Biodiversity" »