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

The urea cycle, also known as the ornithine cycle, is a critical metabolic pathway that primarily occurs in the liver, and to a lesser extent, in the kidneys. Its main function is to convert excess nitrogen from protein and amino acid breakdown into urea, a less toxic compound than ammonia, for safe excretion in urine.

Steps in the Urea Cycle

The urea cycle involves several enzymatic reactions within the mitochondria and cytoplasm of liver cells. Key molecules include ammonia, carbon dioxide, ornithine, citrulline, argininosuccinate, and arginine.

1. Formation of Carbamoyl Phosphate

• Ammonia (NH₃) and carbon dioxide (CO₂) combine in the mitochondria.
• This reaction, catalyzed by carbamoyl phosphate synthetase I (CPS I), produces carbamoyl phosphate.

The Human Digestive System: Definition and Function

The digestive system is a set of organs responsible for carrying out digestion. It transforms food into simple substances that pass into the blood and eliminates undigested remains. Its primary role is to provide nutrients to cells by digesting food.

Organs of the Digestive System

Mouth

• Lips: Fleshy muscles that surround the mouth.
• Palate: The roof of the mouth, separating the mouth and nostrils. The anterior part is the hard palate, and the posterior part is the soft palate.
• Uvula: A structure that hangs from the soft palate, preventing the passage of substances into the nostrils.
• Teeth: Used to crush food. Types include incisors, canines, premolars, and molars. Adults typically have 32 teeth (8

1. DNA: The Molecule of Inheritance

• In eukaryotic cells, genetic material is condensed into chromosomes, which consist of two chromatin strands made of DNA and proteins.
• The double helix model of the DNA molecule was proposed by Watson and Crick in 1953.

Basic Components of DNA

A molecule of DNA is formed from thousands of nucleotides. Each nucleotide is made up of:

• Deoxyribose
• Nitrogenous base
• Phosphate

There are 4 types of nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). When nucleotides join together, they form a chain where deoxyribose alternates with phosphate. The nitrogenous bases are attached to the deoxyribose.

Structure of DNA

• DNA is made up of two chains (strands) of nucleotides twisted around each other in the shape

Endocrine Coordination and the Hormonal System

Endocrine coordination is a mechanism which regulates the action of many of the body’s organs in a slow way over a long period of time.

It is carried out by the endocrine system, which is made up of a network of endocrine glands specialized in manufacturing and secreting hormones into the blood. Blood transports hormones all around the body, but the hormones only affect certain organs or cells called target cells.

The Role of the Pituitary Gland

The pituitary gland is located at the base of the brain. It is the most important gland, since some of the hormones that it manufactures control secretion by the rest of the glands.

Other Key Endocrine Glands

Other endocrine glands include:

• Thyroid gland
• Parathyroid

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" »