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

Water: Properties and Cycle

Properties of Water

Freshwater: Salinity below 35g/L.

Saltwater (Ocean Water): Salinity over 35g/L.

General Properties: Colorless, odorless, tasteless. Higher density in liquid state than solid state. Universal solvent. High heat capacity. Facilitates many chemical reactions. Exhibits adhesive capacity.

States of Water

• Solid (S)
• Liquid (L)
• Gas (G)

Transitions: S --(fusion)--> L --(vaporization)--> G --(condensation)--> L --(solidification)--> S S --(sublimation)--> G --(inverse sublimation)--> S

Water as a Thermal Regulator

Water's high heat capacity means significant temperature changes require large amounts of energy. This explains why coastal regions experience milder climates compared to inland areas.

The

Biology Study Notes

Enzymes and Molecules

• Enzymes are organic molecules that function to start and regulate chemical reactions.
• The largest molecules in our bodies are nucleic acids.
• The human body is primarily composed of oxygen, nitrogen, hydrogen, and carbon.

Genetics and DNA Structure

• A genome is an organism’s complete set of DNA, containing all the information needed to build and maintain that organism.
• DNA molecules exist in the shape of a double helix.
• There are about 3 billion chemical base pairs in human DNA, with approximately 1%–2% coding for a gene.
• A gene is essentially a sequence of many codons in a DNA molecule.
• Portions of DNA molecules that do not contain codes for proteins are called introns.
• The DNA code is shared by all living

The Discovery of Cells

a) In 1655, scientist Robert Hooke made an observation while examining a dried section of cork tree with a crude light microscope. He observed small chambers and named them "cells."

What are Cells?

b) The cell is known as the basic structural and functional unit of life, as all organisms are composed of cells.

c) Single-celled organisms are called unicellular (e.g., amoeba), while those having more than one cell are called multicellular.

Functions of Cells

d) All basic chemical and physiological functions of living beings - for example, repair, growth, movement, immunity, communication, and digestion - are carried out inside the cells.

Structure of a Cell

e) Cells are mostly round, spherical, or elongated. Some cells are quite... Continue reading "Exploring the Building Blocks of Life: An Introduction to Cells" »

The Excretory System: Function and Components

The **excretory system** is primarily composed of the kidneys, which play a central role in filtering waste from the blood. While other organs like the large intestine remove waste (feces) from the body, the excretory system specifically handles metabolic waste products dissolved in blood.

What is Excretion?

**Excretion** is the biological process of removing waste products of metabolism and other useless materials from an organism. The **kidney** is the key organ in this process, forming the core of the excretory system.

Key Components of the Excretory System

• Kidneys
• Ureters
• Bladder
• Urethra

Blood Filtration in the Kidneys

Toxin-laden blood reaches the kidneys via the **renal artery**. Within the kidneys,... Continue reading "Human Excretory System: Kidney Function & Waste Removal" »

Water and Salts

Water

More than half of our body is water. Water is used for carrying out chemical reactions and for transporting substances.

Mineral Salts

Make up the hard and solid parts of our bodies.

Glucids

Glucids are bio-molecules made up of carbon, hydrogen, and oxygen.

Types of Glucids

• Monosaccharides: The simplest glucids.
• Disaccharides: The union of two monosaccharides.
• Polysaccharides: Many monosaccharide molecules joined together.

Proteins

Proteins have carbon, hydrogen, nitrogen, oxygen, and a smaller proportion of sulfur.

They are made of the joint of many molecules called amino acids.

Functions of Proteins

• Are an important part of cell structure.
• Defense.
• Transporting substances.

Lipids

Lipids are a group of different substances. Lipids are not... Continue reading "The Building Blocks of Life: Cells, Molecules, and Processes" »

1. What Is Peripheral Neuropathy?

Peripheral neuropathy is a chronic disease characterized by varied sensory, motor, and autonomic symptoms. It often appears as a systemic illness, with complications linked to metabolic, toxic, infectious, nutritional, neoplastic, and immunologic factors.

2. What Is Axonal Degeneration?

In response to injury, nerves may undergo axonal degeneration. When the axon's continuity is interrupted, it loses its connection to the cell body and the ability to receive necessary nutrients. Consequently, the myelin bands degenerate secondarily.

3. What Is Demyelination?

Demyelination is a primary reaction where the myelin sheath degenerates. This process leads to:

• Slowing of nerve conduction
• Nerve conduction block
• Initiation of

Nuclear Pore Complex (NPC) Structure and Function

NPC as Gatekeepers

Embedded within the nuclear envelope are nuclear pore complexes (NPCs), large protein structures situated in circular openings where the inner and outer nuclear membranes fuse. These aqueous protein channels regulate the transport of proteins and RNA across the nuclear envelope, acting as gatekeepers of the nucleus and facilitating nearly all transport between the nucleoplasm and cytoplasm.

NPC Architecture

The main NPC structure features rings on both the cytoplasmic and nucleoplasmic sides, with a luminal ring (LR) in between, creating twofold symmetry across the nuclear membrane.

Transport Across the Nuclear Envelope

Selective Permeability

While small molecules like metabolites... Continue reading "Nuclear Pore Complex Structure and Transport Mechanism" »

Osmosis

Osmosis is the diffusion of water through a selectively permeable membrane. Water molecules move from an area of higher concentration to an area of lower concentration.

Isotonic Solutions

Isotonic means "same strength" and refers to the solute concentration. In isotonic solutions, water moves equally in both directions. For example:

• Animal cells: Water goes in and out.
• Plant cells: Water goes in and out.

Hypertonic Solutions

Hypertonic means "stronger." In hypertonic solutions, there is a net movement of water molecules out of the cell, causing it to shrink. For example:

• Animal cells: Water goes out.
• Plant cells: Water goes out.

In a hypertonic environment, the outside is more concentrated than the inside of the cell. The cell shrinks because... Continue reading "Cell Biology: Osmosis, Homeostasis, and Specialization" »

Sex Determination Mechanisms

Haploid-Diploid Sex Determination

In this system, the total number of chromosomes in a cell determines the sex of a new individual.

X Chromosome to Autosome Ratio

Sex is determined by the ratio between the number of X chromosomes and the total number of autosomes.

Environmental Sex Determination

In this system, individuals are affected by several environmental variables after fertilization. Generally, the most influential of these is temperature. However, other factors, such as the number of hours of daylight, nutrition, humidity, and the pH of water can also affect sex determination.

Inheritance Linked to Sex

Genes found on sex chromosomes are transmitted differently in males and females because these chromosomes differ... Continue reading "Sex Determination and Inheritance Patterns" »

Evolutionary Biology: Core Principles

1. What is a fossil? A fossil is the preserved remains of an organism.

2. Natural Selection: Natural selection refers to the adaptation of species in different environments. Only the fittest organisms survive to reproduce.

3. Evolutionary Structures:

• Homologous Structures: Structures that share the same evolutionary origin and arrangement of function.
• Analogous Structures: Body parts that have similar functions but do not share a common evolutionary ancestor.
• Vestigial Structures: A body part that no longer serves its original purpose but was likely useful to an ancestor.

4. Darwin's Theory of Evolution: Darwin's theory posits that each living being adapts to its environment. Observations of tortoises and finches... Continue reading "Evolution, Taxonomy, and Plant Anatomy: Key Concepts" »