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

The Origin of Life: Two Key Processes

1. Chemical Evolution

This process created the molecules that make up living things (biomolecules) and subsequently formed structures called protocells.

• Biomolecule Formation: Simple organic molecules originated from meteorites.
• Complexification: More complex biomolecules were created from simple molecules in the primordial soup (the first biomolecules on the planet).
• Protocell Formation: Protocells were formed when biomolecules became organized into hollow, spherical membranes containing proteins and nucleic acids.

2. Biological Evolution

This process led protocells to become different types of cells, resulting in all the organisms that have ever inhabited the Earth.

• Primitive Cells: Similar to prokaryotic cells,

Core Concepts in Biology

Biodiversity

Species that inhabit or have ever inhabited the Earth.

Adaptation

The accumulation of changes in a living being to suit the environment in which it lives.

Types of Adaptation

• Structural: Affects organs and allows for specific functions, e.g., birds' beaks.
• Physiological: Affects the organism's function and metabolism.
• Behavioral: Actions that provide advantages, e.g., migration.

Evolutionary Theories

Biodiversity and Evolution

Slow changes in living beings over millions of years.

Fixism (Georges Cuvier)

Organisms were created through divine creation and became extinct due to catastrophes. This theory posited that species could not change, a view contrasted by later evolutionary theories.

Lamarckism (Jean-Baptiste de

The Digestive System

The digestive system is responsible for the ingestion, digestion, absorption, and elimination of food. It transforms food into nutrients through three main processes:

1. Mechanical Digestion: Chewing, grinding, crushing, and mixing of food to break it down into smaller pieces.
2. Chemical Digestion: Digestive juices break down macromolecules in food into smaller molecules that can be absorbed.
3. Absorption: Nutrients are absorbed into the bloodstream and transported to cells throughout the body.

Ingestion

Ingestion begins when food enters the mouth. Key steps include:

• Mastication (Chewing): Teeth tear and break food into smaller pieces.
• Salivation: Saliva mixes with food, forming a bolus and aiding in swallowing.
• Swallowing: The tongue

Contraceptive Methods

Rhythm Method

Observes the menstrual cycle to calculate the day of ovulation. Advantages: A natural method with no side effects. Disadvantages: Imprecise; not a barrier method and does not protect against STIs.

Body Temperature Method

Observes the basal body temperature in women to calculate the day of ovulation.

Male Condom

A plastic sleeve placed on the penis to stop sperm during ejaculation. Advantages: Very cheap, easy to find, and a barrier method. Disadvantages: 98% effectiveness; some people experience side effects.

Female Condom

A plastic sleeve placed inside the vagina to stop sperm during ejaculation. Advantages: Cheap and a barrier method. Disadvantages: 95% effectiveness; more difficult to find; potential side effects.... Continue reading "Contraceptive Methods and Sexually Transmitted Infections" »

Photosynthesis Fundamentals

Photosynthesis: Carbon Compound Production

• Living organisms require complex carbon compounds to carry out life processes and build the structures in their cells.
• Photosynthesis involves the conversion of light energy into chemical energy (carbohydrates, lipids, proteins, and nucleic acids).
• Chloroplasts absorb light energy from the sun and convert this energy into chemical energy (glucose) to be used by the organisms for energy.

Visible Light Spectrum and Wavelengths

• Light from the sun is composed of a range of wavelengths.
• The visible spectrum is the portion of the electromagnetic spectrum that is visible to or can be detected by the human eye.
• Electromagnetic radiation in this range of wavelengths (380 to 750 nm) is called

Genetic Disorders and Their Causes

Genetic disorders: Most genetic disorders are caused by mutations in one or more genes or by abnormal numbers of chromosomes.

Genetic Disorders Caused by Mutations

Some disorders are caused by mutations in autosomal genes. In the table below, there is a list of genetic disorders caused by a mutation in a single gene.

Inorganic biomolecules

Essential for non-living things.

• Water: The most abundant substance found in living things. It makes up about 65% of the human body.
• Mineral salts: Substances that can be found in living things in the form of dissolved ions, such as sodium ion.

Organic biomolecules

Unique to living things. Structures made up of carbon.

• Carbohydrates: Made of carbon and water.
• Lipids: Fats, phospholipids, and cholesterol.
• Proteins: Chains of amino acids.
• Nucleic acids: Groups of nucleotides.

The cell: Functions

• Structural
• Functional
• Basic
• Biological

Prokaryotic cell

• No nucleus
• Organelles: Ribosomes
• Bacteria are prokaryotes
• Membranes: Cell membrane, cell wall, and bacterial capsule (not always)
• Flagella and Fimbriae

Eukaryotic cell

• Nucleus
• Cell membrane: two

Cell Organelles

Mitochondria: Oval-shaped organelles with two membranes. Through cellular respiration, mitochondria produce energy for the cell.

Vesicles: Small, rounded organelles that store, transport, or digest cellular substances. Lysosomes are rounded vesicles produced by the Golgi body.

Endoplasmic Reticulum: A network of interconnected membranous sacs and channels. There are two types:

• Rough ER: Connected with the nuclear envelope and ribosomes.
• Smooth ER: This type has no attached ribosomes.

Golgi Body: Flat, membranous sacs arranged in layers. Secretory vesicles transport substances out of the cell.

Centrosome: Consists of two centrioles: perpendicular cylindrical structures composed of microtubules. They are surrounded by other microtubules... Continue reading "Cell Organelles and Food Preservation Techniques" »

Human Reproduction: Fundamental Processes

Human reproduction is sexual, meaning that both the mother and father contribute genetic material to their offspring via gametes. Offspring will have a mix of their parents' characteristics, and each person obtains their own unique genetic make-up.

The female gametes, ovules, and the male gametes, sperm, fuse together in the process called fertilisation, inside the female reproductive system, to form a zygote.

The embryo develops from the zygote inside the mother's uterus, undergoing repeated cell divisions. The new cells created specialise to form tissues and organs.

Sexual Characteristics and Puberty

Boys and girls are born with different reproductive organs, which constitute the so-called primary sexual