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

Understanding Cells: Structure, Functions, and Types

The cell is the smallest unit of a living organism that can carry out vital functions: nutrition, interaction, and reproduction.

Essential Cell Components

All cells possess a plasma membrane, cytoplasm, and DNA.

• Plasma Membrane: This is a very thin and stretchy cover that separates a cell from its environment. Its primary function is to regulate the movement of substances in and out of the cell. It also detects environmental stimuli and allows cells to communicate.
• Cytoplasm: This is the substance contained inside the cell, in which the cell organelles are found. Metabolic processes occur within the cytoplasm.
• Genetic Material (DNA): A complex chemical substance that contains the information needed

The Origin of Life

The Concept of Life

In biology, life refers to the ability of living organisms to perform vital functions: nutrition, interaction, and reproduction.

These vital functions are common and essential to all living organisms, regardless of their level of complexity or organization. This is known as the constancy principle of vital functions.

Significance of Vital Functions

All living organisms interact with their environment.

The biological significance of vital functions lies in their ability to enable continuous interaction between living organisms and their environment.

The reproduction function allows new organisms to form, ensuring the species' longevity and evolution over time.
The interaction function enables organisms to respond... Continue reading "Life's Journey: From Origin Theories to Evolutionary Mechanisms" »

The Endocrine System

Endocrine glands: are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct.

Hormones: are any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.

Blood vessels: are the part of the circulatory system, and microcirculation, that transports blood throughout the human body.

Target cell: are cells that respond to a hormone because they possess specific receptors for that hormone.

Receptor: A molecule, usually a protein, that binds to a specific hormone, initiating a cellular response.

Endocrine Signaling Pathway Example

Understanding the Endocrine System: Glands, Hormones, and Functions

Exocrine vs. Endocrine Glands

Exocrine glands have ducts that secrete substances such as mucus, saliva, cerumen, sebaceous oils, and sweat.

Endocrine glands produce hormones (chemical messengers) and secrete them directly into the bloodstream.

The Pituitary Gland: Master Regulator of Hormones

The pituitary gland (hypophysis), often called the "master gland," primarily functions to secrete vital hormones into the bloodstream.

Key Pituitary Hormones and Their Functions

• ACTH (Adrenocorticotropic hormone or corticotropin): Stimulates the release of steroid hormones by the adrenal cortex.
• TSH (Thyroid-stimulating hormone or thyrotropin): Targets the thyroid gland and triggers the release

Wood Structure and Properties

Sapwood and Heartwood

Sapwood

• Width varies with species, growth rate, and tree age.
• Typically represents 20-50% of the total radius (except in very young trees).

Heartwood

• Formed from former sapwood cells.
• Acidity increases, extractives form, and color changes.
• Resistance to fungal and insect attack increases.
• Many timbers develop gums and resins in the heartwood.

Functions of Cells in a Growing Tree

• Primary function: Conduction of water and dissolved minerals from roots to leaves.
• Secondary function: Mechanical support of the tree.
• Tertiary function: Food storage for spring growth.

Characteristic Differences between Softwoods and Hardwoods

• Hardwoods: Water-conducting elements distributed throughout the annual ring.
• Softwoods:

Understanding Digestion

What is Digestion?

Digestion is the process by which food is transformed into simpler substances (nutrients) so they can be used by our cells. It involves two main processes:

• Mechanical Process: Chewing and the muscular action of organs crush and mix foods with digestive juices.
• Chemical Process: Digestive enzymes in digestive juices cause chemical reactions that break food into simple substances.

Mechanical vs. Chemical Digestion

The digestive system employs both mechanical and chemical digestion:

• Mechanical: Mouth
• Chemical: Stomach, liver, small and large intestine

Swallowing: The Process

Swallowing allows substances to pass from the mouth to the pharynx. It involves three main stages:

1. The bolus is moved to the oral cavity as

Human Nutrition

The cells of all organisms require nutrients to grow and function. Heterotrophic organisms, like humans, cannot produce their own nutrients, so they obtain them from food. Multicellular organisms have many organs grouped into systems, such as the digestive and respiratory systems.

Digestive System

Like all animals, humans obtain proteins, fats, and sugars from food through the digestive system. Food processing involves three phases: digestion, absorption, and waste expulsion. Food moves through the digestive tract via peristaltic movements—muscle contractions in the tract walls that narrow the tube.

Respiratory System

Besides nutrients from digestion, our cells need oxygen for cellular respiration, the process that converts glucose... Continue reading "Human Nutrition and Respiration: A Comprehensive Guide" »

Cellular Respiration

Glycolysis

• Enzymes break down a 6-carbon glucose molecule into two 3-carbon pyruvate molecules.
• A small amount of ATP is synthesized through substrate-level phosphorylation, an enzyme-catalyzed reaction transferring a phosphate group from a substrate to ADP.

Oxidative Phosphorylation

• High-energy electrons are delivered to oxygen through a series of electron carriers in the electron transport system.
• The free energy released by electron flow generates an H+ gradient via chemiosmosis.
• ATP synthase utilizes the H+ gradient as the energy source for ATP production.

Reaction Locations

• Glycolysis: Occurs in the cytosol.
• Pyruvate oxidation and citric acid cycle: Take place in the mitochondrial matrix.
• Electron transfer system and ATP synthase

Twins and Multiple Births

Twins originate from the same egg and sperm that then divides into two embryos. These embryos share the same genetic material. On the other hand, fraternal twins develop from two separate eggs and two sperm cells. Genetically, they are like siblings but born at the same time.

Puberty

Puberty is the life stage where a person develops secondary sexual characteristics and achieves reproductive capability. It's the initial phase of adolescence, marking the transition from childhood to adulthood.

Diseases and Health

Causes of Diseases

Degenerative diseases involve the progressive destruction of tissues. Affected organs gradually deteriorate, as seen in Alzheimer's disease.

Health

Health is a state of complete physical, mental,... Continue reading "Understanding Health, Diseases, and the Immune System" »