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

The Skeletal System: The Internal Framework of the Body

The skeletal system is the internal framework (structure) of the body. It is made up of 206 bones and tissue.

Support

Bones hold our body and give us shape. For example, the spinal cord provides support.

Protection

The skeleton protects our vital organs. For instance, the skull protects the brain, and the ribs protect our heart and lungs.

Movement

Bones allow us to move as a whole body or as individual parts.

Blood Production

Certain bones in the skeleton contain red bone marrow, which produces red blood cells, white blood cells, and platelets.

Storage

Our bones can store different minerals, such as calcium.

Endocrine Regulation

Endocrine glands produce hormones, and the skeletal system helps regulate... Continue reading "The Importance of the Skeletal System in the Human Body" »

The Human Eye

Structure and Function

The Retina

The retina is a structure at the back of the eye that contains light-sensitive cells called rods and cones.

• Rods: Detect different light intensities, see in black and white, sensitive to low light levels, used to see in dim light.
• Cones: Different types sensitive to different colors (especially primary colors), need bright light to work, cannot see in dim light.

The central part of the retina has a lot of cone cells and no rod cells. The outer part of the retina has no cone cells and a lot of rod cells.

Blind Spot

The blind spot is the point where the optic nerve leaves the eye. There are no receptor cells in this area.

Cornea

The cornea is the transparent front part of the eye. It protects the eye and... Continue reading "The Human Eye: Structure, Function, and Vision" »

The Nervous System

The nervous system receives information from the receptors, processes and coordinates it, and generates orders to the effectors.

Central Nervous System (CNS)

The central nervous system coordinates all the body's functions. It is formed by the encephalon and the spinal cord.

The Encephalon

The encephalon is protected by the skull or cranium and by three membranes, the meninges, between which a liquid called the cerebrospinal fluid circulates. This liquid protects the encephalon from knocks and blows. The encephalon is divided into three parts: the brain, the cerebellum, and the brainstem.

• The brain is divided into two hemispheres, separated by a fissure. Its surface, called the cerebral cortex, is rough and full of folds and furrows,

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

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" »

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" »

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" »