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

The Human Digestive System

All animals need to eat food to get energy to live. In order to use this food, they must break it down in a process called digestion. Consequently, all animals have a group of connected organs known as the digestive system.

The Process of Digestion

In humans, digestion begins in the mouth, where food is chewed into small pieces by the teeth. The tongue assists by moving these pieces around. These pieces are covered by saliva, which makes the food slippery for easier swallowing and helps break down the food.

Once swallowed, food passes through the pharynx, which acts as a gate, sending food down the esophagus and into the stomach. In the stomach, food is mixed with acid and crushed further.

After spending time in the stomach,... Continue reading "Human Digestive System and Biological Science Basics" »

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,

Understanding Cnidarians: Phylum Characteristics

The phylum Cnidaria represents one of the more primitive animal phyla. It encompasses diverse aquatic organisms such as jellyfish, sea anemones, corals, and hydras. While most cnidarians are marine, a few species, like the familiar hydra, inhabit freshwater environments.

A defining characteristic of all cnidarians is their **radially symmetric body plan**, a contrast to the bilaterally symmetric body plans found in most other animal phyla. Though more advanced than sponges (Phylum Porifera) due to their distinct tissue layers, cnidarians lack many features of more complex animal phyla, such as true internal organs and central nervous systems. Most cnidarians possess tentacles, and many also feature... Continue reading "Marine Life Essentials: Cnidarians, Coral Symbiosis, and Reef Types" »

• Centrioles: Located near the nucleus, they help to organize cell division.

Cell Membrane

• Regulates what enters and leaves the cell.
• Protects and supports the cell.
• Structure: Lipid bilayer—a double-layered sheet that gives it a flexible structure.

Vacuole

• Large, saclike, membrane-enclosed structures.
• Function: Store materials like water, salts, proteins, and carbohydrates.
• Structure: In many cells, there is a single central vacuole filled with liquid.

Vesicles

• Smaller membrane-enclosed structures.
• Function: Store and move materials between cell organelles, and to and from the cell surface.

Lysosome

• Small organelles filled with enzymes (lysosomes).
• Function: Break down lipids, carbohydrates, and proteins into small molecules that can be used by the rest

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" »