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

Understanding Ecosystems

An ecosystem encompasses all plants, animals, and other organisms in a specific location, along with its climate. It also includes the relationships among organisms (e.g., for food) and between organisms and their environment.

Biotope: The Physical Environment

The Lymphatic System

The lymphatic system is a crucial part of the immune system, especially in the immune response.

• Lymphatic vessels allow accumulating lymph to carry and filter out pathogens through lymph nodes.
• The majority of lymphocytes are found in the lymphatic system. For example, T cells mature in the thymus while B cells mature in the bone marrow.

Humoral Immune System

The humoral response, which occurs in blood and lymph, primarily uses B cells to combat pathogens directly. B cells are triggered and activated by helper T cells before they can fight pathogens. When B cells encounter a pathogen they recognize, they engulf the foreign substance and display the antigens on their cell surface. Helper T cells then bind to these antigens, triggering... Continue reading "The Lymphatic System and Immunity Explained" »

Understanding Cells: The Building Blocks of Life

Cells are the fundamental building blocks of all living organisms.

Cell Structure Essentials

A typical cell consists of several key components:

• Plasma membrane: A very thin, stretchy cover composed of lipids, proteins, and carbohydrates that separates the cell from its external environment.
• Cytoplasm: The jelly-like substance filling the cell, enclosing the organelles.
• Genetic material (DNA): A complex chemical substance containing the genetic information necessary to regulate the cell's functions.

Prokaryotic vs. Eukaryotic Cells

Cells are broadly classified into two types based on the location and organization of their DNA:

Prokaryotic Cell Characteristics

• Kingdom: Monera (bacteria).
• Cellularity: Typically

Cellular Respiration Stages

Glycolysis: Sugar Breakdown

Breaks down a 6-carbon sugar into two 3-carbon groups.

Krebs Cycle Location and Output

Occurs in the inner membrane of the mitochondria.

Forms 2 ATP.

ETC and ATP Synthase Function

Finishes the breakdown of pyruvic acid molecules to CO₂.

Forms 34 ATP.

ATP and ADP Explained

ATP (Adenosine Triphosphate) becomes ADP (Adenosine Diphosphate) when one phosphate is given away, leaving only two.

ADP becomes ATP when one phosphate is added to complete the three phosphates.

Electron Transport Chain Role

A sequence of electron carrier molecules that transfers electrons and releases energy during cellular respiration.

Fermentation: ATP Without Oxygen

When cells exercise and there is not enough O₂, they use fermentation... Continue reading "Biology Essentials: Cells, Respiration, Anatomy" »

Sensory Receptors and Human Senses

Types of Sensory Receptors

• Chemoreceptors: Located in the nose and tongue, sensitive to chemical substances.
• Mechanoreceptors: Located in the skin and ears, sensitive to physical stimuli, such as touch.
• Photoreceptors: Located in the retina, sensitive to light.
• Thermoreceptors: Located in the skin, sensitive to temperature changes.
• Nociceptors: Located throughout the body, sensitive to stimuli that cause pain.

The Five Sense Organs

• Sense of Sight (Eyes): Detected by the eyes. Each eye consists of the eyeball and accessory structures.
• Sense of Touch (Skin): The skin has two layers: the epidermis (the outer layer) and the dermis (the inner layer).
• Sense of Smell (Nose): Enables the body to detect chemical molecules in

Photosynthesis produces glucose using

Photosynthesis produces food in plants, called glucose. It happens in chloroplasts. Chloroplasts contain chlorophyll, that absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose. Oxygen is also produced. EQUATION: CARBON DIOXIODE + WATER= GLUCOSE + OKYGEN. Photosynthesis converts light energy into chemical energy.

Adaptation for efficient photosynthesis

Leaves are broad so there is a large surface area exposed to light. Most of chloroplasts are found in the palaside layer. This is so that they are near the top of the leaf where they can get the most light. The upper epidermis is transparent so that light can pass through it to the palisade layer. Leaves have a network of vascular... Continue reading "Photosynthesis and Efficient Adaptations for Multicellular Organisms" »

Introduction

In this process, energy, in the form of adenosine triphosphate (ATP), is released and utilized by the cell for basic biological functions. This guide will delve into the intricacies of cellular respiration, exploring its different stages and the molecules involved.

Steps in Cellular Respiration

Oxidation-Reduction (Redox) Reactions

Electrons are transferred from one molecule to another, playing a pivotal role in cellular respiration.

ATP Synthesis Methods

• Substrate-Level Phosphorylation: Depends on the interaction between enzymes.
• Oxidative Phosphorylation: Powered by the proton motive force and occurs through the use of ATP Synthase.

Glycolysis

Glycolysis produces 4 ATP molecules, all formed through the use of a substrate-enzyme complex.... Continue reading "Cellular Respiration: A Comprehensive Guide to Energy Production" »

Proteins are composed of 20 amino acids.

Functional groups influence reactivity.

Nonpolar side chains are green.

Polar side chains are pink.

Electrically charged side chains:

• Acidic: red
• Basic: blue

Condensation reactions form a peptide bond by bonding the carboxyl group of one amino acid to the amino group of another. Multiple peptide bonds create a polypeptide. Polypeptides containing more than 50 amino acids are called proteins.

Protein Structure

Primary structure: The unique sequence of amino acids.

Secondary structure: Hydrogen bonds between the carbonyl group of one amino acid and the amino group of another form a protein's secondary structure.

Secondary structure depends on the primary structure.

Tertiary structure: Results from interactions between... Continue reading "Understanding Protein Structure, Enzymes, and Nucleic Acids" »

Actin Cytoskeleton Dynamics and Regulation

The actin cytoskeleton provides thin, flexible mechanical support to cells. Actin monomers are added and removed at distinct ends of the filaments, influencing their dynamics and cellular functions.

• Actin-ATP Addition: ATP-bound actin is primarily added to the barbed (plus) end of the filament.
• Molecular Timer: Older filaments contain ADP-bound actin, making them unstable and prone to disassembly. This acts as a molecular timer for filament turnover.
• Cellular Movement: Actin dynamics are crucial for various cellular processes, including movement and phagocytosis.

Key Regulators of Actin Filaments

Several proteins precisely control actin filament assembly and disassembly:

• Nucleation Factors: Dictate the rate

Darwin and the Theory of Natural Selection

The principal merit of Darwin's theory, in addition to the many evidence that he provided to it, is the discovery of the mechanism that governs the entire evolutionary process of species: the natural selection.

1. Firstly, when environmental resources become scarce, an inevitable competition occurs and, consequently, the struggle for survival begins in which most individuals die.
2. Secondly, it is also obvious that individuals of the same species have different features or characteristics that appear randomly and make individuals different from each other.
3. Third, these characteristics make some individuals more advantaged than others. Those whose characteristics are favorable to the demands of the environment