IGCSE Biology (0610)
Complete Revision Modules
1. Characteristics and Classification of Living Organisms
Living organisms feature a set of shared characteristics regulated by cellular processes.
1.1 The Seven Characteristics of Life
- Movement: An action by an organism or part of an organism causing a change of position or place.
- Respiration: Chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
- Sensitivity: The ability to detect and respond to changes in the internal or external environment.
- Growth: A permanent increase in size and dry mass.
- Reproduction: The processes that make more of the same kind of organism.
- Excretion: Removal from organisms of toxic materials and the substances in excess of requirements.
- Nutrition: Taking in of materials for energy, growth, and development.
1.2 Classification System Framework
Organisms are classified into logical groups based on shared features. The **binomial system** introduces a scientific two-word name format comprised of the Genus (capitalized) followed by the species (lowercase).
The standard classification features five main kingdoms: Animals, Plants, Fungi, Prokaryotes, and Protoctists. Vertebrates are divided into Mammals, Birds, Reptiles, Amphibians, and Fish.
2. Organisation of the Organism
Cell structures differentiate to perform specific duties within tissues, organs, and organ systems.
2.1 Cell Structures & Organelles
- Cell Wall: Rigid cellulose framework found only in plant cells; provides structural support.
- Cell Membrane: Partially permeable barrier that controls the movement of substances into and out of the cell.
- Cytoplasm: Gel-like metabolic site where chemical reactions occur.
- Nucleus: Houses the genetic material (DNA) and controls cellular activity.
- Mitrochondria: The site of aerobic respiration, providing ATP energy for the cell.
- Ribosomes: Tiny structures responsible for protein synthesis.
- Chloroplasts: Chlorophyll-containing organelles in plants where photosynthesis occurs.
2.2 Size of Specimens & Magnification Formula
3. Movement Into and Out of Cells
Substances cross cellular interfaces through passive movement or active metabolic mechanisms.
- Diffusion: The net movement of particles from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement.
- Osmosis: The net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
- Hypotonic solution: Plant cells become turgid; animal cells may burst (lysis).
- Hypertonic solution: Cells lose water; plant cell membranes pull away from the wall (plasmolysis), animal cells shrink.
- Active Transport: The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration, against a concentration gradient, using energy from respiration via protein carriers.
4. Biological Molecules
Chemical structures that form the foundation of organic life forms.
- Carbohydrates: Made of Carbon, Hydrogen, and Oxygen. Starch/Glycogen are built from glucose subunits.
- Proteins: Composed of Amino Acids linked together. Contain Carbon, Hydrogen, Oxygen, and Nitrogen.
- Lipids: Formed from three fatty acid chains bound to a single glycerol molecule.
4.2 Biochemical Qualitative Food Tests
| Nutrient Target | Reagent Chemical | Positive Color Change |
|---|---|---|
| Reducing Sugars | Benedict's Solution (and heat) | Blue → Green / Brick-Red precipitate |
| Starch | Iodine Solution | Yellow-Brown → Blue-Black |
| Proteins | Biuret Reagent | Blue → Purple / Violet |
| Lipids (Fats) | Ethanol Emulsion Test | Clear → Cloudy-White milky emulsion |
| Vitamin C | DCPIP | Blue → Colorless decolored state |
5. Enzymes
Enzymes act as biological catalysts that speed up metabolic reactions without being altered in the process.
They follow a strict Lock and Key mechanism where a specific substrate fits perfectly into the enzyme's active site. Extreme temperatures or extreme pH variations disrupt these structural bonds, permanently altering the active site shape and causing the enzyme to become **denatured**.
6. Plant Nutrition
Plants synthesize vital carbohydrates using solar radiation via leaf tissues.
\[ \text{Carbon Dioxide} + \text{Water} \xrightarrow{\text{Light + Chlorophyll}} \text{Glucose} + \text{Oxygen} \] Chemical Equation:
\[ 6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \]
6.2 Leaf Anatomical Structure
The leaf cross-section is optimized for gas exchange and light absorption: the upper cuticle prevents water loss, the **palisade mesophyll layer** is closely packed with chloroplasts to maximize photosynthesis, and the **spongy mesophyll layer** features large air spaces to facilitate gas diffusion.
7. Human Nutrition
A balanced diet contains appropriate proportions of carbohydrates, fats, proteins, vitamins (C and D), minerals (calcium and iron), fiber, and water.
7.1 Mechanical vs Chemical Digestion
- Mechanical Digestion: Breaking down food into smaller pieces without chemical changes to the molecules (e.g., teeth chewing, stomach churning).
- Chemical Digestion: The breakdown of large, insoluble molecules into small, soluble molecules by enzymes.
- Amylase: Breaks starch down into maltose.
- Protease: Breaks down proteins into amino acids.
- Lipase: Breaks down lipids into fatty acids and glycerol.
Bile: Produced in the liver and stored in the gall bladder. It neutralizes stomach acid to create the ideal alkaline conditions for enzymes in the small intestine, and **emulsifies fats** to increase their surface area for lipase action.
8. Transport in Plants
Vascular bundles distribute fluids throughout the plant structure.
- Xylem: Hollow, lignified vessels that transport water and mineral ions unidirectionally from roots up to the leaves.
- Phloem: Sieve tubes and companion cells that transport sucrose and amino acids bidirectionally from sources to sinks (**translocation**).
Transpiration: The loss of water vapor from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapor through the stomata. This creates a transpiration pull that draws water up the xylem column.
9. Transport in Animals
Humans have a double circulatory system where blood passes through the heart twice for each complete circuit of the body.
9.1 Blood Vessel Characteristics
| Vessel Type | Structural Thickness | Lumen Diameter | Functional Trait |
|---|---|---|---|
| Arteries | Thick, elastic muscular walls | Narrow lumen | Carries blood away from the heart under high pressure |
| Veins | Thin walls with less muscle | Wide lumen | Carries blood back to the heart under low pressure; contains valves |
| Capillaries | One-cell thick endothelial layer | Microscopic lumen | Allows efficient exchange of substances between blood and tissue cells |
10. Diseases and Immunity
The human immune network defends the body against pathogenic vectors.
- Pathogen: A disease-causing organism.
- Phagocytosis: Phagocytes engulf and digest pathogens using digestive enzymes.
- Antibody Production: Lymphocytes produce highly specific antibodies that bind to matching antigens on pathogens, clumping them together for destruction.
- Vaccination: Injection of dead or weakened pathogens to stimulate lymphocytes to create memory cells, providing rapid long-term active immunity.
11. Gas Exchange and Respiration
Respiration releases chemical energy from nutrient molecules within living cell pathways.
11.1 Aerobic vs Anaerobic Respiration Equations
\[ \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy} \] Anaerobic Respiration (Human Muscles):
\[ \text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{Lactic Acid} \] Anaerobic Respiration (Yeast Fermentation):
\[ \text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{Ethanol} + 2\text{CO}_2 \]
12. Coordination and Response
Organisms coordinate behavioral responses using electrical nerve circuits alongside hormonal networks.
12.1 The Reflex Arc Component Pathway
12.2 Homeostasis & Synapses
Homeostasis: The maintenance of a constant internal environment (e.g., regulating blood glucose concentration via insulin, controlling core body temperature). A **synapse** is the junction between two neurones where electrical impulses are converted into chemical neurotransmitters to cross the gap.
13. Reproduction
Processes that ensure the continuity of species populations.
- Asexual Reproduction: The process resulting in the production of genetically identical offspring from one parent.
- Sexual Reproduction: A process involving the fusion of the nuclei of two gametes to form a zygote, producing genetically dissimilar offspring.
In humans, the male gamete (sperm) is mobile and produced in vast numbers, whereas the female gamete (egg/ovum) is larger, structural, contains nutrient reserves, and is released singly during the menstrual cycle.
14. Inheritance and Genetic Technology
Chromosomes carry structural genes that determine individual phenotypes.
- Mitosis: Nuclear division giving rise to genetically identical cells. Used for growth, repair, and asexual reproduction.
- Meiosis: Reduction division in which the chromosome number is halved from diploid to haploid, producing genetically different gametes.
- Monohybrid Crosses: Uses a Punnett square to predict genotype ratios (e.g., homozygous dominant vs heterozygous recessive alleles).
Genetic Engineering: Modifying an organism's genome by inserting genes from another organism (e.g., inserting the human insulin gene into bacterial plasmids to mass-produce insulin for medical use).