IGCSE Biology Specification Summary

A comprehensive vocabulary review deck of 175 flashcards covering all IGCSE Biology syllabus points, from cell biology and human organ systems to genetics, ecology, and biotechnology.

Characteristics of Living Organisms

The eight fundamental features shared by all living organisms: nutrition, respiration, excretion, response to surroundings, movement, homeostasis (control of internal conditions), reproduction, and growth and development.

Eukaryotic Organisms

Organisms with complex cells containing a nucleus and membrane-bound organelles; comprises plants (cellulose walls, chloroplasts, stores starch/sucrose), animals (no cell walls/chloroplasts, nervous coordination, stores glycogen), fungi (hyphae mycelium, chitin walls, saprotrophic nutrition, stores glycogen), and protoctists (microscopic single-celled organisms like Amoeba and Chlorella).

Bacteria

Microscopic single-celled prokaryotic organisms possessing a cell wall, cell membrane, cytoplasm, and ribosomes, but lacking a true nucleus and membrane-bound organelles; genetic material exists as a single circular chromosome free in the cytoplasm alongside plasmids.

Pathogen

A microorganism that causes infectious disease in another living organism; includes fungi, bacteria, protoctists, or viruses.

Levels of Organisation

The structural hierarchy in living organisms: organelles (microscopic functional cell structures), cells (fundamental structural and functional units), tissues (layers of similar specialized cells), organs (units made of multiple tissues), and organ systems (groups of organs executing coordinated processes).

Cell Structures

Core cellular components including the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes, and vacuole.

Organelle Functions

Specific roles: nucleus houses chromosomes and coordinates gene expression; cytoplasm acts as a reaction medium; cell membrane controls entry/exit; cell wall prevents osmotic bursting; mitochondria release ATP; chloroplasts perform photosynthesis; ribosomes assemble proteins; vacuole maintains turgor pressure.

Plant vs. Animal Cell Structures

Both possess a nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes. Plant cells uniquely feature a rigid cellulose cell wall, large permanent vacuole, and chloroplasts, whereas animal cells lack these and possess a flexible, irregular shape.

Cell Differentiation

The developmental process by which unspecialized cells acquire distinct structural modifications to carry out dedicated physiological functions (e.g., forming red blood cells or root hair cells).

Stem Cells in Medicine

Unspecialized cells capable of differentiating into any cell type to replace damaged tissues (treating paralysis, diabetes, leukemia); disadvantages include ethical issues surrounding human blastocyst destruction and risks of viral infection or tumor formation.

Elements in Biological Molecules

The elemental building blocks: carbohydrates (Carbon, Hydrogen, Oxygen), proteins (Carbon, Hydrogen, Oxygen, Nitrogen, and sometimes Sulfur), and lipids (Carbon, Hydrogen, Oxygen).

Structure of Carbohydrates, Proteins, and Lipids

Carbohydrates (starch and glycogen) are large polymers of glucose monomers; proteins are polymer chains assembled from amino acid monomers; lipids are large molecules formed from one glycerol molecule bound to three fatty acid tails.

Food Tests

Chemical tests: Benedict's solution heated above $70\,^\circ\text{C}$ changes blue to green/yellow or brick-red for glucose; iodine changes orange-brown to blue-black for starch; Biuret changes blue to purple/violet for protein; ethanol mixed with water forms a milky-white emulsion for lipids.

Enzymes

Specialized globular proteins acting as biological catalysts that lower activation energy to accelerate metabolic reactions without being consumed or permanently altered.

Enzyme Denaturation (Temperature)

The permanent alteration of an enzyme's active site shape occurring when heated past its optimum temperature, which disrupts internal protein bonds so the substrate cannot fit.

Investigating Temperature and Enzyme Activity

Practical mixing starch and amylase at set water bath temperatures (e.g., $20\,^\circ\text{C}$, $40\,^\circ\text{C}$, $60\,^\circ\text{C}$) and sampling into iodine on a spotting tile to time the complete loss of blue-black coloration.

Enzyme Denaturation (pH)

The loss of enzyme active site shape caused by moving away from optimum pH, which alters amino acid ionic charges, disrupts tertiary protein structure, and halts substrate binding.

Investigating pH and Enzyme Activity

Practical measuring the volume of oxygen released in a measuring cylinder over a fixed timeframe when catalase (e.g., from potato) decomposes hydrogen peroxide at different buffer pH levels.

Diffusion, Osmosis, and Active Transport

Diffusion is passive net particle movement down a concentration gradient; osmosis is passive net water movement across a partially permeable membrane to lower water potential; active transport is particle movement against a gradient using ATP energy.

Factors Affecting Cellular Transport Rates

Higher surface area to volume ratio, shorter diffusion distance, higher temperature, and steeper concentration gradients increase transport rates (concentration gradients do not affect active transport).

Diffusion and Osmosis Practicals

Non-living diffusion: potassium manganate(VII) spreading in water; non-living osmosis: sucrose solution rising in visking tubing; living osmosis: weighed potato cylinders gaining mass in dilute sucrose or losing mass in concentrated sucrose.

Photosynthesis

The chemical process in chloroplasts that absorbs light energy using chlorophyll and converts it into chemical energy stored within glucose chemical bonds.

Photosynthesis Equations

Word equation: Carbon Dioxide + Water $\rightarrow$ Glucose + Oxygen (with light and chlorophyll); Balanced symbol equation: $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.

Limiting Factors of Photosynthesis

Environmental factors that restrict the photosynthetic rate when in short supply: light intensity, carbon dioxide concentration, and temperature (which denatures enzymes if raised past optimum).

Leaf Adaptations for Photosynthesis

Waxy cuticle (waterproofing), upper epidermis (transparent), palisade mesophyll (densely packed with chloroplasts), spongy mesophyll (air spaces for gas diffusion), and stomata with guard cells (controlled gas exchange).

Magnesium and Nitrate Ions in Plants

Magnesium ions are required to synthesize chlorophyll (deficiency causes leaf yellowing/chlorosis); nitrate ions are needed to produce amino acids for protein synthesis (deficiency causes stunted growth).

Investigating Light Intensity and Photosynthesis

Practical submerging Elodea pondweed in sodium hydrogencarbonate solution and recording oxygen bubbles emitted per minute as a lamp is placed at measured distances (e.g., $10\,\text{cm}$, $20\,\text{cm}$, $30\,\text{cm}$).

Balanced Diet

An intake supplying appropriate proportions of carbohydrates, proteins, lipids, vitamins, minerals, water, and dietary fiber to satisfy energetic and metabolic requirements.

Dietary Nutrients and Functions

Carbohydrates (energy), proteins (growth/repair), lipids (energy storage/insulation), vitamin A (vision), vitamin C (collagen synthesis), vitamin D (calcium absorption), calcium (bones/teeth), iron (haemoglobin), water (cytoplasmic/transport medium), and fiber (gut bulk for peristalsis).

Variations in Energy Requirements

Energy demands increase with higher physical activity levels (muscular work), younger age and adolescence (tissue development), and pregnancy (fetal development).

Alimentary Canal Organs

Mouth (teeth and salivary amylase), oesophagus (peristalsis), stomach (churning, HCl, pepsin), duodenum (bile and pancreatic enzyme action), ileum (villi absorption), large intestine (colon water reabsorption, rectum storage), and pancreas (enzyme secretion).

Peristalsis

Coordinated, alternating waves of contraction and relaxation of circular and longitudinal muscles in the alimentary canal wall that propel food boluses independently of gravity.

Digestive Enzymes

Amylase (digests starch to maltose), maltase (digests maltose to glucose), proteases (break proteins into amino acids), and lipases (cleave lipids into fatty acids and glycerol).

Bile Production and Storage

Bile is continuously synthesized by liver cells and stored in the gall bladder before transport through the bile duct into the duodenum.

Functions of Bile

Neutralisation of acidic stomach chyme to create optimum alkaline duodenum conditions for pancreatic enzymes, and emulsification of large lipid globules into tiny droplets to expand surface area for lipase.

Villus Adaptations

Microvilli (increase surface area), one-cell thick epithelium (short diffusion pathway), extensive capillary bed (sweeps glucose/amino acids away to maintain steep gradients), and central lacteal (absorbs fatty acids and glycerol).

Food Calorimetry Practical

Burning a weighed food sample (e.g., crisp) directly beneath a boiling tube with a set volume of water (e.g., $20\,\text{cm}^3$) to calculate energy release via water temperature rise.

Respiration and ATP

The chemical breakdown of glucose inside cytoplasm and mitochondria to release energy stored in chemical bonds to synthesize Adenosine Triphosphate (ATP).

ATP Hydrolysis

The rapid removal of a phosphate group from an ATP molecule, releasing an immediate packet of localized energy to power cellular tasks such as active transport, protein synthesis, and muscle contraction.

Aerobic vs. Anaerobic Respiration

Aerobic respiration uses oxygen, achieves complete glucose breakdown, produces $CO_2$ and water, and yields high ATP; anaerobic respiration lacks oxygen, incompletely breaks down glucose, yields low ATP, and forms lactic acid (animals) or ethanol and $CO_2$ (plants/yeast).

Aerobic Respiration Equations

Word equation: Glucose + Oxygen $\rightarrow$ Carbon Dioxide + Water (+ATP); Balanced symbol equation: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$.

Anaerobic Respiration Equations

In animals: Glucose $\rightarrow$ Lactic Acid; In plants and yeast (fermentation): Glucose $\rightarrow$ Ethanol + Carbon Dioxide.

Investigating Respiration in Germinating Seeds

Demonstrating $CO_2$ release by bubbling seed gases through limewater (turns milky-white) and heat release by measuring temperature increases inside insulated vacuum flasks containing living vs. dead boiled seeds.

Diffusion in Plant Gas Exchange

The passive net transport of carbon dioxide and oxygen down concentration gradients through open stomata and intercellular air spaces without metabolic energy expenditure.

Net Gas Exchange in Light vs. Dark

In light, photosynthesis exceeds respiration, resulting in net carbon dioxide uptake and net oxygen release; in dark, photosynthesis stops while respiration continues, yielding net oxygen uptake and net carbon dioxide release.

Leaf Gas Exchange Adaptations

A thin profile (short diffusion distance), extensive spongy mesophyll air spaces (increased internal surface area), and lower epidermis stomatal pores (regulated gas access).

Stomata in Gas Exchange

Regulated microscopic pores that open during daylight to allow carbon dioxide uptake for photosynthesis, and close in darkness or drought to limit transpiration water loss.

Light Intensity and Gas Exchange Balance

The dynamic shifts in net gas movement resulting from continuous 24-hour background respiration interacting with variable light-dependent photosynthetic rates.

Hydrogen-Carbonate Indicator Practical

Testing leaf net gas exchange: indicator turns purple in bright light (alkaline, $CO_2$ used), yellow in dark (acidic, $CO_2$ produced), and stays red in dim light (compensation point).

Thorax Structure

The thoracic cavity structures: ribs, intercostal muscles, diaphragm, trachea (with C-shaped cartilage rings), bronchi, bronchioles, alveoli, and double-layered pleural membranes.

Ventilation Mechanism

Inhalation: diaphragm contracts and flattens, external intercostals contract (ribs move up/out), volume increases, pressure drops below atmospheric. Exhalation: diaphragm relaxes and domes upward, external intercostals relax (ribs move down/in), volume decreases, pressure rises.

Alveoli Adaptations

Massive collective surface area (millions of air sacs), one-cell thick walls, dense surrounding capillary network (maintaining steep diffusion gradients), and a moist internal surface to dissolve gases.

Biological Consequences of Smoking

Emphysema (destruction and fusing of alveolar elastic walls), smoker's cough (tar paralyzing ciliated epithelial cells), and coronary heart disease (nicotine narrowing arteries; carbon monoxide binding haemoglobin).

Breathing and Exercise Practical

Exhaling into limewater to confirm $CO_2$ release (turns cloudy), and tracking breathing rate and depth increases after $3\text{ minutes}$ of exercise to supply oxygen and remove carbon dioxide.

Unicellular Transport by Diffusion

The ability of single-celled organisms to rely purely on surface diffusion to meet metabolic demands due to their large surface area to volume ratio and short transport distances.

Need for Multicellular Transport Systems

The requirement for specialized internal transport networks (like blood vessels) in large organisms due to their low surface area to volume ratio and long internal diffusion pathways.

Phloem and Translocation

Tubes of living cells that transport manufactured organic nutrients (sucrose and amino acids) bidirectionally between leaves, roots, and growing regions via an active process called translocation.

Xylem Vessels

Non-living hollow tubes reinforced with lignin that conduct water and dissolved mineral ions upward from roots to leaves driven by transpiration pull.

Water Absorption by Root Hair Cells

The osmotic movement of water from high water potential in soil into root hair cells, facilitated by elongated hair-like extensions that increase absorptive surface area.

Transpiration

The loss of water vapor from a plant via evaporation from moist spongy mesophyll cell walls into internal air spaces, followed by diffusion out of the leaf through stomata.

Factors Affecting Transpiration Rate

Increased wind speed, higher temperature, and higher light intensity increase transpiration; higher environmental humidity decreases transpiration by reducing the concentration gradient.

Bubble Potometer Practical

An apparatus used to estimate plant water uptake by tracking the distance an air bubble moves along a capillary scale over a set time (e.g., $10\text{ minutes}$) under varied conditions.

Blood Composition

The four main constituents of blood: plasma (straw-colored fluid matrix), red blood cells (erythrocytes), white blood cells (phagocytes and lymphocytes), and platelets (cellular fragments).

Functions of Blood Plasma

The liquid vehicle transporting carbon dioxide (as hydrogencarbonate ions), digested nutrients (glucose and amino acids), urea, hormones, and distributing heat energy evenly.

Red Blood Cell Adaptations

Biconcave shape (maximizes surface area to volume ratio), lack of a nucleus (frees space for haemoglobin), and presence of haemoglobin (binds reversibly with oxygen to form oxyhaemoglobin).

Phagocytes and Lymphocytes

Phagocytes engulf and digest pathogens using enzymes in vacuoles via phagocytosis; lymphocytes produce specific antibodies that bind foreign antigens to agglutinate pathogens or mark them for destruction.

Vaccination and Memory Cells

The introduction of dead, harmless, or weakened antigens to stimulate lymphocyte antibody production and memory cell formation, enabling rapid, high-volume antibody release upon reinfection.

Blood Clotting

Platelets adhere to damaged blood vessel walls and release factors that convert soluble plasma fibrinogen into an insoluble mesh of fibrin threads, trapping red blood cells to seal wounds.

Heart Structure and Circulation

A four-chambered pump: deoxygenated blood enters the right atrium via the vena cava, passes the tricuspid valve into the right ventricle, and exits via pulmonary artery; oxygenated blood enters the left atrium via pulmonary vein, passes the bicuspid valve into the left ventricle, and leaves through the aorta.

Heart Rate Regulation (Exercise and Adrenaline)

Elevated blood $CO_2$ during exercise causes the brain to send nerve impulses accelerating pacemaker rate; adrenaline released during fear/stress binds pacemaker cells to rapidly elevate heart rate and stroke volume.

Coronary Heart Disease (CHD)

Blockage of coronary arteries by fatty plaques, reducing oxygen delivery to heart muscle; risk factors include high-fat diet, smoking, chronic stress, hypertension, lack of exercise, and genetic predisposition.

Arteries, Veins, and Capillaries

Arteries have thick muscular walls and elastic fibers for high-pressure blood; veins have thin walls, a wide lumen, and valves for low-pressure blood; capillaries have one-cell thick walls for rapid tissue exchange.

Major Systemic Blood Vessels

To/from lungs: pulmonary artery and pulmonary vein; To/from liver: hepatic artery, hepatic vein, and hepatic portal vein; To/from kidneys: renal artery and renal vein.

Plant Metabolic Waste Excretion

Carbon dioxide from cellular respiration is excreted via stomata when respiration exceeds photosynthesis; oxygen from photolysis in photosynthesis is excreted via stomata when photosynthesis exceeds respiration.

Human Excretory Products

Lungs excrete carbon dioxide and water vapor; kidneys excrete urea, excess mineral ions, and water as urine; skin excretes water and mineral salts via sweat.

Kidney Roles: Excretion and Osmoregulation

Excretion involves filtering toxic urea out of the bloodstream; osmoregulation involves adjusting the volume of water reabsorbed into the blood to maintain stable plasma water potential.

Urinary System Organs

Two kidneys (filter blood and form urine), two ureters (transport urine to bladder), a bladder (muscular urine storage bag), and a urethra (channel discharging urine externally).

Nephron Structure

The functional filtration unit of the kidney: glomerulus, Bowman's capsule, proximal convoluted tubule (PCT), loop of Henle, and collecting duct.

Ultrafiltration

The filtration of blood under high hydrostatic pressure in the glomerulus, forcing small molecules (water, glucose, amino acids, urea, ions) into Bowman's capsule to form glomerular filtrate while retaining cells and large proteins.

Collecting Duct Water Reabsorption

The osmotic movement of water from urine inside the collecting duct into the surrounding hypertonic tissue fluid of the medulla, where it is reabsorbed into blood capillaries.

Selective Reabsorption of Glucose

The complete reabsorption of all glucose from the glomerular filtrate back into the blood at the proximal convoluted tubule via active transport against a concentration gradient.

ADH in Water Balance

When dehydrated, the pituitary secretes more ADH, making collecting ducts more permeable so more water is reabsorbed (producing low volume, concentrated urine); when hydrated, less ADH is released (producing high volume, dilute urine).

Normal Urine Composition

A sterile solution of water, urea, and excess mineral ions (e.g., sodium and chloride); healthy urine contains zero glucose, protein, or blood cells.

Organism Response to Stimuli

The mechanism where environmental changes (stimuli) are detected by specialized receptors and coordinated via nervous or endocrine pathways to trigger effectors (muscles or glands).

Homeostasis

The maintenance of a constant internal environment via negative feedback mechanisms, such as regulating water potential (osmoregulation) and core body temperature (thermoregulation).

Coordinated Response Sequence

The biological response pathway: Stimulus (change) $\rightarrow$ Receptor (detector) $\rightarrow$ Coordinator (CNS) $\rightarrow$ Effector (muscle/gland) $\rightarrow$ Response (action).

Plant Tropisms

Directional plant growth movements toward or away from environmental directional stimuli such as light and gravity.

Phototropism and Geotropism

Stems show positive phototropism (grow toward light) and negative geotropism (grow away from gravity); roots show negative phototropism and positive geotropism (grow downward with gravity).

Auxin in Stem Phototropism

A plant hormone synthesized at shoot tips that diffuses to the shaded side; high auxin concentrations cause shaded cells to elongate, bending the stem toward light.

Nervous vs. Hormonal Communication

Nervous coordination uses fast electrical impulses along neurones for localized, short-lived responses; hormonal coordination uses chemical messengers in the blood for widespread, slow, and long-lasting responses.

Central Nervous System (CNS)

The primary coordinator comprising the brain and spinal cord, connected to sense organs and effectors by sensory and motor nerves.

Sense Organ Receptor Transmission

Stimulated receptors fire electrical impulses along sensory axons into the CNS, which integrates signals and dispatches motor impulses to effectors for rapid action.

Synapse and Neurotransmitters

A microscopic gap between neurones across which chemical neurotransmitters diffuse from vesicles and bind specific receptors on the subsequent neurone to initiate a new electrical impulse.

Reflex Arc (Finger Withdrawal)

Involuntary sequence: heat stimulus $\rightarrow$ skin receptor $\rightarrow$ sensory neurone $\rightarrow$ spinal relay neurone $\rightarrow$ motor neurone $\rightarrow$ biceps effector contraction $\rightarrow$ withdrawal response.

Eye Structures as a Receptor

Cornea (refracts light), iris (controls pupil size), lens (focuses light), retina (contains light-intensity rod cells and color cone cells), and optic nerve (transmits impulses to brain).

Accommodation and Pupil Reflexes

Near vision: ciliary muscles contract, suspensory ligaments slacken, lens rounds; Distant vision: ciliary muscles relax, ligaments tighten, lens flattens; Dim light: radial muscles contract (pupil dilates); Bright light: circular muscles contract (pupil constricts).

Skin Thermoregulation

When hot: sweat evaporates, surface arterioles dilate (vasodilation) to radiate heat, hairs lie flat. When cold: arterioles narrow (vasoconstriction), shivering generates metabolic heat, hairs stand erect to trap air.

Hormones: Adrenaline, Insulin, Testosterone, Oestrogen, Progesterone

Adrenaline prepares for fight-or-flight; insulin promotes glucose uptake into glycogen; testosterone drives male secondary sexual traits; oestrogen repairs the uterus lining; progesterone maintains the thickened uterus lining.

Pituitary Hormones (ADH, FSH, LH)

ADH controls kidney collecting duct water reabsorption; FSH stimulates ovarian follicle development and oestrogen release; an LH surge triggers ovulation.

Sexual vs. Asexual Reproduction

Sexual reproduction involves gamete fusion (meiosis) from two parents to create genetic variation; asexual reproduction involves one parent (mitosis) producing genetically identical clones.