IGCSE Biology: Comprehensive Review of Biological Molecules, Organisms, Gas Exchange, Nutrition, and Respiration

A set of vocabulary flashcards reviewing key biological terms, chemical equations, cell structures, gas exchange concepts, nutrition, and cellular respiration.

Monosaccharide

A simple single sugar unit, such as glucose ($\text{C}_6\text{H}_{12}\text{O}_6$), which serves as a basic building block for larger carbohydrates.

Polysaccharide

A large, insoluble carbohydrate polymer formed when many monosaccharides join together, such as starch, glycogen, or cellulose.

Triglyceride

A lipid molecule composed of one molecule of glycerol bonded to three fatty acid tails.

Benedict's Test

A chemical test for reducing sugars (like glucose) using Benedict's solution, which turns from light blue to green, yellow, or brick-red when heated with the sample.

Biuret Test

A chemical test used to detect proteins using Biuret solution, producing a colour change from blue to lilac/purple in a positive result.

Emulsion Test

A chemical test for lipids where the food sample is dissolved in ethanol and mixed with distilled water, forming a cloudy white emulsion if lipids are present.

Enzyme

A protein that acts as a biological catalyst, speeding up metabolic chemical reactions in cells without being consumed or permanently altered.

Active Site

The specific region of an enzyme molecule with a complementary shape where the substrate binds to form an enzyme-substrate complex.

Denaturation

An irreversible structural change in a protein or enzyme caused by high temperatures or extreme pH, breaking bonds and distorting the active site shape so substrates can no longer fit.

MRS C GREN

An acronym for the eight fundamental characteristics of living organisms: Movement, Respiration, Sensitivity, Control, Growth, Reproduction, Excretion, and Nutrition.

Excretion

The biological process of eliminating toxic materials, metabolic waste products (such as carbon dioxide, urea, and excess water), and substances in excess of requirements from an organism.

Homeostasis

The maintenance and regulation of a constant internal environment within an organism, such as thermoregulation ($37^\text{o}\text{C}$ in humans) or osmoregulation.

Saprotrophic Nutrition

A mode of heterotrophic nutrition used by fungi where extracellular digestive enzymes are secreted onto organic matter and the soluble digested products are absorbed.

Mycelium

A network of microscopic, thread-like filaments called hyphae that make up the body structure of multicellular fungi.

Prokaryotic Organism

A microscopic single-celled organism (such as a bacterium) that lacks a membrane-bound nucleus and membrane-bound organelles, containing genetic material as a circular DNA chromosome in the cytoplasm.

Typical Bacterial Cell Structure

A microscopic single-celled prokaryotic structure with a cell wall made of peptidoglycan, cell membrane, cytoplasm, ribosomes, circular loop of DNA, and plasmids, lacking a nucleus.

Pathogen

A disease-causing organism, which can be a bacterium, virus, fungus, or protoctist.

Virus

A non-living, microscopic parasitic particle consisting of a protein coat surrounding nucleic acid (DNA or RNA) that can only reproduce inside a host cell.

Gas Exchange

The exchange of gases (oxygen and carbon dioxide) across a specialized surface between an organism or cell and its surrounding environment down concentration gradients.

Hydrogen-carbonate Indicator

A chemical indicator used to measure carbon dioxide levels, showing orange in normal atmospheric conditions, yellow at high carbon dioxide levels, and purple at low carbon dioxide levels.

Thorax

The chest cavity in humans bounded by the ribs, intercostal muscles, and diaphragm, housing the lungs, trachea, and heart.

Alveoli

Tiny, balloon-like air sacs located at the terminals of bronchioles in the lungs that act as specialized gas exchange surfaces.

Inhalation

The process of breathing air in, achieved when the diaphragm contracts and flattens and external intercostal muscles contract to lift the ribcage up and out, increasing thorax volume and dropping pressure inside the lungs.

Chronic Bronchitis

A respiratory disease linked to smoking where tar stimulates excess mucus secretion and damages cilia, resulting in blocked bronchioles, infections, and severe coughing.

Emphysema

A smoking-induced lung condition where elastase released by phagocytes breaks down elastic fibers in alveolar walls, causing alveoli to burst and significantly reducing the surface area for gas exchange.

Photosynthesis

The chemical reaction by which green plants synthesize carbohydrates like glucose from carbon dioxide ($\text{CO}_2$) and water ($\text{H}_2\text{O}$) using light energy absorbed by chlorophyll, releasing oxygen ($\text{O}_2$) as a byproduct.

Limiting Factor

An environmental component (such as temperature, light intensity, or carbon dioxide concentration) present in shortest supply that restricts the rate of a process like photosynthesis.

Palisade Mesophyll

The layer of column-shaped cells located near the upper surface of a leaf, tightly packed with chloroplasts to maximize light absorption for photosynthesis.

Leaf Structure for Gas Exchange

Anatomy of a plant leaf arranged in layers: protective wax cuticle, upper epidermis, palisade mesophyll, spongy mesophyll with air spaces, vascular bundle (xylem and phloem), lower epidermis, and stomata with guard cells.

Chlorosis

A plant condition caused by magnesium ion ($\text{Mg}^{2+}$) deficiency, characterized by yellowing between leaf veins due to a lack of chlorophyll synthesis.

Peristalsis

Rhythmic wave-like contractions of circular and longitudinal muscle layers in the alimentary canal wall that push food boluses and chyme along the digestive tract.

Amylase

A digestive carbohydrase enzyme produced in the salivary glands, pancreas, and small intestine that catalyzes the breakdown of starch into maltose.

Bile

An alkaline fluid synthesized in the liver and stored in the gall bladder that neutralizes stomach acid and mechanically emulsifies large lipid droplets into smaller droplets in the duodenum.

Villi

Microscopic, finger-like projections extending from the wall of the small intestine that increase surface area for the efficient absorption of digested food molecules and water.

Villus Structure

A single villus adapted for rapid absorption, featuring microvilli on its epithelial surface, a thin wall one cell thick, a capillary network for absorbing glucose and amino acids, and a central lacteal for absorbing fatty acids and glycerol.

Aerobic Respiration

The cellular chemical process occurring in mitochondria that uses oxygen ($\text{O}_2$) to completely break down glucose ($\text{C}_6\text{H}_{12}\text{O}_6$), releasing carbon dioxide ($\text{CO}_2$), water ($\text{H}_2\text{O}$), and a large amount of ATP energy.

ATP (Adenosine Triphosphate)

The universal chemical energy currency synthesized during respiration that supplies usable energy for cellular work such as active transport, cell division, and muscle contraction.

Anaerobic Respiration

The cellular chemical breakdown of glucose without oxygen, yielding incomplete breakdown products and releasing a smaller quantity of ATP energy compared to aerobic respiration.

Lactic Acid

The toxic organic acid produced in animal muscle cells during high-intensity exercise as a product of anaerobic respiration.

Fermentation

The form of anaerobic respiration carried out by yeast and plant cells that breaks down glucose into ethanol and carbon dioxide.