Unit 1: Cells and Multicellular Organisms

Topic 1: Cells as the Basis of Life, Topic 2: Exchange of Nutrients and Wastes, Topic 3: Cellular Energy, Gas Exchange and Plant Physiology

Prokaryotic Cell

A cell without a nucleus or membrane-bound organelles. Example: bacteria.

Eukaryotic Cell

A cell with a nucleus and membrane-bound organelles. Example: plant or animal cell.

Mitochondrion

Organelle that performs aerobic respiration and produces ATP.

Chloroplast

Organelle in plant cells responsible for photosynthesis.

Fluid Mosaic Model

Describes the flexible, dynamic structure of the plasma membrane.

Osmosis

Passive movement of water across a membrane from high to low concentration.

Active Transport

Movement of substances against the concentration gradient using energy (ATP).

SA:V Ratio

Surface area to volume ratio; higher ratios enable more efficient diffusion.

Ribosomes

Organelle that synthesises proteins.They can be found free in the cytoplasm or attached to the endoplasmic reticulum.

Stem Cells

Undifferentiated cells capable of becoming specialised cell types.

Amylase

Enzyme that breaks down starch into simple sugars.It is produced primarily by the pancreas and salivary glands.

Lipase

Enzyme that breaks down lipids into fatty acids and glycerol.

Protease

Enzyme that breaks down proteins into amino acids.

Peristalsis

Wave-like muscle contractions that move food through the digestive tract.

Villi

Finger-like projections in the small intestine that increase surface area for absorption.

Glomerulus

Capillary network in the nephron where filtration of blood occurs.

Bowman’s Capsule

Part of the nephron that collects filtrate from the glomerulus.

Selective Reabsorption

Process in the nephron where useful substances are reabsorbed into the blood.

Large Intestine

Absorbs water and compacts waste into faeces.

Chemical Digestion

The enzymatic breakdown of food molecules into smaller units.

ATP

Adenosine triphosphate; main energy currency of the cell.

Glycolysis

First step of cellular respiration; occurs in cytoplasm and breaks glucose into pyruvate.

Krebs Cycle

Series of reactions in the mitochondrial matrix that release energy via NADH and FADH₂.

Electron Transport Chain

Final stage of aerobic respiration; occurs in mitochondria and produces the most ATP.

Anaerobic Respiration

Respiration without oxygen; produces less ATP and byproducts like lactic acid or ethanol.

Alveoli

Tiny air sacs in lungs where gas exchange occurs.

Photosynthesis

Process by which plants use light to convert CO₂ and H₂O into glucose and O₂.

Light-Dependent Reactions

Stage of photosynthesis that requires light; produces ATP and O₂.

Stomata

Pores on leaves controlled by guard cells that regulate gas exchange and transpiration.

Transpiration

Evaporation of water from plant leaves that helps pull water upward through xylem.

Simple Diffusion

Passive movement of molecules (not water) from high to low concentration without needing proteins.

Facilitated Diffusion

Passive transport of molecules via protein channels or carriers.

Endocytosis

Active transport process where the cell takes in substances via vesicles.

Exocytosis

Active transport process that expels materials from the cell via vesicles.

Phospholipid Bilayer

The two-layered structure forming the cell membrane, with hydrophilic heads and hydrophobic tails.

SA:V Limitation

As a cell grows, its SA:V ratio decreases, reducing diffusion efficiency — limiting cell size.

Nephron

Functional unit of the kidney, responsible for filtering blood and forming urine.

Loop of Henle

Nephron section that concentrates urine by reabsorbing water and salts.

Collecting Duct

Final nephron structure where water reabsorption occurs before urine exits.

Enzyme Specificity

Property of enzymes where only one substrate fits its active site, like a lock and key.

Denaturation

Structural change in an enzyme that causes it to lose function (often due to high heat or pH).

Induced Fit Model

Enzyme model where the active site slightly changes shape to fit the substrate.

Substrate

The reactant molecule that binds to an enzyme’s active site.

Catabolism

Metabolic pathway that breaks molecules down and releases energy (e.g. cellular respiration).

Anabolism

Metabolic pathway that builds complex molecules and stores energy (e.g. photosynthesis, protein synthesis).

ATP-ADP Cycle

The constant conversion between ATP (energy storing) and ADP (used form) to power cellular functions.

Aerobic Respiration

Cellular respiration using oxygen, producing ~36–38 ATP, CO₂ and H₂O.

Fermentation

Anaerobic respiration in yeast, producing alcohol + CO₂ with low ATP yield.

Phloem

Plant tissue that transports sugars from source to sink.

Xylem

Plant tissue that transports water from roots to leaves via transpiration.

Guard Cells

Cells that open and close stomata to control gas exchange and water loss.