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Biology

A1.2 Nucleic acids

What Is 5' to 3' Direction in DNA? (AHL)

Learn what 5' to 3' direction means in DNA, why strands are antiparallel, and how directionality controls DNA replication and transcription in IB HL.

A1.2 Nucleic acids

What Was Chargaff's Rule and How Did It Disprove the Tetranucleotide Hypothesis? (AHL)

Learn how Chargaff's rule-A equals T and G equals C-and species-specific base ratios disproved the equal-base tetranucleotide model of DNA.

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A1.2 Nucleic acids

Why Do AtoT and CtoG Pairs Have the Same Length? (AHL)

Learn why AtoT and CtoG DNA base pairs have equal width, how purinetopyrimidine pairing stabilizes DNA, and what IB Biology AHL answers must include.

A1.2 Nucleic acids

Why Is the Genetic Code the Same in All Living Things?

Learn why the genetic code is nearly universal, how this supports common ancestry, and what IB Biology exam answers must distinguish clearly.

A1.2 Nucleic acids

What Was the Hershey-Chase Experiment and What Did It Prove?

Learn how the Hershey-Chase experiment used radioactive bacteriophages to show that DNA, rather than protein, carries genetic information in cells.

A1.2 Nucleic acids

What Is a Nucleosome? (AHL)

Learn the AHL structure of a nucleosome: DNA wrapped around eight histone proteins, plus the additional histone associated with linker DNA.

Why Are Some Molecules in Cells Hydrophobic Instead of Dissolving in Water?

Learn why non-polar molecules are hydrophobic in cells, how water drives them together, and why this property is essential for cell membranes.

A1.2 Nucleic acids

What Is Complementary Base Pairing?

Learn how complementary base pairing links nucleic acid bases through hydrogen bonds and enables accurate DNA replication, transcription and translation.

A1.2 Nucleic acids

Why Is DNA Antiparallel?

Learn why DNA strands run in opposite 5′ to 3′ directions, how this supports complementary base pairing, and what IB Biology examiners expect.

A1.2 Nucleic acids

What's the Difference Between DNA and RNA?

Learn the key structural and functional differences between DNA and RNA, including sugars, bases, strands and roles, for IB Biology exams at SL and HL.

What Is Specific Heat Capacity and Why Does It Matter for Aquatic Habitats?

Learn why water’s high specific heat capacity stabilizes aquatic habitats, moderates temperature change and supports organisms in IB Biology A1.1.

A1.2 Nucleic acids

What Is the Sugar-Phosphate Backbone of DNA?

Learn how alternating deoxyribose sugars and phosphate groups form DNA’s strong sugar-phosphate backbone and how to describe it in IB exams.

A1.2 Nucleic acids

Why Does DNA Form a Double Helix?

Learn why DNA forms a stable double helix through complementary base pairing, hydrogen bonding, base stacking and antiparallel nucleotide strands.

A1.2 Nucleic acids

What Are the 4 Bases in DNA vs RNA?

Learn the four nitrogenous bases in DNA and RNA, how complementary base pairing differs, and the terminology required for IB Biology exams.

Why Do Fish Need Less Energy to Move Than Land Animals? (Viscosity/Buoyancy)

Learn how buoyancy reduces support costs in fish while water’s viscosity increases drag, and how to explain this balance clearly in IB Biology A1.1.

How Do Plants Move Water Without a Pump (Capillary Action + Transpiration)?

Learn how transpiration pull, cohesion, adhesion and capillary action move continuous water columns through xylem from roots to leaves for IB Biology exams.

Where Did Earth's Water Come From? (AHL)

Learn the IB Biology AHL explanation that asteroids supplied Earth's water, and how gravity and sufficiently low temperatures retained it over time.

Why Does Water Have Cohesion and Adhesion?

Learn how water’s polarity and hydrogen bonding cause cohesion and adhesion, supporting surface tension, capillary action and transport in xylem.

What Is the “Goldilocks Zone” and Why Does It Matter for Finding Alien Life? (AHL)

Learn how the Goldilocks zone identifies planets where liquid water may persist and why this guides the IB Biology search for extraterrestrial life.

A1.2 Nucleic acids

What Is a Nucleotide Made Of?

Learn the three components of a nucleotide, how DNA and RNA nucleotides differ, and the precise structures and diagram labels expected in IB Biology exams.

Why Is Water Polar?

Learn why water is polar through oxygen’s electronegativity, polar covalent bonds and molecular shape, with precise IB Biology exam terminology.

What Is a Hydrogen Bond in Water?

Learn how water’s polarity creates hydrogen bonds between molecules and how these bonds explain cohesion, surface tension, and water transport in plants.

Why Is Water a Good Solvent for Life?

Learn how water’s polarity and hydrogen bonding make it an effective solvent for metabolism and transport in IB Biology A1.1 Water at SL and HL for exams.

Why Can Water Striders Walk on Water? (Surface Tension)

Learn how hydrogen bonding creates surface tension and how water striders use hydrophobic, widely spread legs to remain and move on the water surface.

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