International Baccalaureate · IB Diploma · Biology · HL

4:06 Topic 1 Water A water droplet holds together on a leaf. Its behaviour comes from interactions between molecules, not a… 3:57 Topic 2 Nucleic acids A change in DNA can affect a protein, but not every DNA change changes the amino-acid sequence. The effe… 3:56 Topic 3 Origins of cells Mitochondria have their own DNA and divide within cells. These features invite an evolutionary explanati… 3:48 Topic 4 Cell structure A cell can look larger on a screen without changing its real size. Two photographs at different zoom set… 3:46 Topic 5 Viruses An antibiotic may help against a bacterial infection but fail against a viral illness. Treatment depends… 3:27 Topic 6 Diversity of organisms Two species look similar but their DNA comparison places them in different branches. Classification uses… 3:59 Topic 8 Evolution and speciation Leaves in dry environments often have features that reduce water loss. The value of a feature depends on… 3:45 Topic 9 Conservation of biodiversity A site with many individuals can still be dominated by one species. Abundance, richness and evenness 均匀度… 4:36 Topic 10 Carbohydrates and lipids Starch, a triglyceride and a protein can all contain carbon, hydrogen and oxygen, yet their structures a… 4:14 Topic 12 Membranes and membrane transport A potato cylinder gains mass in one solution and loses mass in another. Its mass change provides evidenc… 3:46 Topic 14 Cell specialization A root-hair cell and a red blood cell have different shapes because their functions impose different demands. 3:59 Topic 15 Gas exchange An exchange surface can be very thin yet fail to deliver enough oxygen when ventilation 通气 or blood flow… 3:52 Topic 16 Transport Two foods can have the same mass but provide different nutrients. A health claim must distinguish the nu… 3:41 Topic 17 Muscle and motility A sarcomere 肌节 becomes shorter during contraction although its thick and thin filaments keep approximate… 4:29 Topic 19 Ecological niches Two species can share a habitat while using different resources or using the same resource at different … 3:52 Topic 20 Enzymes and metabolism An enzyme 酶 works quickly at one temperature and slowly at another. Heating can increase successful coll… 4:36 Topic 21 Cell respiration A muscle can use oxygen while you exercise without producing a flame. Respiration 呼吸作用 transfers energy … 3:52 Topic 22 Photosynthesis A brighter lamp does not always produce more oxygen from pondweed. Another factor may limit the process … 3:41 Topic 23 Chemical signalling Two cell types encounter the same signal but respond differently. Their receptors 受体 and internal pathwa… 3:50 Topic 24 Neural signalling A stronger stimulus can increase impulse frequency while each action potential 动作电位 remains a similar size. 3:56 Topic 25 Integration of body systems Blood glucose rises after a meal, but usually does not keep rising indefinitely. A control system respon… 3:59 Topic 27 Populations and communities A field edge looks richer in plants than its centre. Choosing only the richest patches would build the d… 4:45 Topic 28 Transfer of energy and matter Energy available as new biomass usually decreases along a food chain. Energy is conserved overall, but s… 4:32 Topic 29 DNA replication After DNA replication, each daughter double helix contains one pre-existing strand and one newly synthes… 3:51 Topic 32 Cell and nuclear division A root-tip image contains cells at different stages of mitosis. A snapshot can estimate the fraction of … 3:38 Topic 33 Gene expression Two cells with the same genome make different proteins. Regulation changes which information is used and when. 5:06 Topic 34 Water potential A plant cell can stop gaining net water even while its contents contain solute. The cell wall permits pr… 4:47 Topic 35 Reproduction Gametes normally contain one set of chromosomes, while fertilization 受精 joins two sets. Maintaining chro… 3:53 Topic 36 Inheritance Two parents can carry a recessive allele 等位基因 without expressing the associated phenotype. Their childre… 4:11 Topic 40 Climate change One cold day does not disprove a warming climate. Weather describes short-term conditions; climate descr… 4:05 Topic 41 Experimental programme A line passing near every data point is useful, but its gradient can still be uncertain. A graph is evid…