Videos
International Baccalaureate · IB Diploma · Biology · HL
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16 video lessons
3:57
Nucleic acids
A change in DNA can affect a protein, but not every DNA change changes the amino-acid sequence. The effe…
3:56
Origins of cells
Mitochondria have their own DNA and divide within cells. These features invite an evolutionary explanati…
3:46
Viruses
An antibiotic may help against a bacterial infection but fail against a viral illness. Treatment depends…
3:27
Diversity of organisms
Two species look similar but their DNA comparison places them in different branches. Classification uses…
3:59
Evolution and speciation
Leaves in dry environments often have features that reduce water loss. The value of a feature depends on…
3:45
Conservation of biodiversity
A site with many individuals can still be dominated by one species. Abundance, richness and evenness 均匀度…
4:36
Carbohydrates and lipids
Starch, a triglyceride and a protein can all contain carbon, hydrogen and oxygen, yet their structures a…
4:14
Membranes and membrane transport
A potato cylinder gains mass in one solution and loses mass in another. Its mass change provides evidenc…
3:46
Cell specialization
A root-hair cell and a red blood cell have different shapes because their functions impose different demands.
3:59
Gas exchange
An exchange surface can be very thin yet fail to deliver enough oxygen when ventilation 通气 or blood flow…
4:29
Ecological niches
Two species can share a habitat while using different resources or using the same resource at different …
3:52
Enzymes and metabolism
An enzyme 酶 works quickly at one temperature and slowly at another. Heating can increase successful coll…
3:43
Chemical signalling
Two cell types encounter the same signal but respond differently. Their receptors 受体 and internal pathwa…
3:50
Neural signalling
A stronger stimulus can increase impulse frequency while each action potential 动作电位 remains a similar size.
3:51
Cell and nuclear division
A root-tip image contains cells at different stages of mitosis. A snapshot can estimate the fraction of …
3:38
Gene expression
Two cells with the same genome make different proteins. Regulation changes which information is used and when.