Uploaded March 2025 | Updated September 2026, 9 hours ago
In this video, we look at multiple alleles. First we explore what is meant by multiple alleles. We then look at how the ABO blood group system in humans is an example of multiple alleles. Finally, we look at genetic crosses involving the ABO blood group alleles.
In this video, we look at multiple alleles. First we explore what is meant by multiple alleles. We then look at how the ABO blood group system in humans is an example of multiple alleles. Finally, we look at genetic crosses involving the ABO blood group alleles.






![GCSE Biology Revision Animal Cells
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In this video, we explore the structure of animal cells. I take you through the key structures and their functions and then give you a cell to label yourself.
This video is based on the AQA spec. This video may be appropriate for iGCSE / O Level Biology. Please consult your specification. The Amazon link above is an affiliate link. This provides a small commission which helps to support freesciencelessons. The cost remains the same to you. If you prefer not to use this, you can search Amazon for the Freesciencelessons workbooks.
Image credits:
HeLa cell By TenOfAllTrades at English Wikipedia - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1583880
Fluorescent mitochondria By 8x57is - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44771036
Mitochondria https://commons.wikimedia.org/wiki/File:Mitochondria,_mammalian_lung TEM_(2).jpg
By Louisa Howard [Public domain], via Wikimedia Commons
Cheek cells
https://commons.wikimedia.org/wiki/File:Cheekcells_stained.jpg
Mulletsrokk, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons GCSE Biology Revision Animal Cells](https://i.ytimg.com/vi/mZLSJOVI4l8/mqdefault.jpg)



![GCSE Chemistry Revision Elements, Compounds and Mixtures
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In this video, we look at elements, compounds, mixtures and molecules. First we look at the idea of an element, using examples from the periodic table. I then show you the definition of a compound and what is meant by fixed proportions. We then explore the definition of a mixture and the differences between mixtures and compounds. Finally, we look at what is meant by the word molecule and see how molecules can be elements or compounds.
This video is based on the AQA spec. This video may be appropriate for iGCSE / O Level Chemistry. Please consult your specification. The Amazon link above is an affiliate link. This provides a small commission which helps to support freesciencelessons. The cost remains the same to you. If you prefer not to use this, you can search Amazon for the Freesciencelessons workbooks.
Image credits:
Magnesium https://commons.wikimedia.org/wiki/File:Magnesium-2.jpg
By Jurii (http://images-of-elements.com/magnesium.php) [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
Sulfur https://commons.wikimedia.org/wiki/File:Sulfur-sample.jpg
By Ben Mills [Public domain], from Wikimedia Commons
Magnesium sulfide https://commons.wikimedia.org/wiki/File:Lithium_chloride.jpg GCSE Chemistry Revision Elements, Compounds and Mixtures](https://i.ytimg.com/vi/nUzOXy9V-K0/mqdefault.jpg)