Circulatory System 3 - Blood

This lesson covers:

  1. The roles of red blood cells, white blood cells, platelets, and blood plasma
Illustration showing red blood cells.

What is the role of red blood cells?

To carry oxygen from the lungs to the tissues 

To clot the blood when a blood vessel breaks 

To carry substances and cells around the body

To defend against pathogens 

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Red blood cells are packed full of a large proteins called , which bind to oxygen. 

haemoglobin

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How are red blood cells adapted for their function?

(Select all that apply)

They have no nucleus to fit in more haemoglobin 

They have a biconcave shape to increase their surface area

They have a nucleus so they can divide by mitosis 

They have spherical shape to fit in more haemoglobin 

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What is the role of white blood cells?

To carry oxygen from the lungs to the tissues 

To carry substances and cells around the body

To defend against pathogens 

To clot the blood when a blood vessel breaks 

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is the process by which a white blood cell binds to, and then engulfs a pathogen, in order to destroy it. 

Phagocytosis

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Illustration showing antibodies with antigen-binding sites highlighted.

How do antibodies help defend against pathogens? 

They bind to pathogens and help immune cells destroy them

They activate our immune system 

They stop pathogens from entering the body 

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Do white blood cells have a nucleus? 

Yes

No

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What is the role of platelets?

To clot the blood when a blood vessel breaks 

To carry oxygen from the lungs to the tissues 

To defend against pathogens 

To carry substances and cells around the body

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Give two reasons why it is so important that our blood clots when we are cut.

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Do platelets have a nucleus? 

Yes

No

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What is the role of blood plasma?

To carry substances and cells around the body

To clot the blood when a blood vessel breaks 

To carry oxygen from the lungs to the tissues 

To defend against pathogens 

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The blood plasma is a yellowish liquid that makes up 55% of the bloods volume. Its role is to carry large structures like red blood cells, white blood cells, and platelets, as well as smaller dissolved substances.


Name as many of these smaller dissolved substances as you can. 

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