Components of Blood Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Learn about blood as a tissue and identify the main components - plasma, red blood cells, white blood cells and platelets. Understand what each componen...

• Identify the four main components of blood and their locations
• Explain the specific functions of red blood cells, white blood cells, platelets and plasma
• Compare the structures of different blood components and relate them to their functions
• Evaluate how blood components work together as a tissue to maintain health

Key ideas to keep in view

Use this lesson to stay inside B2.2 The challenges of size while connecting the detail back to the wider B2: Scaling up topic.

• B2: Scaling up
• B2.2 The challenges of size
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Components of Blood before testing yourself from memory.

• Picture a busy motorway system carrying everything your body needs to survive. That's blood - but it's not just a simple liquid. Blood is actually a tissue made up of different components, each with a specific job. When you look at blood under a microscope, you'll see it's like a soup with different ingredients floa...
• Blood consists of a liquid called plasma with three types of cells suspended in it: red blood cells, white blood cells, and platelets. Think of plasma as the delivery truck, and the cells as the cargo - each type of cargo has a different destination and purpose.
• The pale yellow liquid component of blood that makes up about 55% of blood volume. Contains water, dissolved nutrients, hormones, antibodies, and waste products.
• Plasma is the transport medium - it's like the river that carries everything else. It's mostly water (about 90%) but contains hundreds of dissolved substances. Glucose travels in plasma to feed your cells, hormones use plasma as their highway, and waste products like carbon dioxide dissolve in plasma to be carried a...
• Biconcave disc-shaped cells packed with haemoglobin protein. They have no nucleus, allowing maximum space for oxygen transport.
• Red blood cells are the oxygen delivery service. Their unique biconcave shape (like a doughnut that's been squashed) gives them a large surface area for gas exchange. The red colour comes from haemoglobin - an iron-containing protein that binds to oxygen in the lungs and releases it in body tissues.
• Larger cells with nuclei that defend the body against pathogens. Include phagocytes that engulf bacteria and lymphocytes that produce antibodies.
• White blood cells are your body's security force. Unlike red blood cells, they have nuclei and can change shape. Some white blood cells (phagocytes) patrol the bloodstream looking for invaders to engulf and destroy. Others (lymphocytes) remember previous infections and produce specific antibodies to fight them.
• Small cell fragments without nuclei that help blood clot at injury sites. They stick together and release chemicals to form a plug.
• Platelets are the emergency repair crew. When you cut yourself, platelets rush to the scene and stick together like biological glue. They're not complete cells - they're fragments of larger cells made in bone marrow. Despite being tiny, they're essential for preventing blood loss.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.