Edexcel A Level (IAL) Biology -1.6-1.7 Blood Vessels: Structure & Function - Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -1.6-1.7 Blood Vessels: Structure & Function- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -1.6-1.7 Blood Vessels: Structure & Function- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
- understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms)
- understand how the structures of blood vessels (capillaries, arteries and veins) relate to their functions
Why Many Animals Have a Heart and Circulation
🌱 Introduction
All living cells need oxygen, nutrients, and removal of wastes (like CO₂) to survive.
In small organisms, substances can diffuse directly through the body because the surface area to volume ratio is large.
As animals get larger, diffusion alone becomes insufficient due to:
- ↓ Surface area to volume ratio
- ↑ Distance for substances to diffuse
- ↑ Metabolic rate → higher demand for nutrients and oxygen
Solution: Animals have evolved a mass transport system a heart and circulation to efficiently transport substances around the body.
🧩 Key Reasons for Having a Heart & Circulation
- Overcoming diffusion limits
Diffusion is too slow for large, multicellular organisms.
Circulation ensures fast movement of substances to all cells. - Transport of essential substances
Oxygen, glucose, hormones, and other nutrients delivered efficiently.
Waste products like CO₂ and urea removed quickly. - Controlled direction
Blood moves in a specific direction from the heart → arteries → capillaries → veins.
Valves prevent backflow. - Maintaining pressure and speed
Heart contraction + elastic recoil of vessels → maintains blood pressure.
Ensures consistent flow rate for all tissues. - Support for high metabolic rates
High-energy animals (e.g., mammals, birds) need continuous oxygen supply.
Heart and circulation meet the energy demands of active tissues.
⚡ Quick Recap
Small animals: Diffusion sufficient → no heart needed
Large animals: Diffusion insufficient → heart + circulation required
Mass transport system features:
– Network of vessels
– Fluid medium (blood/hemolymph)
– Controlled direction (valves + pressure)
– Maintains speed of transport
Purpose: Deliver nutrients & O₂, remove wastes, support high metabolism
Blood Vessels: Structure & Function
🌱 Introduction
Blood vessels form a network to transport blood around the body.
Different vessels are specialised structurally to carry out their functions efficiently:
- Arteries: carry blood away from the heart under high pressure
- Veins: carry blood toward the heart under lower pressure
- Capillaries: connect arteries and veins, allowing exchange of substances with tissues
🧩 Structures and Functions
| Blood Vessel | Structure | Function | Key Adaptations |
|---|---|---|---|
| Arteries | – Thick muscular wall – Elastic fibres – Narrow lumen | Carry blood away from the heart under high pressure | – Thick wall resists pressure – Elastic fibres stretch and recoil → maintain pressure – Narrow lumen maintains high blood flow speed |
| Veins | – Thin muscular wall – Less elastic tissue – Wide lumen – Valves | Carry blood toward the heart under low pressure | – Valves prevent backflow – Wide lumen eases low-pressure blood flow – Less elastic tissue needed due to low pressure |
| Capillaries | – One cell thick walls (endothelium) – Very narrow diameter | Exchange of gases, nutrients, and wastes between blood & tissues | – Thin wall → short diffusion distance – Narrow diameter → blood moves slowly → efficient exchange – Large number → huge surface area for exchange |
⚡ Key Points
- Structure matches function: thickness, elasticity, lumen size, valves
- Arteries: withstand high pressure → away from heart
- Veins: low pressure → return blood to heart efficiently
- Capillaries: allow diffusion of materials to cells
💡 Quick Recap
📌 Arteries: thick, elastic, narrow → high-pressure transport
📌 Veins: thin, wide, valves → low-pressure return
📌 Capillaries: one-cell wall → efficient exchange