# Transport in Mammals

> CIE A-Level Biology · CIE 9700 (2022-2024)
> Source: https://www.owlsprep.com/study/cie-9700-u8-overview/
> Weight: n/a

This unit explores the mammalian circulatory system, covering blood composition, clotting, heart structure/function, blood vessel biology, gas transport, and regulation of heart rate to support whole-body homeostasis.

**Prerequisites:** [Cell membrane transport and cellular respiration](https://www.owlsprep.com/study/cie-9700-u4-cell-membranes-transport/)

## Learning objectives

- Describe the structure and function of mammalian blood components and the blood clotting cascade
- Relate the structure of the heart and blood vessels to their functional roles in circulation
- Explain the sequence of the cardiac cycle and how pressure changes drive valve function
- Describe how oxygen and carbon dioxide are transported in blood, and how heart rate is regulated

## Unit at a Glance

This unit follows a logical learning arc, starting from the transport fluid (blood) moving through the vessels that carry it, the pump that drives circulation (the heart), and ending with how the system adjusts to meet changing body demands. A core theme throughout is how structure is specifically adapted to function at every level of organization.

Below are all sub-topics included in this unit:
- [Blood composition](https://www.owlsprep.com/study/cie-9700-u8-blood-composition/) — Covers plasma and formed elements (RBC, WBC, platelets) and their core functions.
- [Blood clotting](https://www.owlsprep.com/study/cie-9700-u8-blood-clotting/) — Explains the clotting cascade that prevents blood loss and blocks pathogen entry after injury.
- [Heart structure](https://www.owlsprep.com/study/cie-9700-u8-heart-structure/) — Explores the internal and external structure of the mammalian heart and associated blood vessels.
- [Cardiac cycle](https://www.owlsprep.com/study/cie-9700-u8-cardiac-cycle/) — Covers the sequence of systole and diastole, pressure changes, and valve movement.
- [Blood vessels structure and function](https://www.owlsprep.com/study/cie-9700-u8-blood-vessels-structure-and-function/) — Compares the structure and function of arteries, veins, and capillaries.
- [Gas transport in blood](https://www.owlsprep.com/study/cie-9700-u8-gas-transport-in-blood/) — Explains how oxygen and carbon dioxide are transported, including the role of haemoglobin.
- [Regulation of heart rate](https://www.owlsprep.com/study/cie-9700-u8-regulation-of-heart-rate/) — Covers nervous and hormonal control of heart rate in response to changing activity levels.

## Common pitfalls

- **Wrong:** Confusing systole and diastole when describing the cardiac cycle
  - Why it fails: This leads to incorrect conclusions about pressure changes and which valves are open/closed
  - Correct: Remember: systole = contraction, diastole = relaxation; always link chamber state to pressure
- **Wrong:** Stating all carbon dioxide is carried as bicarbonate ions in blood
  - Why it fails: Students often forget the other two methods of carbon dioxide transport
  - Correct: Recall: ~70% as bicarbonate, ~23% bound to haemoglobin, ~7% dissolved in plasma
- **Wrong:** Mixing up the structural adaptations of arteries and veins
  - Why it fails: Students often memorize labels instead of linking structure to function
  - Correct: Arteries have thick elastic/muscle walls to withstand high pressure; veins have valves to prevent backflow

## Cheatsheet

| Key Concept | Unit-Level Summary |
| --- | --- |
| Blood composition | 55% plasma, 45% formed elements (erythrocytes, leukocytes, platelets) |
| Clotting cascade | Thromboplastin → prothrombin → thrombin → fibrinogen → fibrin mesh clot |
| Heart structure | Right side pumps deoxygenated blood to lungs; left side pumps oxygenated blood to the body |
| Cardiac cycle order | Atrial systole → Ventricular systole → Complete diastole |
| Vessel structure comparison | Arteries: thick elastic/muscle; Capillaries: 1-cell thick endothelium; Veins: valves, thin walls |
| Oxygen-haemoglobin binding | $Hb + 4O_2 \rightleftharpoons HbO_8$ |
| Heart rate regulation | Medulla oblongata: sympathetic = increase rate, parasympathetic = decrease rate |

## What's next

Begin your study of this unit by opening the first sub-topic on blood composition to get started. Once you complete all sub-topics in this unit, you will move on to the next unit covering transport in plants, which explores similar core themes of exchange and bulk transport in multicellular organisms.

- [Blood composition](https://www.owlsprep.com/study/cie-9700-u8-blood-composition/)
- [Heart structure](https://www.owlsprep.com/study/cie-9700-u8-heart-structure/)

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