How does surface area to volume ratio relate to the need for a circulatory system?

Large organisms have small surface area to volume ratios, meaning their surface area is insufficient for diffusion alone to supply all their cells with nutrients and oxygen.

Why do active organisms require a mass transport system?

Active organisms have high metabolic demands, requiring rapid delivery of oxygen and nutrients and removal of waste products that diffusion alone cannot achieve.

How does mass transport overcome the limitations of diffusion?

Mass transport moves substances in bulk over long distances quickly, overcoming the slow rate of diffusion over large distances.

What happens during atrial systole?

The atria contract, forcing blood through the open atrioventricular valves into the ventricles.

Which valves are open during atrial systole and why?

The atrioventricular valves are open, allowing blood to pass from the atria into the ventricles.

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Lifestyle, Health and Risk

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Lifestyle, Health and Risk

The cardiac cycle and the structure of the heart

3 things to know
Papers 1, 2 and 3

Overview

Recall questions on why large organisms need mass transport, the three stages of the cardiac cycle, and the chambers, valves and vessels of the heart.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What happens in each stage of the cardiac cycle?

Process

What is cardiac diastole?

Key term

Why is diffusion alone insufficient to meet the needs of large organisms?

Questions from this subtopic

Each one with the model answer underneath.

1
Why is diffusion alone insufficient to meet the needs of large organisms?
Model answer
Diffusion is only effective over short distances, so it cannot transport substances quickly enough across the larger distances within large organisms.
2
How does surface area to volume ratio relate to the need for a circulatory system?
Model answer
Large organisms have small surface area to volume ratios, meaning their surface area is insufficient for diffusion alone to supply all their cells with nutrients and oxygen.
3
Why do active organisms require a mass transport system?
Model answer
Active organisms have high metabolic demands, requiring rapid delivery of oxygen and nutrients and removal of waste products that diffusion alone cannot achieve.
4
How does mass transport overcome the limitations of diffusion?
Model answer
Mass transport moves substances in bulk over long distances quickly, overcoming the slow rate of diffusion over large distances.
5
What happens during atrial systole?
Model answer
The atria contract, forcing blood through the open atrioventricular valves into the ventricles.
6
Which valves are open during atrial systole and why?
Model answer
The atrioventricular valves are open, allowing blood to pass from the atria into the ventricles.

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Systole means phase when cardiac muscle contracts.

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