What happens to surface area to volume ratio as an organism gets bigger?

It decreases, because volume increases faster than surface area.

What is mass transport?

The bulk movement of substances over long distances by the flow of a fluid, such as blood pumped by the heart.

Which vessel brings oxygenated blood to the heart?

The pulmonary vein, into the left atrium.

Which vessel carries blood out of the left ventricle?

The aorta, carrying oxygenated blood to the body.

What is the function of the septum?

It separates the left and right sides so that oxygenated and deoxygenated blood do not mix.

Why are tendons attached to the atrioventricular valves?

They stop the valves turning inside out when the ventricle contracts.

Why is the left ventricle wall thicker than the right?

It must generate a higher pressure to pump blood around the whole body.

What happens in atrial systole?

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

When do the atrioventricular valves close?

When the ventricles contract and ventricular pressure exceeds atrial pressure.

When do the semilunar valves open?

When the pressure in the ventricle exceeds the pressure in the aorta or pulmonary artery.

What happens during cardiac diastole?

The heart muscle relaxes and the chambers refill with blood; the semilunar valves are closed.

How is heart rate calculated from the length of the cardiac cycle?

Heart rate = 60 ÷ time for one cycle in seconds.

Mass transport and the mammalian heartEdexcel A-Level Biology A: Flashcards

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Why do large animals need a heart and circulatory system?

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Why do large animals need a heart and circulatory system?: Their small surface area to volume ratio and long diffusion distances make diffusion too slow, so mass transport by a pump is needed.
What happens to surface area to volume ratio as an organism gets bigger?: It decreases, because volume increases faster than surface area.
What is mass transport?: The bulk movement of substances over long distances by the flow of a fluid, such as blood pumped by the heart.
Which vessel brings oxygenated blood to the heart?: The pulmonary vein, into the left atrium.
Which vessel carries blood out of the left ventricle?: The aorta, carrying oxygenated blood to the body.
What is the function of the septum?: It separates the left and right sides so that oxygenated and deoxygenated blood do not mix.
Why are tendons attached to the atrioventricular valves?: They stop the valves turning inside out when the ventricle contracts.
Why is the left ventricle wall thicker than the right?: It must generate a higher pressure to pump blood around the whole body.
What happens in atrial systole?: The atria contract, pushing blood through the open atrioventricular valves into the ventricles.
When do the atrioventricular valves close?: When the ventricles contract and ventricular pressure exceeds atrial pressure.
When do the semilunar valves open?: When the pressure in the ventricle exceeds the pressure in the aorta or pulmonary artery.
What happens during cardiac diastole?: The heart muscle relaxes and the chambers refill with blood; the semilunar valves are closed.
How is heart rate calculated from the length of the cardiac cycle?: Heart rate = 60 ÷ time for one cycle in seconds.

Exam questions on Mass transport and the mammalian heart

A flatworm is a flat animal about 1 mm thick with no heart or blood. It obtains oxygen and nutrients directly from the surrounding water. A mouse is a small mammal with a very high metabolic rate, a heart and a circulatory system.
Explain why the mouse needs a heart and circulatory system.2 marks
In a practical lesson a student dissects a sheep's heart. She cuts across both ventricles to compare the walls and then opens the atria and ventricles to look at the valves.
Explain why the wall of the left ventricle is thicker than the wall of the right ventricle.2 marks
In a healthy adult at rest one cardiac cycle lasts 0.8 s. Atrial systole lasts 0.1 s, ventricular systole lasts 0.3 s and cardiac diastole lasts 0.4 s. During ventricular systole the pressure in the left ventricle rises from about 0.5 kPa to about 16 kPa, while the pressure in the aorta is about 11 kPa.
Explain how the pressure changes in the left ventricle control the opening and closing of valves during ventricular systole.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).