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Biology - The Human Circulatory System

Grade 7IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The human circulatory system is a double circulatory system, meaning blood passes through the heart twice for every complete circuit of the body: the pulmonary circuit (to the lungs) and the systemic circuit (to the rest of the body).

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The heart consists of four chambers: the right atrium and right ventricle (pump deoxygenated blood) and the left atrium and left ventricle (pump oxygenated blood).

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Arteries carry blood away from the heart at high pressure; they have thick, muscular walls. Veins carry blood towards the heart at low pressure and contain valves to prevent backflow.

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Capillaries are tiny vessels (one cell thick) where the exchange of gases like O2O_2 and CO2CO_2, nutrients, and waste occurs between blood and tissues via diffusion.

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Red Blood Cells (RBCs) contain a protein called hemoglobin which binds to oxygen to form oxyhemoglobin: Hb+4O2ightleftharpoonsHb(O2)4Hb + 4O_2 ightleftharpoons Hb(O_2)_4.

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White Blood Cells are part of the immune system, defending against pathogens through phagocytosis or antibody production.

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Plasma is the liquid part of the blood that transports CO2CO_2, glucose, amino acids, hormones, and heat energy.

📐Formulae

Heart Rate (bpm)=Number of BeatsTime in minutes\text{Heart Rate (bpm)} = \frac{\text{Number of Beats}}{\text{Time in minutes}}

Cardiac Output=Stroke Volume×Heart Rate\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}

C6H12O6+6O2→6CO2+6H2O+Energy (ATP)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}

💡Examples

Problem 1:

A student measures their pulse and counts 1515 beats over a period of 1010 seconds. Calculate the student's heart rate in beats per minute (bpm).

Solution:

Heart Rate=15 beats10 seconds×60 seconds/minute=90 bpm\text{Heart Rate} = \frac{15 \text{ beats}}{10 \text{ seconds}} \times 60 \text{ seconds/minute} = 90 \text{ bpm}

Explanation:

To find the heart rate per minute, we multiply the number of beats in a 10-second interval by 6, as there are 60 seconds in a minute.

Problem 2:

If a person has a stroke volume (the volume of blood pumped per beat) of 70 ml70\text{ ml} and a heart rate of 75 bpm75\text{ bpm}, calculate the Cardiac Output in liters per minute (L/minL/min).

Solution:

Cardiac Output=70 ml/beat×75 beats/min=5250 ml/min=5.25 L/min\text{Cardiac Output} = 70\text{ ml/beat} \times 75\text{ beats/min} = 5250\text{ ml/min} = 5.25\text{ L/min}

Explanation:

Cardiac output is the total volume of blood pumped by the heart per minute. We multiply stroke volume by heart rate and then convert mlml to LL by dividing by 10001000.

The Human Circulatory System - Revision Notes & Key Formulas | IGCSE Grade 7 Science