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Biology - Transport in animals (Heart, Blood vessels, and Blood components)

Grade 9IGCSE

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

🔑Concepts

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The heart is a pump consisting of four chambers: the right atrium, right ventricle, left atrium, and left ventricle. The left ventricle has a thicker muscular wall to pump blood at higher pressure to the systemic circulation.

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Mammals have a double circulatory system: the pulmonary circuit (to the lungs) and the systemic circuit (to the rest of the body). This ensures oxygenated and deoxygenated blood do not mix.

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Blood vessels are specialized for their functions: Arteries have thick, elastic walls to withstand high pressure; Veins have thinner walls and valves to prevent the backflow of blood at low pressure; Capillaries are one-cell thick to allow for the diffusion of substances like O2O_2, CO2CO_2, and glucose.

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Red blood cells (erythrocytes) are adapted for oxygen transport through a biconcave shape (increased surface area), lack of a nucleus (more space for hemoglobin), and the presence of hemoglobin which binds to oxygen to form oxyhemoglobin: Hb+4O2⇌Hb(O2)4Hb + 4O_2 \rightleftharpoons Hb(O_2)_4.

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White blood cells (leukocytes) include phagocytes, which engulf and digest pathogens through phagocytosis, and lymphocytes, which produce antibodies to neutralize specific pathogens.

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Platelets are fragments of cells involved in blood clotting, preventing excessive blood loss and the entry of pathogens into the circulatory system.

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Plasma is the liquid part of the blood that transports dissolved substances including CO2CO_2, urea, glucose, amino acids, and hormones.

📐Formulae

Cardiac Output=Stroke Volume×Heart RateCardiac\ Output = Stroke\ Volume \times Heart\ Rate

Hb+4O2→Hb(O2)4Hb + 4O_2 \rightarrow Hb(O_2)_4

Rate of Diffusion∝Surface Area×Concentration GradientThickness of MembraneRate\ of\ Diffusion \propto \frac{Surface\ Area \times Concentration\ Gradient}{Thickness\ of\ Membrane}

💡Examples

Problem 1:

During exercise, an athlete's heart rate increases to 150 bpm150\ bpm and their stroke volume is measured at 120 cm3120\ cm^3. Calculate the Cardiac Output in dm3/mindm^3/min.

Solution:

Step 1: Use the formula Cardiac Output=Stroke Volume×Heart RateCardiac\ Output = Stroke\ Volume \times Heart\ Rate. Step 2: 120 cm3×150 bpm=18,000 cm3/min120\ cm^3 \times 150\ bpm = 18,000\ cm^3/min. Step 3: Convert to dm3dm^3 (1 dm3=1000 cm31\ dm^3 = 1000\ cm^3). Step 4: 18,0001000=18 dm3/min\frac{18,000}{1000} = 18\ dm^3/min.

Explanation:

The cardiac output represents the total volume of blood pumped by the left ventricle per minute. It increases during exercise to supply more O2O_2 to respiring muscles.

Problem 2:

Identify the type of blood vessel that has a lumen diameter of 8 μm8\ \mu m and a wall thickness of 1 μm1\ \mu m. Explain why this structure is beneficial.

Solution:

The vessel is a capillary.

Explanation:

Capillaries have walls that are only one cell thick (approx. 1 μm1\ \mu m). This minimizes the diffusion distance for gases such as O2O_2 and CO2CO_2, facilitating efficient gas exchange between the blood and the tissues.

Problem 3:

A patient is diagnosed with a low red blood cell count (anemia). How will this affect the concentration of O2O_2 reaching the brain?

Solution:

The concentration of O2O_2 reaching the brain will decrease.

Explanation:

Since red blood cells contain hemoglobin, which binds to O2O_2 to form Hb(O2)4Hb(O_2)_4, a lower count of these cells reduces the total oxygen-carrying capacity of the blood, leading to fatigue and reduced aerobic respiration in tissues.