3.3.4 Mass transport for A-Level Biology (AQA)

What protein in red blood cells is responsible for transporting oxygen in the blood?

Haemoglobin

A globular protein with a quaternary structure that binds oxygen reversibly.

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Which cells in the blood are specialised for carrying oxygen around the body?

Red blood cells

Also called erythrocytes; they contain haemoglobin and lack a nucleus in mammals.

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What is the name of the curve that shows the percentage saturation of haemoglobin with oxygen at different partial pressures of oxygen?

Oxyhaemoglobin dissociation curve

Demonstrates how readily haemoglobin loads and unloads oxygen under different conditions.

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What property of haemoglobin means that the binding of the first oxygen molecule increases the affinity for additional oxygen molecules?

Cooperative binding

Caused by a conformational change in haemoglobin after the first oxygen binds.

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How does increasing carbon dioxide concentration affect the affinity of haemoglobin for oxygen?

Decreases

This shift promotes oxygen release in respiring tissues.

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What term describes the effect of carbon dioxide concentration on the dissociation of oxyhaemoglobin?

Bohr effect

Higher CO₂ lowers haemoglobin affinity for oxygen, aiding oxygen delivery to tissues.

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True or False:

The oxyhaemoglobin dissociation curve is linear because each oxygen molecule binds independently.

False

The curve is sigmoidal due to cooperative binding between haemoglobin subunits.

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Why do animals living in low-oxygen environments often possess different types of haemoglobin?

They have different oxygen affinity.

Adapted haemoglobins bind oxygen more readily when oxygen availability is low.

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Which blood vessels supply oxygenated blood directly to the heart muscle?

Coronary arteries

These branch from the aorta and provide the heart’s own oxygen supply.

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Which blood vessel carries deoxygenated blood from the body into the right atrium?

Vena cava

Includes the superior and inferior vena cava.

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Which artery carries deoxygenated blood from the heart to the lungs?

Pulmonary artery

The only artery that normally carries deoxygenated blood.

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Which vein carries oxygenated blood from the lungs to the heart?

Pulmonary vein

Returns oxygenated blood to the left atrium.

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What term describes the volume of blood pumped by one ventricle of the heart per beat?

Stroke volume

Usually measured in cm³ per beat.

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What term describes the volume of blood pumped by the heart per minute?

Cardiac output

Calculated as stroke volume × heart rate.

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Fill in the blank:

Cardiac output equals stroke volume multiplied by ______.

heart rate

CO = stroke volume × heart rate.

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What structure in the heart prevents backflow of blood during the cardiac cycle?

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Valves

Include atrioventricular valves and semilunar valves.

True or False:

During ventricular systole, the semilunar valves open to allow blood to leave the heart.

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True

Blood is ejected into the aorta and pulmonary artery.

Which type of blood vessel has thick muscular walls and elastic fibres to withstand high pressure?

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Arteries

Their elastic tissue allows stretching and recoil during the cardiac cycle.

Which small blood vessels control the distribution of blood to capillary beds?

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Arterioles

Smooth muscle in their walls allows vasoconstriction and vasodilation.

Which type of blood vessel contains valves that help return blood to the heart?

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Veins

Blood pressure is low, so valves prevent backflow.

Which blood vessels consist of a single layer of endothelial cells for efficient exchange of substances?

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Capillaries

Their thin walls allow diffusion between blood and tissues.

What network of capillaries within a tissue provides a large surface area for exchange?

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Capillary bed

Enables efficient transfer of gases, nutrients and wastes.

What fluid surrounds cells and forms when plasma is forced out of capillaries?

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Tissue fluid

Formed by hydrostatic pressure at the arterial end of capillaries.

What causes fluid to leave capillaries at the arterial end to form tissue fluid?

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High hydrostatic pressure

Driven by hydrostatic pressure exceeding oncotic pressure.

Which **system** returns **excess tissue fluid** to the **blood circulation**?

Lymphatic system ## Footnote Lymph vessels eventually return fluid to the bloodstream.

Which **plant tissue** is responsible for transporting **water and dissolved mineral ions** from the roots to the leaves?

Xylem ## Footnote Xylem vessels are formed from dead cells and provide a continuous column for water movement.

Which **plant tissue** transports **sugars and other organic molecules** around the plant?

Phloem ## Footnote Phloem transports products of photosynthesis such as sucrose to growing or storage tissues.

What **theory** explains how **water moves upward through the xylem** due to evaporation from leaves and the cohesion of water molecules?

Cohesion–tension theory ## Footnote Transpiration creates tension that pulls a continuous column of water upward through the xylem.

What **process at the leaf surface** generates the **pulling force** that moves water up the xylem?

Transpiration ## Footnote Water evaporates from mesophyll cell walls and diffuses out through stomata.

# Fill in the blanks: The movement of dissolved sugars through the **phloem** from **sources to sinks** is explained by the \_\_\_\_\_\_ \_\_\_\_\_\_ hypothesis.

Mass flow ## Footnote The hypothesis proposes that pressure differences drive the bulk movement of sap through sieve tubes.

What type of **molecule** is most commonly transported in the **phloem** as the main product of photosynthesis?

Sucrose ## Footnote Sucrose is the main sugar transported because it is soluble and chemically stable.

What term describes a **region of a plant** that produces or releases **sugars for transport in the phloem**?

Source ## Footnote Examples include photosynthesising leaves or storage organs releasing sugars.

What term describes a **region of a plant** that **uses or stores transported sugars**?

Sink ## Footnote Examples include growing roots, fruits, and developing buds.

# True or False: **Xylem vessels** are made of **living cells** that actively pump water upwards.

False ## Footnote Mature xylem vessels are dead and transport water passively.

# True or False: The **cohesion of water molecules** helps maintain a **continuous water column in the xylem**.

True ## Footnote Hydrogen bonding between water molecules allows the column to resist breaking.

What **experimental method** uses **radioactive or labelled carbon compounds** to track movement of substances through plants?

Tracer experiments ## Footnote Radioactive carbon dioxide can be used to label sugars formed during photosynthesis.

What **experimental method** involves **removing a ring of bark from a stem** to investigate transport pathways?

Ringing experiment ## Footnote Removing bark removes phloem but leaves xylem intact.

# True or False: If a **ring of bark** is removed from a tree, **sugars accumulate above the cut** because phloem transport is interrupted.

True ## Footnote This supports the role of phloem in translocation of organic substances.

In the **mass flow mechanism**, what drives the **movement of phloem sap from source to sink**?

Pressure gradient ## Footnote High hydrostatic pressure at sources pushes sap towards lower pressure at sinks.

3.3.4 Mass transport Flashcards

Explain how substances are moved to and from exchange surfaces in both animals and plants. (39 cards)