B3.1 Gas exchange

What is gas exchange?

Gas exchange is the process by which organisms absorb one gas from the environment and release another. For example, redwood trees absorb carbon dioxide for photosynthesis and release oxygen.

How do humans perform gas exchange?

Humans absorb oxygen for cell respiration and release carbon dioxide produced in the process.

How do aquatic animals exchange gases?

Aquatic animals like fish exchange gases with water.

Why is diffusion important for gas exchange?

Diffusion is the process through which gases move randomly from areas of high concentration to low concentration, and it's the basis of gas exchange.

How can gas exchange be rapid enough?

Gas exchange is rapid if it occurs over a large surface area and the distance for diffusion is short.

Why do unicellular organisms not need specialized gas-exchange surfaces?

Unicellular organisms have a large surface-area-to-volume ratio, and the distance from the center of the organism to the exterior is small, allowing gas exchange through the outer surface.

What is needed for larger organisms to perform gas exchange?

Larger organisms require specialized gas-exchange surfaces, such as alveoli in lungs or spongy mesophyll in leaves.

What are the four properties of gas-exchange surfaces?

1. Permeable, 2. Large surface area, 3. Moist, 4. Thin.

Why must gas-exchange surfaces be permeable?

They must be permeable to allow gases like oxygen and carbon dioxide to diffuse across freely.

How does the surface area of gas-exchange surfaces help gas exchange?

A large surface area allows more gas to diffuse across the surface, improving efficiency.

Why must gas-exchange surfaces be moist?

Moisture allows gases like oxygen and carbon dioxide to dissolve and diffuse across the surface.

Why should gas-exchange surfaces be thin?

Thin surfaces reduce the distance gases must diffuse, making the exchange more efficient.

What is necessary for diffusion to occur?

Diffusion occurs when there is a concentration gradient, meaning different concentrations of a substance across a membrane.

How do concentration gradients help maintain gas exchange in small organisms?

Cell respiration maintains concentration gradients by continuously using oxygen and producing carbon dioxide, keeping oxygen levels low and carbon dioxide high within the organism.

How do larger organisms maintain concentration gradients?

In larger organisms, blood flows through capillaries in the gas-exchange organs, maintaining low oxygen concentration and high carbon dioxide concentration.

What role does ventilation play in maintaining concentration gradients?

Ventilation helps maintain concentration gradients by bringing in fresh air or water to ensure continuous exchange of gases.

How do mammals maintain ventilation?

Mammals periodically inhale and exhale air to prevent the oxygen concentration in the lungs from dropping too low and to avoid excess carbon dioxide.

How do fish maintain ventilation?

Fish pump fresh water through their gills to ensure oxygen concentrations remain high and carbon dioxide concentrations remain low.

What are alveoli?

Alveoli are small air sacs in the lungs where gas exchange occurs, surrounded by a dense capillary network.

How does the structure of alveoli aid in gas exchange?

Alveoli have thin walls, a large surface area, and are surrounded by capillaries, allowing for efficient gas exchange.

What is the role of pulmonary surfactant in the alveoli?

Pulmonary surfactant reduces surface tension in the alveoli, preventing collapse during exhalation.

What is the function of the trachea and bronchi?

The trachea and bronchi carry air to and from the lungs and have cartilage to prevent collapse.

What is the role of bronchioles in ventilation?

Bronchioles have smooth muscle fibers that control the width of airways, adjusting airflow to the lungs.

How does ventilation affect pressure in the thorax?

Ventilation involves muscle contractions that decrease pressure in the thorax during inspiration, drawing air into the lungs.

What happens during expiration?

During expiration, the thoracic pressure increases, forcing air out of the lungs.

What is tidal volume?

Tidal volume is the amount of air inhaled or exhaled with each breath.

What is ventilation rate?

Ventilation rate is the number of breaths taken per minute.

What is vital capacity?

Vital capacity is the total volume of air that can be exhaled after a maximum inhalation or inhaled after a maximum exhalation.

What is inspiratory reserve volume?

Inspiratory reserve volume is the extra amount of air a person can inhale after normal tidal volume inspiration.

What is expiratory reserve volume?

Expiratory reserve volume is the extra amount of air a person can exhale after a normal exhalation.

What is the waxy cuticle on leaves?

The waxy cuticle is a waterproof layer on the leaf surface that prevents excessive water loss.

What is the function of guard cells?

Guard cells control the opening and closing of stomata to regulate gas exchange and water loss.

What is a stoma?

A stoma is a pore in the leaf that allows the passage of gases like carbon dioxide and oxygen.

How do stomata help plants conserve water?

Stomata close to prevent water loss during periods of water stress or when photosynthesis is not needed.

What is the role of the spongy mesophyll in leaves?

The spongy mesophyll provides a large surface area for gas exchange and is moistened for efficient diffusion of gases.

How does photosynthesis affect gas concentrations in leaves?

Photosynthesis consumes carbon dioxide and produces oxygen, creating a concentration gradient for gas exchange.

What is transpiration?

Transpiration is the loss of water vapor from plant leaves, which occurs through stomata.

How do temperature and humidity affect transpiration rates?

Higher temperatures increase transpiration rates, while high humidity decreases it.

What is stomatal density?

Stomatal density is the number of stomata per unit area of leaf surface, affecting gas exchange and water loss.

How can stomatal density be measured?

Stomatal density can be measured by counting stomata on a leaf epidermis sample under a microscope.

What is haemoglobin?

Haemoglobin is the oxygen transport protein in red blood cells that binds to oxygen for delivery to tissues.

How does haemoglobin bind to oxygen?

Haemoglobin binds oxygen reversibly at its haem groups, with each molecule binding up to four oxygen molecules.

What is cooperative binding in haemoglobin?

Cooperative binding means that when one oxygen molecule binds to haemoglobin, it increases the affinity of the remaining binding sites for oxygen.

What is the R state of haemoglobin?

The R state is when haemoglobin is fully saturated with oxygen, with all four binding sites occupied.

What is the T state of haemoglobin?

The T state is when haemoglobin is unsaturated, with no oxygen bound to it.

How does the partial pressure of oxygen affect haemoglobin's oxygen saturation?

As the partial pressure of oxygen increases, the oxygen saturation of haemoglobin also increases until it reaches 100%.

What is the significance of the oxygen dissociation curve for haemoglobin?

The curve shows how haemoglobin's oxygen saturation changes with varying oxygen concentrations, ensuring efficient oxygen delivery.

Why does haemoglobin unload oxygen at tissues?

Haemoglobin unloads oxygen in tissues with low oxygen concentrations due to the Bohr effect and cooperative binding.

What causes the Bohr shift?

The Bohr shift occurs when increased carbon dioxide concentration reduces the affinity of haemoglobin for oxygen, promoting oxygen release.

How do carbon dioxide and water affect haemoglobin's affinity for oxygen?

Carbon dioxide and water reduce blood pH, which decreases haemoglobin's affinity for oxygen, promoting oxygen release in active tissues.

What is carbaminohaemoglobin?

Carbaminohaemoglobin is haemoglobin bound to carbon dioxide at the amino terminal of its polypeptides.

How does carbaminohaemoglobin affect oxygen release?

Carbaminohaemoglobin reduces haemoglobin's affinity for oxygen, aiding in the release of oxygen to tissues.

What is the role of foetal haemoglobin?

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin, allowing the fetus to absorb oxygen from maternal blood.

Why does foetal haemoglobin have a higher affinity for oxygen?

Foetal haemoglobin's higher affinity for oxygen ensures efficient oxygen transfer from the mother's blood to the fetus.

How does increased aerobic respiration affect haemoglobin's oxygen release?

Increased aerobic respiration leads to higher carbon dioxide concentrations, which lower the pH and promote the release of oxygen from haemoglobin.

What is the significance of oxygen dissociation curves?

Oxygen dissociation curves help illustrate how haemoglobin's oxygen saturation varies with partial pressures of oxygen in different environments.

Why is cooperative binding important for oxygen delivery?

Cooperative binding allows haemoglobin to readily release oxygen at tissues with low oxygen concentrations, ensuring tissues get sufficient oxygen.

What happens to haemoglobin in the lungs?

In the lungs, haemoglobin binds to oxygen due to the low carbon dioxide concentration and high oxygen partial pressure.

How does carbon dioxide affect haemoglobin?

High carbon dioxide concentrations in tissues promote oxygen dissociation from haemoglobin, aiding in oxygen delivery to those tissues.

What are the effects of the Bohr effect?

The Bohr effect ensures that haemoglobin releases oxygen in tissues where it is most needed, like muscles during exercise.

What is the primary role of the alveoli?

The alveoli are responsible for gas exchange, where oxygen enters the blood, and carbon dioxide is removed.

What type of cells make up the alveolar wall?

The alveolar wall consists of a single layer of cells, which makes it thin and efficient for gas exchange.

What is the function of the capillaries around alveoli?

The capillaries surrounding the alveoli allow for efficient gas exchange by maintaining a low oxygen concentration in the blood.

How do lung volumes differ?

How does the structure of the trachea assist in ventilation?

The trachea has cartilage that ensures it remains open for airflow into the lungs.

How do the bronchioles help in lung ventilation?

Bronchioles have smooth muscle that adjusts the airway diameter to control airflow into the lungs.

Why is the alveolar surface area important for gas exchange?

A large surface area in the alveoli maximizes the efficiency of gas exchange.

What is the role of collagen and elastic fibers in the lungs?

Collagen strengthens lung tissue, while elastic fibers allow for passive exhalation after inhalation.

What is the role of guard cells in water conservation?

Guard cells regulate the opening and closing of stomata, preventing excessive water loss when necessary.

How do stomata affect photosynthesis?

Stomata must remain open for carbon dioxide to enter the leaf for photosynthesis but can close to prevent water loss.

What happens during forced exhalation?

Forced exhalation involves expelling air beyond normal tidal volume, utilizing expiratory reserve volume.

How does diffusion maintain concentration gradients?

Diffusion continues to move gases across the exchange surface, helping to maintain concentration gradients for efficient gas exchange.

Why do plants need a moist gas-exchange surface?

Moist surfaces are necessary for gases like carbon dioxide and oxygen to dissolve and diffuse efficiently.

How does evaporation relate to transpiration?

Water evaporates from the spongy mesophyll during transpiration, contributing to water loss from plants.

What environmental factors influence transpiration rates?

Environmental factors like temperature and humidity can increase or decrease transpiration rates in plants.

How does oxygen dissociation work in active tissues?

Oxygen dissociates from haemoglobin in active tissues where carbon dioxide concentrations are high, allowing oxygen to be used for cellular respiration.

Why is diffusion slower in larger organisms?

What is the importance of ventilation in fish?

How does the structure of the spongy mesophyll help gas exchange?

The spongy mesophyll provides a large surface area for gas exchange while keeping the surface moist.

How does a leaf adapt to reduce water loss?

A leaf adapts with a waxy cuticle, guard cells, and stomata to balance gas exchange with water conservation.