B3.1 gas exchange

What is transpiration?

The movement of H₂O through a plant, and its evaporation from aerial parts of the plant such as leaves.

Factors affecting transpiration

1. light intensity: + light intensity = stomata open = more water can diffuse out of the leaf = increased rate of transpiration

2. temperature: + temperature = water particles gain kinetic energy and move faster = faster rate of diffusion through the stomata of the leaf [higher temperatures increase the rate of evaporation increase in rate of transpiration]

3. humidity: + humidity = higher concentration of H₂O outside leaf = lower concentration gradient b/w inside and outside of the leaf = H₂O particles will diffuse slower = slower rate of transpiration

4. Air flow (wind): air flows past the leaf → moves H₂O vapour away from the leaf = reduces concentration of H₂O outside the stomata of a leaf and increases concentration gradient = increase in rate of transpiration

What is stomatal density?

The number of stomata per unit area of a leaf.

What is the partial pressure of a gas?

The pressure exerted by a single gas when it is found in a mixture of gases.

What does the oxygen dissociation curve illustrate?

It shows the affinity of haemoglobin for oxygen as the partial pressure of oxygen increases, which has a sigmoid shape.

What is cooperative binding of oxygen in relation to haemoglobin?

The phenomenon where the binding of one O2 molecule to a haemoglobin molecule facilitates the binding of additional O2 molecules.

How does foetal haemoglobin differ from adult haemoglobin?

Foetal haemoglobin contains 2 α and 2 γ chains of polypeptides, giving it a greater affinity for O2 than adult haemoglobin.

What is the Bohr effect?

The shift of the oxygen dissociation curve to the right due to CO2 partial pressures, which affects (reduces) haemoglobin's affinity for oxygen

What are the adaptations of gas exchange surfaces?

Large surface area, very thin tissue layers, permeable membranes, high concentration gradients, and a layer of moisture.

What is ventilation in the context of the lungs?

The movement of air in and out of the alveoli in the lungs, facilitating gas exchange

What is tidal volume?

The volume of air that moves in and out of the lungs in a normal breath.

Steps in inspiration

1. Diaphragm contracts → moves down

2. External intercostal muscles contract → moves ribcage up and out

3. Volume in the thorax increases → decrease in lung pressure

4. Air passively moves from the surrounding air (with high pressure) in the lungs (low pressure)

How does the structure of alveoli facilitate gas exchange?

Alveoli have a large surface area, are moist (since type II pneumocytes secrete surfactant to prevent adhesion and increase efficiency of gas exchange) and are surrounded by capillaries

What is the significance of guard cells in plants?

Guard cells control the opening and closing of stomata, regulating gas exchange and water loss.

What are the two main processes for gas exchange in mammals?

Ventilation and respiration

What adaptations do leaves have for gas exchange?

Waxy cuticle, large surface area, epidermis, spongy mesophyll surrounded by air spaces, the presence of stomata and veins

Steps in expiration

1. Abdominal muscles contracts → diaphragm relaxes and moves up

2. Internal intercostal muscles contract as external intercostal muscles → moves ribcage in and down

3. Volume in the thorax decreases → increase in lung pressure

4. Air moves from the lungs (with high pressure) in the surrounding air (low pressure)

Lng adaptations for efficient gas exchange

1. Branching bronchioles which connect to many alveoli → large surface area for gas exchange

2. Alveoli secrete a surfactant

3. Alveoli are surrounded by an extensive capillary bed → maintains high concentration gradients for O2 and CO2 between the blood and alveoli

4. Capillaries provide a continuous supply of blood to maintain concentration gradients

Define inspiratory/expiratory reserve

Additional volume of air that can be inhaled or exhaled with maximum effort

Define vital capacity

Greatest volume of air that can be expelled from the lungs after the deepest possible breath

Adaptations of gills for gas exchange

Large surface area, water continuously flowing through them and continuous supply of blood flowing through themto maintain concentration gradients for oxygen and carbon dioxide.