B3.1 Bio Gas Exchange

SL and HL

Properties of specialized gas exchange structures

Large surface area, composed of a thin tissue layer, having a moist surface, concentration gradient.

Properties that maintain concentration gradient in exchange surfaces

A dense network of blood vessels, continuous blood flow, ventilation.

Ventilation

The mechanical movement of air/water into and out of the gas-exchange surface in order to maintain a concentration gradient of oxygen and carbon dioxide between the external environment and the blood.

Alveoli

Structures on bronchioles of the lungs; tiny sacs with a large surface area across which oxygen and carbon dioxide are exchanged between the air and the blood.

Type II pneymocytes

Cells in the alveoli that secrete alveolar fluid which moistens the surface of the alveoli, allowing gases to dissolve into the surfactant before diffusing across the wall of the alveoli and capillary into the blood.

Bronchiole

A small airway in the lungs that branches from the bronchi and leads to the alveoli, where gas exchange occurs.

During inspiration:

Diaphragm contracts and moves downwards, external intercostal muscles contract, internal intercostal muscles relax, the ribcage moves up and out, volume of thoracic cavity increases, pressure inside the lungs decreases, air movies into the lungs down its pressure gradient.

During expiration:

Diaphragm relaxes and moves upwards and inwards, external intercostal muscles relax, internal intercostal muscles relax, the ribcage moves down and in, volume of thoracic cavity dereases, pressure inside the lungs increases, air movies out of the lungs down its pressure gradient.

Thoracic cavity

The chamber of the body enclosed by the ribs, sternum, and vertebral column that contains the lungs and heart.

Forced vital capacity

The volume of air that can be exhaled with maximum effort after inhailing the maximum possible volume of air.

Tidal volume

The volume of air moving into and out of one’s lungs with every normal breath.

Residual volume

The volume of air remaining in the lungs that cannot be exhaled.

Inspiratory reserve

The additional volume of air that can be inhaled after taking a normal breath.

Expiratory reserve

The additional volume of air that can be exhaled after exhaling normal amount of air.

Stomata

Pores in the epidermis of leaves and stems, surrounded by guard cells that can open and close these pores, that regulate gas exchange (CO₂ in, O₂ out) and water loss through transpiration.

Veins

Vascular bundles within the leaf that contain xylem and phloem; they provide structural support and transport water, minerals, and sugars.

Xylem

The vascular tissue that transports water and dissolved minerals from the roots to the leaf mesophyll, supplying the water needed for photosynthesis.

Phloem

The vascular tissue that transports the products of photosynthesis (sugars and amino acids) from the mesophyll cells to other parts of the plant for use or storage.

Transpiration

The loss of water vapor from the leaves of a plant, mainly through stomata, as a result of evaporation from mesophyll cell surfaces and diffusion out into the atmosphere.

Factors affecting transpiration rate:

Temperature, humidity, wind intensity, light intensity.

Stomatal density

The number of stomata in a particular unit of area of a leaf/other plant organ.

Palisade mesophyll

A layer of tightly packed cells located beneath the upper epidermis of the leaf, containing many chloroplasts and specialized for absorbing light and carrying out photosynthesis.

Spongy mesophyll

A layer of loosely arranged cells located closer to the lower epidermis, with large intercellular air spaces that facilitate diffusion of gases (CO₂, O₂, and water vapor).

Haemoglobin

A protein found in red blood cells of vertebrates which is responsible for the transport of oxygen from the lungs to the respiring tissues, and the transport of CO2 from respiring tissues back to the lungs.

Oxyhaemoglobin complex

Form of haemoglobin bound to oxygen, present in oxygenated blood.

Deoxyhaemoglobin

Foetal haemoglobin (HbF)

Type of haemoglobin produced by the developing foetus during pregnancy. It will remain the infant until it’s 6 months old and then will be gradually replaced with HbA. It consists of 2 beta and 2 gamma polypeptide chains and thus has a higher affinity for oxygen.

Adult haemoglobin (HbA)

The normal form of haemoglobin found in adult humans, made up of 2 alpha and 2 beta polypeptide chains. It has a lower affinity to oxygen than HbF but has a better affinity to CO2.

Myoglobin

A type of haemoglobin found in muscles which has a much higher affinity to oxygen than both HbA and HbF.

Cooperative binding

A property of haemoglobin in which the binding of one oxygen molecule to a heme group increases the affinity of the remaining haem groups for oxygen. This results in the characteristic sigmoid (S-shaped) oxygen dissociation curve.

Allosteric binding

The binding of CO2 to haemoglobin at sites other than the oxygen-binding sites, which changes haemoglobin’s conformation, forming carbaminohaemoglobin, and reduces its affinity for oxygen. This effect is part of the Bohr shift, facilitating oxygen release in respiring tissues.

Bohr shift

The decrease in haemoglobin’s affinity for oxygen when CO2 levels increase. In respiring tissues, CO₂ diffuses into red blood cells and reacts with water to form carbonic acid. This lowers blood’s pH, causing haemoglobin to change conformation and release oxygen more readily into tissues with high CO2 concentration (like active muscles) and load up more oxygen in areas of higher concentration of oxygen (lungs). This shifts the oxygen dissociation curve to the right, ensuring more oxygen is delivered to tissues with high rates of respiration.