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Gas Exchange in Organisms

• Cellular respiration happens in all living cells.
• ATP is produced when substrate molecules, like glucose, are oxidized.
• Organisms perform functions like nutrition and excretion using this energy.
• Aerobic respiration needs oxygen and makes carbon dioxide as a waste product.
• Organisms get oxygen and release carbon dioxide into their surroundings.
• Gas exchange involves uptake of oxygen and release of carbon dioxide.
• In plants, carbon dioxide is absorbed and oxygen released during the day due to photosynthesis.
• Diffusion is the process by which gases are exchanged.
• The size of the respiratory surface impacts gas exchange, rate increases with surface size.
• The process is also impacted by concentration gradients; gas exchange is faster with steeper gradients.
• The diffusion distances effect gas exchange; shorter distances increase efficiency.
• Amoebas have large surface area compared to cytoplasm volume for sufficient oxygen supply.
• Organisms require diffusion to supply oxygen for function.

Challenges of Gas Exchange

• Challenges of gas exchange increase as an organism becomes larger.
• Smaller surface area to volume ratio occurs as organisms increase in size.
• A greater diffusion distance also occurs as organisms increase in size.
• Multicellular organisms cannot rely on diffusion alone for oxygen.
• External surfaces of some organisms protect those delicate tissues and are often unsuitable to act as respiratory surfaces.
• The cells of large, active organisms require more oxygen.
• Active organisms need to meet their metabolic demands.
• Organisms will require specialised organs for gas exchange.

Gas Exchange Surfaces: Properties

• Surfaces require permeability for gases to move across.
• Thin tissue layers create short diffusion distances.
• Moisture is needed, so gases can dissolve, this facilitates diffusion.
• Large surface area allows many gas molecules to diffuse.

Maintaining a Concentration Gradient

• Steep concentration gradients ensure high diffusion rates across gas exchange surfaces.
• In organisms, oxygen diffuses into the body, carbon dioxide out.
• Dense networks of blood vessels create diffusion surface areas and transport gases.
• Continuous blood flow ensures constant transport away from the exchange surface.
• Ventilation with air and water containing oxygen close to the exchange surface to remove carbon dioxide.

Mammalian Lungs: Adaptations

• The role of the trachea is to carry air into the lungs.
• The trachea is supported by cartilage rings to maintain its shape while allowing movement.
• The trachea branches into two bronchi also with cartilage.
• Both are lined with ciliated epithelium to remove particles.
• Each bronchus leads to a lung.
• Bronchi split into a network of narrow tubes called bronchioles.
• Bronchiole walls are lined with smooth muscle and alter the tubes' diameter to regulate air flow.
• Alveoli groups are found at the end of bronchioles.
• Extensive capillary networks surround each alveolus to maximize gas exchange via good blood supply.
• Lungs are comprised of small alveoli, increasing the surface area for gas exchange.
• Alveoli are at the end of bronchioles across each lung ensuring even distribution of gas.
• Clusters of alveoli are surrounded by an extensive capillary bed.
• Alveolar cell walls secrete surfactant to lower surface tension preventing alveoli collapse.
• Deoxygenated blood enters the capillary beds from a branch of the pulmonary artery while oxygenated leaves via the pulmonary vein; maintaining the gradient..

Mechanism of Ventilation

• Ventilation helps maintain the concentration gradient.
• Ventilation involves inspiration and expiration.
• Volume of the chest increases to decrease air pressure is lower during inspiration.
• Air then rushes into the lungs down the pressure gradient.
• Diaphragm flattens, and external intercostal muscles contract, increasing chest volume.
• Volume decreases and pressure increases during expiration.
• Occurs mainly due to the recoil of the lungs after being stretched during inhalation.
• External intercostal muscles relax and the diaphragm returns to a dome shape.
• Internal intercostal and abdominal muscles contact to force breath.

Measuring Lung Volumes

• Spirometers determine lung capacity and measure oxygen consumption.
• Spirometers are chambers filled with water and a plastic lid connected to a mouthpiece through which the patient breathes.
• Spirometer readings are measured on a graph showing tidal volume, vital capacity, and ventilation rate.
• Spirometer can be used to measure the effect of exercise on the ventilation.

Tidal Volume

• The volume of air inhaled and exhaled during normal breathing.
• Exercise increases is the tidal volume as more air is moved because more air is needed
• Reserve volumes of the lungs: the extra volume can be inhaled or exhaled when taking an extra deep breath.
• Vital capacity (VC): the total amount of air exhaled after a deep breath.
• VC = TV + IRV + ERV where IRV is inspiratory reserve volume and ERV expiratory reserve volume.
• Ventilation Rate (VR) is determined by counting breaths per minute which increase with exercise.

Gas Exchange in Plants

• In plants, gas exchange happens through structures within the leaf.
• The leaf contains epidermal tissues that forms the outer boundary of the leaf
• Also contains mesophyll tissue that make up the bulk of the leaf.
• In addition, vascular transports substance.
• A single layer of tightly packed cells make up the epidermis.
• The leaf has upper and lower epidermis.
• Tiny pores called stomata (singular stoma), are contained within the lower epidermis.
• Stomata are surrounded by guard cells that that control the opening and closure of the pore.
• An impermeable barrier is formed by the cuticle.
• Photosynthesis occurs in mesophyll tissue formed by parenchyma cells with chloroplasts.
• Palisade mesophyll is beneath the upper epidermis containing many chloroplasts.
• Spongy mesophyll contains gaps between cells for gas exchange.
• Vascular tissue arranged in vascular bundles, forming leaf veins and transporting water via the Xylem from the soil.
• The vascular tissue also transports products of photosynthesis.

Adaptations for Gas Exchange

• Waxy cuticle that allows restricted gas exchange.
• Epidermis containing stomata which permits gas exchange and is mainly found in lower epidermis where temperatures are lower.
• Air movement is facilitated through movement of gasses via airspaces maintaining concentration gradients.
• Gas exchange is made easier by spongy mesophyll that increases surface area.
• Gas exchange can be controlled by the guard cells closing and opening stoma.
• Veins bring xylem vessels and water to the leaf for photosynthesis.

Transpiration: Consequence of Gas Exchange

• Photosynthesis occurs in the leaves of plants, where carbon dioxide is taken up by the leaf and oxygen is released.
• Gas exchange occurs through stomata in the epidermis.
• Open stomata permit gas exchange for photosynthesis.
• Open stomata permit water in the form of vapour to exit the leaf.
• Transpiration involves movement and loss of water.
• Guard cells help reduce the water loss.

Rate of Transpiration

• Increased air movement increases transpiration.
• Humidity can lower transpiration rates.
• Air outside the leaf usually contains less water vapour, increasing the transpiration rate.
• Accumulation of water molecules in the external air slows loss.
• Transport of water molecules increases when air currents move water from the leaf.
• Higher temperatures lead to higher transpiration, up to a point.
• High temperatures can cause the stomata to prevent water loss.
• Transpiration is reduced under high heat because the stomata close.
• Higher light intensity increases transpiration, but plateaus.
• Stomata close in the dark reducing transpiration rates.
• Stomata enable gas exchange for photosynthesis when it is light which increases rate of transpiration
• Transpiration is measured using a potometer.

Drawing Leaf Structure

• Chloroplasts
• Cuticle
• Guard cells
• Stomata
• Upper and lower epidermiseses
• Palisade mesophyll
• Spongy mesophyll
• Air spaces
• Vascular bundles (xylem and phloem)

Determining Stomatal Density

• Stomatal density indicates the number of stomata per area.
• Geraniums make good subjects for study.
• Nail vanish is uses to collect a stomatal imprint and study it under the mass.
• The nail varnish should dry before being handled.
• Clickers and phone app could to help accurately count large quantities of stomata.
• Count stomata in the field of view, repeating 3 times for accuracy.
• The diameter of the field of view is measured using a micrometer.
• A high number indicates a reliable data set.
• Anomalies can omit anomalies when calculating date.

Haemoglobin & Oxygen

• Haemoglobin binds oxygen in blood.
• It consists of globular proteins in red blood cells.
• Each has four polypeptide subunits that combine with iron-containing haem groups.
• Each group binds to one O2 transport four O2 molecules.
• Each gas in air exerts partial pressure; symbol is 'p' (pO2)

Cooperative Binding

• The haemoglobin molecule changes shape after the first oxygen molecule bonds for a quicker conformation.
• Affinity describes ability to bind.
• Oxygen readily associates with haemoglobin in high partial pressures (such as in lungs).
• Areas with low partial pressures such as muscle have low affinity.
• Hemoglobin easily releases oxygen to the blood.
• Hemoglobin easily binds oxygen in lung capillaries and releases oxygen.

Foetal Haemoglobin

• Fetal haemoglobin has more oxygen affinity than adult.
• Binding oxygen is easier at the placenta from the mother's blood at low pO2.
• Adult hemoglobin is replaced after birth.
• Fetal shifts left and has a higher percentage than adult.

Bohr Shift

• The relationship between carbon dioxide levels and oxygen is known as the Bohr shift/effect.
• Hemoglobin's oxygen affinity decreases when blood carbon dioxide is high.
• High affinity occurs where cells produce carbon dioxide.
• Low pH in the blood and respiration results.

Oxygen Dissociation Curve

• Oxygen dissociation curves indicate the way in which hemoglobin interacts with oxygen.
• In other liquids would display oxygen dissolving at a constant rate and creating a straight like.
• The curve shapes indicates the binding creates.
• Oxygen associates at different partial pressures.
• The result is that affinity for oxygen changes partial pressures