AQA A level Biology
AQA A level Biology
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Topic 3: Organisms exchange substances with their environment
Topic 3: Organisms exchange substances with their environment
Gas exchange in humans
Gas exchange in humans
Gas exchange in humans
Gas exchange in humans
Gas exchange in humans occurs in the lungs, which are specialised structures connected to the external environment via the respiratory system. The pathway of air begins at the mouth and nose, passes through the trachea, which branches into the bronchi, and further divides into bronchioles. These bronchioles end in clusters of alveoli, the primary sites of gas exchange.
The human respiratory system.
Adaptations for efficient gas exchange
Adaptations for efficient gas exchange
The human gas exchange system is adapted to maximise efficiency through the following features:
Alveoli:
Millions of alveoli provide a large surface area for diffusion.
Their thin walls (one cell thick) minimise the diffusion distance.
Proximity to Capillaries:
Alveoli are surrounded by a dense network of capillaries, ensuring a short diffusion distance.
Continuous blood flow maintains a steep concentration gradient for oxygen and carbon dioxide.
Ventilation:
Regular breathing movements maintain the concentration gradient, facilitating efficient gas exchange.
The diffusion of gases between the alveoli and capillaries.
Mechanism of breathing
Mechanism of breathing
Breathing, or pulmonary ventilation, involves two main processes:
Inhalation:
The diaphragm contracts and flattens.
The external intercostal muscles contract, raising the ribcage.
Thoracic volume increases, reducing pressure in the lungs and drawing air in.
Exhalation:
The diaphragm relaxes and becomes dome-shaped.
The internal intercostal muscles contract, lowering the ribcage.
Thoracic volume decreases, increasing pressure and forcing air out.
Ventilation rate
Ventilation rate
Definition: Pulmonary ventialtion rate (PVR) is the volume of air moved into the lungs in one minute (dm3.min-1)
Formula:
PVR = Tidal volume x Breathing rate
Where:
Tital volume is the volume of air inhaled in one breath (dm3)
Breathing rate is the number of breaths taken in 1 minute
Risk factors
Risk factors
A risk factor is any condition or behavior that increases the likelihood of developing a disease. Risk factors are identified by analyzing correlations between behaviors or exposures and diseases. However, correlation does not equal causation, as confounding factors may be involved.
Examples:
Smoking: Strongly linked to lung cancer and chronic obstructive pulmonary disease (COPD).
Pollution: Associated with respiratory diseases but may interact with other risk factors like smoking.
Definitions
Definitions
Adaptation: feature of an organism that better enables it to survive or reproduce.
Alveoli (alveolus): tiny air sacs in the lungs, across the surface of which gas exchange occurs.
Antagonistic: when two things have opposing roles, such as one muscle causing a joint to bend and another causing it to straighten.
Bronchi (bronchus): tubes lined with cartilage in the lungs that link the trachea with the bronchioles.
Bronchiole: tube that branches from a bronchus and eventually form alveoli.
Causal relationship: when one variable influences another.
Correlation: when two variables change at the same time, though one might not necessarily be influencing the other.
Diaphragm: sheet of muscle that beneath the lungs, responsible for controlling breathing Dicotyledonous plant: one of the two groups into which all the flowering plants are divided, characterised by their seeds containing two embryonic leaves (cotyledons).
Diffusion: the movement of particles from a region where they are in high concentration toto a region of lower concentration.
Epithelium: cells that line the exterior surface of an organism or surfaces responsible for exchanging substances with the environment.
External intercostal muscles: skeletal muscles found between ribs that, when contracting, cause the ribs to move upward and outward, so increasing the volume and decreasing the pressure of the thorax and causing inhalation.
Gas exchange: the diffusion of a gas between the environment and an organism, normally for the purpose of respiration or photosynthesis.
Intercostal muscles: muscles between ribs, responsible for controlling breathing.
Internal intercostal muscles: skeletal muscles found between ribs that, when contracting, cause the ribs to move downward and inward, so decreasing the volume and increasing the pressure of the thorax and causing exhalation. Internal intercostal muscles are not used during normal breathing, only during forced exhalation.
Lung: organ found in many vertebrates where gas exchange occurs.
Risk factor: something that increases chance of something (normally a disease) occurring.
Stoma (plural stomata): pore in a plant leaf through which gases can diffuse.
Thoracic cavity: space within the ribs of a vertebrate animal.
Tidal volume: volume of air inhaled or exhaled in a single breath.
Ventilation: the movement of air in an out of the lungs as a result of the contraction of the intercostal and diaphragm muscles. Also known as breathing.
Ventilation rate: number of breaths per minute.
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