GASEOUS EXCHANGE

What is gaseous exchange?

Gaseous exchange is the movement of oxygen into an organism and carbon dioxide out of an organism by diffusion across a respiratory surface.

Explain why gaseous exchange is important in living organisms.

Gaseous exchange supplies oxygen needed for aerobic respiration and removes carbon dioxide produced during respiration. This allows cells to release energy for essential life processes.

Where does gaseous exchange occur in humans?

Gaseous exchange occurs in the alveoli of the lungs where oxygen diffuses into the blood and carbon dioxide diffuses from the blood into the alveoli.

Explain the role of blood in gaseous exchange.

Blood transports oxygen from the lungs to body cells for aerobic respiration and carries carbon dioxide produced by cells back to the lungs for removal during exhalation.

Explain how gaseous exchange occurs between blood and body cells.

Oxygen diffuses from the blood into body cells because its concentration is lower in the cells. Carbon dioxide diffuses from the cells into the blood because its concentration is higher in the cells due to respiration.

Identify the main structures of the human respiratory system and state their functions.

Nose and nasal cavity: Filter warm and moisten air. Mouth: Provides an alternative air passage. Pharynx: Carries air towards the larynx. Larynx: Contains vocal cords and allows air into the trachea. Trachea: Carries air towards the bronchi and is supported by cartilage. Bronchi: Carry air into each lung. Bronchioles: Distribute air towards the alveoli. Alveoli: Allow gaseous exchange between air and blood. Lungs: Contain the alveoli. Ribs: Protect the lungs and move during breathing. External intercostal muscles: Raise the rib cage during inspiration. Internal intercostal muscles: Assist forced expiration. Diaphragm: Changes thoracic volume during breathing. Pleural membranes: Reduce friction during breathing.

Describe the pathway taken by air from the nose to the alveoli.

Air enters through the nose or mouth and passes through the pharynx and larynx into the trachea. It then travels through the bronchi and bronchioles before reaching the alveoli where gaseous exchange occurs.

Explain why the trachea contains C-shaped rings of cartilage.

The C-shaped rings of cartilage support the trachea and prevent it from collapsing during breathing. This ensures that air can pass freely into and out of the lungs.

Distinguish between the bronchi and bronchioles.

The bronchi are the two main air passages branching from the trachea into the lungs. Bronchioles are smaller branches that distribute air throughout the lungs and lead towards the alveoli.

What are alveoli and what is their main function?

Alveoli are tiny air sacs located at the ends of bronchioles. They provide a large surface area for oxygen to diffuse into the blood and carbon dioxide to diffuse out.

Explain how mucus and cilia protect the respiratory system.

Mucus traps dust and microorganisms entering the air passages. Cilia beat rhythmically to move the mucus towards the throat where it can be swallowed or expelled.

What is the function of the pleural membranes?

The pleural membranes surround the lungs and contain a thin layer of fluid that reduces friction between the lungs and chest wall during breathing.

Describe how gaseous exchange occurs in the alveoli.

Deoxygenated blood reaches capillaries surrounding the alveoli. Oxygen dissolves in the moist alveolar surface and diffuses into the blood because its concentration is higher in the alveoli. Carbon dioxide diffuses from the blood into the alveoli because its concentration is higher in the blood. Carbon dioxide is then removed during exhalation.

Explain how alveoli are adapted for efficient gaseous exchange.

Numerous alveoli provide a large surface area. Their walls are one cell thick to create a short diffusion distance. Their surfaces are moist to allow gases to dissolve. Numerous capillaries provide a rich blood supply. Continuous ventilation maintains steep concentration gradients.

Why are the walls of alveoli and capillaries only one cell thick?

Their thin walls provide a short diffusion distance so oxygen and carbon dioxide can diffuse rapidly between the alveoli and blood.

Why must the surfaces of alveoli remain moist?

Moist surfaces allow oxygen and carbon dioxide to dissolve before diffusing across the alveolar walls.

Explain why alveoli are surrounded by numerous capillaries.

Capillaries provide a continuous blood supply that carries oxygen away and brings carbon dioxide to the alveoli. This maintains concentration gradients for rapid diffusion.

Compare the blood entering and leaving the capillaries surrounding an alveolus.

Blood entering the alveolar capillaries is deoxygenated and contains relatively little oxygen and more carbon dioxide. Blood leaving is oxygenated and contains more oxygen and less carbon dioxide.

Explain how a concentration gradient allows gaseous exchange to occur.

A concentration gradient is a difference in the concentration of a substance between two regions. Oxygen and carbon dioxide diffuse from regions of higher concentration to regions of lower concentration.

Explain how continuous breathing and blood circulation maintain gaseous exchange.

Breathing replaces alveolar air with fresh oxygen-rich air and removes carbon dioxide. Blood circulation carries absorbed oxygen away and brings carbon dioxide to the lungs. These processes maintain concentration gradients.

Compare the composition of inspired and expired air.

Inspired air contains approximately 21% oxygen and 0.04% carbon dioxide and 78% nitrogen. Expired air contains approximately 16% oxygen and 4% carbon dioxide and 78% nitrogen. Expired air is usually warmer and contains more water vapour.

Explain why expired air contains less oxygen than inspired air.

Some inhaled oxygen diffuses from the alveoli into the blood and is transported to body cells where it is used during aerobic respiration.

Explain why expired air contains more carbon dioxide than inspired air.

Carbon dioxide is produced during cellular respiration and transported by the blood to the lungs where it diffuses into the alveoli and is exhaled.

Explain why expired air usually contains more water vapour than inspired air.

The respiratory surfaces are moist and water evaporates into the air passing through them.

Explain why expired air is usually warmer than inspired air.

Air is warmed as it passes through the respiratory passages and lungs because heat is transferred from surrounding body tissues.

Explain why the percentage of nitrogen remains approximately the same in inspired and expired air.

Nitrogen is not significantly used or produced during respiration so its proportion remains approximately unchanged.

Define breathing and inspiration and expiration.

Breathing is the movement of air into and out of the lungs. Inspiration is breathing air into the lungs. Expiration is breathing air out of the lungs.

Describe the mechanism of inspiration in humans.

The external intercostal muscles contract while the internal intercostal muscles relax. The ribs move upwards and outwards. The diaphragm contracts and flattens and moves downwards. Thoracic volume increases and pressure inside the lungs decreases below atmospheric pressure. Air enters the lungs.

Describe the mechanism of expiration in humans.

The external intercostal muscles relax and the ribs move downwards and inwards. The diaphragm relaxes and becomes dome-shaped. Thoracic volume decreases and pressure inside the lungs increases above atmospheric pressure. Air leaves the lungs. During forced expiration the internal intercostal muscles contract.

Compare inspiration and expiration.

During inspiration the external intercostal muscles contract and the ribs move upwards and outwards. The diaphragm contracts and flattens. Thoracic volume increases and lung pressure decreases so air enters. During expiration these movements reverse and thoracic volume decreases and lung pressure increases so air leaves.

Explain the relationship between thoracic volume and air pressure during breathing.

When thoracic volume increases during inspiration the pressure inside the lungs decreases and air enters. When thoracic volume decreases during expiration the pressure increases and air leaves.

Explain why the lungs expand during inspiration.

Contraction of the diaphragm and external intercostal muscles increases thoracic volume and lowers pressure inside the lungs. Air enters and the lungs expand.

Explain why breathing rate increases during exercise.

During exercise muscle cells respire more rapidly and produce more carbon dioxide. Breathing rate and depth increase to supply sufficient oxygen and remove excess carbon dioxide.

Distinguish between breathing and respiration.

Breathing is the physical movement of air into and out of the lungs. Respiration is the chemical process in cells that releases energy from food substances such as glucose.

Where does gaseous exchange occur in plants?

Gaseous exchange occurs mainly through stomata in leaves where gases diffuse between the atmosphere and the internal air spaces of the leaf.

What are stomata and what is their function in gaseous exchange?

Stomata are tiny pores in the leaf epidermis that allow carbon dioxide and oxygen to diffuse into and out of the leaf. Their opening and closing are controlled by guard cells.

Describe gaseous exchange in plants during the day.

During the day plants carry out both photosynthesis and respiration. Photosynthesis usually uses more carbon dioxide than respiration produces so carbon dioxide diffuses into the leaf while excess oxygen diffuses out.

Describe gaseous exchange in plants at night.

At night photosynthesis stops because light is absent but respiration continues. Oxygen diffuses into the leaf for respiration while carbon dioxide produced during respiration diffuses out.

Explain why plants require oxygen even though they produce oxygen during photosynthesis.

Plants require oxygen for aerobic respiration which releases energy needed for growth and active transport and other life processes. Respiration occurs during both day and night.

Explain how the structure of a leaf allows efficient gaseous exchange.

Leaves are broad and thin and provide a large surface area and short diffusion distance. Stomata allow gases to enter and leave while internal air spaces allow gases to diffuse rapidly towards cells.

Explain the role of intercellular air spaces in leaves.

Intercellular air spaces allow oxygen and carbon dioxide to diffuse throughout the leaf and bring gases close to the surfaces of cells.

Identify the gaseous exchange surfaces in humans and fish and plants and Amoeba.

Humans: Alveoli in the lungs. Fish: Gill lamellae. Plants: Mainly internal leaf surfaces with gases entering and leaving through stomata. Amoeba: Cell membrane.

State the characteristics of an efficient gaseous exchange surface.

An efficient gaseous exchange surface has a large surface area and a thin moist surface and a continuously renewed transport medium that maintains concentration gradients.

Explain why a large surface area is important for gaseous exchange.

A large surface area allows more oxygen and carbon dioxide molecules to diffuse across the respiratory surface at the same time and increases the rate of gaseous exchange.

Explain why a thin respiratory surface is important.

A thin respiratory surface reduces the distance gases must travel by diffusion and allows rapid movement of oxygen and carbon dioxide.

Explain why respiratory surfaces must remain moist.

Oxygen and carbon dioxide dissolve in moisture before diffusing through cell membranes so moist surfaces make gaseous exchange more efficient.

Explain why a constantly moving transport medium is important for gaseous exchange.

A moving transport medium continually supplies oxygen and removes carbon dioxide and maintains concentration gradients that allow diffusion to continue.

Explain how fish gills are adapted for efficient gaseous exchange.

Fish gills contain numerous thin gill lamellae that provide a large surface area. Their surfaces are thin and contain many capillaries allowing oxygen to diffuse from water into the blood and carbon dioxide to diffuse out.

Explain the function of gill lamellae.

Gill lamellae are thin structures containing capillaries that provide a large surface area for oxygen to diffuse from water into blood and carbon dioxide to diffuse from blood into water.

Explain the functions of gill bars and gill rakers in fish.

Gill bars support the gill structures while gill rakers help filter food particles and debris from water passing through the gills.

Explain how water movement over fish gills maintains gaseous exchange.

Water continuously passes over the gill lamellae and supplies dissolved oxygen while removing carbon dioxide. This maintains concentration gradients for diffusion.

Explain why Amoeba does not require specialised respiratory organs.

Amoeba is a small unicellular organism with a large surface-area-to-volume ratio. Oxygen and carbon dioxide diffuse directly across its cell membrane rapidly enough to meet its needs.

Compare gaseous exchange in humans and fish and plants and Amoeba.

Humans exchange gases through alveoli using air and blood. Fish exchange gases through gill lamellae using water and blood. Plants exchange gases through leaf surfaces using air. Amoeba exchanges gases directly across its cell membrane using surrounding water.

Identify three harmful substances found in cigarette smoke.

Nicotine and tar and carbon monoxide.

State the harmful effects of nicotine on the body.

Nicotine is highly addictive and increases heart rate and blood pressure. It can also affect blood vessels and cardiovascular health.

Explain how nicotine contributes to addiction.

Nicotine affects the brain reward pathways and produces pleasurable effects that encourage repeated use. Continued exposure can lead to dependence and withdrawal symptoms.

Explain how smoking damages cilia in the respiratory tract.

Cigarette smoke damages and interferes with the movement of cilia and reduces their ability to remove mucus and dust and microorganisms. This increases the risk of respiratory infections.

State the harmful effects of tar on the respiratory system.

Tar contains harmful chemicals that damage lung tissues and increase the risk of lung cancer and contribute to bronchitis. It can damage alveoli and reduce the efficiency of gaseous exchange.

Explain how smoking can reduce the surface area available for gaseous exchange.

Smoking can damage the walls of alveoli and cause them to break down and merge into larger air spaces. This reduces the total surface area available for diffusion.

Explain how cigarette smoking can cause bronchitis.

Cigarette smoke irritates and inflames the lining of the bronchi and increases mucus production and damages cilia. This can cause persistent coughing and difficulty breathing.

Explain why smokers may develop a persistent cough.

Smoking damages the cilia that normally remove mucus and trapped particles. As mucus accumulates in the respiratory passages coughing becomes necessary to help remove it.

Explain how carbon monoxide affects oxygen transport in the blood.

Carbon monoxide binds very strongly to haemoglobin and forms carboxyhaemoglobin. This reduces the amount of haemoglobin available to transport oxygen so less oxygen reaches body tissues.

Explain why smoking can reduce a person's ability to exercise.

Smoking damages lung tissues and reduces oxygen transport because carbon monoxide binds to haemoglobin. Muscles receive less oxygen for aerobic respiration and this causes breathlessness and reduced exercise performance.

Explain how smoking during pregnancy can affect the developing baby.

Carbon monoxide from cigarette smoke reduces the oxygen-carrying capacity of the mother's blood and can affect oxygen delivery to the fetus. This increases the risk of restricted fetal growth and low birth weight.

Explain the relationship between cigarette smoking and lung cancer.

Cigarette smoke contains carcinogenic chemicals that damage DNA in lung cells. These mutations may cause uncontrolled cell division and the development of malignant tumours.

Explain how passive smoking can affect a non-smoker.

Passive smoking occurs when a person inhales tobacco smoke from the surrounding environment. Exposure can damage the respiratory system and increase the risk of respiratory illnesses and heart disease and lung cancer.

Identify the main psychoactive substance in marijuana.

The main psychoactive substance in marijuana is tetrahydrocannabinol or THC which affects brain activity and produces changes in mood and perception and behaviour.

State five short-term effects of marijuana use.

Short-term effects may include impaired memory and difficulty learning and distorted perception and reduced coordination and increased heart rate and anxiety and panic attacks.

Explain how marijuana smoking can affect the respiratory system.

Marijuana smoke contains irritants and tar and carbon monoxide that can damage respiratory tissues and irritate the air passages. Repeated smoking may cause coughing and bronchitis-like symptoms.

Explain why inhaling marijuana smoke deeply may increase respiratory exposure to harmful substances.

Deep inhalation and prolonged breath-holding may increase the deposition of smoke particles and exposure to harmful substances in the respiratory tract.

Explain why a person may become breathless during strenuous exercise.

During strenuous exercise muscles require more oxygen and produce more carbon dioxide. Breathing becomes faster and deeper to increase oxygen uptake and remove excess carbon dioxide.

Predict what would happen if the alveolar walls became thicker.

Thicker alveolar walls would increase the distance over which gases must diffuse and reduce the rate of gaseous exchange. This would make it more difficult for oxygen to enter the blood.

Explain why a person with damaged alveoli may experience difficulty breathing.

Damaged alveoli may provide a smaller surface area for gaseous exchange and reduce the amount of oxygen entering the blood. This can cause breathlessness especially during physical activity.

Predict the effect of blocked bronchioles on gaseous exchange.

Blocked bronchioles reduce the amount of air reaching the alveoli and decrease oxygen availability and limit carbon dioxide removal. This reduces the efficiency of gaseous exchange.

Explain why removing carbon dioxide from the body is important.

Carbon dioxide is continuously produced during respiration. If it accumulates it can disturb the body's acid-base balance and interfere with normal cellular functions.

Describe an experiment to demonstrate that expired air contains carbon dioxide.

Bubble expired air through clear limewater using a suitable apparatus. The limewater turns milky because carbon dioxide reacts with calcium hydroxide to form insoluble calcium carbonate.

Describe an experiment to compare carbon dioxide levels in inspired and expired air.

Pass inspired and expired air separately through equal volumes of limewater using an appropriate breathing apparatus. Limewater exposed to expired air becomes milky more quickly because expired air contains more carbon dioxide.

Explain why limewater turns milky when carbon dioxide is passed through it.

Carbon dioxide reacts with calcium hydroxide in limewater to form insoluble calcium carbonate. This produces a white precipitate that makes the solution appear milky.

Describe how to investigate the effect of exercise on breathing rate.

Measure and record a person's resting breathing rate. Have the person perform a standardised exercise for a fixed time. Immediately measure breathing rate again and record it at regular intervals during recovery. Compare the results to determine how exercise affects breathing rate.

Explain why breathing rate gradually returns to normal after exercise.

As activity decreases muscles require less oxygen and produce less carbon dioxide. Breathing rate gradually decreases as the body returns towards its resting condition and recovers from exercise.

Identify the independent and dependent and controlled variables in an investigation of exercise and breathing rate.

The independent variable is the exercise condition or intensity. The dependent variable is breathing rate measured in breaths per minute. Controlled variables may include exercise duration and environmental conditions and the method of counting breaths.

Explain why repeated measurements are important when investigating breathing rate.

Repeated measurements help identify unusual results and reduce the effect of random errors. They also allow a mean to be calculated and improve the reliability of the investigation.