Exchange Surfaces (OCR A Level Biology): Flashcards

• Oxygen consumption (using a respirometer)

• Carbon dioxide production (using a carbon dioxide probe)

• Heat generation (using a calorimeter)

Heat is lost to the environment at the body's surface.

Small animals have a higher SA:V ratio, so they lose more heat to their surroundings.

To replace this heat and maintain body temperature, they need a relatively high metabolic rate.

Smaller animals have a higher metabolic rate per unit of body mass than larger animals.

However, larger organisms support more cells overall, so they still consume more oxygen in total within a given period of time.

They do not move around their habitat and do not have to maintain a high body temperature.

False — as an organism increases in size, its SA:V ratio decreases.

True

• Large surface area

• Short diffusion distance (thin)

• Good blood supply

• Ventilation mechanism

It is very small, so it has a large surface area to volume ratio and a short diffusion distance to the centre of the cell.

This means oxygen can diffuse across the cell surface membrane quickly enough to meet the cell's needs, without a specialised exchange surface.

They have a root hair (an extension of the cytoplasm) that increases the surface area of the cell in contact with the soil.

The larger surface area increases the rate of water uptake by osmosis and allows more mineral ions to be absorbed.

The walls of the alveoli are only one cell thick and these cells are flattened.

This gives gases a very short diffusion distance, so gas exchange is quick and efficient.

It greatly increases the surface area available for oxygen and carbon dioxide to diffuse across, increasing the rate of gas exchange.

The constant flow of blood carries oxygenated blood away from the alveoli and brings deoxygenated blood to them.

This maintains the concentration gradient needed for oxygen and carbon dioxide to continue diffusing.

The blood is continuously flowing, carrying away substances that have just entered the blood from the exchange site.

This keeps the concentration difference high, so diffusion continues for a prolonged period of time.

An arrangement in the gills where blood flows in the opposite direction to the flow of water. This maintains the concentration gradient for oxygen diffusion along the whole length of the capillary/gill.

Blood flows in the opposite direction to the flow of water over the gills.

This maintains a concentration gradient along the whole length of the capillary, so oxygen diffuses from the water into the blood along the entire gill.

The mass flow of gases (the movements of breathing) that refreshes the air at an exchange surface, helping to maintain the concentration gradient across it.

• Breathing constantly changes the air in the alveoli

• It removes air with a low oxygen and high carbon dioxide concentration and replaces it with air high in oxygen and low in carbon dioxide

• This ensures there is always a higher oxygen concentration in the alveoli than in the blood, maintaining the gradient

The walls of the alveoli are only one cell thick, giving gases a short diffusion distance.

In fish gills, blood flows in the opposite direction to the water in a counter-current system.

False — the walls of the alveoli are only one cell thick, giving a short diffusion distance.

True

The chest cavity: a collection of organs and tissues where gas exchange takes place in mammals.

It is a strong, flexible tissue that forms rings supporting the trachea (and bronchi), keeping the airway open while still allowing it to move and flex during breathing.

Each cell has small projections of cilia that sweep mucus, dust and bacteria upwards, away from the lungs and the epithelium itself.

They are mucus-producing cells that secrete viscous mucus.

The mucus traps dust, bacteria and other microorganisms, preventing them from reaching the lungs.

The trapped material is swept upwards by cilia, swallowed, and destroyed by acid in the stomach.

It forms the alveolar wall and is very thin and permeable, allowing the easy, rapid diffusion of gases.

It is found in the walls of the bronchi and bronchioles.

Elastic fibres enable the lungs to stretch and then recoil.

Elastic fibres allow the lungs to stretch and then recoil, making expiration a passive process.

Carbon dioxide diffuses out of the capillaries into the alveoli to be exhaled.

Oxygen diffuses the other way, from the alveoli into the capillaries, to be carried around the body.

The capillaries are narrow enough for only one red blood cell to pass at a time, ensuring sufficient time and opportunity for gas exchange.

The C-shape prevents friction from rubbing against the oesophagus located close behind, while still keeping the air channel open at all times.

Bronchi have a similar structure to the trachea but with thinner walls and a smaller diameter.

Their cartilage does not form a C-shape; it can form full rings or irregular blocks.

• They are narrow, self-supporting tubes with thin walls

• They are not usually supported by cartilage

• They are lined with ciliated epithelium but usually do not contain goblet cells

• Larger bronchioles contain elastic fibres and smooth muscle to adjust airflow; the smallest have elastic fibres but no smooth muscle

• The wall consists of a single layer of (squamous) epithelium

• Elastic fibres are present in the extracellular matrix

• It is surrounded by an extensive capillary network

• A watery fluid lines the alveoli, facilitating the diffusion of gases

Goblet cells and mucous glands produce mucus in the trachea, which is swept upwards by the cilia of the ciliated epithelium.

It regulates the flow of air into the lungs by dilating when more air is needed and constricting when less air is needed.

Their recoil pushes air out of the lungs, so expiration requires no active muscular effort.

False — bronchioles are narrow, self-supporting tubes that are not usually supported by cartilage.

True

The mass flow of gases into and out of the lungs (breathing), which continually refreshes the air in the alveoli.

Ventilation, together with the continuous flow of blood in the capillaries, ensures there is always a higher concentration of oxygen in the alveoli than in the blood.

This maintains a steep concentration gradient for oxygen to diffuse from the alveoli into the blood.

The movements of breathing change the air in the alveoli, which:

• supplies fresh oxygen to the alveoli

• removes carbon dioxide from the alveoli

1. Nose / mouth

1. Trachea (windpipe)

1. Bronchi

1. Bronchioles

1. Alveoli

• The volume in the chest increases

• The air pressure in the lungs decreases until it is slightly lower than atmospheric pressure

• Air then moves down the pressure gradient and rushes into the lungs

The diaphragm contracts and flattens, increasing the volume of the chest.

This decreases the pressure in the lungs, so air is drawn in.

In addition to the diaphragm flattening, the external intercostal muscles contract, causing the ribcage to move upwards and outwards.

This further increases chest volume, drawing in more air.

• The volume in the chest decreases

• The pressure in the lungs increases

• Air is forced out of the lungs

• The external intercostal muscles relax

• The recoil of elastic fibres surrounding the alveoli forces air out

• The diaphragm relaxes and becomes dome-shaped

• The internal intercostal muscles contract to pull the ribs downwards and inwards

• The abdominal muscles contract to push the organs upwards against the diaphragm, increasing the internal pressure

This produces a forced exhalation.

As one set of intercostal muscles contracts, the other set relaxes.

The external and internal intercostal muscles work against each other to move the ribcage up (breathing in) and down (breathing out).

During inhalation at rest, the diaphragm contracts and flattens, increasing the volume of the chest.

Exercise causes oxygen demand to increase.

An increased rate of ventilation supplies oxygen and removes carbon dioxide more quickly, helping to meet this higher demand.

Alternative terms for breathing in and breathing out. Inspiration (= inhalation) is breathing in; expiration (= exhalation) is breathing out.

True — a flattened diaphragm increases chest volume and lowers lung pressure, drawing air in.

False — at rest these muscles relax; air is forced out mainly by the elastic recoil of the lungs.

The maximum volume of air that can be breathed in or out in one breath.

The volume of air breathed in or out during normal breathing (at rest).

The number of breaths taken in one minute (one breath = taking air in and breathing it back out again).

The volume of oxygen used up by someone in a given time.

The small amount of air always retained in the lungs after as much air as possible has been breathed out.

• Vital capacity

• Tidal volume

• Breathing rate

• Oxygen uptake

A spirometer is a piece of apparatus used to measure different aspects of breathing.

The subject breathes in and out through it, allowing their vital capacity, tidal volume, breathing rate and oxygen uptake to be calculated.

Soda lime absorbs carbon dioxide from the exhaled air.

This stops the concentration of carbon dioxide in the re-breathed air from getting too high, which could otherwise cause respiratory distress.

As the subject breathes, a trace is drawn on a rotating drum of paper, or a graph is formed digitally and viewed on a computer.

From this, vital capacity, tidal volume and breathing rate can be calculated.

As the subject breathes, carbon dioxide is removed from the exhaled air by soda lime.

Oxygen is continually extracted from the air by the subject's breathing, so the total volume of air in the spirometer gradually decreases.

This change in volume is used as a measure of oxygen uptake.

• Count the number of breaths in 60 seconds (one breath = the trace going up and then down)

• Express the value in the correct units: breaths min⁻¹

For example, 12 up-and-down movements in the first 60 seconds = 12 breaths min⁻¹.

Measure the difference between the top and bottom of the trace for a single breath, in terms of the volume of air in the lungs.

For example, at rest: 3 dm³ − 2.6 dm³ = 0.4 dm³.

Carbon dioxide is absorbed from the exhaled air in a spirometer by soda lime.

Residual volume is the volume of air always retained in the lungs after as much air as possible has been breathed out.

False — soda lime absorbs carbon dioxide, not oxygen.

True

Openings in the exoskeleton of an insect that allow air to flow into the internal system of tubes (the tracheal system).

Tubes within the insect respiratory system that carry air inwards and lead to narrower tubes called tracheoles.

It is rigid and has a waxy coating that makes it impermeable to gases, so gases cannot diffuse across it.

• Rigid rings of chitin keep the tracheae open

• Many tracheoles carry oxygen directly to the muscle fibres, where gas exchange takes place

• The large number of tracheoles in contact with the cells provides a large surface area for gas exchange

Gases dissolve in the tracheal fluid before diffusing to the cells, allowing gas exchange to take place.

At rest, energy requirements are low, so diffusion alone is fast enough to supply oxygen to the cells.

Contracting and relaxing the muscles of the thorax and abdomen alters the volume, and therefore the pressure, inside the tracheae, drawing air in and out.

The tracheal fluid at the narrow ends of the tracheoles is drawn into the respiring muscle.

Removing the fluid reduces the diffusion distance between the air and the muscle cells, speeding up diffusion.

Oxygen dissolves less readily in water; a given volume of air contains about 30 times more oxygen than the same volume of water.

Fish gills are adapted to directly extract this smaller amount of oxygen from water.

• A series of gills sits on each side of the head

• Each gill arch is attached to two stacks of filaments

• On the surface of each filament are rows of lamellae

• Each lamella is covered by a single layer of flattened cells over a vast network of capillaries

An arrangement in which blood in the lamellae flows in the opposite direction to the flow of water, maintaining the concentration gradient along the whole length of the capillary so oxygen diffuses into the blood along the entire lamella.

In the counter-current system, the water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood.

The fish opens its mouth and lowers the floor of the buccal cavity.

This increases the volume and so decreases the pressure within the cavity.

Pressure is higher outside the mouth, so water flows into the buccal cavity.

The fish raises the floor of the buccal cavity, closing its mouth and increasing the pressure inside.

Water flows from the buccal cavity (high pressure) into the gill cavity (low pressure).

Pressure builds in the gill cavity, forcing the operculum open so water exits the fish.

A flap of tissue covering the gills of a bony fish; it is forced open to let water leave and is pulled shut when the floor of the buccal cavity is lowered at the start of the next ventilation cycle.

They may close their spiracles to reduce water loss by evaporation.

True

False — blood flows in the opposite direction to the water, which maintains the concentration gradient along the whole lamella.

They allow the internal structures of organs to be examined, so that theories can be made about how those organs function.

• Concerns about how the animals are raised and killed

• It goes against the religious beliefs of some individuals

The specimen should be obtained from a reputable source and disposed of correctly.

They should be taken from individual organisms of the same species and of roughly the same age.

To avoid contamination with biological material, which could otherwise cause an allergic reaction.

• Scissors: used for cutting large sections of tissue, where cuts do not need to be precise

• Scalpel: enables finer, more precise cutting and needs to be sharp to ensure this

• Cut away from your body

• Keep your fingers far from the blade to reduce the chance of cutting yourself

To move sections of the specimen aside, leaving the desired structure exposed.

• It can be hard to see the smaller, finer structures within organs

• The specimens do not reflect how tissue looks in a living organism

• With only a single specimen, anomalies may be ignored or glossed over

• Gill arch

• Filaments

The smaller lamellae can be hard to distinguish in a dissected fish.

• Trachea

• Bronchi

• Bronchioles

The smaller alveoli can be hard to distinguish in a dissected lung.

The insect tracheal system is very small, so specialised equipment and skills are sometimes required to dissect it, and microscopes are needed to observe the structures.

In a photomicrograph of stained mammalian lung tissue, the alveoli appear as different sizes and shapes because they are no longer inflated as they would be in a living lung.

Real tissue often appears very different from idealised textbook diagrams, so it is important to be able to identify the gas exchange surface and its key structures.

Electron microscopes can take clear images of the spiracle structures found on the surface of insects.

False — the smaller lamellae can be hard to distinguish in a dissected fish.

False — specimens do not reflect how tissue looks in a living organism.

An external opening on the surface of an insect through which air enters the tracheal system.

The structure that resembles a backbone for the gills, supporting the filaments.