3.1.1 - Exchange Surfaces Flashcards (PMT)

Why do multicellular organisms require specialised gas exchange surfaces?

Smaller SA:V ratio = distance that needs to be crossed is larger

• Substances cannot easily enter the cells as in a single-celled organism

SA:V ratio calculation?

Ratio = SA/V

Name three features of an efficient gas exchange surface.

1. Large SA (e.g. root hair cells)

2. Thin/short diffusion distance (e.g. alveoli)

3. Steep concentration gradient, maintained by blood supply or ventilation (e.g. gills)

Describe the trachea.

• Wide tube

• Supported by C-shaped cartilage

  • Keeps air passage open during pressure changes

• Lined by ciliated epithelium cells

  • Move mucus produced by goblet cells towards throat

    • Swallowed, prevents infections

Describe the trachea’s function in the mammalian gaseous exhange system.

Carries air to the bronchi

Describe the bronchi.

• Supported by rings of cartillage

• Lined by ciliated epithelium cells and goblet cells

• Narrower than trachea

• Two of them; one for each lung

Describe the bronchi’s function in the mammalian gaseous exchange system.

Allow passage of air into bronchioles

Describe the bronchioles.

• Narrower than the bronchi

• Mostly smooth muscle and elastic fibres

  • Don’t need to be kept open by cartilage

  • So they can contract and relax easily during ventilation

Describe the bronchioles’ function in the mammalian gaseous exchange system.

Allow passage of air into the alveoli

Describe the alveoli.

• Mini air sacs

• Lined with epithelium cells

• Walls only one cell thick

• Covered with a network of capillaries; 300 million in each lung

Describe the alveoli’s function in the mammalian gaseous exchange system.

• Site of gas exchange

• Wall and capillary network facilitates gas diffusion

Explain the process of inspiration and the changes that occur throughout the thorax.

• External intercostal muscles contract (internal relax)

  • Pulls the ribs up and out

• Diaphragm contracts and flattens

• Volume of thorax increases

• Air pressure outside lungs is higher than inside

  • So air moves in to rebalance

Explain the process of expiration and the changes that occur throughout the thorax.

• External intercostal muscles relax (internal contract)

  • Brings ribs down and in

• Diaphragm relaxes and domes upwards

• Volume of thorax decreases

• Air pressure inside lungs higher than outside

  • So air moves out to rebalance

Explain how a spirometer works.

Used to measure lung volume

1. A person breathes into an airtight chamber

2. This leaves a trace on a graph which shows the volume of the breaths

Define vital capacity.

The maximum volume of air that can be taken in or expelled from the lungs in one breath

• Can be calculated from the spirometer graph by finding the maximum amplitude

Define tidal volume.

The volume of air we breathe in and out during each breath at rest

• Can be calculated from the spirometer graph by finding the amplitude at rest

Define breathing rate.

The number of breaths we take per minute

• Can be calculated from the spirometer graph by counting the number of peaks in one minute

Describe the gills.

• Located within the body

• Supported by arches

  • Multiple projections of gill filaments along this

    • Stacked up in piles

Describe the lamellae.

• At right angles to the gill filaments

  • Give an increased SA

• Blood and water flow across them in opposite directions (countercurrent mechanism)

Explain the process of gas exchange in fish.

1. Buccal cavity volume increased

   • Enables water to flow in

   • Reduced to increase pressure

2. Water is pumped over the lamellae by the operculum

3. Oxygen diffuses into the bloodstream

4. Waste carbon dioxide diffuses into the water and flows back out of the gills

How does the countercurrent mechanism maximise oxygen absorbed by the fish?

• Maintains a steep concentration gradient

  • Water is always next to blood of a lower oxygen concentration

• Keeps rate of diffusion constant

• Enables 80% of available oxygen to be absorbed

Describe the spiracles.

• Holes on the body’s surface

  • May be opened or closed by a valve for gas or water exchange

Describe the tracheae.

• Large tubes extending through all body tissues

• Supported by rungs to prevent collapse

Describe the tracheoles.

Smaller branches dividing off the tracheae

Explain the process of gas exchange in insects.

• Gases move in and out of the tracheae through the spiracles

• A diffusion gradient allows oxygen to diffuse into the body tissue while waste carbon dioxide diffuses out

• Contraction of muscles in the tracheae allows mass movement of air in and out