Specialised Exchange Surfaces

Question 1

Organisms Need to Exchange Substances with their Environment

Answer 1

•Cells need to take in things like oxygen and glucose for aerobic respiration and other metabolic reactions.
•They also need to excrete waste products from these
reactions - like carbon dioxide and urea.

Question 2

Single called

Answer 2

In single-celled organisms, these substances can diffuse directly into (or out of) the cell across the cell surface membrane. The diffusion rate is quick because of the small distances the
substances have to travel

Question 3

multicellular animals, diffusion across the outer membrane is too slow, for several reasons:

Answer 3

multicellular animals, diffusion across the outer membrane is too slow, for several reasons:

•Some cells are deep within the body
- there’s a big distance between them and the outside environment
•Larger animals have a low surface area to volume ratio - it’s difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.
• Multicellular organisms have a higher metabolic rate than single-celled organisms, so they use up oxygen and glucose faster.

Question 4

Most Exchange Surfaces Have A Large Surface Area: ROOT HAIR CELLS

Answer 4

1) The cells on plant roots grow into long ‘hairs’ which stick out into the soil.
Each branch of a root will be covered in millions of these microscopic hairs.

2) This gives the roots a large surface area, which helps to increase the rate of absorption of water (by osmosis) and mineral ions (by active transport) from the soil.

Question 5

Most Exchange Surfaces Have A Large Surface Area: the ALVEOLI

Answer 5

1)The alveoli are the gas exchange surface in the lungs.
2) Each alveolus is made from a single layer of thin, flat cells called the alveolar epithelium.
3) O, diffuses out of the alveolar space into the blood.
CO, diffuses in the opposite direction.
The thin alveolar epithelium helps to decrease the distance over which O, and CO, diffusion takes place, which increases the rate of diffusion (see p. 54).

Question 6

They Have a Good Blood Supply and/or Ventilation: ALVEOLI

Answer 6

1)The alveoli are surrounded by a large capillary network, giving each alveolus its own blood supply.
The blood constantly takes oxygen away from the alveoli, and brings more carbon dioxide.
2) The lungs are also ventilated (you breathe in and out - see page 72)
so the air in each alveolus is constantly replaced.
3) These features help to maintain concentration gradients of 0, and CO,.

Question 7

They Have a Good Blood Supply and/or Ventilation: FISH GILLS

Answer 7

1) The gills are the gas exchange surface in fish. In the gills, O, and CO,
are exchanged between the fish’s blood and the surrounding water.
2) Fish gills contain a large network of capillaries - this keeps them well-supplied with blood.
They’re also well-ventilated - fresh water constantly passes over them. These features help to maintain a concentration gradient of O, - increasing the rate at which O, diffuses into the blood.

Question 8

In Mammals the Lungs are Exchange Organs

Answer 8

1) As you breathe in, air enters the trachea (windpipe).
2) The trachea splits into two bronchi - one bronchus leading to each lung.
3) Each bronchus then branches off into smaller tubes called bronchioles.
4) The bronchioles end in small ‘air sacs’ called alveoli (see previous page) where gases are exchanged.
5)The ribcage, intercostal muscles and diaphragm all work together to move air in and out

Question 9

Structures in the Gaseous Exchange System Have Different Functions: Goblet cells

Answer 9

Goblet cells (lining the airways) secrete mucus. The mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveolt.

Question 10

Structures in the Gaseous Exchange System Have Different Functions: cillia

Answer 10

Cilia (on the surface of cells lining the airways) beat the mucus. This moves the mucus (plus the trapped microorganisms and dust upward away from the alveoll towards the throat, where it’s swallowed. This helps prevent lung infections

Question 11

Structures in the Gaseous Exchange System Have Different Functions: Elastic fibres

Answer 11

Elastic fibres in the walls of the trachea, bronchi, bronchioles and alveoli help the process of breathing out (see p. 72). On breathing in, the lungs inflate and the elastic
fibres are stretched. Then, the fibres recoil to help push the air out when exhaling.

Question 12

Structures in the Gaseous Exchange System Have Different Functions: Smooth muscle

Answer 12

Smooth muscle in the walls of the trachea, bronchi and bronchioles allows their diameter to be controlled. During exercise the smooth muscle relaxes, making the tubes wider. This means there’s less
resistance to alriow and air can move in ana out or te runes more eastry.

Question 13

Structures in the Gaseous Exchange System Have Different Functions: Rings of cartilage

Answer 13

Rings of cartilage in the walls of the trachea and bronchi provide support. It’s strong but flexible it stops the trachea and bronchi collapsing when
vou breathe in and the pressure drops (see p. 72).

Question 14

What is ventilation

Answer 14

Ventilation consists of inspiration (breathing in) and expiration (breathing out).
It’s controlled by the movements of the diaphragm, internal and external intercostal muscles and ribcage.

Question 15

Inspiration

Answer 15

1) The external intercostal and diaphragm muscles contract.
2) This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax (the space where the lungs are).
3) As the volume of the thorax increases the lung pressure decreases (to below atmospheric pressure).
4)This causes air to flow into the lungs.
5) Inspiration Is an active process - it requires energy.

Question 16

Expiration

Answer 16

1)The external intercostal and diaphragm muscles relax.
2)The ribcage moves downwards and inwards and the diaphragm becomes curved again.
3) The thorax volume decreases, causing the air pressure to increase (to above atmospheric pressure).
4) Air is forced out of the lungs.
5) Normal expiration is a passive process
- it doesn’t require energy.
6) Expiration can be forced though (e.g. if you want to blow out the candles on your birthday cake). During forced expiration, the internal intercostal muscles contract, to pull the ribcage down and in.

Question 17

Tidal Volume is the Volume of Air in a Normal Breath

Answer 17

1) Tidal volume (TV) - the volume of air in each breath - usually about 0.4 dm’.
2) Vital capacity - the maximum volume of air that can be breathed in or out.
3) Breathing rate - how many breaths are taken - usually in a minute.
4) Oxygen consumption or oxygen uptake - the rate at which an organism uses up oxygen (e.g. the number of dm’ used per minute).

Question 18

Spirometers Can be Used to Investigate Breathing

Answer 18

1) A spirometer has an oxygen-filled chamber with a movable lid.
2) The person breathes through a tube
connected to te oxyeen cnamber.
3) As the person breathes in and out, the lid of the chamber moves up and down.
4) These movements can be recorded by a pen atacned to the nia or the cnamber - this writes on a rotating drum, creating a spirometer trace. Or the spirometer can be hooked up to a motion sensor - this will use the movements to produce electronic signals, which are picked up by a data logger.
5)The soda lime in the tube the subject breathes into absorbs carbon dioxide.

The total volume of gas in the chamber decreases over time. This is because the air that’s breathed out is a mixture
of oxygen and carbon dioxide. The carbon dioxide is absorbed by the soda lime - so there’s only oxygen in the chamber which the subject inhales from. As this oxygen gets used up by respiration, the total volume decreases

Question 19

Fish Use a Counter-Current System for Gas Exchange

Answer 19

1) Water, containing oxygen, enters the fish through its mouth and passes out through the gills (see below).
2) Each gill is made of lots of thin branches called gill filaments or primary lamellae, which give a big surface area for exchange of gases. The gill filaments are covered in lots of tiny structures called gill plates or secondary lamellae, which increase the surface area even more. Each gill is supported by a gill arch.
3) The gill plates have lots of blood capillaries and a thin surface layer of cells to speed up diffusion.
4)Blood flows through the gill plates in one direction and water flows over in the opposite direction.
This is called a counter-current system.
It maintains a large concentration gradient between the water and the blood.
The concentration of oxygen in the water is always higher than that in the blood. so as much oxygen as possible diffuses from the water into the blood.

Question 20

You Need to Know How Fish Gills are Ventilated

Answer 20

The fish opens its mouth, which lowers the floor of the buccal cavity (the space inside the mout). ine volume or the buccal cavitv increases.
decreasing the pressure inside the cavity. Water is then sucked in to the cavity.
2) When the fish closes its mouth, the floor of the buccal cavity is raised again. The volume inside the cavity decreases, the pressure increases, and water is forced out of the cavity across the gill filaments
3) Each gill is covered by a bony flap called the operculum (which protects the gill). The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills.

Question 21

You Need to Know How to Dissect Fish Gills

Answer 21

1) First up, fish dissection is messy so make sure you’re wearing an apron or lab coat, and gloves.
2) Place your chosen fish (something like a perch or salmon worKs well) in a dissection tray or on a cutuing board.
3) Push back the operculum and use scissors to carefully remove the gills. Cut each gill arch through the bone at
A single gill arch the top and bottom.
4) If you look closely, you should be able to see the gill filaments.
5)Finish off by drawing the gill and labelling it.

Question 22

Insects use Tracheae to Exchange Gases

Answer 22

1) Insects have microscopic air-filled pipes called tracheae which they use for gas exchange.
2) Air moves into the tracheae through pores on the insect’s surface called spiracles.
3) Oxygen travels down the concentration gradient towards the cells.
carbon dioxide from the cens moves down its own concentration gradient towards the spiracles to be released into the atmosphere
4) The tracheae branch off into smaller tracheoles which have thin, permeable walls and go to individual cells. The tracheoles also contain fluid, which oxygen dissolves in.
5) The oxygen then diffuses from this fluid into body cells. Carbon dioxide diffuses in the opposite direction
6) Insects use rhythmic abdominal movements to change the volume of their bodies and move air in and out of the spiracles. When larger insects are flying, they use their wing movements to pump their thoraxes too.

Question 23

You Can Dissect the Gaseous Exchange System in Insects too

Answer 23

Big insects like grasshoppers or cockroaches are usually best for dissecting because they’re easier to handle.
For dissection, vou’ll need to use an insect that’s been humanely killed fairly recently.

1)First fix the insect to a dissecting board. You can put dissecting pins through its legs to hold it in place.
2)To examine the tracheae, you’ll need to carefully cut and remove a piece of exoskeleton (the insect’s hard outer shell) from along the length of the insect’s abdomen.
3) Use a syringe to fill the abdomen with saline solution. You should be able to see a network of very thin, silvery-grey tubes - these are the tracheae. They look silver because they’re filled with air.
4) You can examine the tracheae under a light microscope using a wet mount slide (see page 18).
Again, the tracheae will appear silver or grey. You should also be able to see rings of chitin in the
walls of the tracheae - these are there for support (like the rings of cartilage in a human trachea)