Exchange and Transport

Question 1

Why do organisms need to exchange substances with their environment?

Answer 1

• cells need to take in oxygen and glucose for aerobic respiration and other metabolic reactions
• they need to excrete waste products from these reactions- like carbon dioxide and urea

Question 2

Why do single-celled organisms not need exchange surfaces/systems?

Answer 2

Substances can diffuse quickly into and out of the cell across the cell surface membrane. The diffusion rate is quick because of the small distances the substances have to travel. They have a high surface area-to-volume ratio.

Question 3

Why do multi-cellular organisms need exchange surfaces/systems?

Answer 3

Diffusion across the outer membrane is too slow, for several reasons:
- some cells are deep within the body (big distance between them and the outer environment)
- larger animals have a low surface area to volume ratio- it is 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

How are root hair cells adapted?

Answer 4

They have a large surface area:
- 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.
- This gives the roots a large surface area, which helps to increase the rate of absorption of water and mineral ions from the soil.

Question 5

How are alveoli adapted?

Answer 5

They have thin walls:
- They are the gas exchange surface in the lungs.
- Each alveolus is made from a single layer of thin, flat cells, called the alveolar epithelium
- Oxygen diffuses out of the alveolar space into the blood. Carbon dioxide diffuses in the opposite direction.
- The thin alveolar epithelium helps to decrease the distance over which oxygen and carbon dioxide diffusion take place, which increases the rate of diffusion.

Question 6

How are fish gills adapted?

Answer 6

They have a good blood supply:
- The gills are the gas exchange surface in fish. In the gills oxygen and carbon dioxide are exchanged between the fish’s blood and the surrounding water
- Fish gills contain a large network of capillaries which keeps them well supplied with blood. They’re also well-ventilated with fresh water constantly passing over them. These features help to maintain a concentration gradient of oxygen which increases the rate at which oxygen diffuses into the blood.

Question 7

What is your trachea?

Answer 7

It is your windpipe where air enters. It is made up of C-shaped cartilage.

Question 8

What is the bronchus?

Answer 8

The trachea splits into two bronchi

Question 9

What are bronchioles?

Answer 9

Each bronchus then branches off into smaller tubes called bronchioles

Question 10

What are alveoli?

Answer 10

The bronchioles end in small ‘air sacs’ called alveoli where gases are exchanged

Question 11

What are goblet cells and their function?

Answer 11

Goblet cells that line the airways secrete mucus. The mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli.

Question 12

What are Cilia and their function?

Answer 12

They are found on the surface of cells lining the airways and beat the mucus. This moves the mucus (plus the trapped microorganisms and dust) upwards away from the alveoli towards the throat where it is swallowed. This helps prevent lung infections.

Question 13

What are elastic fibers and their function?

Answer 13

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

Question 14

What is smooth muscle and its function?

Answer 14

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 airflow and air can move in and out of the lungs more easily.

Question 15

What are the rings of cartilage used for in the trachea?

Answer 15

Rings of cartilage in the walls of the trachea and bronchi provide support. It’s strong but flexible- it stops the trachea and bronchi from collapsing when you breathe in and the pressure drops.

Question 16

What components will we find in the trachea?

Answer 16

• large c shaped cartilage
• smooth muscle
• elastic fibers
• goblet cells
• ciliated epithelium

Question 17

What components will we find in the bronchi?

Answer 17

• Smaller pieces of cartilage
• smooth muscle
• elastic fibers
• goblet cells
• ciliated epithelium

Question 18

What components will we find in the larger bronchiole?

Answer 18

• no cartilage
• smooth muscle
• elastic fibers
• goblet cells
• ciliated epithelium

Question 19

What components will we find in the smaller bronchiole?

Answer 19

• no cartilage
• smooth muscle
• elastic fibers
• ciliated epithelium

Question 20

What components will we find in the smallest bronchiole?

Answer 20

• no cartilage
• elastic fibers

Question 21

What components will we find in the alveoli?

Answer 21

• no cartilage
• elastic fibers

Question 22

What happens during inspiration?

Answer 22

• external intercostal muscles contract
• diaphragm muscles contract
• ribcage moves up and out
• The diaphragm flattens which increases the volume of the thorax
• lung pressure decreases
• This process requires energy

Question 23

What happens during expiration?

Answer 23

• external intercostal muscles relax
• diaphragm relaxes
• ribcage moves downwards and inwards
• The diaphragm becomes concave which decreases the volume of the thorax
• Lung pressure increases
• This process is passive

Question 24

What is tidal volume?

Answer 24

It is the volume of air in each breath- usually about 0.4dm3

Question 25

What is vital capacity?

Answer 25

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

Question 26

What is breathing rate?

Answer 26

How many breaths are taken- usually in a minute

Question 27

What is oxygen consumption/oxygen uptake?

Answer 27

It is the rate at which an organism uses up oxygen

Question 28

What is a spirometer and how does it work?

Answer 28

It gives readings about a person’s breathing.
- It has an oxygen-filled chamber with a movable lid
- The person breathes through a tube connected to the oxygen chamber
- as a person breathes in and out the lid of the chamber moves up and down
- These movements can be recorded by a pen attached to the lid of the chamber- 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.
- The soda lime in the tube the subject breathes into absorbs carbon dioxide

Question 29

Why does the total volume of gas in a spirometer decrease over time?

Answer 29

The total volume decreases because the air that is 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 30

Why do fish need gills?

Answer 30

There’s a lower concentration of oxygen in water than in air so they have adaptations to get enough of it.

Question 31

How does water pass through a fish?

Answer 31

It enters the fish through its mouth and passes out through the gills.

Question 32

What is the structure of fish gills?

Answer 32

Each gill is made of lots of thin branches called gill filaments or primary lamellae, which give a big surface area for the 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.

Question 33

What is the structure of gill plates?

Answer 33

The gill plates have lots of blood capillaries and a thin surface layer of cells to speed up diffusion

Question 34

What is a counter-current system in fish?

Answer 34

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 35

How are fish gills ventilated? (bony)

Answer 35

• the fish opens its mouth and lowers the floor of the buccal cavity
• the volume of the buccal cavity increases
• pressure decreases
• water enters
• when the mouth closes and raises the floor of the buccal cavity
  -the volume of the buccal cavity decreases
• the pressure increases and forces the operculum on each side of the head to open
• water exits via the gills

Question 36

How do insects use Trachae to Exchange gases?

Answer 36

• air moves into the tracheae through pores on the insect’s surface called spiracles.
• oxygen travels down the concentration gradient toward the cells. Carbon dioxide from the cells moves down its concentration gradient towards the spiracles to be released into the atmosphere.
• The trachea branches off into smaller tracheoles which have thin, permeable walls and go to individual cells. The tracheoles have thin, permeable walls and go to individual cells. The tracheoles also contain fluid, which oxygen dissolves in.
• the oxygen then diffuses from this fluid into body cells. Carbon dioxide diffuses in the opposite direction
• 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 37

How do you dissect the gaseous exchange system in insects?

Answer 37

• fix it to a dissecting board
• put dissecting pins through its legs
• cut and remove a piece of exoskeleton from its abdomen
• fill the abdomen with saline solution and see the silver-grey tubes which are the tracheae (chitin walls of tracheae)