Module 3: Section 1- Exchange and Transport

Question 1

why do organisms need exchange surfaces?

Answer 1

• cells need to take in things like Oxygen and Glucose for aerobic respiration and other metabolic reactions
• They also need to secrete waste products from these reactions eg. urea and carbon dioxide

Question 2

SA:V ratio in smaller animals

Answer 2

• higher SA:V ratios

Question 3

Why do multicellular organisms need exchange surfaces

Answer 3

• diffusion across the outer membrane is too slow because:
  ~some cells are deep within the body (big distance between them and outside environment)
  ~larger animals have lower SA:V ratio- difficult to exchange enough substances to supply large volume of animal
  ~multicellular organisms have a higher metabolic rate than single celled organisms so use up O2 and glucose faster

Question 4

Why do single celled organisms not need exchange surfaces?

Answer 4

• the diffusion rate is quick due to the shorter distance the substances have to travel
• substances can diffuse directly into (or out of) the cell across the cell-surface membrane

Question 5

Specialised Exchange surfaces features

Answer 5

• Large SA: eg root hair cells, increases rate of absorption of water (by osmosis) and mineral ions (by active transport) from the soil
• Thin: eg alveoli, thin alveolar epithelium helps decrease the distance over which O2 and CO2 diffusion takes place
• Good Blood Supply and/or Ventilation: eg alveoli + fish gills, helps maintain concentration gradients of O2 and/or CO2

Question 6

Gaseous exchange in the lungs

Answer 6

• air enters trachea
• trachea splits into 2 bronchi- one bronchus leading to each lung
  -each bronchus branches off into smaller tubes called bronchioles
• bronchioles end up in small ‘air sacs’ called alveoli where gases are exchanged
• The ribcage, intercostal muscles and diaphragm all work together to move air in and out

Question 7

Goblet cells

Answer 7

• (lining the airways) secret mucus
• the mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli

Question 8

Cilia

Answer 8

• on the surface of cells lining the airways
• beat the mucus
• moves the mucus upwards away from the alveoli towards the throat, where it’s swallowed. This prevents lung infections

Question 9

Elastic fibres

Answer 9

• in walls of trachea, bronchi, bronchioles and alveoli
• help the process of breathing out
• on breathing in, lungs inflate and elastic fibres are stretched
• fibres then recoil to help push the air out when exhaling

Question 10

Smoot muscle

Answer 10

• in walls of the trachea, bronchi and bronchioles
• allows their diameter to be controlled
  -during exercise, smooth muscle relaxes, making tubes wider
• less resistance to airflow and air can move in+out of lungs easily

Question 11

Rings of cartilage

Answer 11

• in walls of the trachea and bronchi to provide support
• strong but flexible- stops trachea and bronchi collapsing when you breathe in and pressure drops

Question 12

Trachea

Answer 12

cartilage: large C-shaped pieces
-smooth muscle, elastic fibres, goblet cells
- ciliated epithelium

Question 13

Bronchi

Answer 13

cartilage: smaller pieces
-smooth muscle, elastic fibres, goblet cells
- ciliated epithelium

Question 14

larger bronchiole

Answer 14

cartilage: none
-smooth muscle, elastic fibres, goblet cells
-ciliated epithelium

Question 15

Alveoli

Answer 15

cartilage: none
- elastic fibres
no cilia
no goblet cells or smooth muscle

Question 16

Inspiration

Answer 16

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

Question 17

Expiration

Answer 17

1. External intercostal and diaphragm muscles relax
2. rib cage moves downwards and inwards and the diaphragm becomes curved again
3. The thorax volume decreases, causing the air pressure to increase ( above atmospheric pressure)
4. Air is forced out of the lungs
5. Normal expiration is a passive process- doesn’t require energy

Question 18

Forced expiration

Answer 18

• intercostal muscles contract, to pull the ribcage down and in

Question 19

Tidal volume

Answer 19

-volume of air in each breath (usually about 0.4 dm3)

Question 20

Vital capacity

Answer 20

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

Question 21

Breathing rate

Answer 21

-how many breaths are taken , usually in a minute

Question 22

Oxygen consumption or oxygen uptake

Answer 22

• rate at which an organism uses up oxygen

Question 23

Spirometer method

Answer 23

1. spirometer has oxygen-filled chamber with a movable lid
2. person breathes through tube connected to oxygen chamber
3. as person breathes in and out, lid of the chamber moves up and down
4. These movements can be recorded by a pen attached to the lid of chamber, writes on a rotating drum, creating a spirometer trace or hooked to motion sensor + data logger
5. soda lime in the tube the subject breathes into, absorbs CO2

Question 24

Fish gas exchange

Answer 24

1. water enters mouth and passes out through gills
2. Each gill made up of lots of thin branches called gill filaments or primary lamellae. gill filaments= covered in tiny structures called gill plates/ secondary lamellae, which increase SA even more. each gill- supported by gill arch
3. Gill plates have lots of blood capillaries and thin surface layer of cells to speed up diffusion

Question 25

Fish gas exchange Part 2

Answer 25

• Blood flow through gill plates in one direction and water flows over in the opposite direction
  (counter-current system)
• maintains a large concentration gradient between water and blood
• conc of oxygen in water is always higher than that in blood, so as much oxygen as possible diffuses from water into the blood

Question 26

How fish gills are ventilated

Answer 26

1) fish opens mouth, lowers floor of buccal cavity. Volume of the buccal cavity increases, decreasing pressure inside the cavity, water sucked in
2) Fish closes mouth, floor of buccal cavity is raised again. Volume inside cavity decreases, pressure increases and water is forced out of cavity across gill filaments
3) Each gill is covered by a bony flap called the operculum (protects the gill). The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills