Module 3: Exchange and transport

Question 1

Do smaller organisms have a bigger or smaller SA:Vol than larger organisms?

Answer 1

Bigger

Question 2

What is diffusion?

Answer 2

Net movement of particles down a concentration gradient from an area of higher concentration to an area of lower concentration.

Question 3

Describe how single-celled organisms exchange substances with the environment

Answer 3

Substances can diffuse directly into or out of cell across cell surface membrane.

Question 4

Why is diffusion quick in single-celled organisms?

Answer 4

short diffusion pathway and high SA:Vol

Question 5

Give three reasons as to why diffusion across outer membrane is slow in multicellular organisms

Answer 5

Some cells deep within body - long diffusion pathway between cells and outside environment

Larger animals have low SA:Vol - difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface.

Higher metabolic rate - use up oxygen and glucose faster.

Question 6

What three features improve efficiency of exchange surface?

Answer 6

Large SA
Thin - short diffusion pathway
Good blood supply and/or ventilation

Question 7

Describe an example of how large SA increases efficiency of exchange surface.

Answer 7

Root hair cells

Cells on plant roots grow into long hair like structures which stuck out into soil.
Each branch of root is covered in millions of these root hair cells
Gives root large SA, helping to increase rate of absorption of water ( by osmosis) and mineral ions (by active transport) from the soil.

Question 8

Why does being thin increase efficiency of exchange surface?

Answer 8

Decreased distance that substances being exchanged have to travel over.

Question 9

Describe an example of how being thin increases efficiency of exchange surface.

Answer 9

Alveoli

Alveoli are gas exchange surface in the lungs.
Each alveolus is made from a single layer of flat, thin cells called alveolar epithelium.
Oxygen diffuses out of alveolar air space and into blood, CO2 diffuses in opposite direction.
Thin alveolar epithelium helps prover shorter diffusion pathway, increasing rate of diffusion.

Question 10

Describe two examples of how good blood supply/ventilation helps increase efficiency of exchange surface.

Answer 10

Alveoli

Surrounded by large capillary network, giving each alveolus its own blood supply.
Blood constantly takes O2 away and brings CO2.
Lungs also well ventilated (you breathe in and out) so air in each alveolus is constantly replaced.
These features help maintain concentration gradients of O2 and CO2.

Gills

Gas exchange surface in fish
O2 and CO2 exchanged between fish’s blood and surrounding water
Contain large network of capillaries, keeping them well supplied with blood
Well ventilated as fresh water constantly passes over them
These features help maintain concentration gradient of O2, increasing rate at which O2 diffuses into blood.

Question 11

What do cells need to exchange with the environment?

Answer 11

Take in things like Oxygen & glucose for aerobic respiration and other metabolic reactions and excrete waste products like carbon dioxide and urea.

Question 12

What are the gas exchange organs in mammals?

Answer 12

Lungs

Question 13

Describe the basic structure of gaseous exchange system

Answer 13

As you breathe in air enters trachea

Trachea splits into two bronchi - one bronchus leading to each lung

Each bronchus then branches off into smaller tubes called bronchioles.

Bronchioles end in alveoli - this is where gases are exchanged.

Question 14

Why are there lots of alveoli in the lungs?

Answer 14

Provide larger surface area for diffusion

Question 15

Name the 5 key cells and tissues found in gaseous exchange system

Answer 15

Goblet cells
Cilia
Elastic fibres 
Smooth muscle 
Cartilage

Question 16

State where goblet cells are found and describe their function.

Answer 16

Trachea, bronchi, larger bronchiole

secrete mucus which traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli

Question 17

State where cilia are found and describe their function

Answer 17

Trachea, bronchi, larger bronchiole, smaller bronchiole

Hair-like structures on surface of epithelial cells lining the airways.
Beat mucus secreted by goblet cells, moving it up away from alveoli and towards throat, where it’s swallowed.
Prevents lung infections

Question 18

State where elastic fibres are found and describe their function.

Answer 18

Found in walls of trachea, bronchi, bronchioles, and alveoli.

Help process of breathing out

On breathing in, lungs inflate & elastic fibres are stretched.

Then, fibres recoil to help push air out when exhaling.

Question 19

State where smooth muscle is found and describe its function

Answer 19

Trachea, bronchi, largest bronchiole, smaller bronchiole

Allows diameter to be controlled

During exercise smooth muscle relaxes, making tubes wider

Means less resistance to airflow and air can move in and out of lungs more easily

Question 20

State where cartilage is kind and describe it’s function

Answer 20

Trachea in large C-shaped rings, bronchi in smaller pieces

Provide support

Strong but flexible - stops trachea and bronchi from collapsing when you breathe in and pressure drops

Question 21

What is ventilation?

Answer 21

Ventilation consists of inspiration and exploration. It’s controlled by movements of diaphragm, intercostal muscles and ribcage.

Question 22

Describe the process of inspiration.

Answer 22

External intercostal and diaphragm muscles contract

Causes rib cage to move up and out and diaphragm to flatten

This increases volume of thorax and therefore decreases lung pressure (to below atmospheric pressure)

Causes air to flow into lungs from area of higher pressure (atmospheric) to area of lower pressure (lung)

Active process - requires energy

Question 23

Describe process of expiration.

Answer 23

External intercostal and diaphragm muscles relax

Ribcage moves down and in and diaphragm become curved again

Causes thorax volume to decrease and air pressure to increase

Air forced out of lungs

Normal expiration is passive process - doesn’t require energy

Question 24

What happens during forced expiration?

Answer 24

Internal intercostal muscles contract, pulling rib cage down and in

Question 25

What is tidal volume?

Answer 25

Volume of air in each breath

Usually about 0.4dm3

Question 26

Vital capacity?

Answer 26

Maximum volume of air that can be breathed in or out

Question 27

Breathing rate?

Answer 27

How many breaths are taken per unit time

Usually per minute

Question 28

Oxygen uptake/consumption?

Answer 28

Rate at which a person uses up oxygen

Question 29

Describe how a spirometer is used.

Answer 29

Oxygen-filled chamber with a movable lid

Person using spirometer breathes through tube connected to oxygen chamber

As person breathes in and out, kid of chamber moves up and down

Movements recorded by a pen attached to lid of chamber which writes on rotating drum, creating spirometer trace

Or spirometer can be hooked to motion sensor - this will use the movements to produce electronic signals which picked up by data logger

Soda lime in tube subject exhales into absorbs CO2

Question 30

Why does total volume of gas in oxygen chamber decrease over time?

Answer 30

Air exhaled is mixture of CO2 and O2

CO2 absorbed by soda lime so that only oxygen in chamber subject inhales from

But lots of oxygen used up by respiration so not much exhaled meaning total volume decreases.

Question 31

How do you get a valid reading from a spirometer?

Answer 31

Person using it must wear nose clip to ensure they only breathe in and out through mouth so all air they breathe goes through spirometer

Machine must also be airtight

Question 32

What is the gas exchange surface in fish?

Answer 32

Gills

Question 33

Describe the structure of gills

Answer 33

Water, containing oxygen, enters fish through mouth and passes out through gills.

Each Gill made of lots of thin plates called gill filaments/primary lamellae.

These increase SA for diffusion

Gill filaments covered in many tiny structures called gill plates/secondary lamellae

Increase SA further

Each Gill supported by gill arch

Gill plates have extensive capillary network and thin surface layer of cells to speed up diffusion between water and blood.

Question 34

Describe the counter-current system

Answer 34

Blood flows through gill plates in one direction and water flows in opposite direction

this is called counter-current system

means that water with a relatively high concentration always flows next to blood with a lower concentration of oxygen

Ensure steep concentration gradient is maintained between water and blood - so as much oxygen as possible diffuses into blood

Question 35

Describe ventilation in bony fish

Answer 35

Fish opens mouth, lowering floor of buccal cavity (space inside mouth)

Vol of buccal cavity increases, pressure decreases inside cavity

Water sucked into mouth from higher pressure to lower pressure

fish closes mouth, floor of buccal cavity raised

vol inside decreases, pressure increases

Water forced out of cavity across gill filaments

Question 36

What is the operculum and what role does it play in ventilation in fish?

Answer 36

Bony flap which covers each gill, protecting them

increase in pressure forces operculum on each side of head to open, allowing water to leave the gills

in some bony fish operculum bulges out, increasing vol of cavity behind operculum, just after floor of buccal lowers

this helps to decrease pressure, causing water to enter fishes mouth

Question 37

Describe gas exchange and ventilation in insects

Answer 37

terrestrial insects have microscopic air-filled pipes called tracheae which they use for gas exchange

Air moves into tracheae through pores on the surface called spiracles

Oxygen travels down concentration gradient towards cells

Carbon dioxide from cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere

Tracheae branch off into smaller trachea led which have thin, permeable walls (short diffusion pathway) and go to individual cells

Tracheoles also contain fluid which oxygen dissolves in

Oxygen then diffuses from this fluid into body cells

CO2 diffuses in opposite direction

Question 38

What do insects use rhythmic abdominal movements for?

Answer 38

Change vol of their bodies and move air in and out of spiracles

When larger insects are flying, use wing movements to pump their thoraxes too