3.1-2 Gas Exchange in Organisms

Question 1

What needs to be exchanged between an organism and its environment?

Answer 1

Respiratory gases - oxygen, carbon dioxide, water
Nutrients- vitamins, minerals, glucose
Excretory products - urea, faeces, fibre
Heat

Question 2

What kind of exchanges can take place?

Answer 2

Passive - simple diffusion and osmosis

Active - facilitated diffusion and active transport

Question 3

What happens to SA:V ratio when you increase the surface area?

Answer 3

As surface area increases
Volume will eventually become bigger than the surface area

Therefore SA:V ratio decreases

Question 4

What is fick’s law?

Answer 4

Large SA x steep concentration gradient

Divided by

Short diffusion distance

Question 5

What are some single cell organisms?

Answer 5

Bacteria
Fungi
Yeast
Algae

Question 6

How does gas exchange take place in single celled organisms?

Answer 6

High SA:V ratio
1 cell thick therefore short diffusion distance
They use O2 for respiration constantly and water for chemical reactions (like protein synthesis) therefore steep concentration gradient as more O2 and water outside the cell

Question 7

Describe the pathway of oxygen into insects?

Answer 7

Spiracle
Trachea
Tracheoles
Capillaries 
Cells

Question 8

How is steep concentration gradient achieved in gas exchange of insects?

Answer 8

Oxygen is constantly used by the cells for aerobic respiration therefore there is always more oxygen outside the cells

Abdominal pumping (rhythmic contractions) moves the gas in and out

Question 9

How is large surface area achieved in gas exchange of insects?

Answer 9

Thin flat body surface

Leads to many spiracles available for oxygen to move in

Question 10

How is short diffusion distance achieved in gas exchange of insects?

Answer 10

The tubes have a thin permeable membrane adjacent to individual cells for aerobic respiration

Mitochondria are rarely more than a few micrometers away from an air capillary

Question 11

How does the trachea in insects being filled with water at the end help gas exchange?

Answer 11

In major activity anaerobic respiration takes place producing lactate = lower water potential
Therefore water moves into the cells and the volume of water in the trachioles decreases drawing air further in
This means the final stage of diffusion takes place as a gas and not a liquid making diffusion happen quicker

Question 12

What is important about the trachea in insects?

Answer 12

They are supported by strengthened rings to prevent them form collapsing

Question 13

How do insects limit water loss?

Answer 13

Small SA:V ratio - minimising area for water to be lost
Water proof covering on their whole body
Spiracles can be closed

Question 14

How does water move into a fish?

Answer 14

Open mouth
= volume increases
∴ pressure decreases
Drawing water in because of the pressure concentration gradient

Water is forced over the gills for gas exchange

Question 15

How does water move out of a fish?

Answer 15

Close mouth
= volume decreases
∴ pressure increases
Forcing water out because of the pressure concentration gradient

Question 15

How is steep concentration gradient achieved in gas exchange of fish?

Answer 15

The blood in the gills acquiring oxygen moves around the body
∴ maintaining a steep concentration gradient
As always more oxygen in the water

Question 16

How is large surface area achieved in gas exchange of fish?

Answer 16

The gill filaments and lamella

Question 17

How is short diffusion distance achieved in gas exchange of fish?

Answer 17

1 cell thick to move through

Question 19

What property do fish have?

Answer 19

A waterproof coating and therefore it is gas tight

Question 20

What is the gill lamella?

Answer 20

Where the actual exchange takes place

A little disk perpendicularly placed at the end of the gill filaments that make up the gill rakers

Question 21

How does the water move within the gills of a fish?

Answer 21

Countercurrent flow

The water moves in the opposite direction to the blood flow
A constant concentration gradient is maintained across the whole lamella

This allows for 80% of oxygen available to be absorbed into the blood

Question 22

What would happen if the fish gills used a parallel flow?

Answer 22

You reach an equilibrium where no diffusion can take place as the concentration gradient becomes isotonic

Only 50% of oxygen available can be absorbed into the blood

Question 23

What are the features of the cross section of a leaf? Top to bottom

Answer 23

Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongey mesophyll (containing air spaces)
Lower epidermis- containing guard cells and stomata

Question 24

What is the equation for photosynthesis?

Answer 24

6H20 + 6CO2 -> C6H12O6 + 6O2

Question 25

What is different about gas exchange in plants?

Answer 25

They respire and photosynthesise therefore the products produced can be used as the reactants in the other This can reduce gas exchange with the external medium (air) However depends on the balance of the rates as most of the reactants are acquired from the external medium

Question 26

How do stomata work in gas exchange?

Answer 26

They are surrounded by guard cells which can open and close the stomatal pore to control gas exchange

Question 27

How is large surface area achieved in gas exchange of plants?

Answer 27

They are flat and thin due to air spaces in the spongey mesophyll

Question 28

How is steep concentration gradient achieved in gas exchange of plants?

Answer 28

O2, water and CO2 are constantly being used up in respiration and photosynthesis Through transpiration a constant flow of water is achieved through the plant with the stomata helping

Question 29

How is short diffusion distance achieved in gas exchange of plants?

Answer 29

Between the stomata the gas travels through the numerous interconnecting air spaces and only has to go through 1 cell Diffusion takes place in the gas phase which makes it faster than if it was in water

Question 30

What is a xerophyte?

Answer 30

A plant that is adapted to live in areas where water is in short supply

Question 31

What are the adaptations of xerophytic plants to limit water loss?

Answer 31

``` Thick waxy cuticle Hairs on its lower surface Leaf rolled up Stomata in pits Shallow roots close to the surface Reduced SA:V ratio of leaves ```

Question 32

How does the thick waxy cuticle in xerophytes help reduce water loss?

Answer 32

Reduces water evaporation from its surface

Question 33

How does hairs on the lower surface, leaf rolled up and stomata in pits help reduce water loss in xerophytes?

Answer 33

Traps the still moist air inside/next to the stomata | Which reduces the water potential gradient

Question 34

How do the shallow roots in xerophytes help reduce water loss?

Answer 34

Allows more water to be absorbed

Question 35

How does the reduced SA:V ratio of leaves in xerophytes help reduce water loss?

Answer 35

They are small and circular in cross as so not to compromise large SA for photosynthesis

Question 36

Describe inspiration in mammals?

Answer 36

The external intercostal muscles and the diaphragm contract whilst the internal intercostal muscles relax The ribcage moves up and out which increases the volume of the thorax and decreases the pressure inside the lungs Because of the concentration gradient of pressure air is forced in

Question 37

Describe expiration in mammals?

Answer 37

The external intercostal muscles and the diaphragm relax whilst the internal intercostal muscles contract (if expiration is forced) The ribcage moves down and in which decreases the volume of the thorax and increases the pressure inside the lungs Because of the concentration gradient of pressure air is forced out

Question 38

What is the equation for pulmonary ventilation?

Answer 38

Pulmonary ventilation = tidal volume (dm3) X ventilation rate (min-1)

Question 39

What is pulmonary ventilation?

Answer 39

Total volume of air moved into the lungs per minute

Question 40

What is tidal volume?

Answer 40

Total volume of air taken in each breath

Question 41

What is ventilation rate?

Answer 41

Number of breaths per min

Question 42

How is short diffusion distance achieved in gas exchange of mammals?

Answer 42

Thin cell surface membrane The capillaries are immediately next to the alveoli The cell wall of the alveolus is 1 cell thick

Question 43

How is large surface area achieved in gas exchange of mammals?

Answer 43

Lots of alveoli create a large SA in a small space

Question 44

How is steep concentration gradient achieved in gas exchange of mammals?

Answer 44

The movement of the internal medium of blood is constant - O2 is moved away around the body The movement of external medium of air is constant - due to changes in volume and pressure (always more oxygen in alveoli) This keeps oxygen and carbon dioxide levels at a constant concentration gradient

Question 45

What does the alveolus and capillary include?

Answer 45

Cell wall Thin layer of moisture Plasma Red blood cells Cell wall O2 and CO2 diffusing between the two

Question 46

What is the cause, symptoms and treatment of pulmonary tuberculosis? Risk factors?

Answer 46

Caused by a bacterium Difficulty breathing Chest pain Coughing Antibiotics Smoker, HIV, Age

Question 47

What is the effect on gas exchange in the lungs of pulmonary tuberculosis?

Answer 47

The white blood cells surrounding the bacteria prevent a path to the cell membrane of the alveoli so oxygen struggles to diffuse in

Question 48

What is the cause, symptoms and treatment of pulmonary fibrosis? Risk factors?

Answer 48

Dust, mould - viral infection Short of breath Cough Nutritional advice, oxygen therapy, lung transplant Age, gender(men)

Question 49

What is the effect on gas exchange in the lungs of pulmonary fibrosis?

Answer 49

A lot of scaring on the alveoli creating irregular/abnormal air spaces Leading to less surface area for exchange Fibrous connective tissue also builds up in the lungs reducing elasticity

Question 50

What is the cause, symptoms and treatment of asthma? Risk factors?

Answer 50

Unknown Breathlessness Tight chest Inhalers Genetic, smoking

Question 51

What is the effect on gas exchange in the lungs of asthma?

Answer 51

Bronchiole tubes become constricted due to muscle spasms therefore a lack of oxygen reaches the alveoli

Question 52

What is the cause, symptoms and treatment of emphysema? Risk factors?

Answer 52

Smoking Air-pollution Coughing Exhaustion Bronchodilators Inhaled steroids SMOKING! Air pollution, genetics, age