Gaseous exchange

Question 1

why is gas exchange necessary?

Answer 1

-ensure that sufficient oxygen reaches all cells in an organism and that CO2 is excreted

Question 2

what are the two ways gas exchange may occur in organisms?

Answer 2

-across the surface of the organism
-may involve specialized gas exchange surfaces that are adapted for gas exchange

Question 3

how do all organisms exchange substances? what are some examples of substances that are exchanged?

Answer 3

-through diffusion
-food, water, gases and heat

Question 4

what are 5 adaptations that respiratory surfaces have to maximize that rate of exchange?

Answer 4

-large surface area
-moist surface into which gases dissolve
-diffusion gradient for o2 and co2
-permeable to 02 and co2
-short diffusion path as they are thin

Question 5

what is ficks law ?

Answer 5

-the rate of diffusion is proportional to surface area multiplied by difference in concentration divided by the thickness of the membrane

Question 6

what does the rate of exchange of surfaces depend on?

Answer 6

-the surface area that is in contact with the surroundings

Question 7

what is meant by total demand being proportional to its volume?

Answer 7

• the ability to meet requirements depends on the surface area to volume ratio
  -as organism gets bigger their volume increases by the cube of their size and their surface area increases by the square of their length

Question 8

In relation to sa:v as an organism gets bigger…

Answer 8

-their sa:v ratio gets smaller

Question 9

what is am example of an organism with a large sa:v and why?

Answer 9

-bacterium are unicellular and most of their cells are in contact with their surroundings meaning that they have less cells inside

Question 10

what is an example of an organism with a small sa:v and why?

Answer 10

-whales are multicellular without much surface as many of their cells are on the inside
-this mean that they have more difficulty exchanging materials with their surroundings

Question 11

what are the two processes in flowering plants that involve gas exchange?

Answer 11

-respiration and photosynthesis

Question 12

when does respiration occur and what does it produce and use?

Answer 12

-it takes place in all living tissues all the time to produce energy
-oxygen is used and carbon dioxide in produced as a waste product

Question 13

when and where does photosynthesis take place and what does it produce and use?

Answer 13

-takes place in the chlorophyll and only occurs during daylight hours as it requires lights energy
-it happens most rapidly when light intensities are high
-it produces oxygen and uses carbon dioxide to make glucose

Question 14

when are both photosynthesis and respiration occurring?

Answer 14

-during the day both are happening but respiration will also continue to happen during the night

Question 15

at midday what is the rate of photosynthesis like ?

Answer 15

-the rate of photosynthesis is greater than the rate of respiration so there is a net production of oxygen

Question 16

during low light intensities what is the rate of photosynthesis like?

Answer 16

-the rate of photosynthesis equals the rate of respiration this is known as the compensation point so the amount of oxygen used in respiration is equal to the amount of oxygen produced during photosynthesis

Question 17

what is the organ in the plant?

Answer 17

-the leaf

Question 18

what are the four ways the leaf is adapted for photosynthesis?

Answer 18

• thin
  -large moist gas exchange surfaces
  -intercellular air spaces in the spongy mesophyll
  -stomata

Question 19

how does the thinness of the leaf maximize gas exchange ?

Answer 19

ensures that the surface area to volume ratio is high and also ensures a short diffusion distance as no cell is far form an exchange surface

Question 19

what is the site for gas exchange in a leaf and why?

Answer 19

-the cell surface membranes of the spongy mesophyll cells that form metabolic contacts with air spaces and they are the site for gas exchange
-the loose arrangement ensures a large surface area for diffusion
- due to their position gases involved in respiration and photosynthesis can diffuse between spongy and palisade mesophyll cells easily

Question 20

why do the intercellular air spaces in the spongy mesophyll maximize gas exchange?

Answer 20

-it facilitates diffusion in the leaf

Question 21

where are the stomata found? and how do they maximize gas exchange?

Answer 21

-found on the lower side of the leaf
-allow respiratory gases to diffuse in and out of the leaf

Question 22

how is the leaf adapted for photosynthesis?

Answer 22

-the upper epidermis is transparent which allows light to the palisade layer
-most photosynthesis takes place in the palisade layer which contain chloroplasts

Question 23

when do the stomata open and close?

Answer 23

-they will open during the day when the diffusion of gases in and out of the leaf is the greatest
-they will close at night when there is no light and no photosynthesis to ensure that there is enough o2 for respiration to take place and that is no diffused out of the leaf, this will also reduce water loss in the leaf at night

Question 24

what surrounds the stomata and how do they control when the stomata are open or closed ?

Answer 24

-by two guard cells which depending in turgor will be able to open or close the stomata

Question 25

what us another name for water plants?

Answer 25

-hydrophytes

Question 26

how are hydrophytes adapted to facilitate the uptake of o2 and co2 ?

Answer 26

-they have stomata on the upper layer of the leaf to avoid the plant from flooding
-flexible stems and leaves so they can bend to water current
-thin waxy cuticle that allows gas exchange in and out of the leaf

Question 27

what is the concentration of co2 and o2 inside and outside the cell of a mammal?

Answer 27

-inside the cell co2 concentration is high and o2 is low
-outside the cell the co2 concentration is low and the o2 is high

Question 28

what are the four stages of the movement of o2 and co2 in and out of the cell?

Answer 28

-diffusion of gases between respiring cells and blood
-transport of gases in blood
-diffusion of gases from blood through the alveolar wall
-ventilation of lungs with fresh air

Question 29

are mammals bodies permeable or impermeable and why?

Answer 29

-impermeable because they have specialized exchange surfaces because they have a small sa:v

Question 30

what are the specialized exchange surfaces in mammals?

Answer 30

-pulmonary respiration system and the exchange surface is the alveolar wall

Question 31

what is surfactant?

Answer 31

-this reduces surface tension in the moisture coating of the alveoli
-prevents their collapse

Question 32

what are macrophages?

Answer 32

-originate from monocytes in the alveoli
-protect against infection by carrying out phagocytosis

Question 33

what are 3 way that a short diffusion is achieved in the alveoli?

Answer 33

-thin squamous epithelium ensures short diffusion distance
-capillaries lie close to alveolar wall
-red blood cells squeeze through capillaries ensuring contact with endothelium wall creating short diffusion distance

Question 34

how is a large surface area created in the alveoli?

Answer 34

-in the lungs there are millions of alveoli which increases the surface area

Question 35

how is a concentration gradient maintained in the alveoli?

Answer 35

-the capillary network creates a good blood supply which brings deoxygenated blood to the alveoli and oxygenated blood away
-the ventilation system also supplies a steep concentration gradient which bring o2 in and co2 out

Question 36

what is the definition of breathing?

Answer 36

-the term used to describe the process involved in ventilating the lungs and alveoli

Question 37

list the steps of the process if inhalation

Answer 37

-external intercostal muscles contract
-ribs and sternum move up and out
-width of thorax increases front to back and side to side
-diaphragm contracts
-diaphragm moves down and flattens
-depth of thorax increases top to bottom so the;
-volume of thorax increases
-pressure between pleural surfaces decreases
-lungs expand to fill thoracic cavity
-air pressure in alveoli is less than atmospheric pressure
-air is forced in by the higher external atmospheric pressure

Question 38

list the steps of exhalation

Answer 38

-external intercostal muscles relax
-ribs and sternum move down and in
-width of thorax decreases front to back and side to side
-diaphragm relaxes
-diaphragm moves up
-depth of thorax decreases top to bottom so;
-volume of thorax decreases
-pressure between pleural surfaces increases
-lung tissue recoils from sides of thoracic cavity
-air pressure in alveoli is more than atmospheric pressure
-air is forced out

Question 39

what are the three main effects of smoking on the lungs?

Answer 39

-build up of tar
-emphysema
-bronchitis

Question 40

what is tar ?

Answer 40

-general name given to a collection of toxic chemicals in cigarette smoke which can cause cancer

Question 41

how can tar cause cancer? what happens during lung cancer?

Answer 41

-tar damages DNA in epithelial cells lining the lungs which can cause lung cancer.
-some of the cells divide uncontrollably producing a tumor and when the tumor grows it can block airways or damage large sections of the lungs

Question 42

what causes emphysema? what happens because of emphysema?

Answer 42

-tar causes irritation in the alveolar lining which causes may alveoli to break down
-this means the surface area is reduced which limits the diffusion of gases. It also breaks down the lining of the alveoli which reduces the ability of it to recoil during expiration

Question 42

what is bronchitis caused by?

Answer 42

-caused by inflammation of the bronchial tubes

Question 43

what happens as a result of bronchitis ?

Answer 43

-bronchial tubes narrow
-mucus production increases reducing air flow
-tar will also paralyse the cilia which removes mucus and microbes, increases risk of infection.