4.2- gas exchange

Question 1

how to find surface area

Answer 1

-number of faces multiplied by (length of them squared)

Question 2

how to find volume

Answer 2

-length of faces cubed

Question 3

surface area to volume ratio

Answer 3

-always try to use 1 in the ratio
-e.g a small cube will have a large surface area to vol ratio as the area in contact with the outside is very large relative to the volume inside of the organism
-large sa:v ratio means diffusion can happen faster

Question 4

factors affecting rate of diffusion

Answer 4

1. surface area- bigger sa means more particles can be exchanged at same time
2. conc gradient of particles diffusing- e.g down a gradient
3. distance over which diffusion is taking place- shorter means faster
4. rich blood supply- maintain conc gradient
   5.moist surfaces allowing gases to dissolve and diffuse faster
   6.permeable surfaces- allow gases to pass through

Question 5

why do mammals gas exchange surfaces need to be large and moist

Answer 5

-gases dissolve in the moisture helping them to pass across the gas exchange surface

Question 6

where is the human gas exchange system/ where does it take place

Answer 6

-most is in the chest cavity
-exchange only takes place in the lungs, not the passages that take gases in and out
-The passages have linings that secrete mucus and are lined with cilia. This means the external air is filtered of dust & pathogens before entering the lungs
-external air is heated on entry due to good blood supply and moist surfaces creating water vapour

Question 7

what is the alveoli?

Answer 7

-where gas exchange happens
-they are tiny air sacs in the lungs
-they are made of a single layer of flattened epithelial cells

Question 8

adaptations of the alveoli

Answer 8

-epithelial wall is one cell thick to allow faster gas exchange
-capillaries surrounding the alveoli also have a wall which is one cell thick
-elastic tissue holding capillary to alveoli helps force air in/out by elastic recall
-lung surfactant coats them, preventing them collapsing

Question 9

what happens in the alveoli

Answer 9

-gas enters from pulmonary artery
-oxygen diffuses into red blood cells in alveoli
-carbon dioxide diffuses into alveolus
-gas leaves towards pulmonary vein

Question 10

stages of breathing/ ventillation

Answer 10

1. inhalation- active process, diaphragm contracts and flattens, intercostal muscles contract, moving ribs up and out, increased volume and decreased pressure, air rushes in to equalise pressure
   2.exhalation- passive process by the exact opposite steps

Question 11

forced exhalation

Answer 11

1. you can force air out of your lungs by contracting your internal intercostal muscles and abdominal muscles
2. ribs move down and in and diaphragm moves up

Question 12

how does water flow through fish for gas exchange?

Answer 12

1.water flows in through the mouth
2.water flows over the gills
3.water flows out through operculum
4. fish without operculum have to constantly move

Question 13

how are fish adapted for efficient gas exchange?

Answer 13

-gills made up of overlapping gill filaments called lamellae
-lamellae have a good blood supply and this is where gas exchange takes place
-lamellae have a large surface srea
-overlap of filaments can slow down water flow
-The water moving over the gills moves in the opposite direction to the blood in the blood vessels- this is called countercurrent exchange
-this maintains the concentration gradient, allowing diffusion of oxygen into the blood

Question 14

components of gas exchange system in insects

Answer 14

-insects have a high oxygen requiremet and have evolved to deliver oxygen straight to their cells and remove the carbon dioxide
-maid up of 3 main parts- spiacles, trachea and tracheoles
-spricales are tiny holes in the thorax or abdomen which allow air to enter and leave
-trachea are the largest tubes, they carry air directly into the body, running into but also along the body. thy are supported by chitin spirals which hold them open, chitin makes them impermeable so no gas exchange happens here
-tracheoles are single elongated cells with no chitin, they are therefore permeable to gas and spread through tissues

Question 15

key points of gas exchange in insects

Answer 15

-air moves along through trachea and tracheoles by diffusion
-network of tracheoles provide a large surface area
-opening and closing of spiracles controls the rate of gas exchange , when inactive most are closes to prevent water loss

Question 16

methods used by active insects to increase gas exchange

Answer 16

1. mechanical pumping- insect moves its thorax in muscular pumping motion, drawing air in and out of spircales
   2.Collapsible tracheae act as air reservoirs. Movement of the thorax can inflate or deflate them.

Question 17

what is a countercurrent exchange system

Answer 17

• a system in which 2 fluid components flow in opposite directions and some properties are exchanges between two fluids

Question 18

why do plants need to exchange gases?

Answer 18

-for photosynthesis and respiration

Question 19

net movement of gases in plants- day Vs night

Answer 19

-more carbon dioxide out during the night when the plant is just respiring, but during the day more carbon dioxide needs taken in

Question 20

parts of leaf structure

Answer 20

-spongy mesophyll (where exchange takes place)
-stomata (specialised pores where gas diffuses in and out of cell)
-guard cells (open and close stomata, controlling gas exchange)
-lenticels (spongy areas with loosely packed cells where gas exchange takes place in woody stems)
-waxy cuticle (prevents water loss)
-upper and lower epidermis
-xylem vessel
-phloem tissue
-palisade mesophyll
-air spaces

Question 21

controlling gas exchange in plants

Answer 21

-have to balance need for CO2 and O2 with water loss
-need water to evaporate as this pulls water up throughout the plant for chemical reactions
-guard cells open and close stomata, depending on conditions
-opening and closing is a turgor driven process
-stomata open when turgor cells are full of water and ions
-found on underside of leaves