Gas Exchange

Question 1

Where does the exchange of materials take place

Answer 1

On the surface of an organism, the materials absorbed and used and assimilated by the cell

Question 2

What happens to surface area to volume ration, depending on the size of the organism

Answer 2

As the organism gets larger, the surface area to volume ration gets smaller

Question 3

Gas exchange in single celled organisms

Answer 3

• O2 required to produce ATP during aerobic respiration
• CO2 is a waste product and creates a concentration gradient of these gases in opposite directions
• all organisms rely on diffusion for exchange of O2 and CO2 down their gradients
• these organisms have large enough SA:Vol ratio to meet their gas exchange needs by diffusion across their meme faces

Question 4

What is fick’s law

Answer 4

Rate of diffusion= surface area x concentration gradient / diffusion distance or pathway

Question 5

Adaptations to gas exchange in insects - limiting water loss

Answer 5

-Waterproof covering over their body surfaces- a rigid outer Skelton (exoskeleton) covered with a waterproof cuticle
-Small SA:Vol ratio to minimise the area over which water is lost

Question 6

Movement of oxygen through an insect

Answer 6

• o2 enters the insect through spiracles and into the trachea
• spiracles close
• O2 diffuses through the tracheae into the tracheoles down a conc gradient
• O2 delivered directly to respiring tissues

Question 7

Describe what a spiracle is

Answer 7

Gas enters and exits the insect through these tiny pores- opened and closed to control water loss by evaporation- open when CO2 levels increasw

Question 8

Describe what a tracheole is

Answer 8

1. Small tubes with thin walls so that the diffusion distance is reduced
2. Highly branched so that there is a large surface area

Question 9

Describe what a trachea is

Answer 9

Network of tubes supported by the strengthened rings- provides tubes full of air so that diffusion is fast

Question 10

Oxygen diffusion in the tracheal system

Answer 10

• tissues respire using oxygen which reduces the concentration of O2 at the tissue
• O2 moves from an area of higher concentration to lower concentration so moved from the trachea to the tissue
• this lowers the O2 concentration in the tracheae so oxygen moves into the trachea from outside the insect via spiracles

Question 11

CO2 diffusion in the spiracles

Answer 11

• respiration produces CO2, increasing the concentration at the tissue
• CO2 moves from an area of high concentration at the tissue to the low concentration in the trachea
• CO2 then moved from high concentration in trachea to low concentration out of the insect via spiracles

Question 12

Ventilation- abdominal pumping

Answer 12

Movement creates a mass movement of air in and out of the trachea- increasing the rate of gaseous exchange- they also have small air sacs in the trachea. Muscles around the trachea contract and pumps the air in the sacs deeper in the tracheoles

Question 13

Getting additional oxygen during flight

Answer 13

At rest- water can build up in the tracheoles
During flight- insect may partly respire anaerobically and produce some lactate - this lowers the water potential of the muscle cells
As lactate builds up, water passes via osmosis from the tracheoles into the muscle cells
- adaptation draws air into tracheoles closer to the muscle cells and reduces diffusion distance

Question 14

Explain the structure of the gas exchange in fish

Answer 14

• four gills
• water moves in through mouth and over gills
• gill filaments with many lamaellea at 90o to increase surface area
• water carrying oxygen enters through mouth, passes over lamaellea on the gil filament where most of the oxygen is removed

Question 15

Give two features of the lamellae

Answer 15

Contain capillaries
Thin epithelium for short diffusion distances

Question 16

A fish uses its gills to absorb oxygen from water- explain how the gills of a fish are adapted for efficient gas exchange

Answer 16

• large surface area provided by many lamellae
• thin epithelium of lamellae so short diffusion distance
• water and blood flow in opposite directions so that a concentration gradient is maintained across the length of the lamellae
• as water always next to blood with lower concentration of oxygen
• circulation replaces blood saturated with oxygen
• ventilation replaces water

Question 17

Explain how the counter current mechanism in fish gills ensures the maximum amount of oxygen passes into the blood flowing through the gills

Answer 17

• water and blood flow in opposite directions
• blood always passing water with a higher concentration of oxygen
• oxygen concentration gradient mainted across the length of the lamellae

Question 18

Adaptations of leaf for gaseous exchange

Answer 18

• flat—> gives a large surface area to volume ratio
• many stomata—> pores allow air to move in and out of leaf
• air spaces—> short diffusion distance between mesophyll cells and air

Question 19

Diffusion of CO2 for photosynthesis

Answer 19

• mesophyll cells photosynthesise and this reduces the concentration of CO2 in the cells
• CO2 diffuses from the air spaces into the cells
• this in turn reduces the CO2 concentration in the air spaces causing CO2 to move into the air spaces from the air outside the leaf through the stomata

Question 20

Diffusion of O2

Answer 20

• mesophyll cells produce O2 as a result of photosynthesis
• O2 diffuses into the air spaces from the cells
• this increases the concentration of O2 in the air spaces, causing O2 to move from the air spaces to outside the leaf view the stomata

Question 21

How does a plant reduce water loss

Answer 21

Guard cells close the stomata to reduce water loss
Upper and lower surfaces have a waxy cuticle
Most stomata distributed on the lower leaf

Question 22

Scribe how the CO2 in the air outside a leaf reaches mesophyll cells inside the leaf

Answer 22

• CO2 enters via stomata
• stomata opened by guard cells
• diffuses through air spaces
• down diffusion gradient

Question 23

Adaptations of xerophytic plants

Answer 23

• reduced number of stomata—> less SA for water loss
• stomata in pits—> reduced concentration gradient
• hairs to trap water vapour—> reduced concentration gradient
• rolled leaves—> reduced conc gradient
• leaves reduced to spines—> less surface area for water loss
• thick waxy cuticle—> increased diffusion distance