2G GAS EXCHANGE

what is diffusion’s role in gas exchange?

waste products are diffused through the stomata of leaves.

what happens during respiration at the stomata

• oxygen diffuses from a high concentration outside the leaf to a low concentration inside the lead

• carbon dioxide diffuses from a high concentration inside the leaf to a low concentration outside the leaf

what happens during photosynthesis at the stomata

• carbon dioxide diffuses from a region of high concentration outside the leaf to a region of low concentration inside the leaf

• oxygen diffuses from a region of high concentration inside the leaf to a region of low concentration outside the leaf

adaptions of the whole leaf for gas exchange

• they are thin and have thin cell walls, giving a short diffusion distance

• they are flat, which means large SA:V

• they have many stomata

• there are air spaces around the spongy mesophyll

adaptions of the stomata for gas exchange

• guard cells open the stomata when they become turgid, allowing gases to diffuse in, when there is lots of water and sunlight

• guard cells close the stomata when they become flaccid, stopping gas exchange, when there is low light and little water available.

how does gas exchange depend on light intensity

• photosynthesis only happens when light is available, but plants must respire all the time to live

• during the day plants photosynthesize too much, so they release oxygen and take in carbon dioxide.

• at night plants only respire, so they just take in oxygen and release carbon dioxide

practical: investigating gas exchange in plants

1. add the same volume of hydrogen-carbonate indicator to four boiling tubes

2. put similar sized, healthy-looking leaves into three of the tube and seal with a rubber bung, trapping the leaf stem.

3. completely wrap one tube in aluminum foil and one in gauze.

4. place all the tubes in bright light

5. leave the tubes for an hour and check the colour of indicator

6. the control should stay the same, foil tube will be yellow, gauze tube will be orange, uncovered tube will be purple

what colour do hydrogen-carbonate indicator turn

• CO2 concentration decreased - purple

• CO2 concentration normal - orange

• CO2 concentration increased - yellow

Label the diagram

• oesophagus

• Trachea

• Bronchus

• Alveoli

• Bronchiole

• Intercostal muscle

• Heart

• Pleural membranes

• Rib

• Diaphragm

role of intercostal muscles and diaphragm in ventilation

• when breathing in, intercostal muscles and diaphragm contract, and thorax volume increases. this decreases pressure, drawing pressure in

• when breath out, intercostal muscles and diaphragm relax and thorax volume decreases as air is forced out.

how do alveoli carry out gas exchange?

• the lungs contain millions of air sacs, alveoli

• the bloody passing next to the alveoli has just returned to the lungs so contains CO2 and little oxygen

• oxygen diffuses out of the alveoli and into the blood

• CO2 diffuses into the alveoli to be breathed out

how are alveoli specialized for gas exchange

• the huge number of alveoli give the lungs a massive surface area

• there is a moist lining for gases to dissolve in

• alveoli have very thin walls

• they have a great blood supply to maintain high concentration gradient

• the walls are permeable

how does smoking cause smoker’s cough and bronchitis

• smoking damages the walls inside the alveoli, reducing the surface area

• the tar in cigs damage the cilia in lungs and trachea, making infection more likely

• the cilia and mucus catch dust and bacteria before reaching the lungs and help keep the trachea clear

• tar irritates the bronchi and bronchioles, encouraging mucus to be produced which cannot be cleared by damaged cilia

how does smoking cause coronary heart disease and cancer

• the CO in smoke reduces the amount of oxygen the blood can carry, so heart rate increases, leading to increase of blood pressure

• high blood pressure can damage the artery walls, forming blood clots and increasing risk of coronary heart disease

• tobacco smoke also contains carcinogens, which are chemicals which can lead to cancer

INVESTIGATION: effect of exercise on breathing rate

1. sit still for five minutes and count number of breaths in one minute

2. do four minutes of exercise and count breaths for a minute as soon as you stop

3. repeat the steps and work out mean average for resting and exercise

results should show that exercise increases breathing rate as muscles respire more during exercise

INVESTIGATION: release of CO2 in breathing humans

1. set up two boiling tubes and place same amount of limewater in each

2. connect a mouthpiece to both and also the air out/in in one each

3. put your mouth around the mouthpiece and breath in and out several times

4. as you breath in, air is drawn from tube A, containing little CO2 so solution remains colourless

5. in tube B, the exhale bubbles are CO2, turning the limewater cloudy