2g) Gas Exchange

Flowering Plants 

When plants photosynthesise they use up CO2 from the atmosphere and produce O2 which is a waste product

When plants respire -----> use up O2 and produce CO2 which is a waste product. Movement of gases happens through diffusion. 

Net exchange of gases:

• depends on light intensity 
• photosynthesis -----> during day, but plants respire all the time = energy = live 
• day -----> make oxygen and release use up > CO2 than take in 
• night -----> plants ONLY respire, NOT ENOUGH light so- take in O2 and release CO2 

Leaf Adaption:

1. leaves are broad -----> large surface area: diffusion
2. thin -----> gases travel short distance 
3. air spaces -----> large surface area: gas exchange 
4. stomata -----> let gases and water diffuse/osmosis in and out, closes in the dark, close when water from the roots start to dry up and open and close controlled by guard cells. 

Hydrogen carbonate indicator:effect of light 

Low CO2: Purple <----- Normal: Red -----> High CO2: Yellow 

Humans 

Trachea- takes air to the bronchus 
Bronchi- split air in two lungs (left and right)
Lungs- organ where gas exchange takes place  
Bronchiole- takes air to the alveoli
Alveoli- allows gas exchange to occur 

Intercostal muscles- contract and relax ribs 
Ribs- protect lungs and heart 
diaphragm- muscle holds lungs together

Inhalation:

requires energy: active 

• intercostal muscles and diaphragm contract 
• volume increases 
• ribs up and out 
• pressure goes down 
• air flows in 

Exhalation:

passive 

• Intercostal muscles and diaphragm relaxes 
• volume decreases 
• ribs down and in 
• pressure goes up 
• air flows out

Alveoli:

• large surface area- quick gas diffusion
• thin- gas exchange is quicker and doesn't have to go through loads of cells 
• moving blood-allows more red blood cells to be oxygenated
• air sack 

Smoking:

• damages alveoli- reduces surface area. emphysema- disease
• tar damages cilla- chest infections are more likely
• irritates bronchioles and bronchi[tar]- smokers cough
• carbon monoxide reduces the amount of O2 blood can carry- increase blood pressure
• chemicals can lead to cancer- carcinogens  

Investigation:

• sit still for 5 mins. 1 min count number of breaths you take. 4 mins exercise- stop count breaths (1 min) 
• exercise- increases breathing rate, more O2 and less CO2 
• control variable e.g. temperature of room/area and time spent exercising 

Paper Two in bold, italics