2.40-2.50 Gas exchange and breathing

Question 1

Define respiration

Answer 1

Process of transferring energy from glucose, which happens constantly in every living cell
Energy transferred can’t be used directly by cells so makes a substance called ATP

Question 2

What is ATP and its function?

Answer 2

ATP stores the energy for cell processes

When energy is needed, ATP molecules are broken down and energy is released

Question 3

Describe a practical to investigate temperature change during respiration

Answer 3

1) Soak dried beans in water so they will germinate
2) Boil another set of the same beans so they can’t respire - control
3) Add each set of beans to a vacuum flask with some air left in the flask for aerobic respiration
4) Place a thermometer into each flask and seal the top with cotton wool
5) Record the temperature of each flask daily for a week
6) Repeat and take an average of the temperatures using the same size, mass, species beans
7) When the germinating beans respire the flask temperature increases compared to the control flask

Question 4

What is aerobic respiration and give the word and symbol equation

Answer 4

Respiration with plenty of oxygen available
glucose + oxygen –> carbon dioxide + water
C6H12O6 + 6O2 –> 6CO2 + 6H2O

Question 5

What is anaerobic respiration and how does it differ from aerobic respiration?

Answer 5

Without oxygen respiration
Not the best way to convert glucose to energy - releases less energy - and glucose only partially broken down
Lactic acid also produced ( glucose –> lactic acid) and leads to cramps

Question 6

What is the word equation for anaerobic respiration in plants?

Answer 6

glucose –> ethanol + carbon dioxide

Question 7

Describe plant gas exchange by diffusion

Answer 7

Photosynthesis uses up lots of CO2 so there is hardly any left in the leaf - this makes more diffuse into the leaf
At the same time lots of O2 is being made as a waste product of photosynthesis - some is used in respiration and the rest diffuses out through the stomata

Question 8

What is the effect of light intensity on the net exchange of gases?

Answer 8

Photosynthesis = only day
Respiration = day and night for energy
High light intensity during day–> more photosynthesis than respiration so releases oxygen and use more carbon dioxide than produce so take in CO2
Low light intensity during night –> only respiration so take in oxygen and release carbon dioxide

Question 9

How are leaves adapted for efficient gas exchange?

Answer 9

• Leaves are broad so large surface area for diffusion
• Thin so gases only have to travel a short distance to the cells
• Air spaces inside the leaf to let gases like carbon dioxide and oxygen move easily between cells and increase surface area
• Stomata let gases like CO2 and O2 diffuse in and out and allow water to escape

Question 10

What is the function of stomata?

Answer 10

• Stomata begin to close as it gets dark as no photosynthesis so don’t need to let carbon dioxide in. Also don’t let water escape to stop plant drying out
• Also close when supplies of water from roots start to dry up to stop photosynthesis and to stops the plant drying out and dying
• Opening and closing of stomata controlled guard cells around them

Question 11

How do guard cells open and close stomata?

Answer 11

By changing their shape and volume
Increase in volume –> open stomata
Decrease in volume –> close stomata

Question 12

What is the thorax?

Answer 12

The top part of your body

Question 13

What do the pleural membranes do?

Answer 13

Moist, thin layers
Separate the inside of the thorax from the lungs by 2 pleural membranes
Form an airtight seal around the lungs

Question 14

What is the gap between the two pleural membranes called and what does it do?

Answer 14

Pleural cavity and is filled with pleural fluid

Pleural fluid acts as lubrication between the lungs and inside of the chest

Question 15

Describe breathing in

Answer 15

External intercostal muscles contract - ribs move up and out
Diaphragm contracts and goes down
Thorax volume increases and pressure decreases - air enters lungs

Question 16

Describe breathing out

Answer 16

External intercostal muscles relax - ribs move inwards and down
Diaphragm relaxes - goes up
Thorax volume decreases and pressure increases - air forced out

Question 17

Describe the structure of the thorax - diagram

Question 18

Describe a practical to investigate the effect of exercise on breathing rate

Answer 18

C - Change the intensity of the exercise
O - I will test this on humans of the same gender and age who are all moderately active (S)
R - I will test a range of mild, medium and high intensity exercise
R - I will repeat 3 times and take an average excluding anomalies
M - I will test this by doing 15,30 or 45 star jumps in a minute,
M - after the exercise I will count how many breaths the test subject takes in the minute using a stopwatch after they stop exercising

Question 19

Why do you breathe more during exercise?

Answer 19

Your muscles respire more O2 during exercise so need to be supplied with more O2 and have more CO2 removed

Question 20

Describe an experiment to investigate the release of carbon dioxide in your breath

Answer 20

1) Set up 2 boiling tubes with a mouthpiece connected and the same volume of limewater in each
2) Put your mouth around the mouthpiece and breathe in and out
3) Breathing in –> air from room is drawn in through boiling tube A containing little CO2 so the limewater remain colourless
4) Breathing out –> the exhaled air bubbles through the limewater in boiling tube B containing CO2 during respiration so the limewater turns cloudy

Question 21

How does alveoli carry out gas exchange in the body?

Answer 21

• Millions in the lungs
• The blood passing next to the alveoli has come from the body so is high in CO2 and low in O2
• Oxygen diffuses out of the alveolus to the blood and carbon dioxide diffuses from the blood to the alveolus to be breathed out (high conc to low conc)
• The oxygen diffuses from red blood cells to body cells
• The carbon dioxide does the opposite and is carried back to the lungs

Question 22

How are alveoli adapted for gas exchange?

Answer 22

1. ‘Bumpy surface’ and millions of them = large surface area for faster diffusion
2. One cell thick (thin) walls = faster diffusion due to short distance
3. Great blood supply = maintain a high concentration gradient (faster diffusion)
4. Moist walls = dissolve gases for faster diffusion
   (5. CGP - permeable walls so gases can diffuse across easily)

Question 23

Practical: Investigate the role of anaerobic respiration by yeast in different conditions

Answer 23

I will change the temperature of the yeast solution
I will test a range of 20,40,60 and 80C and repeat each temperature three time
I will put a layer of oil on top of my yeast solution to stop oxygen entering, then measure the volume of carbon dioxide produced in 2 minute using a gas syringe
I will use the same species of yeast, and I will keep the volume of yeast solution and the type of sugar used the same
I will also use sugar at the same concentration each time

Question 24

What is nicotine and the effect of it on smokers?

Answer 24

Addictive - not particularly harmful itself, more exposure to cigarette smoke
Stimulant - causes the release of more dopamine at the synapses of nerves in the reward centre of the brain
Side effects:
- Increases heart rate and blood pressure
- Decreases appetite

Question 25

What is tar and the effect of it on smokers?

Answer 25

Carcinogenic - can cause cancer

Question 26

What is carbon monoxide and the effect of it on smokers?

Answer 26

Binds irreversibly to haemoglobin in red blood cells to form carboxyhaemoglobin
Prevent O2 binding (reduces O2 carrying capacity of blood) less respiration in body cells = cell death and to make up for this, heart rate increase = increase in blood pressure
High blood pressure damages the artery walls, making the formation of blood clots more likely = heart disease

Question 27

What effect does smoking have on the likelihood of infections?

Answer 27

• Cells lining the trachea and bronchi produce mucus to trap bacteria
• Fine hairs called cilia move the mucus up and out of the lungs
• The heat and chemicals form the cigarette smoke (tar) damages the cilia, so infections are more likely

Question 28

What is emphysema?

Answer 28

• Destruction of alveoli causes the surface area of the lungs to decrease making them feel out of breath
• Chemicals in cigarettes also break down elastic proteins structures in the lungs, reducing their elasticity and so causes the bronchioles and alveoli to collapse