Biology
- #83 Question 6
The diagram below shows pressure changes in the left atrium and left ventricle of the heart and the aorta during the cardiac cycle. (a) Calculate how many heart beats there will be in one minute. (2 marks)(b) (i) On the diagram, indicate the point at...
- #81 Question 4
The diagrams below show five molecules found in living organisms. (a) Give the letter of one molecule that fits each of these descriptions. You can use each letter once, more than once or not at all. (i) the form in which carbohydrates...
- #77 Questions And Answers
In this section is a practice examination paper, similar to the Cambridge International AS Level Biology paper 2. All of the questions are based on the topic areas described in the previous sections. Youhave 1 hour and 15minutes to do the paper....
- #51 Summary Of Gas Exchange
1 Multicellular organisms often have surfaces that are specialised to allow exchange of gases to take place between their bodies and the environment. Alveoli in the lungs form the gas exchange surface in mammals. 2 In the human...
- #50 The Gas Exchange System
All organisms take in gases from their environment and release gases to the environment. Animals take in O2 for aerobic respiration and release CO2. Plants also respire, but during daylight hours they photosynthesise at a greater rate than...
Biology
#82 Question 5
The diagram below shows a small part of a human lung as it appears through a microscope.
(a) Name the type of blood vessel in which the red blood cell is present.
Candidate A
(a) capillary ü
* This is correct. 1/1
(b) They have a large surface area ü
They are thin, so oxygen can diffuse across quicklyü
* The statement about a large surface area is correct, but the answer also needs to say why this enables gas exchange to take place rapidly (because the question asks you to 'explain'). The second answer is not sufficiently clear - what is thin? It is not the whole alveoli that are thin, but their walls. The second part of this answer does give a clear explanation of why this helps gas exchange to
take place quickly. 2/4
(c) Large organisms have small surface areas compared to their volume,ü so they need extra surface üto be able to get enough oxygen.
* There is a correct and clear statement about surface area to volume ratio, and the answer also lust gets a second mark. However, this isn't really very clear - see candidate B for a better explanation. 2/2
Candidate B
(a) capillary ü
* Correct. 1/1
(b) large surface area ü - so more oxygen and carbon dioxide molecules can diffuse across at the same time ü
good supply of oxygen - to maintain a diffusion gradient between the alveoli and the blood
* The first way is correct and well explained. However, the second, although true, does not answer the question which is about the structure of the alveoli. So just 2/04.
(c) They have small surface area to volume ratios, übut an Amoeba has a large surface area to volume ratio. The oxygen that diffuses in across the surface has to supply the whole volume ü of the animal, so in a large animal that is not enough and they have specialised gas exchange surfaces to increase the surface areaü and let more oxygen diffuse in.
* This is a good answer. All the important points are there and it is clearly expressed. 2/2
(a) Name the type of blood vessel in which the red blood cell is present.
(1 mark)
(b) Describe and explain two ways in which the structure of the alveoli, shown in the diagram, enables gas exchange to take place rapidly.(4 marks)
(c) Explain why large organisms such as mammals need specialised gas exchange surfaces, whereas small organisms such as a single-celled Amoebo do not.(2 marks)
(Total 7 marks)
Candidate A
(a) capillary ü
* This is correct. 1/1
(b) They have a large surface area ü
They are thin, so oxygen can diffuse across quicklyü
* The statement about a large surface area is correct, but the answer also needs to say why this enables gas exchange to take place rapidly (because the question asks you to 'explain'). The second answer is not sufficiently clear - what is thin? It is not the whole alveoli that are thin, but their walls. The second part of this answer does give a clear explanation of why this helps gas exchange to
take place quickly. 2/4
(c) Large organisms have small surface areas compared to their volume,ü so they need extra surface üto be able to get enough oxygen.
* There is a correct and clear statement about surface area to volume ratio, and the answer also lust gets a second mark. However, this isn't really very clear - see candidate B for a better explanation. 2/2
Candidate B
(a) capillary ü
* Correct. 1/1
good supply of oxygen - to maintain a diffusion gradient between the alveoli and the blood
* The first way is correct and well explained. However, the second, although true, does not answer the question which is about the structure of the alveoli. So just 2/04.
(c) They have small surface area to volume ratios, übut an Amoeba has a large surface area to volume ratio. The oxygen that diffuses in across the surface has to supply the whole volume ü of the animal, so in a large animal that is not enough and they have specialised gas exchange surfaces to increase the surface areaü and let more oxygen diffuse in.
* This is a good answer. All the important points are there and it is clearly expressed. 2/2
- #83 Question 6
The diagram below shows pressure changes in the left atrium and left ventricle of the heart and the aorta during the cardiac cycle. (a) Calculate how many heart beats there will be in one minute. (2 marks)(b) (i) On the diagram, indicate the point at...
- #81 Question 4
The diagrams below show five molecules found in living organisms. (a) Give the letter of one molecule that fits each of these descriptions. You can use each letter once, more than once or not at all. (i) the form in which carbohydrates...
- #77 Questions And Answers
In this section is a practice examination paper, similar to the Cambridge International AS Level Biology paper 2. All of the questions are based on the topic areas described in the previous sections. Youhave 1 hour and 15minutes to do the paper....
- #51 Summary Of Gas Exchange
1 Multicellular organisms often have surfaces that are specialised to allow exchange of gases to take place between their bodies and the environment. Alveoli in the lungs form the gas exchange surface in mammals. 2 In the human...
- #50 The Gas Exchange System
All organisms take in gases from their environment and release gases to the environment. Animals take in O2 for aerobic respiration and release CO2. Plants also respire, but during daylight hours they photosynthesise at a greater rate than...