1. 3.3: Organisms exchange substances with their environment
External Assessments:
AS – Paper 1 and Paper 2
A-level – Paper 1 and Paper 3
Internal Assessments:
1. SA:V, gas exchange, digestion and absorption exam questions (due: )
2. Mass transport exam questions
(due: )
3. End of topic test
Required Practicals:
5. Dissection of animal or plants gas exchange system or of organ within such a system.
Comments:

2. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
3.3.1 Surface area to volume ratio
How does the size of an organism and its structure relate to its surface area to volume ratio?
How do larger organisms increase their surface area to volume ratio?
How are surfaces specially adapted to facilitate exchange?
Key words:
diffusion; osmosis; surface area to volume ratio
List examples of things that need to be interchanged between an organism and its environment:
Why is it essential for larger, multicellular organisms to have developed a specialised exchange system?
List examples of adaptations that facilitate exchange of substances in larger organisms.
Compare the volumes (V), surface areas (SA) and SA:V ratios of a cube of 1cm3 to a cube of 1000cm3.

3. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
3.3.2 Gas exchange in single-celled organisms and insects
How do single-celled organisms exchange gases?
How do terrestrial insects balance their need to exchange gases with the need to conserve water?
How do insects exchange gases?
Key words:
diffusion gradient; ventilation; spiracle; tracheae; tracheoles
How do single-celled organisms exchange gases?
Describe two adaptations of insects to prevent water loss.
Explain how the tracheal system of an insect allows efficient gas exchange to occur. You may use diagrams in your explanation.

4. Unit 2: Exchange and transport
3.3: Organisms exchange substances with their environment
3.3.2 Gas exchange in fish
What is the structure of fish gills?
How is water passed along fish gills?
What is the difference between parallel flow and counter-current flow?
How does counter-current flow increase the rate of gas exchange?
Key words:
gill filaments; gill lamellae; counter-current principle
Draw and label the structure of the gills in a fish.
Compare parallel flow with counter-current flow.

5. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
3.3.2 Gas exchange in the leaf of a dicotyledonous plant
How do plants exchange gases?
What is the structure of a dicotyledonous plant leaf?
How is the leaf adapted for efficient gas exchange?
Key words:
Stomata (stoma); epidermis; mesophyll; spongy; palisade; air space; waxy cuticle
Label the diagram of the leaf section and describe the function of each part.
Explain why the following features are important with regards to exchange of gases/water:
Waterproof cuticle
Stomata on underside of leaf
Airspaces in mesophyll layer
Elongated palisade cells with large numbers of chloroplasts

6. Unit 2: Exchange and transport
3.3: Organisms exchange substances with their environment
3.3.2 Limiting water loss in plants
What are xerophytes?
Key words:
stomata; xerophytes; cuticle; water potential; transpiration
How is a cactus adapted to live in very hot, dry conditions?
What is a xerophyte?
Explain how the features of a xerophytic plant reduce water loss by transpiration.
List the most common xerophytic adaptations of plants.
How is marram grass adapted to live in very dry conditions?

7. 3.3: Organisms exchange substances with their environment
3.3.2 Structure of the human gas exchange system
How is the human gas exchange system arranged?
What are the functions of its main parts?
Key words:
alveoli; bronchioles; bronchi; lungs; trachea
Label the structures of the human gas exchange system and give the functions of the main parts:

8. 3.3: Organisms exchange substances with their environment
3.3.2 Exchange of gases in the lungs
What are the essential feature of exchange surfaces?
How are gases exchanged in the alveoli of humans?
Key words: alveoli; ; capillary; diffusion pathway; partially permeable; surface-area to volume ratio;
List the general features that improve the efficiency of a gas exchange system.
Use the diagram below to explain how the alveolus is adapted for gas exchange.
Describe how a concentration gradient is maintained in the lungs.

9. 3.3: Organisms exchange substances with their environment
3.3.2 Ventilation of the lungs
How is air moved into the lungs when breathing in?
How is air moved out of the lungs when breathing out?
What is meant by pulmonary ventilation and how is it calculated?
Key words: antagonistic; diaphragm; expiration; external intercostal muscles; inspiration; internal intercostal muscles; pulmonary ventilation; tidal volume; ventilation
Describe the process of inspiration, referring to the volume and pressure changes within the thoracic cavity.
Describe the process of expiration, referring to the volume and pressure changes within the thoracic cavity.
State the equation used to calculate pulmonary ventilation rate. Include units!

10. 3.3: Organisms exchange substances with their environment
3.3.3 Digestion
What is the structure of the digestive system?
What is the role of enzymes in digestion?
Key words: absorption; amylases; bile salts; carbohydrates; dissacharidases; endopeptidases; exopeptidases; lipase; lipids
Label the parts of the digestive system and identify the organs in which digestion and absorption occur.
Describe how carbohydrates are digested.
Describe how lipids are digested.
Describe how proteins are digested.

11. 3.3: Organisms exchange substances with their environment
3.3.3 Absorption in the ileum
What part do villi and microvilli play in absorption?
How are amino acids and monosaccharides absorbed in the ileum?
How are lipids absorbed in the ileum?
Key words:
Co-transport; ileum; micelles; microvilli; villi
How does the structure of the villi and microvilli help the absorption of molecules in the ileum?
Explain how co-transport enables the uptake of amino acids and monosaccharides.
Explain the role of micelles in the absorption of lipids.

12. 3.3: Organisms exchange substances with their environment
Exam questions
The diagram shows the position of the diaphragm at times P and Q.
Describe what happens to the diaphragm between times P and Q to bring about the change in its shape.
(2 marks)
Air moves into the lungs between times P and Q. Explain how the diaphragm causes this.
(3 marks)
Describe how oxygen in air in the alveoli enters the blood in capillaries.
(2 marks)

13. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
Exam questions
A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.
(6 marks)
The body of a flatworm is adapted for efficient gas exchange between the water and the cells inside the body.
Using the diagram, explain how two features of the flatworm’s body allow efficient gas exchange 1 2
(2 marks)

14. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
Exam questions
Endopeptidases and exopeptidases are involved in the digestion of proteins in mammals.
(i) Describe the action of endopeptidases on a protein.
(2 marks)
(ii) Explain how the action of endopeptidases increases the rate of action of exopeptidases.
(1 mark)
Heat from respiration helps mammals to maintain a constant body temperature. Use this information to explain the relationship between body mass and oxygen uptake shown in the graph.
(3 marks)

15. Unit 2: Haemoglobin, Starch, Cellulose, Glucose, Glycogen
3.3: Organisms exchange substances with their environment
Haemoglobin
What are haemoglobins and what is their role?
How do haemoglobins from different organisms differ and why?
What is loading and unloading of oxygen?
Key words:
Haemoglobin; loading; unloading; affinity; quaternary structure
What are the haemoglobins?
Explain the role of haemoglobin
Haemoglobin has a quaternary structure. Explain what this statement means.
Some haemoglobin has a high affinity for oxygen and others a low affinity. Why do animals have different haemoglobins?
Describe what we mean by oxygen loading and unloading and say where in the body these processes are likely to take place.

16. 3.3: Organisms exchange substances with their environment
Unit 2: Haemoglobin, Starch, Cellulose, Glucose, Glycogen
Oxygen dissociation curves
What is an oxygen dissociation curve?
What is the effect of carbon dioxide concentration on the curve and why?
Key words:
Affinity; dissociation; sigmoid; partial pressure; saturation; loading; unloading; haemoglobin; oxyhaemoglobin
Sketch an oxygen dissociation curve and label its main features.
Explain the Bohr effect, using the graph to help.
Describe how red blood cells are adapted for efficient loading, transport and unloading of oxygen.

17. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
Circulatory system of a mammal
How do mammals move substances around their bodies?
What are the features of the transport systems of mammals?
Key words:
diffusion; metabolism; oxygenated; deoxygenated
Explain what we mean by the following terms:
Closed circulation
Double circulation
Label the plan of the mammalian circulatory system, including the names of the relevant veins and arteries:
Describe the path of an oxygen molecule from an alveolus to a muscle cell in the small intestine.

18. 3.3: Organisms exchange substances with their environment
Unit 1: The heart and heart disease
The structure of the heart
What is the appearance of the heart and its associated blood vessels?
How is the structure of the heart related to its functions?
Key words:
aorta; atrioventricular valves; atrium; coronary arteries; pulmonary artery; pulmonary vein; semilunar valves; vena cava; ventricle
Label the parts of the heart:
State the equation for cardiac output, giving units.
How is the structure of the heart related to its functions?
Thicker muscular walls of ventricle:
Left ventricular wall thicker than right:
Atria have thin walls:
Valves:

19. 3.3: Organisms exchange substances with their environment
Unit 1: The heart and heart disease
The cardiac cycle
What are the stages of the cardiac cycle?
How do the valves control the flow of blood through the heart?
Key words: atrial systole; atrioventricular valves; cardiac cycle; diastole; semilunar valves; ventricular systole
Use the diagrams to help you describe the three main stages of the cardiac cycle. Refer to pressure and volume changes in the atria and ventricles, and the movement of the valves.
Label the main features of the cardiac cycle:

20. Unit 2: Exchange and transport
3.3: Organisms exchange substances with their environment
Blood vessels and their functions
What are the structures of arteries, arterioles and veins?
How is the structure of each of the above vessels related to its function?
What is the structure of capillaries and how is it related to their function?
Key words: arteries; arterioles; veins; capillaries; muscle; endothelium; lumen; elastic; valves; hydrostatic pressure
Label the blood vessels and their structures, stating the function of the structure and how this relates to the function of the blood vessel:

21. Unit 2: Exchange and transport
3.3: Organisms exchange substances with their environment
Tissue Fluid
How is tissue fluid formed and how does it return to the circulatory system?
Key words: arterioles; venules; capillaries; arterial; venous; hydrostatic pressure, osmosis, water potential gradient, lymph, protein, plasma
Explain how tissue fluid is formed and how it returns to the circulatory system.

22. 3.3: Organisms exchange substances with their environment
Transport of water in plants
How is water transported in the xylem of plants?
Key words: xylem; cohesion-tension theory; water potential gradient; osmosis; diffusion
Label the features of the xylem vessel below and describe the functions of each part.
Explain how cohesion-tension enables the movement of water up the xylem.

23. Unit 2: Exchange and transport
3.3: Organisms exchange substances with their environment
Investigating water movement in plants (own research):
What equipment can we use to measure the rate of transpiration?
Key words:
Transpiration, potometer.
Use the diagram below to explain how the potometer can be used to investigate the rate of transpiration of a leafy shoot.
Function of capillary tube
Function of air bubble
Function of volume scale
Function of reservoir
Why is the shoot to be tested cut and placed into the equipment whilst underwater?
Why is all of the equipment sealed with rubber bungs (or tubing) and vaseline?
What measurements do we need in order to calculate the rate of transpiration?

24. 3.3: Organisms exchange substances with their environment
Transport of organic substances in plants
How are organic substances transported in the phloem of plants?
Key words: phloem; mass flow hypothesis; translocation; tracers; ringing experiments
Label the features of the phloem on the diagrams below and describe the functions of each part.

25. 3.3: Organisms exchange substances with their environment
Transport of organic substances in plants
How are organic substances transported in the phloem of plants?
Key words: phloem; mass flow hypothesis; translocation; tracers; ringing experiments
Explain how the mass flow hypothesis allows the translocation of organic substances.
Discuss the evidence for and against the mass flow hypothesis.

26. 3.3: Organisms exchange substances with their environment
Transport of organic substances in plants
How are experiments used to investigate the mass flow hypothesis?
Key words: phloem; mass flow hypothesis; translocation; tracers; ringing experiments
Explain how ringing experiments are used to investigate transport in plants.
Explain how tracer experiments can be used to investigate transport in plants.

27. 3.3: Organisms exchange substances with their environment
Unit 1: The heart and heart disease
Exam questions
The table shows pressure changes in the left side of the heart during one cardiac
cycle.
Between which times is the valve between the atrium and the ventricle closed?
Explain your answer.
Times ……………… s and ………………… s
Explanation
(2 marks)
The maximum pressure in the ventricle is much higher than that in the atrium.
Explain what causes this.
(2 marks)
Use the information in the table to calculate the heart rate in beats per minute.
Answer beats per minute
(1 mark)

28. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
Exam questions
The diagram shows a molecule of haemoglobin.
What is the evidence from the diagram that haemoglobin has a quaternary structure?
(1 mark)
A gene codes for the α-polypeptide chain. There are 423 bases in this gene that code for amino acids. How many amino acids are there in the α-polypeptide chain?
The total number of bases in the DNA of the α-polypeptide gene is more than Give two reasons why there are more than 423 bases.
(2 marks)
The graph shows oxygen dissociation curves for horse haemoglobin and for llama haemoglobin. Horses are adapted to live at sea level and llamas are adapted to live in high mountains.
Use the graph to explain why llamas are better adapted to live in high mountains than horses.
(3 marks)

29. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
Exam questions
A student investigated the rate of transpiration from a leafy shoot. She used a potometer to measure the rate of water uptake by the shoot. The diagram shows the potometer used by the student.
Give one environmental factor that the student should have kept constant during this investigation.
(1 mark)
The student cut the shoot and put it into the potometer under water. Explain why.
The student wanted to calculate the rate of water uptake by the shoot in cm3 per minute. What measurements did she need to make?
(2 marks)
The student assumed that water uptake was equivalent to the rate of transpiration. Give two reasons why this might not be a valid assumption. 1. 2.

30. 3.3: Organisms exchange substances with their environment
Unit 2: Exchange and transport
Exam questions
A leaf on a growing plant was exposed to radioactive carbon dioxide, 14CO2, as shown in the diagram. After a few hours, radioactivity was detected in the phloem at two
positions, A and B, in the stem.
Explain how radioactive substances had reached positions A and B.
(7 marks)