Energy Transfers Between Organisms Exam Qs

Question 1

Suggest one reason for conserving woodlands. (1 mark)

Answer 1

1. Conserving / protecting habitats / niches;
2. Conserving / protecting (endangered) species / maintains / increases
   (bio) diversity;
3. Reduces global warming / greenhouse effect / climate change / remove / take up carbon dioxide;
4. Source of medicines / chemicals / wood;
5. Reduces erosion / eutrophication.

Question 2

Give a biological molecule that contains:

1. nitrogen
2. phosphorus

Answer 2

1 Amino acid / protein / enzyme / urea / nucleic acid /
chlorophyll / DNA / RNA / / ATP / ADP / AMP / NAD /

2 DNA / RNA / nucleic acid / ATP / ADP / AMP / NADP / TP / GP /
RuBP / phospholipids;

Question 3

Describe the role of microorganisms in producing nitrates from the remains of dead organisms. (3 marks)

Answer 3

1. Saprobiotic (microorganisms / bacteria) break down remains / dead
   material / protein / DNA into ammonia / ammonium;
2. Ammonia / ammonium ions into nitrite and then into nitrate;
3. (By) Nitrifying bacteria / nitrification;

Question 4

Upwelling often results in high primary productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters. (2 marks)

Answer 4

1. Nitrate / phosphate / named ion / nutrients for growth of / absorbed /
   used by plants / algae / producers;
2. More producers / consumers / food so more fish / fish reproduce more /
   fish grow more / fish move to area;

Question 5

Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may
cause the death of fish in fresh water. (5 marks)

Answer 5

1. Growth of algae / surface plants / algal bloom blocks light;
2. Reduced / no photosynthesis so (submerged) plants die;
3. Saprobiotic (microorganisms / bacteria);
4. Aerobically respire / use oxygen in respiration;
5. Less oxygen for fish to respire / aerobic organisms die;

Question 6

Describe a process carried out by microorganisms which adds ammonium
ions to soil. (2 marks)

Answer 6

1. Protein / amino acids broken down (to ammonium ions / ammonia);
2. By saprobionts / saprobiotic (microorganisms).

Question 7

Ploughing aerates the soil.

Explain how ploughing would affect the fertility of the soil.

Answer 7

1. (Fertility increased as) more nitrate formed / less nitrate removed / broken down;
2. Less / no denitrification / process P is decreased / fewer denitrifying bacteria.

Question 8

One farming practice used to maintain high crop yields is crop rotation. This involves growing a different crop each year in the same field.
Suggest two ways in which crop rotation may lead to high crop yields. (2 marks)

Answer 8

1. Grow crops / plants with nitrogen-fixing (bacteria);
2. (Different crops use) different minerals / salts / nutrients / ions (from the
   soil) ;
3. (Different crops have) different pests / pathogens / diseases.

Question 9

Upwelling often results in high primary productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters. (2 marks)

Answer 9

1. Nitrate / phosphate / named ion / nutrients for growth of / absorbed / used by plants / algae / producers;
2. More producers / consumers / food so more fish / fish reproduce more / fish grow more / fish move to area;

Question 10

During the light-independent reaction of photosynthesis, carbon dioxide is converted into
organic substances. Describe how. (6 marks)

Answer 10

1. Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. Produces two glycerate (3-)phosphate / GP;
3. GP reduced to triose phosphate / TP;
4. Using reduced NADP;
5. Using energy from ATP;
6. Triose phosphate converted to glucose / hexose / RuBP / ribulose bisphosphate / named organic substance;

Question 11

The stomata close when the light is turned off.

Explain the advantage of this to the plant. (2 marks)

Answer 11

1. (Because) water is lost through stomata;
2. (Closure) prevents / reduces water loss;
3. Maintain water content of cells.

Question 12

Large areas of tropical forest are still found on some Caribbean islands. The
concentration of carbon dioxide in the air of these forests changes over a period of
24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how
the concentration of carbon dioxide in the air changes:
• over a period of 24 hours
• at different heights above ground. (5 marks)

Answer 12

1. High concentration of / increase in carbon dioxide linked with respiration at night / in darkness;
2. No photosynthesis in dark / night / photosynthesis only in light / day;
3. In light net uptake of carbon dioxide / use more carbon dioxide than produced / (rate of) photosynthesis greater than rate of respiration;
4. Decrease in carbon dioxide concentration with height;
5. (At ground level)
   less photosynthesis / less photosynthesising tissue / more respiration / more micro-organisms / micro-organisms produce carbon dioxide.

Question 13

Farmland previously used for growing crops was left for 30 years and developed into
woodland. During this period, ecologists recorded an increase in the diversity of birds in
the area.
(a) Name the process that resulted in the development of woodland from farmland. (1 mark)

Answer 13

Succession

Question 14

Explain the increase in the diversity of birds as the woodland developed. (3 marks)

Answer 14

1. Greater variety / diversity of plants / insects / more plant / insect species;
2. More food sources / more varieties of food;
3. Greater variety / more habitats / niches;

Question 15

On islands in the Caribbean, there are almost 150 species of lizards belonging to the
genus Anolis. Scientists believe that these species evolved from two species found
on mainland USA. Explain how the Caribbean species could have evolved.
(6 marks)

Answer 15

1. Geographic(al) isolation;
2. Separate gene pools / no interbreeding / gene flow
3. Variation due to mutation;
4. Different selection pressures / different abiotic / biotic conditions / environments / habitats;
5. Different(ial) reproductive success / selected organisms (survive and) reproduce;
6. Leads to change / increase in allele frequency.

Question 16

Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean
islands. Describe how you could use the mark-release-recapture method to estimate
the number of Anolis sagrei on one of these islands. (4 Marks)

Answer 16

1. Capture / collect sample, mark and release;
2. Method of marking does not harm lizard / make it more visible to
   predators;
3. Leave sufficient time for lizards to (randomly) distribute (on island)
   before collecting a second sample;
4. (Population =) number in first sample × number in second sample
   divided by number of marked lizards in second sample / number recaptured.

Question 17

Large areas of tropical forest are still found on some Caribbean islands. The
concentration of carbon dioxide in the air of these forests changes over a period of
24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how
the concentration of carbon dioxide in the air changes:
• over a period of 24 hours
• at different heights above ground. (5 marks)

Answer 17

1. High concentration of / increase in carbon dioxide linked with respiration at night / in darkness;
2. No photosynthesis in dark / night / photosynthesis only in light / day;
3. In light net uptake of carbon dioxide / use more carbon dioxide than produced / (rate of) photosynthesis greater than rate of respiration;
4. Decrease in carbon dioxide concentration with height;

(At ground level)
less photosynthesis / less photosynthesising tissue / more respiration /
more micro-organisms / micro-organisms produce carbon dioxide.

Question 18

Describe how acetylcoenzyme A is formed in the link reaction. (2 marks)

Answer 18

1. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released;
2. Addition of coenzyme A.

Question 19

In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form six-carbon citrate. This reaction is catalysed by the enzyme citrate synthase.
(i) Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. This induces a change in the enzyme, which enables the acetylcoenzyme A to
bind.
Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme. (2 marks)

Answer 19

1. Change (in shape) of active site / active site moulds around the substrate;
2. (Substrate / active site) now complementary.

Question 20

In muscles, some of the lactate is converted back to pyruvate when they are
well supplied with oxygen. Suggest one advantage of this. (1 mark)

Answer 20

(Pyruvate used) in aerobic respiration / (lactate / lactic acid) is toxic /
harmful / causes cramp / (muscle) fatigue.

Question 21

Respiration produces more ATP per molecule of glucose in the presence of oxygen
than it does when oxygen is absent. Explain why. (2 marks)

Answer 21

1. Oxygen is final / terminal (electron) acceptor / oxygen combines with
   electrons and protons;
2. Oxidative phosphorylation / electron transport chain provides (most) ATP
   / only glycolysis occurs without oxygen / no Krebs / no link reaction;