44 Unit 1 Metabolic Processes Copyright © 2003 Nelson

CHAPTER 3 PHOTOSYNTHESIS

Reflect on Your Learning

(Page 136) 1. (a) Cyanobacteria are prokaryotic organisms with their photosynthetic pigments in their cell walls, whereas photosynthetic

protists are eukaryotic organisms with their photosynthetic pigments located in thylakoid membranes inside their chloroplasts.

(b) Only photosynthetic protists have their photosynthetic pigments located in chloroplasts. 2. Endosymbiotic theory states that today’s plant cells were originally produced when ancestral eukaryotic cells devoid of an

organelle similar to a chloroplast engulfed a cyanobacterium. The two organisms formed a symbiotic relationship, with the cyanobacterium eventually developing into the organelle we know as a chloroplast.

3. (a) 6CO2(g) + 6H2O(l) light energy C6H12O6(aq) + 6O2 (g)

(b) The O2 molecules produced by photosynthesis come from H2O molecules. (c) Water is used as both a reactant and a product in photosynthesis. 4. Deciduous leaves are green in the summer due to the high levels of chlorophyll pigments in them and are yellow, orange,

or red in the fall because chlorophyll pigments are degraded, while the carotenoid and xanthophyll pigments are not. 5. Carbon fixation means the incorporation of carbon from carbon dioxide into carbohydrates. 6. Plants obtain ATP from photosynthesis via the generation of an electrochemical potential of protons, which is used by

ATP synthase to create ATP. 7. Photosynthesis requires CO2, which is produced by cellular respiration, and produces O2 and glucose, which are the

reactants in cellular respiration.

Try This Activity: Do Plants “Exhale”?

(Page 137) (a) The glowing splint should ignite into a bright flame when placed into the gas-filled test tube. (b) The gas that collected would be oxygen, which is produced as a product of photosynthesis. (c) We know the gas came from the plant, as the test tube with no plant (the control) did not accumulate any gas, as indicated

by the glowing splint test. 3.1 PHOTOSYNTHETIC ORGANISMS

Try This Activity: Opening and Closing Stomata

(Page 142) Students should observe stomata on both the upper and lower surfaces of terrestrial plants. They should note that the underside of the leaf generally has more stomata than the topside. They should also note that the greater the humidity, the larger the stomatal openings. Depending on the moisture levels in the soil, the stomata will be open or closed. Generally, a plant will have its stomata open when there is sufficient moisture in the soil to replace moisture lost by transpiration.

Explore an Issue Take a Stand: Can Plants Cure Sick Building Syndrome?

(Page 144) Statement: Plants may be used as a treatment for sick building syndrome. Student answers will vary depending on research. i) Symptoms of SBS include headaches; eye, nose, and throat irritation; a dry cough; dry or itchy skin; dizziness and nausea;

difficulty concentrating; fatigue; and sensitivity to odours. ii) Possible causes include chemical contaminants from outdoor sources such as vehicle exhausts, plumbing vents, and

building exhausts, and chemical contaminants from indoor sources such as adhesives, upholstery, carpeting, copy machines, cleaning agents, and pesticides. Biological contaminants include pollen, bacteria, viruses, and moulds.

iii) Two components to identifying SBS are 1. If several people who inhabit the same building complain of common symptoms associated with SBS. 2. Reactions are triggered when in the building and are not triggered when not in the building.

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Copyright © 2003 Nelson Chapter 3 Photosynthesis 45

iv, v) A study conducted by NASA indicated that some plants such as the spider plant (Ficus spp.) absorb toxic chemicals such as formaldehyde from surrounding air. The American Environmental Protection Agency (EPA) reviewed the evidence from experiments such as this and indicated that although it is true that plants remove carbon dioxide from air, the ability of plants to control indoor air pollution is not well established.

Section 3.1 Questions

(Pages 145–146)

Understanding Concepts 1. (a) Wolves and rabbits are heterotrophs and the lettuce is an autotroph. (b) Lettuce relies on sunlight to provide energy to drive photosynthesis and make chemical potential energy, in the form of

sucrose or starch. Because wolves and rabbits are heterotrophs, they cannot make their own chemical potential energy; therefore, they must consume it. The rabbit consumes its chemical potential energy in the form of lettuce, whereas the wolf consumes its energy in the form of the rabbit.

2. (a) All photosynthetic organisms contain the molecule chlorophyll to capture electromagnetic radiation. (b) Chlorophyll molecules are located in infoldings of the cell membrane of cyanobacteria and not in membrane-bound

organelles. 3. (a) The association between prehistoric cyanobacteria and the ancestor of eukaryotic cells provided protection from harsh

conditions for the bacteria, by the eukaryotic cell, and food (glucose) for the eukaryotic cell, produced by the bacteria. (b) There are two pieces of evidence that support the endosymbiosis between eukaryotes and cyanobacteria, rather than

between prokaryotes and the bacteria: (1) Both cyanobacteria and plant chloroplasts contain chlorophyll a, and (2) they both have many similar gene sequences.

4. (a) Broad leaves are thin to minimize the distance that gases, such as carbon dioxide, must travel from the stomata to the chloroplasts, thereby maximizing gas diffusion.

(b) If chloroplasts were removed from a leaf, the leaf would appear clear or purple, depending on the presence of anthocyanins in the vacuoles of the epidermal cells.

(c) Stomata aid in photosynthesis by allowing carbon dioxide to diffuse into the leaf, where it can be captured by the Calvin cycle. Stomata also help regulate the exchange of oxygen with the atmosphere and allow water vapour to escape the leaves via transpiration.

(d) Proton pumps regulate the size of the stomatal pores by pumping protons out of the guard cells, creating an electrochemical gradient, which causes K+ ions to move into the guard cells. Water follows the K+ ions, causing a rise in osmotic pressure that opens the stomatal pore. When the proton pumps cease moving protons out of the guard cells, the osmotic pressure drops and the pore closes.

(e) When the Sun rises in the morning, light energy activates receptors in guard cell membranes. These receptors stimulate the proton pumps, which aid in opening the stomata. Additionally, mesophyll cells begin photosynthesizing and using up CO2 that has accumulated overnight. Decreasing CO2 concentrations around guard cells causes osmosis, opening the stomata. At the end of the day, sucrose concentration in the guard cell decreases, closing the stomatal pores.

5. (a) A: granum B: stroma C: inner envelope membrane D: outer envelope membrane (b) The mitochondrion has two membranes, with the inner membrane folded into the interior, while the chloroplast has a

double membrane system with a separate third membrane system, the thylakoid membrane, that houses chlorophyll molecules.

6. The overall equation for photosynthesis requires the input of light energy, whereas the overall equation for cellular respiration produces chemical potential energy, in the form of ATP.

7. (a) Molecule A is chlorophyll. (b) H: porphyrin ring P: phytol chain

Copyright © 2003 Nelson Chapter 3 Photosynthesis 45

iv, v) A study conducted by NASA indicated that some plants such as the spider plant (Ficus spp.) absorb toxic chemicals such as formaldehyde from surrounding air. The American Environmental Protection Agency (EPA) reviewed the evidence from experiments such as this and indicated that although it is true that plants remove carbon dioxide from air, the ability of plants to control indoor air pollution is not well established.

Section 3.1 Questions

(Pages 145– 146)

Understanding Concepts 1. (a) Wolves and rabbits are heterotrophs and the lettuce is an autotroph. (b) Lettuce relies on sunlight to provide energy to drive photosynthesis and make chemical potential energy, in the form of

sucrose or starch. Because wolves and rabbits are heterotrophs, they cannot make their own chemical potential energy; therefore, they must consume it. The rabbit consumes its chemical potential energy in the form of lettuce, whereas the wolf consumes its energy in the form of the rabbit.

2. (a) All photosynthetic organisms contain the molecule chlorophyll to capture electromagnetic radiation. (b) Chlorophyll molecules are located in infoldings of the cell membrane of cyanobacteria and not in membrane-bound

organelles. 3. (a) The association between prehistoric cyanobacteria and the ancestor of eukaryotic cells provided protection from harsh

conditions for the bacteria, by the eukaryotic cell, and food (glucose) for the eukaryotic cell, produced by the bacteria. (b) There are two pieces of evidence that support the endosymbiosis between eukaryotes and cyanobacteria, rather than

between prokaryotes and the bacteria: (1) Both cyanobacteria and plant chloroplasts contain chlorophyll a, and (2) they both have many similar gene sequences.

4. (a) Broad leaves are thin to minimize the distance that gases, such as carbon dioxide, must travel from the stomata to the chloroplasts, thereby maximizing gas diffusion.

(b) If chloroplasts were removed from a leaf, the leaf would appear clear or purple, depending on the presence of anthocyanins in the vacuoles of the epidermal cells.

(c) Stomata aid in photosynthesis by allowing carbon dioxide to diffuse into the leaf, where it can be captured by the Calvin cycle. Stomata also help regulate the exchange of oxygen with the atmosphere and allow water vapour to escape the leaves via transpiration.

(d) Proton pumps regulate the size of the stomatal pores by pumping protons out of the guard cells, creating an electrochemical gradient, which causes K+ ions to move into the guard cells. Water follows the K+ ions, causing a rise in osmotic pressure that opens the stomatal pore. When the proton pumps cease moving protons out of the guard cells, the osmotic pressure drops and the pore closes.

(e) When the Sun rises in the morning, light energy activates receptors in guard cell membranes. These receptors stimulate the proton pumps, which aid in opening the stomata. Additionally, mesophyll cells begin photosynthesizing and using up CO2 that has accumulated overnight. Decreasing CO2 concentrations around guard cells causes osmosis, opening the stomata. At the end of the day, sucrose concentration in the guard cell decreases, closing the stomatal pores.

5. (a) A: granum B: stroma C: inner envelope membrane D: outer envelope membrane (b) The mitochondrion has two membranes, with the inner membrane folded into the interior, while the chloroplast has a

double membrane system with a separate third membrane system, the thylakoid membrane, that houses chlorophyll molecules.

6. The overall equation for photosynthesis requires the input of light energy, whereas the overall equation for cellular respiration produces chemical potential energy, in the form of ATP.

7. (a) Molecule A is chlorophyll. (b) H: porphyrin ring P: phytol chain

46 Unit 1 Metabolic Processes Copyright © 2003 Nelson

(c)

Applying Inquiry Skills 8. (a) Question: What is the effect of light on the closing and opening of stomata? (b) Hypothesis: The stomata will open when the light is on the leaf and will close in darkness. (c) Experimental design: 1. Obtain two plants and place one in darkness and one in light conditions. 2. Apply nail polish to the lower surface of the each leaf, peel off, and view under the microscope. 3. Count the number of open stomata in five fields of view for both plants. 4. Plot data on a bar graph and interpret.

Making Connections

9. (a) Cyanobacterial blooms are explosive population increases in cyanobacteria because of an influx of nutrients into an ecosystem. These nutrients are generally from nitrates and phosphates in fertilizers and phosphate detergents.

(b) Cyanobacterial blooms adversely affect humans and other animals by producing toxins. For instance, when the cyanobacterium Microcystis aeruginosa forms blooms, a toxin called microcystin is produced. This toxin causes headache, vomiting, diarrhea, and itchy skin. Small animals may become sick and die once exposed to the toxin.

(c) Cyanobacterial blooms are bad for the environment as they disrupt the aquatic food web and rob the water of precious oxygen when the cyanobacteria dies and starts to decompose.

(d) Use phosphate-free detergents in areas where untreated water may enter an aquatic ecosystem. Apply fertilizers in such a way as to reduce runoff or reduce the amount of nitrates and phosphates entering as aquatic ecosystem.

10. (a) Carnivorous plants occupy a grey zone. They are mostly autotrophs, like other plants, but obtain some of their nutrients heterotrophically.

(b) Carnivorous plants digest animals to obtain some of their nutritional requirements, however, they may survive using only photosynthesis as a food source.

11. (a) chlorophyll-containing gum, chlorophyll-containing shoe deodorizers, chlorophyll liquid tonic pure planet chlorella: available at health food stores wheat grass juice bodymint (b) Pure planet chlorella

• available as tablets • used to lower cholesterol, reverse progression of atherosclerosis, aid body in breakdown of heavy metals, enable

better absorption of polysaccharides in cell wall • allows for higher absorption and digestion of essential nutrients

Wheat grass juice • in juice form or can be eaten directly (chewed) • increases hemoglobin production, helps prevent tooth decay, creates unfavourable environment for “ unfriendly”

bacteria growth, neutralizes toxins, improves digestion, reduces high blood pressure

Copyright © 2003 Nelson Chapter 3 Photosynthesis 47

Bodymint • deodorant taken in tablet form • made of chlorophyllin, a special derivative of chlorophyll • one tablet taken each morning and evening

3.2 LIGHT ENERGY AND PHOTOSYNTHETIC PIGMENTS

Section 3.2 Questions

(Pages 154– 155)

Understanding Concepts

1. 6CO2(g) + 6H2O(l) + light energy C6H12O6(aq) + 6O2(g) + 6H2O(l) 2. The products of the light reaction of photosynthesis are oxygen, ATP, and NADPH. 3. (a) Light, or electromagnetic radiation, is a form of energy that travels at 3 × 108 m/s in the form of photons. (b) A photon is a discrete packet of light. (c) As wavelength gets longer, the energy in a photon decreases, and as wavelength increases, the energy increases. (d) Green light possesses a higher energy value than red light because it has a shorter wavelength.

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