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TR 9-88 MHR • Unit 3 Cycling of Matter in Living Systems Some proteins cause allergic reactions in people who ingest them. Peanuts and shellfish contain some of the most dangerous proteins for people without oral tolerance to peanut and shellfish proteins. Ingestion can result in swelling of the lips and other parts of the body and even anaphylaxis. You may want to use Assessment Checklist 24, Using the Internet for assessment of this activity. ICT OUTCOMES This feature could be used to address ICT Outcomes C.1.4.1, C.7.4.1, or C.7.4.3. CHECK YOUR UNDERSTANDING ANSWERS Student Book Page 348 1. (a) light triggers phototropism (b) gravity triggers gravitropism (c) touch triggers nastic responses 2. Phototropism causes plants to orient their leaves toward the light, intercepting more light for photosynthesis. The added photosynthetic capacity helps the plant generate more energy for growth. 3. Auxin causes the cells of plant stems to grow more quickly. When the cells on one side of a stem are exposed to auxin, their rapid growth causes the stem to curve. 4. Uneven rates of cell growth on opposing sides of a root or stem cause it to bend. 5. Apply The plant stems would be in the same position as they were at the start of the experiment. Auxin is the chemical that causes plant stems to bend toward the light during the phototropic response. Without auxin, the plants would be unable to respond to the light source. 6. Thinking Critically Given that there would be no gravity to stimulate gravitropism in the sunflowers, and assuming light struck all the plants at the same angle, the sunflowers would grow horizontally from the walls, straight downward from the ceiling, and straight up from the floor. 7. Thinking Critically Phototropism is triggered by light. The bending of the plant towards light results from the growth of cells in the side of the stem facing away from the light. The closing of the Venus’s-flytrap leaf in response to touch is the result of a drop of turgor pressure in leaf cells, not their growth. 8. Apply One method would be to examine pea plant cells before and after the winding had occurred, on both sides of the tendril. Microscopic examination of the pea plant cells would reveal if there were changes in their growth patterns. CHAPTER AT A GLANCE ANSWERS Student Book Page 349 (a) Single-celled organisms must be able to meet all the requirements for life. These functions are performed by various organelles within the cell. In multicellular organisms, specialized cells are grouped together to perform specific tasks in the organism. Cells can be organized into tissues, organs, and systems, all of which have specialized structures and functions. (b) Epidermal cells, spongy tissue cells, stomata and guard cells, palisade tissue cells, vascular tissue cells (xylem and phloem). (c) Tissue: clusters of similar cells that share structure and function, e.g., epidermal tissue cells. Organs: multiple tissues that are arranged in combination to form organs, e.g., a plant root is an organ. System: organs and tissues that work together to perform a complex function, e.g., vascular system in plants uses roots, stems, and leaves. (d) Air diffuses through the stomata and into the leaf. Air circulates in the spaces between spongy and palisade tissue cells, and carbon dioxide diffuses down the concentration gradient and into fluid around the cells. Eventually the gas diffuses into the cells themselves. The carbon dioxide is used during photosynthesis. Oxygen produced during photosynthesis passes out of the cells and into the air spaces around cells and eventually out of the plant through the stomata. (e) The loss of water vapour from plants. (f) When stomata are open, water vapour also exits from the leaf. (g) Guard cells: As water moves into guard cells, the water pressure inside the cells increase, causing the cells to swell. As they swell, they push against the cell wall and open the stomata. As water is lost, pressure decreases in the guard cells and they get smaller, also causing the stomata to be smaller. Plant structure: With reduced water available to a plant (i.e., when the soil has dried out), all cells in the plant have reduced turgor pressure, causing the plant to droop. Water transport: In roots, fluid is pushed up because of turgor pressure in the root xylem. This is called root pressure. (h) Roots are covered by epidermal cells. At the root tip, epidermal cells are permeable to water so water enters the root at the tips by osmosis. Dissolved minerals are transported into the root cells via active transport, which keeps the concentration of dissolved solutes in the root cells relatively high. The growth of tiny root hairs, which are outgrowths of single epidermal cells, increases the surface area of Chapter 9 From Cell to Organism: Focus on Plants • MHR the root, allowing for greater absorption. (i) Xylem: transports water and dissolved minerals from the roots to the leaves. Phloem: carries sugar-rich sap from the leaves throughout the rest of the plant. (j) Root pressure pushes fluid up. Transpiration in the leaves generates a pulling force. Because of the physical properties of water (cohesion and adhesion), as water evaporates from leaves, the cohesive force of water causes water to be pulled up the xylem vessels and into the leaves, replacing the water that had evaporated. (k) Cohesion is the tendency of water molecules to adhere to other water molecules, just like links in a chain. During transpiration, this property results in water molecules moving upwards to replace those that have just evaporated. Adhesion is the tendency of water molecules to adhere to certain surfaces, such as the inside of the xylem vessels. Cohesion and adhesion both fight the properties of gravity, allowing water to flow upwards against the force of gravity. (l) Temperature: Water evaporates more rapidly at higher temperatures; therefore, transpiration is greater in warmer environments. Humidity: The rate at which vapour diffuses out of the leaves depends on its concentration gradient. In humid environments, the levels of water vapour in the air are high. Therefore, the water vapour concentration gradient in the air and inside the leaf is small. As a result, transpiration is reduced. Wind: As water vapour diffuses through the stomata, it creates a high-humidity environment just around the leaf. Winds carry the humid air away and replace it with dry air. As the water vapour concentration gradient increases to favour diffusion out of the leaf, transpiration increases. Soil water: The ultimate source of water for transpiration is the soil. If there is too little water in the soil to replace the water lost through transpiration, the plant begins to dry out. Reduced turgor pressure in the guard cells causes the stomata to close, and transpiration slows. If there is a loss of turgor pressure in the stem and leaves, the plants will wilt. (m) Plant tropisms cause plants to respond (positively or negatively) to environmental stimuli, such as light, gravity, and touch. (n) The Darwins’ concluded that the tip of a seedling somehow detects light. (o) Auxin stimulates cell elongation or plant growth. Auxin plays a role in gravitropism and phototropism. Prepare Your Own Summary • Students can use the micrograph of a cross section through a leaf on student book page 314 as a guide for their diagrams. Students should label the following leaf cells: – epidermal cells (protect inner leaf cells) TR 9-89 – palisade tissue cells (main site of photosynthesis) – spongy tissue cells (gas exchange and some photosynthesis) – guard cells (regulate gas exchange) – xylem tissue cells (transport water and minerals) – phloem tissue cells (transport sugars) Students can use Figures 9.11 and 9.13 in the student book as a reference for drawing cross sections through a plant stem and root. Diagrams should include labels for xylem and phloem tissue cells. • leaf hair Water and minerals enter leaf through xylem. palisade tissue cells air space leaf vein spongy tissue cells Sugar exits leaf through phloem. guard cell CO2 enters leaf through stoma. O2 and H2O exit leaf through stoma. • Students’ diagrams should address the following points: – transpiration from the leaves draws water up from the roots and stem – turgor pressure keeps non-woody plants upright and causes stomata to open – root pressure forces water up from the roots – as sugars from the leaves are transported into other plant cells, water follows the sugar by osmosis • Students’ diagrams could address any three of the following environmental effects on transpiration: increased/decreased humidity (decreased/increased transpiration); increased air movement (increased transpiration); increased/decreased soil water content (increased/decreased transpiration); increased/decreased temperature (increased/decreased transpiration); increased/decreased sunlight (increased/decreased transpiration). CHAPTER 9 REVIEW ANSWERS Student Book Pages 350–351 Key Terms See glossary in the student book. TR 9-90 MHR • Unit 3 Cycling of Matter in Living Systems Understanding Key Concepts 1. (a) a xylem vessel is a tissue (b) a leaf is an organ (c) a root hair is a cell (d) a sheet of epidermal cell is a tissue (e) a stem is an organ 2. The stomata permit gas exchange across the leaf surface. Guard cells surround each stoma and regulate the size of the stomatal opening. 3. I. cuticle II. epidermis III. palisade tissue cells IV. spongy tissue cells V. vascular tissue (xylem and phloem) VI. stomata and guard cells 4. Gas exchange on leaves occurs through stomata. Lenticels occur in the bark of woody plants, which have layers of dead cork cells and waxy substances that prevent gas exchange with the environment. (Plants that are not woody will have some gas exchange occurring at the surface of stems and roots.) Lenticels allow some gas exchange between the plant and the environment. 5. (a) In response to hot, dry weather, the guard cells lose their turgidity, which closes the stomata. Water vapour is, therefore, unable to exit the leaves. (b) In general, the guard cells are turgid during the day. An opening (a stoma) results between each pair of swollen guard cells. Carbon dioxide, oxygen, and water vapour can pass in and out of the leaf through the stomata. At night, water flows out of the guard cells, causing them to lose their turgidity and close the stomata. 6. (a) palisade tissue cells – site of photosynthesis (b) guard cells – control the opening and closing of the stomata (c) xylem vessels – transport water throughout the plant (d) leaf epidermal cells – protect the inner tissues of the leaf (e) phloem vessels – transport sugars throughout the plant (f) root hair cells – take up water from the soil 7. Plant responses to stimuli include gravitropism, phototropism, sleep movements, and nastic response 8. (a) To perform photosynthesis, plants require light energy, carbon dioxide, and water. Sunlight (or an artificial light) reaching the photosynthetic cells of the leaf is trapped by chlorophyll in the chloroplasts. The light energy is used to power the reactions that make sugars. Water travels from the roots to the leaves through the xylem vessels. Carbon dioxide enters the leaf through open stomata, and diffuses into the leaf cells. (b) Photosynthesis results in the production of oxygen and carbohydrates. Developing Skills 9. Students’ drawings will vary but they should show the following information: • Water from the soil enters the xylem in the root. This happens because root cells actively transport minerals into the xylem. This increases the mineral concentration in the xylem sap and sets up a concentration gradient that results in water diffusing into the root xylem by osmosis. Water flows in and creates root pressure in the xylem vessels, which pushes the water column up. • Tension created by transpiration at the leaves creates a force that pulls the water in thy xylem in the roots and stems upward to the leaves. • The water column is held together by cohesion and adhesion of water molecules to the xylem cell wall keeps the water column in place. water vapour lost through transpiration sugars created in leaves during photosynthesis and transported through the plant in the phloem water and minerals flow into roots and through the plant in the xylem 10. (a) Line B best represents the control. (b) Line C best represents the plant in the bag. (c) Line A best represents the plant placed in front of the fan. (d) The environment of a plant affects its water loss. Moving air around the leaves increases the rate of transpiration. 11. Province D likely has the least rainfall, and province A likely has the greatest rainfall. The number of stomata would be expected to increase with increasing rainfall. Because water is lost through stomata, plants in arid regions would tend to have fewer stomata. Problem Solving/Applying 12. A flower is an organ. It is composed of tissues, which are in turn composed of specialized cells. Differences in the tissue structures are observable at the macroscopic level. For example, petals look and feel different from sepals. A flower could be dissected and examined microscopically to show that the cells making up the different flower tissues also Chapter 9 From Cell to Organism: Focus on Plants • MHR have different structures. These structures may provide clues about the cells’ specialized functions. 13. (a) Cells that carry out photosynthesis contain chloroplasts and are usually green. (Some plants have other pigments that can mask the green of chlorophyll.) (b) Generally, the green parts of plants are capable of photosynthesis although leaves are specialized for this process. 14. Students should design an experiment where plants (or seeds) are exposed to different levels of light and are oriented in different ways. The experiment could have four sprouted seeds (kept in a plastic bag with a moist paper towel), which are kept under the following conditions: (1) seedlings in direct light, initially oriented with roots pointing straight down and stems pointing directly up; (2) seedlings in direct light, initially oriented with roots pointing up and stems pointing straight down; (3) seedlings in a dark box with one opening for light, initially oriented with roots pointing straight down and stems pointing directly up; (4) seedlings in a dark box with one opening for light, initially oriented with roots pointing directly up and stems pointing straight down. All of the seeds must be treated in the same way, except for the above conditions. 15. Sugar, minerals, and other nutrients are pumped into leaf phloem by active transport. As the sugar concentration increases in the phloem cells, water follows by osmosis. Phloem sap then flows down a pressure gradient, from leaves to roots. Phloem sap is forced through pores in the phloem cell walls and flows into neighbouring phloem cells, where the pressure is lower. Critical Thinking 16. When plants are actively photosynthesizing, they transpire as water escapes from the stomata. When this happens, the plant produces a lot of food and grows well; however, there is also the danger of dehydration. As the plant begins to lose water, turgidity in the guard cells decreases and the stomata begin to close; thus photosynthesis decreases as well. 17. Roots are highly permeable, particularly at their tips, as they need to actively absorb water to supply the rest of the plant. Leaves are covered in a waxy cuticle to limit the amount of water lost through the leaves. Water vapour can only exit the leaves through the stomata. 18. An amoeba has a greater chance of survival, as it is a unicellular organism and contains all of the organelles it requires for carrying out life functions. A single cell removed from a multicellular animal would not survive because by itself it cannot carry out all of the functions required for life. TR 9-91 19. Carbon dioxide is used within the cells of the leaf during photosynthesis. 20. As most water loss in plants occurs through the leaves, plants with reduced leaf area lose less water. This is a benefit to plants that are adapted to arid environments, because they conserve what little water is available to the plant. However, the reduced leaf area also reduces the amount of photosynthesis possible. As a result, these plants often grow slowly. This item encourages students to synthesize the knowledge they have learned from Chapters 7, 8, and 9. Encourage students to make connections between cell structures and functions and the functioning of multicellular organisms. UNIT 3 ASK AN EXPERT Student Book Page 352–353 SCIENCE BACKGROUND • Dr. Miller’s source for stem cells from adult skin is much less controversial than using fetal stem cells. Stem cells from adult skin can produce a number of different cell types, including the type of neural cells needed to potentially help patients recover from spinal cord injury or Parkinson’s disease. • Dr. Miller is a co-author of the paper, “Isolation of Multipotent Adult Stem Cells from the Dermis of Mammalian Skin” (by J.G. Toma, M. Akhavan, K.J.L. Fernandes, F. Barnabé-Heider, A. Sadikot, D.R. Kaplan, and F.D. Miller), which was published in the scientific journal, Nature Cell Biology. The paper can be viewed on line at http://www.nature.com/ncb/future_issues/. • Dr. Miller and her colleagues isolated stem cells from the skin of adult rodents and their research showed that the cells would proliferate and differentiate in culture to produce different cell types, including neurons, glial cells, smooth muscle cells, and fat cells. The research team harvested stem cells from the skin of juvenile and adult rodents. Human studies have indicated that similar cells are present in adult human skin. • Dr. Miller’s work is important because it may mean that stem cells harvested from a patient could then be used to help treat the same individual. This would minimize complications that are often seen in donor transplantations where the patient’s body rejects the donor’s cells.