Science Ahead An International Lower Secondary Science Course © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 CHAPTER 1 Photosynthesis and Transport in Plants How does a tree get its food and energy? © 2020 Marshall Cavendish Education Pte Ltd How does water from the soil reach the leaves that are high up on the tree? Science Ahead Stage 8 Chapter 1 Photosynthesis and Transport in Plants What Will You Learn in This Chapter? • Explore how carbon dioxide, water and light are needed for photosynthesis. • Explore how photosynthesis produces biomass and oxygen. • Describe how water and mineral salts are absorbed and transported in flowering plants. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 Chapter 1 Photosynthesis and Transport in Plants 1.1 Photosynthesis 1.2 Absorption and Transport of Water and Mineral Salts © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis At the end of this section, you should be able to answer the following questions: What is photosynthesis? What are needed and produced by plants during photosynthesis? How do plants obtain water and mineral salts from the soil? © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis What is biomass? Where did the log get its mass from? • The log was cut from a tree. • The tree needed food and energy to grow, and to make new cells and tissues to gain mass. • The log has mass as it is made up of cells and tissues. • Matter that is made up of cells and tissues is called biomass. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis Experiment on plant growth In the 1960s, Jan Baptist van Helmont, a Belgian physician, carried out an experiment on plant growth. He found that the gain in the mass of the willow tree did not come from the soil. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis Experiment on plant growth (cont’d) How do plants obtain food? • van Helmont wrongly concluded that the gain in the mass of the willow tree came from the water it was given. • Plants do not get food from the soil. Plants make food through photosynthesis. • Photosynthesis is the process by which plants make food in the presence of light using carbon dioxide and water. • The gain in mass as a plant grows comes from the food that the plant makes. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis What are needed and produced during photosynthesis? • Sunlight, water and carbon dioxide are needed for photosynthesis. • Sugar and oxygen are produced during the process. Carbon dioxide © 2020 Marshall Cavendish Education Pte Ltd presence of light Water Sugar Oxygen Science Ahead Stage 8 1.1 Photosynthesis Chlorophyll in green leaves What makes the leaves green? • Leaves are green because they contain a green pigment called chlorophyll. • Chlorophyll captures sunlight. • Light captured by the chlorophyll is used to make food during photosynthesis. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis Gas exchange during photosynthesis How does carbon dioxide needed for photosynthesis enter the plant? • Bubbles are observed when a leaf is submerged in warm water. Leaf submerged in warm water • These bubbles signify that gases enter and leave the leaf. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis Gas exchange during photosynthesis (cont’d) • Carbon dioxide enters the plant through tiny openings called stomata, which are usually found on the underside of a leaf. • Excess oxygen produced during photosynthesis leaves through the stomata. • Water leaves the plant through the stomata in the form of water vapour. © 2020 Marshall Cavendish Education Pte Ltd stoma Science Ahead Stage 8 1.1 Photosynthesis The use of oxygen and sugar The oxygen produced during photosynthesis is used by plants for an essential life process called respiration. © 2020 Marshall Cavendish Education Pte Ltd The sugar made by plants is mostly converted to starch. This starch is stored in different parts of plants. Science Ahead Stage 8 1.1 Photosynthesis The use of oxygen and sugar (cont’d) Starch is stored in different parts of plants. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis How do we know if a leaf has made food? A leaf will contain starch if it has made food. Iodine solution can be used to test if starch is present in the leaf. A © 2020 Marshall Cavendish Education Pte Ltd B Science Ahead Stage 8 1.1 Photosynthesis The Sun as the primary source of energy • Plants make use of light energy from the Sun to make food during photosynthesis. • The food produced by plants becomes the energy source for animals, which feed on plants directly or indirectly. • The energy in plants and animals is derived from the Sun. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis Key Points • Matter that is made up of cells and tissues is called biomass. • Photosynthesis is the process by which plants use carbon dioxide and water in the presence of light to make food. • The gain in mass as plants grow comes from the food that the plants make. • Plants make food in the form of sugar during photosynthesis. Oxygen is also produced during photosynthesis. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.1 Photosynthesis Key Points (cont’d) • The leaves and some parts of the plants contain a green pigment called chlorophyll to capture sunlight. • Carbon dioxide, which is needed for photosynthesis, enters a plant through the stomata. Stomata are usually found on the underside of leaves. • Excess oxygen produced during photosynthesis leaves the plant through the stomata. • Excess sugar produced during photosynthesis is stored in different parts of a plant as starch. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 Chapter 1 Photosynthesis and Transport in Plants 1.1 Photosynthesis 1.2 Absorption and Transport of Water and Mineral Salts © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Root hair and its function What is the function of the tiny hairs growing out from the root? • Roots absorb water and dissolved mineral salts from the soil. • The root hairs help absorb water much more quickly. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts At the end of this section, you should be able to answer the following questions: How are water and mineral salts absorbed by plants? What is transpiration? How does the transport system of plants with vascular tissues work? © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Absorption of water and mineral salts Water moves into the root hair cells when the soil has a higher concentration of water than the root hair cells. Dissolved mineral salts, such as nitrates and phosphates, are absorbed by the roots when the soil has a higher concentration of mineral salts than the root hair cells. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts How are water and mineral salts transported by flowering plants? • Flowering plants have a transport system to transport minerals around the plant. • Xylem and phloem are the two network vessels of flowering plants. • Phloem transports food made in the leaves during photosynthesis to the other parts of the plant. • Xylem transports water and mineral salts from the roots to other parts of the plant. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Transport system in flowering plants phloem xylem Xylem and phloem are found throughout the plant, from the roots to the stem and to the veins in the leaves. phloem xylem © 2020 Marshall Cavendish Education Pte Ltd After the water and mineral salts are absorbed by the root hairs, they move from cell to cell until they reach the xylem in the roots. Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Transport system in flowering plants (cont’d) The network vessels – xylem and phloem – are often found side by side, forming vascular bundles. upper epidermis stoma vein xylem phloem © 2020 Marshall Cavendish Education Pte Ltd lower epidermis Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Movement of water and mineral salts Water is constantly evaporating through the stomata in the leaves. Water and mineral salts are absorbed by the roots, and travel through the plant. Water and mineral salts travel through the plant. Water is constantly evaporating through the stomata. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts What is xylem and its function? • The xylem is made up of dead cells with thick and stiff walls at the side of the vessel. • The cells join end to end to form a vessel. • Water and mineral salts move up the xylem vessels. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Why do water and mineral salts move up against gravity instead of flowing down? • Water and mineral salts are pulled up by the xylem vessels because of transpiration. • Transpiration is the process by which water evaporates from a plant’s leaves, stem or flowers. The roots absorb more water to replace water that is lost from the leaves and other parts of the plants. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Key Points • Roots have numerous tiny root hairs to absorb water and dissolved mineral salts quickly from the soil or surroundings. • A plant with vascular tissues, such as a flowering plant, has a transport system made up of xylem and phloem vessels. • The phloem vessel transports food made by the leaves to the other parts of the plant. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Key Points (cont’d) • The xylem vessel transports water and dissolved mineral salts from the roots to the other parts of the plant. • Water and dissolved mineral salts that are absorbed by the roots are drawn up through the xylem vessels to the stem and leaves as transpiration takes place. © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 1.2 Absorption and Transport of Water and Mineral Salts Chapter review and extension Reflection (Workbook page 5) Review Questions (Student Book page 12) Revision Worksheet 1 (Workbook pages 6–8) Think-tank (Student Book page 12) © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8 Acknowledgements • • • • • • • • • • • • Slide 2, person standing next to a kapok tree © ammit/123rf.com Slide 6, log © givaga/123rf.com Slide 9, leaves © Sataporn Jiwjalaen/123rf.com Slide 10, tree © zerbor/123rf.com Slide 12, leaf submerged in warm water © Aleksei Filatov/Dreamstime.com Slide 14, carrots © Utima/123rf.com; potatoes © Pincarel/123rf.com; green bananas © Preeda Singhavorasub/123rf.com; paddy rice seed © Piyanart Pila/123rf.com Slide 15, leaves covered with iodine solution © CORDELIA MOLLOY/Science Photo Library Slide 20, root of a seedling © buccaneer/123rf.com Slides 22 and 26, cross-section view of a plant with its roots © Ifong/123rf.com Slides 23, 24 and 25 sunflower © ifong/123rf.com Slide 24, cross-section of a stem © Kontakt931/Dreamstime.com; 24, cross-section of a root © Pitsanu Kraichana/123rf.com Slide 25, cross-section of a leaf © designua/123rf.com © 2020 Marshall Cavendish Education Pte Ltd Science Ahead Stage 8
