JWSS Biology Chapter 8 Transport in Plants

4E/5N Science (Biology) Notes 1 JURONG WEST SECONDARY SCHOOL SECONDARY FOUR/FIVE – SCIENCE BIOLOGY Chapter 9.2: TRANSPORT IN PLANTS Learning Outcomes: Candidates should be able to: a) identify (label) the cellular and tissue structure of a dicotyledonous leaf, as seen in transverse section using the light microscope and describe the significance of these features in terms of their functions, such as the • distribution of chloroplasts for photosynthesis • stomata and mesophyll cells for gaseous exchange • vascular bundles for transport (xylem + phloem) b) identify the positions of and state the functions of xylem vessels and phloem in sections of a herbaceous dicotyledonous leaf and stem, under the light microscope c) explain how the structure of a root hair cell is suited for its function of water and ion uptake d) State that transpiration is the loss of water vapour from the stomata e) (essay) Briefly explain the movement of water through the stem in terms of transpiration pull f) investigate and explain: • the effects of variation of air movement, temperature, humidity and light intensity on transpiration rate • how wilting occurs Define the term translocation as the transport of food (mainly sucrose) in the phloem tissue Quick recap from previous chapter What do you remember from your lesson on Nutrition in Plants? Where does photosynthesis take place in the plant? Mesophyll cells, can take place in the leaf and stem. What are the necessary elements for photosynthesis? Water, carbon dioxide, light energy, chlorophyll How do water and minerals reach the leaves? Via the xylem How do manufactured food reach the leaves? Via the phloem Linking it back to Transport in Plants: 1. What are the two transport vessels that you know in plants: Xylem and phloem 2. Importance of these transport vessels: Transport water and sugars

4E/5N Science (Biology) Notes 2 3. Which parts of the plants do you find these transport vessels? b) identify the positions of and state the functions of xylem vessels and phloem in sections of a herbaceous dicotyledonous leaf and stem, under the light microscope ACTIVITY: What are vascular bundles? ______________transport vessels__________________________ You will be learning about the vascular bundles in different parts of the plants. Identify the xylem and phloem and which part of the plant, the vascular bundle belongs to. Vascular bundle in plant’s ___root_______ Vascular bundle in plant’s ___stem______ Vascular bundle in plant’s _____leaf_______

4E/5N Science (Biology) Notes 3 a) identify the cellular and tissue structure of a dicotyledonous leaf, as seen in transverse section using the light microscope and describe the significance of these features in terms of their functions, such as the o distribution of chloroplasts for photosynthesis o stomata and mesophyll cells for gaseous exchange o vascular bundles for transport What is transport? • Transport is the movement, circulation or flow of substances within living organisms. Functions of the plant transport system • A way of moving water and mineral salts from the roots to the leaves, [XYLEM] • A way of moving sucrose and amino acids from the leaves to other parts of the plant while it is photosynthesising. [phloem] Substances transported in plants 1. Useful ions and small molecules such as Mg2+, K+, NO3-, C6H12O6, and amino acids, dissolved in water for constructional or other functional purposes. 2. Waste products like catabolised enzymes and hormones for excretion. 3. Gases or vapours e.g. O2, CO2 dissolved in water and water vapour. Stretch yourself • How is the plant transport system different from the human circulatory system? In case of human body, the circulation of fluids takes place due to the presence of heart, which acts as a pump. In comparison, there is no pumping mechanism in a plant and the water movement occurs mainly via transpiration pull.

4E/5N Science (Biology) Notes 4 The transport tissues The 2 transport (vascular) tissues of flowering plants are the xylem and phloem. • Xylem transports water and mineral salts from the roots to all parts of the plant. • Phloem transports manufactured food (sucrose and amino acids) from the leaves to other parts of the plant. 1. The Xylem vessel Characteristics (structure) of xylem vessels: 1. Xylem vessels are long and narrow. 2. They are hollow and are without protoplasm (therefore dead cells). 3. The cells are joined end to end, without any cross walls and extend as continuous tubes from roots to stems and into the leaves. 4. The cellulose cell wall is strengthened by lignin. The xylem vessels have 2 functions: 1. Conducting water, with its dissolved mineral salts, from the roots to the stems and leaves. 2. Providing mechanical support within the plant. How the xylem is adapted for its function: 1. It has an empty lumen without protoplasm. This reduces resistance to water flowing through the xylem, allowing water to be conducted /transported up the plant. 2. It has lignified cell walls to provide mechanical support for the plant. 3. The narrow lumen helps to draw water up by capillary action* (*See TB page 195) Xylem vessel showing different patterns of lignification

4E/5N Science (Biology) Notes 5 2. The Phloem vessel Characteristics of phloem vessels: 1. Phloem is a living tissue 2. They have cytoplasm The function of the phloem vessel: • Phloem transports manufactured food (sucrose and amino acids) from the leaves to other parts of the plant. • By Translocation (Refer to the diagram) Definition: Translocation is the movement of manufactured food such as sucrose from the green parts of the plants to the rest of the plant by the phloem vessels. Translocation Studies (refer to TB pages 189 – 191) Discuss with your partner, how these experiments can help to determine the rate & direction of movement of substances? Experiment 1: Ringing Inference: Phloem carries materials from the leaves to other parts of the plant. ____________________________________________________________________________________ _____________________________________________________________________________

4E/5N Science (Biology) Notes 6 Experiment 2: Radioactive isotopes Experiment 3: Using Aphids in Translocation Studies → Refer to TB page 190 Low-level radioactive isotopes emit radioactivity, which can be measured. Plants absorb the isotope through their leaves. The radioactive carbon is converted to glucose. Inference: __carbon dioxide is needed to produce glucose. Manufactured food (sucrose) is transported by the phloem. __________________________________ _________________________________

4E/5N Science (Biology) Notes 7 c) Explain how the structure of a root hair cell is suited for its function of water and ion uptake The structure & function of the root hair 1. Long and narrow extension / protrusion from the epidermal cells. • To increase surface area to volume ratio to increase rate of absorption of water. 2. Large central vacuole. • To store more water and minerals. 3. Cell sap contains sugars, amino acids and salts. • It is more concentrated than soil → lower water potential than soil • Water can enter cell by osmosis. Entry of water into plant from roots • Water in the soil has a higher water potential than the root hair cell sap. Water is absorbed into the root hair cells by osmosis. • The entry of water dilutes the sap. Water will then pass through neighbouring cells via osmosis until it reaches the xylem and moves up the plant. • Dissolved mineral salts are absorbed by diffusion and active transport. T.S of Dicot Root Root hair cell Scan to