1. Topic 4.4c Specialised Plant Cells

2. Specification aims 5 Compare the structures, position in the stem and function of sclerenchyma fibres (support) and xylem vessels (support and transport of water and mineral ions). 4 Explain how the arrangement of cellulose microfibrils in plant cell walls and secondary thickening contribute to the physical properties of plant fibres, which can be exploited by humans. 7 Identify sclerenchyma fibres and xylem vessels as seen through a light microscope. 8 Describe how to determine the tensile strength of plant fibres practically. 9 Explain the importance of water and inorganic ions (nitrate, calcium ions and magnesium ions) to plants. 10Describe how to investigate plant mineral deficiencies practically.

3. Tubes for transport and strength Tall plants need support and water and mineral transport. Which structures make this possible? Xylem tissues Sclerenchyma fibers

4. Three types of plant tissue Epidermis: outer layer of tissue Ground tissue: specialised cells for photosynthesis, storage and support. Parenchyma (cells with thin primary walls that retain their cytoplasm and contents) Collenchyma (cells with thick primary walls that retain their cytoplasm and contents) Sclerenchyma (cells with lignified secondary walls that have lost their protoplasm at maturity, i.e. are 'dead') Vascular tissue: transport

6. Plant organs – leaf, stem, root

7. Stem structure- page 177 Label xylem, phloem, cambium (tissue dividing by mitosis and differentiating into the other vascular tissues- between the xylem and phloem), stoma, sclerenchyma. What is the function of each tissue?

8. Stem Structure

9. Vascular bundle: part of the transport system in plants, consists of vascular tissue (xylem and phloem, separated by cambium) Sunflower stem Vascular bundle

10. Describe a monocotyledon One seed leaf Parallel leaf veins Cannot produce wood Smaller Grasses and some flowering plants Vascular bundles throughout stem with more at the outer edge

11. Describe a dicot Two seed leaves Network of veins Can produce wood Larger Trees and shrubs Vascular bundles found in ring around outer edge Young plant: bundles at outer edge Older plant: continual ring

12. Which is a dicot/monocot? Explain your answer.

13. MonocotDicot

14. Xylem Vessels columns of large cells, with thick walls cells are lignified: lignin impregnates cellulose wall: waterproof vessel autolysis: tonoplast breaks down, cell contents are broken down by enzymes: hollow tube end walls between cell walls: are lost or perforated: continuous tube cellulose microfibrils and lignin provide strength

15. Xylem vessels

16. Types of lignification How can you tell which cells above are xylem vessels?

17. Xylem Vessels for transport of water and support How is xylem adapted to its function? Continuous column of cells one above the other with end wall broken down or perforated – unbroken column of water is formed held together by cohesion Dead – no living contents flow is not restricted, unbroken column of water held together by cohesion Lignified – lignin provides strength and waterproofs xylem so water can not escape Pits – holes in lignin so water can travel laterally Narrow – capillarity increases adhesion ????

18. Sclerenchyma for support Hollow fibres formed from dead cells Cellulose cell walls, lignin Form chisel-shaped, tapering ends Function Support, no transport Trees: need more support, more of the stem is lignified. Cannot only rely on turgid parenchyma cells alone

19. Transpiration

20. Polarity Unequal sharing of electrons between the hydrogen and oxygen atoms. Red: slightly negative Blue: slightly positive

21. Hydrogen bonds What is a H bond? Intermolecular attractions between the positive H atoms and negatively charged atoms of different polar molecules. Give and example: Between the H in water and negatively charged particles of solute.

22. Cohesion versus adhesion Define cohesion and adhesion- Cohesion is the attraction between water molecules due to H bonds. Adhesion is the attraction between water and a polar or ionic substance, e.g. water and the xylem wall.

23. Cohesion and adhesion at work Where do you see- Adhesion? Cohesion?

24. Surface tension Cohesion between water molecules at the surface of a liquid. What happens at the surface? In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, resulting in a net force of zero. The molecules at the surface do not have other molecules on all sides of them and therefore are pulled inwards. This creates some internal pressure and forces liquid surfaces to contract to the minimal area.internal pressure

25. How is water moved through these cells? http://www.kscience.co.uk/animations/transpiration.htm Start at leaf How does water leave the leaf? Diffusion – down a diffusion gradient How does water leave the cells? Evaporation (transpiration) The evaporation of water from the cells creates a pull that draws water through the cell walls and up the xylem. What are the cell walls made up of? Explain their importance here. Cellulose microfibrils and hemicelluloses and pectin The tiny spaces between the microfibrils draw water up by capillary action.

26. How is water moved through these cells? Continued… Stem Water moves up the xylem vessels and through the leaf in a continuous stream called the transpiration stream Water is pulled up by the pull of the water evaporating form the leaf but also pulled down by gravity – this creates a tension. Why do the water molecules stay together in a continuous stream? attraction of the water molecules to each other - hydrogen bonds – cohesion Therefore the way the majority of the water is moved is called the cohesion-tension theory.

27. Transport of Mineral Ions- p181 How do mineral ions enter the root? Get transported up the xylem? Active transport into the roots; mass flow system across the root and up the xylem What is mass flow? Give some examples- Mass flow is the bulk movement of substances due to pressure gradients. Substances will move from an area of higher pressure to an area of lower pressure. Other examples are blood into the heart or air into the lungs.

28. Function of Mineral Ions Why does a plant need mineral ions? Name some mineral ions. Complete the Summary of Some Minerals Used By Plants and Their Effects Nitrate (containing the element Nitrogen) Nucleic acids, amino acids for proteins – growth Magnesium Chlorophyll Phosphorous Component of cell membranes, nucleic acids, ATP Sulphates (containing the element Sulphur) Part of some amino acids (disulphide bridges) Calcium In calcium pectate in middle lamella

29. Deficiency Symptoms What happens to plant if it does not have all minerals needed? Discuss the deficiency symptoms Deficiency: a lack of a certain substance needed for normal growth or function.

31. Activity 4.17  Use the book to complete questions 1-5.

32. Activity 4.17 Q1 Describe the pattern of dark and light shades of green on the new leaves (look at this sheet online to see the photo in colour. Q2 From your knowledge of plant anatomy, explain how the pattern you have described compares with the distribution of xylem vessels in a plant leaf.

33. Activity 4.17 Q1 Describe the pattern of dark and light shades of green on the new leaves (look at this sheet online to see the photo in colour. Q2 From your knowledge of plant anatomy, explain how the pattern you have described compares with the distribution of xylem vessels in a plant leaf.

34. Mexican hat plant Read the rest of Activity 4.17 and plan an experiment...

35. Uses of plant fibres Clothing eg. Cotton Ropes eg. hemp Paper Surrounding tissue must be digested to leave fibres – by enzymes, bacteria or alkali.

36. Other uses of plant fibres Biocomposites – plastic and plant fibres Stronger Biodegradable Renewable Absorb pollutants eg. Heavy metals and hydrocarbons

37. Specification aims 5 Compare the structures, position in the stem and function of sclerenchyma fibres (support) and xylem vessels (support and transport of water and mineral ions). 4 Explain how the arrangement of cellulose microfibrils in plant cell walls and secondary thickening contribute to the physical properties of plant fibres, which can be exploited by humans. 7 Identify sclerenchyma fibres and xylem vessels as seen through a light microscope. 8 Describe how to determine the tensile strength of plant fibres practically. 9 Explain the importance of water and inorganic ions (nitrate, calcium ions and magnesium ions) to plants. 10Describe how to investigate plant mineral deficiencies practically.