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1. NUTRITION IN PLANTS Nutrition : Is the process by which organisms obtain nutrients and assimilate them. Nutrient : any substance required for the nourishment of an Organism. Are obtained from foods e.g. carbohydrates, proteins and fats . Are a source of energy and structural components. 06-May-22 MR. SYLVANOUS OG

2. Types of nutrition Distinguished into two models depending on the way the food is obtained. 1. Autotrophism . 2. Heterotrophism . 06-May-22 MR. SYLVANOUS OG

3. Autotrophism The living organism manufactures its own complex food substances from simple substances The simples materials are Carbon (IV) Oxide, water and light or chemical energy Autotrophs :Living organisms that make their own food Examples : Green plants, photosynthetic bacteria 06-May-22 MR. SYLVANOUS OG

4. Heterotrophism Involves taking complex food materials obtained from bodies of plants ad animals E.g. Carbohydrates, Fats, Proteins Heterotrophs : Organisms that feed on already synthesized food substances 06-May-22 MR. SYLVANOUS OG

5. Autotrophism Divided into two types , depending on the source of energy used in the formation of food: Chemosynthesis Photosynthesis Chemosynthesis The energy for making food is obtained from the oxidation of chemicals Carried out by non-green plants and photosynthetic bacteria 06-May-22 MR. SYLVANOUS OG

6. Photosynthesis Light energy is used in the manufacture of food Exhibited by green plants, mainly on the leaf Is the process by which green plants make food from Carbon iv oxide and water in presence of light 06-May-22 MR. SYLVANOUS OG

7. Cont. The energy from sunlight is finally stored in bonds of carbohydrates, proteins and fats Plants are the primary producers and animals directly depend on them as a source of food 06-May-22 MR. SYLVANOUS OG

8. External structure of a leaf Is a thin flattened organ attached to the stem or branch of plants The features are made in such a manner to ensure optimum rate of photosynthesis 06-May-22 MR. SYLVANOUS OG

9. The structural adaptations 1. Leaf blade /lamina Is the flattened surface , green in color Contains the photosynthetic tissue Most leaves are broad, flattened and thin to provide a large surface area for absorption of light They are thin to reduce the distance through which carbon iv oxide diffuses up to the palisade cells where optimum photosynthesis occurs 06-May-22 MR. SYLVANOUS OG

10. 2. Midrib A region in the middle of the simple leaf of a dicotyledonous plant Is thick and from it small veins arise and run into the lamina to form an extensive network of veins (Network venation) Is absent in monocotyledonous plants but small veins run parallel to each other, (Parallel venation) 06-May-22 MR. SYLVANOUS OG

11. 3. Petiole / Leaf stalk Provides support to the leaf by attaching it to the stem Positions the leaf to trap maximum light In dicotyledonous plants it continues onto the lamina as the midrib, with lateral veins branching from it In some monocots it is absent and the leaf is attached to the stem or branch by a leaf sheath 06-May-22 MR. SYLVANOUS OG

12. Internal structure of a leaf Revealed when a T.S of the leaf is examined under a microscope Consists of: 1.Cuticle 2. Epidermis 3. Guard cells 4. palisade mesophyll layer 5. Stomata 6. Spongy mesophyll layer 7. Leaf veins / vascular tissue 06-May-22 MR. SYLVANOUS OG

13. 1. Cuticle Is a thin noncellular waxy, waterproof and transparent layer that coats the upper and lower leaf surfaces These properties allow light to penetrate to the tissues involved in photosynthesis The waxy material protects the leaf from mechanical damage and entry of disease causing microorganisms 06-May-22 MR. SYLVANOUS OG

14. 2. Epidermis A layer of cells below the cuticle Occurs on the lower and upper surfaces of the leaf Is transparent and lacks chlorophyll except the guard cells Is one cell thick to reduce the distance over which sunlight penetrates into the photosynthetic tissues It secretes the cuticle and protects the inner tissues from mechanical damage and entry of disease causing microorganism 06-May-22 MR. SYLVANOUS OG

15. 3. Stomata Are small pores enclosed by guard cells on the upper and lower epidermis They allow passage of gases into and out of the leaf 06-May-22 MR. SYLVANOUS OG

16. 4. Guard cells Are special bean –shaped epidermal cells Mostly found on the lower surface of the leaf Contain chloroplasts and are able to carry out photosynthesis They control the opening and closing of stomata, hence control water loss through the stomata and allows movement of air in and out of the leaf 06-May-22 MR. SYLVANOUS OG

17. 5. Palisade mesophyll layer A layer of cells located beneath the upper epidermis Cells are cylindrical in shape Cells are closely packed together with a few air spaces between them Location and arrangement facilitates maximum absorption of light Have numerous chloroplasts containing chlorophyll necessary for photosynthesis 06-May-22 MR. SYLVANOUS OG

18. 6. Spongy mesophyll layer Is a layer of cells between the palisade mesophyll and lower epidermis Cells are irregular in shape and loosely arranged creating large air spaces in between them Air spaces allow for air circulation between the cells Have fewer chloroplasts hence lower surface of the leaf are lighter in colour than the upper surface 06-May-22 MR. SYLVANOUS OG

19. 7.Leaf veins / vascular tissue Leaf has an extensive system of veins which ensure that every cell is close to supply of materials Veins have conducting tissues known as xylem and phloem Xylem : Conducts water and mineral salts from the roots to the leaf cells Phloem : Translocates manufactured food from leaf cells to the rest of the plant 06-May-22 MR. SYLVANOUS OG

20. Summary of the leaf adaptations to its photosynthetic function 1. Broad flat lamina provides a large surface area for the absorption of CO 2 and light for photosynthesis 2. The thickness of the leaf allows CO 2 to pass through a short distance to reach the photosynthetic tissue 3. The presence of stomata ensures efficient diffusion of CO 2 into the leaf and O 2 out of the leaf 4. The cuticle and epidermis are transparent enough to allow penetration of light to the palisade cells 06-May-22 MR. SYLVANOUS OG

21. Cont . 5. Palisade cells contain a large no. of chloroplasts and their location and arrangement next to the upper epidermis enables them to receive maximum sunlight for photosynthesis 6. Extensive network veins conduct water and mineral salts to the photosynthetic cells and remove the products of photosynthesis 7. The air spaces in the spongy mesophyll layer are large enough to allow gases to circulate easily 8. The regular arrangement of leaves (leaf mosaic) on the stem minimises overlapping and overshadowing hence ensuring maximum absorption of light 06-May-22 MR. SYLVANOUS OG

22. Question 06-May-22 MR. SYLVANOUS OG

23. Structure and functions of the chloroplast Is a disc shaped organelle found in the cytoplasm of some plant cells Examples of plant cells containing chloroplast 1.Palisade mesophyll cells 2. Spongy mesophyll cells 3. Guard cells Cells that have chloroplasts are Called photosynthetic cells 06-May-22 MR. SYLVANOUS OG

24. Structure Chloroplast is bound by a double unit membrane Inside each chloroplast are small disc-shaped units called grana They are stacked together to form thylakoid membrane Grana are connected to each other by the intergrana 06-May-22 MR. SYLVANOUS OG

25. Cont. Grana provides a large surface area to accommodate a large no. of chlorophyll molecules to absorb light energy for photosynthesis The stroma contains enzymes that speed up the process of photosynthesis Other materials suspended in the matrix are starch grains and fat droplets 06-May-22 MR. SYLVANOUS OG

26. The process of photosynthesis The raw materials are water and Carbon iv oxide Other requirements are light and chlorophyll pigment Water and carbon iv oxide in the presence of chlorophyll and sunlight undergo several chemical processes They result in formation of carbohydrates and give out oxygen 06-May-22 MR. SYLVANOUS OG

27. Demonstration of photosynthesis process 06-May-22 MR. SYLVANOUS OG

28. Photosynthesis equation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 It occurs through a series of chemical reactions, which can be divided into two main stages: light and dark stages 06-May-22 MR. SYLVANOUS OG

29. 06-May-22 MR. SYLVANOUS OG

30. Demonstration of photosynthesis equation 06-May-22 MR. SYLVANOUS OG

31. Light stage / light depended stage Is the initial stage in the process of photosynthesis Depends on light / Cannot occur in absence of light Occurs in the grana of chloroplast which has numerous chlorophyll molecules for absorbing light Light energy is used in two ways: 06-May-22 MR. SYLVANOUS OG

32. Cont. 1. Photolysis : splitting of water molecules into oxygen and hydrogen atoms 2H 2 O Light energy 4H+ O 2 Chlorophyll 2. The rest is used in the formation of energy which is stored in a chemical form called adenosine triphosphate (ATP) 06-May-22 MR. SYLVANOUS OG

33. Cont. The hydrogen atoms enter the dark stage of photosynthesis The oxygen atoms are released through the stomata to the atmosphere and the rest used up by the plant for respiration ATP is later used in the dark stage This process involves the conversion of light energy into chemical energy 06-May-22 MR. SYLVANOUS OG

34. The dark stage / light independent stage Is the second stage of photosynthesis It can proceed in presence or absence of light Takes place in the stroma of the chloroplast since it is controlled by enzymes The hydrogen from light stage combines with carbon iv oxide to from a simple sugar (Glucose) 06-May-22 MR. SYLVANOUS OG

35. Cont. CO 2 + 4H (CH 2 O)n + H 2 O This process is called carbon iv oxide fixation It involves a series of enzyme controlled reactions which utilize the stored ATP from the light stage The glucose formed is directly utilized by the plant cells while the rest is converted to starch and stored in the plant 06-May-22 MR. SYLVANOUS OG

36. Question 06-May-22 MR. SYLVANOUS OG

37. Factors affecting the rate of photosynthesis For photosynthesis to occur, several factors / conditions are necessary and will have an effect on the rate of photosynthesis The rate of photosynthesis will be higher at the optimum point Before this point is reached the factor can be said to be limiting the rate of the reaction Beyond this point other factors affect the rate of photosynthesis 06-May-22 MR. SYLVANOUS OG

38. The factors 1. Carbon iv oxide concentration 2. Temperature 3. Light intensity 4. water 06-May-22 MR. SYLVANOUS OG

39. Light intensity Light is essential for photosynthesis for it provides the energy required in the light stage It varies from day to day and from place to place The rate of photosynthesis increases as the light increases up to optimum light intensity This is a point where increase in light intensity does not increase the rate of photosynthesis 06-May-22 MR. SYLVANOUS OG

40. Cont. Optimum light intensity is not the same for all plants A plant that grows where there is plenty of sunshine will have a higher optimum than one growing in shade The quality of light also affects photosynthesis rate This quality depends on wavelength and blue and red are the most effective in photosynthesis Plants growing in the shade receive low quantities and poor qualities of light which slows down the process of photosynthesis 06-May-22 MR. SYLVANOUS OG

41. Light intensity affects rate of photosynthesis 06-May-22 MR. SYLVANOUS OG

42. Carbon iv oxide concentration The concentration of carbon iv oxide in the atmosphere is about 0.03 % and is relatively constant Under controlled conditions in a green house, an increase in carbon iv oxide concentration results in a linear increase in the rate of photosynthesis upto a certain level (point of optimum Carbon iv oxide concentration) Further increase in concentration of carbon iv oxide beyond this point does not increase the rate of photosynthesis 06-May-22 MR. SYLVANOUS OG

43. Cont. This is because other factors are now limiting the rate of photosynthesis The rate of photosynthesis therefore levels off beyond the point of optimum CO 2 concentration 06-May-22 MR. SYLVANOUS OG

44. How carbon iv oxide concentration affects the rate of photosynthesis 06-May-22 MR. SYLVANOUS OG

45. Temperature Photosynthesis is an enzyme controlled reaction hence affected by temperature Low temperature inactivated the enzymes resulting in low rate of photosynthesis A rise in temperature by 10 o C results in the doubling of the rate of photosynthesis upto 40 C This is the range of optimum temperature and the enzymes are activated The rate of photosynthesis is highest at optimum temperature 06-May-22 MR. SYLVANOUS OG

46. Water Water is a raw material in photosynthesis It is split to provide the hydrogen ions that are used in carbon iv oxide fixation to form carbohydrates However, water is needed for many other purposes, besides photosynthesis The effect of water shortage on photosynthesis may therefore be indirect 06-May-22 MR. SYLVANOUS OG

47. Cont. For instance, water deficiency may lead to guard cells becoming flaccid This results in the closure of stomata, which hinders entry of carbon iv oxide to the leaf A plant whose leaves are withering due to lack of water may photosynthesize at a lower rate 06-May-22 MR. SYLVANOUS OG

48. Practical activity to investigate the presence of starch in a leaf Requirements Water, dopper, beaker, source of heat, boiling tube, a leaf, petridish, white tile Procedure 1. Obtain a leaf that has been exposed to light for at least 5 hours, to allow photosynthesis to occur for starch to form 2. Dip the leaf in boiling water for 3 – 4 minutes This denatures the enzymes, all biochemical reactions stop hence protoplasm dies 06-May-22 MR. SYLVANOUS OG

49. Cont. 3. Put the leaf in a boiling tube containing methylated spirit and stand the tube in a beaker containing water ( water bath) for about 10 minutes Methylated spirit decolorises the leaf / removes chlorophyll Methylated spirit is highly flammable hence should not be heated directly 06-May-22 MR. SYLVANOUS OG

50. Cont. 4. Remove the leaf from the test tube and wash it in the beaker of cold water to soften it and wash off the spirit (methylated spirit makes the leaf to become hard) 5. Spread the leaf in a petridish or white tile and add drops of dilute iodine solution and observe Conclusion A blue black colour indicates the presence of starch Brown colour of iodine is retained if starch is absent 06-May-22 MR. SYLVANOUS OG

51. Demonstration of the experiment to test for starch 06-May-22 MR. SYLVANOUS OG

52. Practical activities to investigate the factors which are necessary for photosynthesis 1. Light Requirements Methylated spirit, iodine solution, water, white tile, droppers, beakers, source of heat, boiling tube, light proof material e.g. aluminium foil, potted plant 06-May-22 MR. SYLVANOUS OG

53. Procedure Cover 2 or more leaves of a potted plant with a light proof material Place the plant in a dark place for 48 hours Transfer the potted plant to light for 2-3 hours Detach and uncover the leaves and immediately carry out the test for starch Observe and record your observations 06-May-22 MR. SYLVANOUS OG

54. Discussion The plant was kept in the dark for about 48 hours to ensure that all the starch in it is used up The plant uses starch reserves found in the leaves when placed in the dark , this is called destarching The plant was transferred to light to investigate whether starch would be formed in its presence 06-May-22 MR. SYLVANOUS OG

55. Cont. The exposed parts of the leaf act as controlled experiment since they have been provided with all the requirements for photosynthesis The part under test lacks carbon iv oxide 06-May-22 MR. SYLVANOUS OG

56. Light is necessary for photosynthesis 06-May-22 MR. SYLVANOUS OG

57. 2. Carbon iv oxide Requirements Potted plant, Sodium hydroxide pellets, Iodine solution, Water, Methylated spirit, Petroleum jelly, Conical flask / Polythene bags, Cork borers, Blades, Beakers, Droppers, White tile, Boiling tubes, Source of heat, Wooden support 06-May-22 MR. SYLVANOUS OG

58. Procedure Keep the potted plant in a dark place for 48 hours Place a few pellets of Sodium hydroxide in the flask (Sodium hydroxide is a deliquescent substance and absorbs water to form a solution which absorbs CO 2 readily) Bore a hole in the cork of the same size as the petiole of the leaf being used 06-May-22 MR. SYLVANOUS OG

59. Cont. Cut the cork lengthwise Remove the plant from the dark and immediately fit the petiole of the leaf in the groove and cork the flask. The leaves outside the flask act as control since they have access to all the requirements of photosynthesis The leaf under test lacks CO 2 06-May-22 MR. SYLVANOUS OG

60. Cont. Seal the mouth of the conical flask with petroleum jelly to make it airtight Keep the set up in the light for 2 to 3 hours Detach and test for the presence of starch in both the exposed leaves and those in the conical flask Record your observations 06-May-22 MR. SYLVANOUS OG

61. Carbon iv oxide is necessary for photosynthesis 06-May-22 MR. SYLVANOUS OG

62. 3. Chlorophyll A variegated leaf is used Variegated : leaf which has some patches that lack chlorophyll They have other colours e.g. yellow and photosynthesis does not take place in them Requirements Variegated leaves , Iodine solution, Methylated spirit, Water, Droppers, White tile, Boiling tubes, Beakers, Source of heat 06-May-22 MR. SYLVANOUS OG

63. Procedure Detach a variegated leaf from a plant that has been exposed to light for at least 3 hours Draw a large diagram of the leaf to show the distribution of the chlorophyll pigment in the leaf Test the leaf for starch in the usual way Record your observations in the form of a diagram 06-May-22 MR. SYLVANOUS OG

64. Chlorophyll is necessary for photosynthesis 06-May-22 MR. SYLVANOUS OG

65. Question 06-May-22 MR. SYLVANOUS OG

66. Question 2 06-May-22 MR. SYLVANOUS OG

67. Practical activity to investigate the gas produced during photosynthesis Submerged water plants are used in this experiment Other plants not adapted to this environment may not work well since the setup provides an aquatic environment The amount of CO 2 dissolved in water may be low The amount may be boosted by adding sodium hydrogen carbonate to accelerate the rate of photosynthesis 06-May-22 MR. SYLVANOUS OG

68. Cont. Requirements A water plant e.g. Elodea species, glass funnels, beakers , small wooden blocks, test tubes, wooden splints, sodium hydrogen carbonate Procedure Place the pod weed in a beaker filled with water Add a pinch of sodium hydrogen carbonate to the water to act as a source of CO 2 06-May-22 MR. SYLVANOUS OG

69. Cont. Invert a funnel over the water plant and support it with a wooden stand Invert a test-tube filled with water over the funnel Leave the setup in bright sunlight for approximately four hours to allow for photosynthesis to take place Leave the set up in the sun until sufficient gas has collected in the test-tube 06-May-22 MR. SYLVANOUS OG

70. Cont. Test the gas collected using a glowing splint Record your observations 06-May-22 MR. SYLVANOUS OG

71. The gas collected relights a glowing splint 06-May-22 MR. SYLVANOUS OG