Or the cacti in the desserts ? Or the algae in the sea ? How does trees on the fertile plain obtain their nutrients ?
Review Question • Which mode of nutrition do the green plants carry out? A. Autotrophic nutrition B. Heterotrophic nutrition
Sorry! You’re wrong! • Heterotrophic nutrition is the mode of nutrition in which organisms have to depend on other organisms or dead organic matters as their food sources. Green plants, however, can make organic food by themselves using simple inorganic substances.
Very Good! • Autotrophic nutrition is the mode of nutrition in which organisms can make organic food by themselves using simple inorganic substances. • The process by which the green plants obtain nutrients is called : Photosynthesis
Nature of photosynthesis • Takes place in Chloroplast • Necessary factors : • Carbon dioxide • Water • Sunlight • Chlorophyll
Chloroplast Spongy Mesophyll Cell Air Space Stoma CO2
Chloroplast Palisade Mesophyll Cell Air Space Stoma CO2
Light reaction • Light energy is trapped by chlorophyll in chloroplast • Light energy absorbed by chlorophyll splits water molecules into hydrogen and oxygen • Oxygen is released as a gas through stoma to outside • Hydrogen is fed into dark reaction
% of light absorbed by chlorophyll blue green red 6
Dark reaction • No light is required; can take place either in light or darkness • Hydrogen produced in light reaction combines with CO2 to form carbohydrates • Water is formed as a by-product
C6H12O6 + 6 O2 6 CO2 + 6 H20 Carbon Dioxide Light Water Light Reaction Oxygen Glucose (C6H12O6) Summary of Photosynthesis H Dark Reaction
photosynthesis carbon dioxide and water carbohydrates (e.g. glucose) release energy by respiration
carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) convert into starch for storage because glucose is not a very good storage molecule
carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) change into sucrose and is transported to other parts through phloem
fatty acids glycerol carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) combine to form fats and oils to form cell membranes and as a food store
carbon dioxide and water photosynthesis mineral salts from soil (e.g. NO3-, SO42-) carbohydrates (e.g. glucose) amino acids join together to become protein molecules
Destarching • Reason: • To avoid any existing starch in the leaves interfering with the result, and to show that any starch found after the experiment is produced during the period of investigation • Method: • By placing the plant in dark for at least 48 hours
Investigation 8.1 To test a leaf for the presence of Starch
boiling alcohol boiling water hot water iodine turn off Bunsen burner turn off Bunsen burner white tile Why is the leaf first boiled in water ? Ans: Because the process can soften the leaf, break down the cuticle and kill the leaf.
boiling alcohol boiling water hot water iodine turn off Bunsen burner turn off Bunsen burner white tile Why is the leaf then boiled in alcohol ? Ans: To decolourize the leaf (to remove chlorophyll).
boiling alcohol boiling water hot water iodine turn off Bunsen burner turn off Bunsen burner white tile Why is it important to turn off the Bunsen burner when you are heating the alcohol ? Ans: Because alcohol catches fire easily.
boiling alcohol boiling water hot water iodine turn off Bunsen burner turn off Bunsen burner white tile Why is the leaf put in hot water after being boiled in alcohol ? Ans: Since the leaf becomes brittle after boiling in alcohol, so dipping it into hot water enables it to be softened.
boiling alcohol boiling water hot water iodine turn off Bunsen burner turn off Bunsen burner white tile What colour change can be observed if starch is present ? Ans: The leaf becomes blue-black when iodine solution is added to it.
Investigation 8.3 To show that Chlorophyll is necessary for Photosynthesis
purple part green part Which part of the leaf turns blue-black when treated with iodine solution ? Ans: Only the green part.
purple part green part Is chlorophyll necessary for photosynthesis ? Ans: Yes.
purple part green part What is the control in this experiment ? Ans: The green part of the leaf acts as the control.
Investigation 8.4 To show that Carbon Dioxide is necessary for Photosynthesis
sunlight B A potassium hydroxide solution water Why is potassium hydroxide solution put in one of the flasks ? Ans: To absorb all the carbon dioxide in flask B.
sunlight B A potassium hydroxide solution water What happens to each leaf after testing the presence of starch at the end of the experiment ? Ans: The leaf in flask A changes to blue-black while the leaf in flask B stains brown.
sunlight B A potassium hydroxide solution water What do your results suggest about the relationship between carbon dioxide and photosynthesis ? Ans: Carbon dioxide is necessary for photosynthesis.
Light Intensity Light intensity Rate of Photosynthesis
Carbon Dioxide Concentration Carbon dioxide concentration Rate of Photosynthesis
Temperature Temperature Rate of Photosynthesis Temperature > 40℃ Rate & Stop soon
Water Supply If no water, stomata close no gaseous exchange photosynthesis ceases
Why is Photosynthesis important ? Green plants: the only organisms capable of trapping light to manufacture food from simple inorganic substances
Why is Photosynthesis important ? • Green plants(producers) starts the food chain & provide food for other organisms
Why is Photosynthesis important ? • Atmospheric carbon dioxide is absorbed & oxygen is released into the atmosphere which maintains the composition of the atmosphere constant
Parts of plant where photosynthesis takes place Mainly in the leaf because • it contains a lot of chloroplasts • it is well adapted for performing photosynthesis
cuticle upper epidermis palisade mesophyll chloroplasts spongy mesophyll intercellular space (air space) guard cell lower epidermis cuticle stoma
upper epidermis protect internal tissues from mechanical damage and bacterial & fungal invasion
Cuticle • a waxy layer • prevent water loss from the leaf surface • protect the leaf