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! Photosynthesis 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 Occurs in Chloroplast Necessary factors : Carbon dioxide Water Sunlight Chlorophyll

Experiments on photosynthesis

Destarching – removing starch Reason: To show that any starch found after the experiment is produced during the period of investigation Method: By placing the plant in dark for for 2 days

To test a leaf for the presence of Starch Investigation 8.1 To test a leaf for the presence of Starch

Why is the leaf first boiled in water ? boiling water turn off Bunsen burner boiling alcohol hot water iodine 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.

Why is the leaf then boiled in alcohol ? boiling water turn off Bunsen burner boiling alcohol hot water iodine white tile Why is the leaf then boiled in alcohol ? Ans: To decolourize the leaf (to remove chlorophyll).

Ans: Because alcohol catches fire easily. boiling water turn off Bunsen burner boiling alcohol hot water iodine white tile Why is it important to turn off the Bunsen burner when you are heating the alcohol ? Ans: Because alcohol catches fire easily.

Why is the leaf put in hot water after being boiled in alcohol ? boiling water turn off Bunsen burner boiling alcohol hot water iodine white tile Why is the leaf put in hot water after being boiled in alcohol ? Ans: To soften the leaf. (The leaf becomes brittle after boiling in alcohol.)

What colour change can be observed if starch is present ? boiling water turn off Bunsen burner boiling alcohol hot water iodine white tile What colour change can be observed if starch is present ? Ans: The leaf becomes blue-black when iodine solution is added.

To show that Chlorophyll is necessary for Photosynthesis Investigation 8.3 To show that Chlorophyll is necessary for Photosynthesis

Ans: Only the green part. purple part Which part of the leaf turns blue-black when treated with iodine solution ? Ans: Only the green part.

Is chlorophyll necessary for photosynthesis ? green part purple part Is chlorophyll necessary for photosynthesis ? Ans: Yes.

What is the control in this experiment ? green part purple part What is the control in this experiment ? Ans: The green part of the leaf acts as the control.

To show that Carbon Dioxide is necessary for Photosynthesis Investigation 8.4 To show that Carbon Dioxide is necessary for Photosynthesis

Why is potassium hydroxide solution put in one of the flasks ? sunlight B A water potassium hydroxide solution Why is potassium hydroxide solution put in one of the flasks ? Ans: To absorb all the carbon dioxide in flask B.

sunlight B A water potassium hydroxide solution 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.

Ans: Carbon dioxide is necessary for photosynthesis. sunlight B A water potassium hydroxide solution What do your results suggest about the relationship between carbon dioxide and photosynthesis ? Ans: Carbon dioxide is necessary for photosynthesis.

Summary of Photosynthesis sunlight 6 CO2 + 6 H20 C6H12O6 + 6 O2 chlorophyll Carbon Dioxide + water Glucose + oxygen (reactants) (products) By photosynthesis, green plants convert solar energy into chemical energy stored in glucose

Route of Carbon Dioxide for Photosynthesis

Chloroplast Spongy Mesophyll Cell H2O Air Space Stoma CO2

Palisade Mesophyll Cell Chloroplast Palisade Mesophyll Cell H2O Air Space Stoma CO2

Mechanism of photosynthesis A series of enzyme-controlled reactions Involved in 2 stages: Light-dependent stage (Light reaction) Light-independent stage (Dark reaction)

Light reaction (Light-dependent stage) Light is required Chlorophyll in chloroplast traps Light energy Light energy absorbed by chlorophyll splits water molecules into hydrogen and oxygen (photolysis)

Oxygen is formed as a by-product & released as a gas through stoma to outside Hydrogen enters light-independent stage

Dark reaction (Light-independent stage) Light is not 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

Summary of Photosynthesis 6 CO2 + 6 H20 C6H12O6 + 6 O2 Light Water Carbon Dioxide H Light Reaction Dark Reaction Glucose (C6H12O6) Oxygen

Fate of carbohydrate products in the plant

carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) release energy by respiration

carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) convert into other products for growth

carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) fatty acids glycerol combine to form lipids for use or as a food store

join together to become protein molecules 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

carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) convert into starch / lipid for storage Glucose is not a good storage molecule because Glucose is a soluble substance it can diffuse out & lost it affects water potential

carbon dioxide and water photosynthesis carbohydrates (e.g. glucose) change into sucrose and is transported to other parts through phloem

Factors affecting the rate of photosynthesis

 Rate of Photosynthesis Light Intensity  Light intensity  Rate of Photosynthesis

Carbon Dioxide Concentration  Rate of Photosynthesis

 Rate of Photosynthesis Temperature  Temperature  Rate of Photosynthesis Temperature > 40℃ Rate  & Stop soon

If no water, stomata close no gaseous exchange photosynthesis ceases 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 are producers It provides food for other organisms & starts the food chain

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

Internal Structure of Leaf

cuticle upper epidermis palisade mesophyll chloroplasts spongy mesophyll intercellular space (air space) guard cell lower epidermis stoma cuticle

Cross-section of a leaf of dicotyledon

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

mesophyll

palisade mesophyll (layer) columnar cells closely packed together absorb light more efficiently contains many chloroplasts

spongy mesophyll (layer) irregular cells loosely packed together to leave numerous large air spaces allow rapid diffusion of gases throughout the leaf some (fewer than palisade mesophyll) chloroplasts for photosynthesis spongy mesophyll (layer)

same as upper epidermis except the cuticle is thinner lower epidermis

opening which allows gases to pass through it to go into or out of the leaf stoma (stomata)

guard cells control the size of stoma

Stoma thinner outer wall Guard cells thicker inner wall stoma

vascular bundle (vein)

Internal Structure of Leaf xylem phloem The .. after a label = the end of labels.

xylem to transport water and mineral salts towards the leaf for mechanical support

phloem to transport organic substances (food/sugar/ glucose/ sucrose) away from the leaf

Adaptation of leaf to photosynthesis

The leaf is broad & flattened The leaf is thin decrease diffusion distance for gases & light The leaf is broad & flattened increase surface area to absorb more sunlight

Cuticle in upper epidermis is transparent Allows most light to pass into photosynthetic mesophyll tissues

Palisade mesophyll cells are closely packed and contain many chloroplasts To carry out photosynthesis more efficiently

Spongy mesophyll cells are loosely packed with numerous large air spaces To allow rapid diffusion of gases throughout the leaf

Numerous stomata on lower epidermis To allow rapid gaseous exchange with the atmosphere

Extensive vein system Allow sufficient water to reach the cells in the leaf To carry food away to other parts of the plant

Mineral requirements in plants In order to synthesize amino acids, nitrate ions which must be taken into the plant from the soil through the root Other minerals are also necessary to maintain the life of the plant (N, Mg, P, K, S, etc)

The importance of nitrogen For synthesis of proteins, chlorophyll, etc Taken in form of nitrate ions Deficiency symptoms: Little growth ( - no protein made) Yellowing of leaves ( - no chlorophyll made)

The importance of magnesium Essential component of chlorophyll Deficiency symptoms: Yellowing of leaves (no chlorophyll made) Poor growth (no food manufactured because of lack of chlorophyll)

Use of fertilizers in agriculture Continuous harvesting crops removes valuable mineral salts from soil Fertilizers are added to replace such loss Two kinds of fertilizers: Natural fertilizers Chemical fertilizers

Natural fertilizers From manure (animal waste) Organic compounds in it are decomposed by the bacteria in soil to form mineral salts

Chemical fertilizers Mainly nitrogenous and phosphorous compounds manufactured artificially

Comparison between natural and chemical fertilizers Natural fertilizers Chemical fertilizers Contain humus which can improve soil texture No humus so cannot improve soil texture Less soluble in water so less likely to be washed away Very soluble in water so more likely to be washed away

Comparison between natural and chemical fertilizers Natural fertilizers Chemical fertilizers Much cheaper Very expensive Less soluble in water so more difficult to be absorbed Very soluble in water so easier to be absorbed Time is needed for the decomposition to complete before nutrients are available to plants More readily to be used by the plants

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