Or the algae in the sea ?
Or the cacti in the desserts ?
How does trees on the fertile plain obtain their nutrients ?
Review QuestionReview Question
• Which mode of nutrition do the green plants carry out?
A. Autotrophic nutrition
B. Heterotrophic nutrition
Sorry! You’re wrong!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!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 photosynthesisNature of photosynthesis
• Takes place in Chloroplast• Necessary factors :
Carbon dioxideWaterSunlightChlorophyll
Route of Carbon Route of Carbon Dioxide for Dioxide for
PhotosynthesisPhotosynthesis
CO2
Stoma
Air Space
Spongy Mesophyll Cell
Chloroplast
CO2
Chloroplast
Palisade Mesophyll Cell
Stoma
Air Space
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
Light reactionLight reaction
blue red
% o
f li
ght
abso
rbed
by
chl
orop
hy
ll
green
66
Oxygen is produce as the by-product of photosynthesis.
Dark reactionDark 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
Dark Reaction
Water
Oxygen Glucose(C6H12O6)
Light ReactionH
Summary of Summary of PhotosynthesisPhotosynthesis
6 CO2 + 6 H20 C6H12O6 + 6 O2
Light Carbon Dioxide
Fate of Fate of
carbohydrate carbohydrate
products in the products in the
plantplant
carbohydrates (e.g. glucose)
carbon dioxide and waterphotosynthes
is
release energy by respiration
convert into starch for storage because glucose is not a very good storage molecule
carbohydrates (e.g. glucose)
carbon dioxide and waterphotosynthes
is
change into sucrose and is transported to other parts through phloem
carbohydrates (e.g. glucose)
carbon dioxide and waterphotosynthe
sis
carbon dioxide and water
photosynthesis
carbohydrates (e.g. glucose)
fatty acids glycerol
combine to form fats and oils to form cell membranes and as a food store
carbon dioxide and waterphotosynthesi
scarbohydrates (e.g.
glucose)
mineral salts from soil
(e.g. NO3-, SO4
2-)
amino acids
join together to become protein molecules
Experiments Experiments on on
photosynthesphotosynthesisis
DestarchingDestarching• 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
To test a leaf for the presence of Starch
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
water
turn off Bunsen burner
boiling
alcohol
hot water
iodine
white tile
turn off Bunsen burner
Why is the leaf then boiled in alcohol ?
Ans: To decolourize the leaf (to remove chlorophyll).
boiling
water
turn off Bunsen burner
boiling
alcohol
hot water
iodine
white tile
turn off Bunsen burner
Why is it important to turn off the Bunsen burner when you are heating the alcohol ?Ans: Because alcohol catches fire easily.
boiling
water
turn off Bunsen burner
boiling
alcohol
hot water
iodine
white tile
turn off Bunsen burner
Why is the leaf put in hot water after being boiled in alcohol ?Ans: Since the leaf becomes brittle after boiling i
n alcohol, so dipping it into hot water enables it to be softened.
boiling
water
turn off Bunsen burner
boiling
alcohol
hot water
iodine
white tile
turn off Bunsen burner
What colour change can be observed if starch is present ?Ans: The leaf becomes blue-black when iodine s
olution is added to it.
boiling
water
turn off Bunsen burner
boiling
alcohol
hot water
iodine
white tile
turn off Bunsen burner
To show that Chlorophyll is necessary
for Photosynthesis
Which part of the leaf turns blue-black when treated with iodine solution ?Ans: Only the green part.
green part
purple part
Is chlorophyll necessary for photosynthesis ?
Ans: Yes.
green part
purple part
What is the control in this experiment ?
Ans: The green part of the leaf acts as the control.
green part
purple part
To show that Carbon Dioxide is
necessary for Photosynthesis
Why is potassium hydroxide solution put in one of the flasks ?Ans: To absorb all the carbon dioxide in flask B.
sunlight
BA
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 whi
le the leaf in flask B stains brown.
sunlight
BA
water
potassium hydroxide solution
What do your results suggest about the relationship between carbon dioxide and photosynthesis ?Ans: Carbon dioxide is necessary for photosynthesis.
sunlight
BA
water
potassium hydroxide solution
Factors Factors affecting the affecting the
rate of rate of photosynthesiphotosynthesi
ss
Light intensity Rate of Photosynthesis
Carbon dioxide concentration
Rate of Photosynthesis
Temperature Rate of Photosynthesis
Temperature > 40℃Rate & Stop soon
If no water, stomata close no gaseous exchangephotosynthesis ceases
Why is Photosynthesis Why is Photosynthesis important ?important ?
Green plants: the only organisms capable of trapping light to manufacture food from simple inorganic substances
Green plants(producers) starts the food chain & provide food for other organisms
Why is Photosynthesis Why is Photosynthesis important ?important ?
Atmospheric carbon dioxide is absorbed & oxygen is released into the atmosphere which maintains the composition of the atmosphere constant
Why is Photosynthesis Why is Photosynthesis important ?important ?
Parts of plant where Parts of plant where photosynthesis takes placephotosynthesis takes place
Mainly in the leaf because – it contains a lot of chloroplasts– it is well adapted for performing photosynthesis
Internal Internal
Structure of Structure of
LeafLeaf
cuticle
upper epidermis
palisade mesophyll
spongy mesophyll
intercellular space (air space)
guard cell
lower epidermis
cuticlestoma
chloroplasts
Cross-section Cross-section of a leaf of dicof a leaf of dic
otyledonotyledon
upper epidermisprotect
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 togetherabsorb light more efficiently
contains many chloroplasts
spongy mesophyll(layer)
irregular cells loosely packed together to leave numerous large air spacesallow rapid diffusion of gases throughout the leaf
some (fewer than palisade mesophyll) chloroplasts for photosynthesis
lower epidermis
same as upper epidermis except the cuticle is thinner
stoma stoma (stomat(stomat
a)a)
opening which allows gases to pass through it to go into or out of the leaf
guard cellsguard cellscontrol the size of stoma
StomaStoma
stoma
Guard cells
thinner outer wall
thicker inner wall
vascular bundle (vein)
Internal Structure of Internal Structure of LeafLeaf
xylem
phloem
xylemxylem
•to transport water and mineral saltstowards the leaf
•for mechanical support
phloemphloem
•to transport organic substances (food/sugar/ glucose/ sucrose) away from the leaf
Adaptation of Adaptation of
leaf to leaf to
photosynthesisphotosynthesis
The leaf is thin decrease diffusion distance for gases & light
The leaf is broad & flattened increase surface area to absorb more sunlight
Cuticle exists in upper epidermis and is transparentAllows most light to pass into photosynthetic mesophyll tissues
Palisade mesophyll cells are closely packed and contain many chloroplastsTo carry out photosynthesis more efficiently
Spongy mesophyll cells are loosely packed with numerous large air spacesTo allow rapid diffusion of gases throughout the leaf
Numerous stomata on lower epidermisTo 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 Mineral requirements in requirements in
plantsplants• 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 The importance of nitrogennitrogen
• 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 The importance of magnesiummagnesium
• 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 Use of fertilizers in agricultureagriculture
• Continuous harvesting crops removes valuable mineral salts from soilFertilizers are added to replace such loss
• Two kinds of fertilizers:– Natural fertilizers– Chemical fertilizers
Natural fertilizersNatural fertilizers
• From manure• Organic compounds in it
are decomposed by the bacteria in soil to form mineral salts
Chemical fertilizersChemical fertilizers
• Mainly nitrogenous and
phosphorous compounds
manufactured artificially
Comparison between Comparison between natural and chemical natural and chemical
fertilizersfertilizersNatural 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 Comparison between natural and chemical natural and chemical
fertilizersfertilizersNatural fertilizers Chemical fertilizers
Less soluble in water so more difficult to be
absorbedVery soluble in water so easier to be absorbed
More readily to be used by the plants
Time is needed for the decomposition to complete before
nutrients are available to plants
Very expensive Much cheaper
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