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

~ ~

ENDEND ~~