YUMMY!!! Sigh, I wish its time for dinner already. I am so hungry! Hmmm, I wonder what we are having tonight!?

YUMMY!!! Sigh, I YUMMY!!! Sigh, I wish it’s time for wish it’s time for dinner already. I dinner already. I am so hungry! am so hungry!

Hmmm, I wonder Hmmm, I wonder what we are what we are

having tonight!?having tonight!?

WOW!!! WOW!!! What a What a pretty pretty

flower!!!!!flower!!!!!

Hey! I wonder Hey! I wonder if plants need if plants need to eat too!? If to eat too!? If they do, then they do, then how do they how do they

get their food?get their food?

Of course we eat!!! Of course we eat!!! And we are able to And we are able to

make our own food. make our own food. That is why we are That is why we are

called called AUTOTROPHSAUTOTROPHS! ! Hmmm, I thought you Hmmm, I thought you learned all about this learned all about this

already!!! Do you already!!! Do you remember how we can remember how we can make our own food???make our own food???

Things needed:Things needed:• LightLight• Carbon dioxideCarbon dioxide• WaterWater• ChlorophyllChlorophyll

Things produced:Things produced:• Carbohydrates Carbohydrates

(which can be (which can be used to form fats used to form fats and proteins)and proteins)

• OxygenOxygen

PhotosynthesisPhotosynthesis

• As one can see, plants need to obtain As one can see, plants need to obtain carbon dioxide in order to carry out carbon dioxide in order to carry out photosynthesisphotosynthesis

• They also release oxygen as a by-They also release oxygen as a by-productproduct

• The process by which plants exchange The process by which plants exchange oxygen and carbon dioxide is calledoxygen and carbon dioxide is called

___________ ___________ gas exchangegas exchange

Gas ExchangeGas Exchange

• Plants exchange gases by Plants exchange gases by diffusiondiffusion

• Where does gas exchange occur Where does gas exchange occur in plants?in plants?

Internal Structure of LeafInternal Structure of Leaf


• Gas exchange mainly occurs in Gas exchange mainly occurs in the the leavesleaves

• How do gases diffuse into and out How do gases diffuse into and out of the leaves?of the leaves?

StomataStomata

StomataStomata


• Gas exchange can also take place Gas exchange can also take place in the stems and rootsin the stems and roots

• Herbaceous plants – diffusion Herbaceous plants – diffusion through stomata on stem surfacethrough stomata on stem surface

• Woody plants - stomata when Woody plants - stomata when youngyoung

- lenticels - lenticels when maturedwhen matured

LenticelsLenticels

• Gases cannot penetrate the Gases cannot penetrate the protective cork layerprotective cork layer

• Lenticels are loosely-packed Lenticels are loosely-packed masses of cells in the bark of a masses of cells in the bark of a woody plant, visible on the woody plant, visible on the surface of a stem as raised surface of a stem as raised spots, through which gas spots, through which gas exchange occursexchange occurs

LenticelsLenticels

LenticelsLenticels

Gas Exchange in RootsGas Exchange in Roots

• The epidermis is usually just one The epidermis is usually just one cell thick. Root epidermal cells cell thick. Root epidermal cells lack a thick cuticle which would lack a thick cuticle which would interfere with water uptake. interfere with water uptake. Moreover, there is no stomata Moreover, there is no stomata present as the cell membrane is present as the cell membrane is very thin and therefore gases can very thin and therefore gases can directly diffuse into and out of the directly diffuse into and out of the cellscells

Adaptation of Adaptation of

Leaves to Leaves to


The leaf is thin The leaf is thin Decreases Decreases diffusion diffusion distance for distance for gasesgases

Adaptation of LeavesAdaptation of Leaves

Numerous Numerous stomata on stomata on lower epidermislower epidermisAllows rapid Allows rapid gaseous gaseous exchange with exchange with the atmospherethe atmosphere


Guard cells Guard cells control the size control the size of stomata of stomata In In presence of presence of light, stomata light, stomata open widely to open widely to allow the allow the diffusion of diffusion of carbon dioxide carbon dioxide and oxygenand oxygen


Guard CellsGuard Cells• When turgor When turgor

develops within the develops within the two guard cells, the two guard cells, the outer walls bulge out outer walls bulge out and force the inner and force the inner walls into a crescent walls into a crescent shape. This opens shape. This opens the stomata. When the stomata. When the guard cells lose the guard cells lose turgor, the elastic turgor, the elastic inner walls regain inner walls regain their original shape their original shape and the stomata and the stomata closes closes

Spongy mesophyll Spongy mesophyll cells are loosely cells are loosely packed with packed with numerous large air numerous large air spacesspacesAllows rapid Allows rapid diffusion and free diffusion and free circulation of circulation of gases throughout gases throughout the leafthe leaf



Most cells in the Most cells in the leaves leaves

are surrounded by a are surrounded by a layer layer

of waterof waterAllows gases to Allows gases to

dissolve dissolve and diffuse into and and diffuse into and

out of out of the cellsthe cells


Carbon Carbon DioxideDioxide

OxygenOxygen

PhotosynthePhotosynthesissis

OxygenOxygen

Carbon Carbon DioxideDioxide

RespirationRespiration

What will be the net What will be the net gas exchange gas exchange

between the leaf and between the leaf and its surrounding air?its surrounding air?

Rate of Gas ExchangeRate of Gas Exchange

The rate of gas exchange is different The rate of gas exchange is different throughout the day due to a change in throughout the day due to a change in

light intensitylight intensity

What is going on here?What is going on here?

Light IntensityLight Intensity

• Night – plants carry out Night – plants carry out RESPIRATIONRESPIRATION and release and release CARBON DIOXIDECARBON DIOXIDE



• Night – plants carry out Night – plants carry out RESPIRATIONRESPIRATION and release and release CARBON DIOXIDECARBON DIOXIDE

• Early morning – Early morning – PHOTOSYNTHESISPHOTOSYNTHESIS begins to take place as light intensity begins to take place as light intensity increases increases

Rate of photosynthesis < Rate of Rate of photosynthesis < Rate of respirationrespiration

Net release of CARBON DIOXIDENet release of CARBON DIOXIDE



• Around 6:00 a.m. – light intensity Around 6:00 a.m. – light intensity increases even moreincreases even more

Rate of photosynthesis = Rate of Rate of photosynthesis = Rate of respirationrespiration

Release of CORelease of CO2 2 = Uptake of CO= Uptake of CO22

That is, there is NO net gas exchangeThat is, there is NO net gas exchange

This is referred to as the This is referred to as the COMPENSATION POINTCOMPENSATION POINT



• Afternoon – light intensity further Afternoon – light intensity further increasesincreases

Rate of photosynthesis > Rate of Rate of photosynthesis > Rate of respirationrespiration

Net uptake of CARBON DIOXIDENet uptake of CARBON DIOXIDE

Net uptake of carbon dioxide reaches Net uptake of carbon dioxide reaches a maximum in early afternoona maximum in early afternoon



• Evening – light intensity begins to decreaseEvening – light intensity begins to decrease

At a certain time period, there will again At a certain time period, there will again be a be a

net release of net release of CARBON DIOXIDECARBON DIOXIDE when when plants plants

only carry out only carry out RESPIRATIONRESPIRATION at night at night


Similarly, we can Similarly, we can study the study the

relationship between relationship between light intensity and light intensity and the exchange of the exchange of

OXYGENOXYGEN

Critical Thinking 8.1 (p. Critical Thinking 8.1 (p. 11)11)

QuestionQuestion1. Does a plant release or absorb

oxygen at night?Ans: Ans: A plant absorbs oxygen at night


QuestionQuestion2. When the light intensity gradually

increases in the morning, will there be any changes in the exchange of oxygen? Why?Ans: The rate of oxygen uptake would gradually decrease and the rate of oxygen release would gradually increase. It is because photosynthesis begins to occur when light intensity gradually increases in the morning

QuestionsQuestions3. Why is there a compensation

point?

4.4. What will happen to the What will happen to the exchange of oxygen when the light exchange of oxygen when the light intensity further increases?intensity further increases?

Ans: Compensation point refers to the light intensity at which there is no net gas exchange


Ans: The rate of oxygen release would increase as light intensity increases

QuestionQuestion5. Draw a graph to show the

relationship between light intensity and the exchange of oxygen of a plant.



INVESTIGATION INVESTIGATION #1#1

Studying the effect of light Studying the effect of light intensity on gas exchange in intensity on gas exchange in

leaves using leaves using hydrogencarbonate indicatorhydrogencarbonate indicator

Introduction to Introduction to InvestigationInvestigation

• In this investigation, you will study the effect In this investigation, you will study the effect of light intensity on gas exchange in leavesof light intensity on gas exchange in leaves

• Green leaves will be put into different light Green leaves will be put into different light intensities, and the level of carbon dioxide intensities, and the level of carbon dioxide will be estimated by using will be estimated by using hydrogencarbonate indicator solutionhydrogencarbonate indicator solution

• Note: Increase in CO2 – Note: Increase in CO2 – OrangeOrange to to YellowYellow

Decrease in CO2 – Decrease in CO2 – OrangeOrange to to PurplePurple

ProcedureProcedure

AA B B C C DD

Please refer to pages 7 and 8 in your Please refer to pages 7 and 8 in your textbooktextbook

Results TableResults Table

Colour of hydrogencarbonate Colour of hydrogencarbonate indicator solution after one indicator solution after one

hourhour

Tube ATube A

Tube BTube B

Tube CTube C

Tube DTube D


Studying the effect of light Studying the effect of light intensity on the gas intensity on the gas

exchange of a plant exchange of a plant using a data loggerusing a data logger


• In this investigation, you will study the effect In this investigation, you will study the effect of light intensity on the gas exchange of a of light intensity on the gas exchange of a water plant using a data loggerwater plant using a data logger

• Gas exchange in plants is affected by both Gas exchange in plants is affected by both the rates of respiration and photosynthesisthe rates of respiration and photosynthesis

• You can measure the rate of oxygen You can measure the rate of oxygen released by a water plant by measuring the released by a water plant by measuring the change in pressure in an enclosed set-upchange in pressure in an enclosed set-up

• A data logger and a low-pressure sensor A data logger and a low-pressure sensor can be used can be used

ProcedureProcedurePlease refer to pages 8 and 9 in your Please refer to pages 8 and 9 in your textbooktextbook

Results TableResults TableDistance between Distance between

the lamp and the lamp and the conical flask the conical flask

(cm)(cm)

Initial Initial pressurpressur

ee

Final Final pressurpressur

ee

Change Change in in

pressure pressure per minute per minute

2020

5050

8080

110110

DiscussionDiscussion

1.1. What is the purpose of putting a What is the purpose of putting a water trough between the conical water trough between the conical flask and the lamp?flask and the lamp?Ans: It is used to reduce the heating effect of the lamp. The result obtained is mainly due to the influence of the light intensity


2.2.What is the purpose of using dilute sodiuWhat is the purpose of using dilute sodium hydrogencarbonate solution in the com hydrogencarbonate solution in the conical flask?nical flask?Ans: It provides carbon dioxide for the plant to carry out photosynthesis


3.3.What is the relationship between the ligWhat is the relationship between the light intensity and the distance between thht intensity and the distance between the conical flask and the table lamp?e conical flask and the table lamp?Ans: The shorter the distance between the lamp and the conical flask, the stronger is the light intensity


4.4.What is the relationship between the preWhat is the relationship between the pressure in the conical flask and the light inssure in the conical flask and the light intensity in this experiment?tensity in this experiment?Ans: The stronger the light intensity, the faster is the increase in pressure detected in the conical flask. The reason is that the rate of photosynthesis increases with light intensity, and the rate of oxygen release also increases


Carbon Carbon

DioxideDioxide

WaterWater

CarbonCarbon OxygenOxygen

HydrogenHydrogen

carbon dioxide and watercarbon dioxide and water

photosynthesiphotosynthesiss

carbohydrates (e.g. glucose)carbohydrates (e.g. glucose)

fatty acidsfatty acids glycerolglycerol

Combine to formCombine to form fatsfats and and oilsoils for for construction of cell membranes and construction of cell membranes and

as a food storageas a food storage

Synthesis of FatsSynthesis of Fats

carbon dioxide and carbon dioxide and waterwater

photosynthesiphotosynthesiss

carbohydrates (e.g. carbohydrates (e.g. glucose)glucose)

mineral salts from mineral salts from soilsoil

(e.g. NO(e.g. NO33--, SO, SO44

2-2-))

amino acidsamino acids

join together to becomejoin together to become proteinprotein moleculesmolecules

Synthesis of ProteinsSynthesis of Proteins

Mineral Requirements in Mineral Requirements in PlantsPlants

• In order to synthesize In order to synthesize amino acidsamino acids (i.e. (i.e. proteins), plants must absorb proteins), plants must absorb minerals minerals through the rootsthrough the roots

• Minerals that are required in large quantities: Minerals that are required in large quantities: nitrogen, phosphorus, potassium, magnesium, nitrogen, phosphorus, potassium, magnesium, sulphur and calcium sulphur and calcium

• Other minerals are also required but in a Other minerals are also required but in a lesser amount: lesser amount: copper, zinc and ironcopper, zinc and iron

• A constant supply of minerals is necessary for A constant supply of minerals is necessary for the healthy development of a plantthe healthy development of a plant


Investigating the effects of minerInvestigating the effects of minerals on plant growth using potted als on plant growth using potted

plantsplants


• In this experiment, you will investigate In this experiment, you will investigate the effects of different minerals on the effects of different minerals on plant growthplant growth

• Some of the plants will be watered with Some of the plants will be watered with a solution lacking certain essential a solution lacking certain essential minerals, such as nitrogen and minerals, such as nitrogen and magnesiummagnesium

• How will a lack of minerals affect the How will a lack of minerals affect the growth of a plant?growth of a plant?

ProcedureProcedurePlease refer to pages 12 and 13 in your Please refer to pages 12 and 13 in your textbooktextbook

A B C

1.1. Why do we use seedlings of similar Why do we use seedlings of similar size?size?

2.2. What differences in appearance of What differences in appearance of seedlings between pots A and B can you seedlings between pots A and B can you find at the end of the experiment?find at the end of the experiment?

Ans: It is because seedlings of different size may differ in nutrient requirements, making it difficult to compare the results

Ans: Seedlings in pot A grow healthy, but those in pot B show poor growth and small, yellowing of leaves


3.3. What differences in appearance of seedlings What differences in appearance of seedlings between pots A and C can you find?between pots A and C can you find?

4.4. Why do we use sand but not garden soil Why do we use sand but not garden soil in the pots?in the pots?

Ans: The seedlings in pot A grow healthy, but those in pot C also show poor growth and yellowing of leaves

Ans: As garden soil may contain different minerals that plants need, accurate result of the effects of different minerals on plant growth may not be obtained



5.5. What conclusion can you make from this What conclusion can you make from this experiment?experiment?

Ans: Both nitrogen and magnesium are important to plant growth. Insufficient supply of these minerals would affect plant development

Note to ExperimentNote to Experiment

• A solution containing ALL the A solution containing ALL the minerals that are required by a plant minerals that are required by a plant is called a is called a complete culture solutioncomplete culture solution

• A solution which lacks certain A solution which lacks certain essential minerals for plant growth is essential minerals for plant growth is called a called a deficient culture solutiondeficient culture solution

• Water culturesWater cultures can be set up for the can be set up for the investigation of the effects of investigation of the effects of minerals on plant growthminerals on plant growth

Hi! It’s me again. Hi! It’s me again. Hmmm, there are a few Hmmm, there are a few things that I still don’t things that I still don’t

understand. You mean, in understand. You mean, in addition to carbon dioxide, addition to carbon dioxide, water and sunlight, plants water and sunlight, plants

also need to take in…also need to take in…arrr…what are those arrr…what are those

things called again? Oh…things called again? Oh…MINERALSMINERALS…in order to …in order to grow healthily? Can grow healthily? Can

someone PLEASE tell me someone PLEASE tell me how are these minerals how are these minerals

important to plants? And important to plants? And what will happen if the what will happen if the

plants do not take in these plants do not take in these minerals? minerals?

NitrogenNitrogen

• Nitrogen is needed for the synthesis Nitrogen is needed for the synthesis of amino acid (which are the building of amino acid (which are the building blocks for proteins) blocks for proteins)

Structure of Amino AcidStructure of Amino Acid

Proteins in PlantsProteins in Plants

Proteins are important for the Proteins are important for the synthesis of various plant structures:synthesis of various plant structures:

• Cell membraneCell membrane

Cell MembraneCell Membrane



• Cell membraneCell membrane• CytoplasmCytoplasm

CytoplasmCytoplasm• Reaction Reaction

catalystcatalyst• In various In various

structures structures of the cellof the cell



• Cell membraneCell membrane• CytoplasmCytoplasm• EnzymeEnzyme• HormoneHormone

Plant HormonesPlant Hormones

• Chemicals made in one part of the Chemicals made in one part of the plant that move to another part of plant that move to another part of the plant where, at very low the plant where, at very low concentrations, they regulate growth concentrations, they regulate growth and/or developmentand/or development

• Many different types of hormonesMany different types of hormones• e.g. promotion of growth, promotion e.g. promotion of growth, promotion

of cell division, etc. of cell division, etc.

Other Functions of Other Functions of NitrogenNitrogen

• DNA (in making DNA (in making the the nitrogenous nitrogenous base)base)

• ChlorophyllChlorophyll

Nitrogen in SoilNitrogen in Soil

• Usable forms of nitrogen include nitrate Usable forms of nitrogen include nitrate (NO(NO33

--) and ammonium (NH) and ammonium (NH44++))

• Nitrate is the more common form of Nitrate is the more common form of nitrogen that is absorbed be plants from nitrogen that is absorbed be plants from soilsoil

• However, most of the nitrogen in soil is However, most of the nitrogen in soil is NOT present as nitrate nor as ammoniumNOT present as nitrate nor as ammonium

• Nitrogen in soil must therefore be Nitrogen in soil must therefore be converted to the usable forms by soil converted to the usable forms by soil microorganismsmicroorganisms

Nitrogen DeficiencyNitrogen Deficiency

A deficiency in nitrogen will A deficiency in nitrogen will result in:result in:

• Small and weak plantsSmall and weak plants• Stunted growthStunted growth• Yellowish leaves (Chlorosis)Yellowish leaves (Chlorosis)

Nitrogen DeficiencyNitrogen Deficiency

MagnesiumMagnesium

• Most of the magnesium in the soil Most of the magnesium in the soil exists in forms which are not directly exists in forms which are not directly available to plantsavailable to plants

• Magnesium is taken up by plants as Magnesium is taken up by plants as magnesium ions (Mgmagnesium ions (Mg2+2+))

• Magnesium is an essential Magnesium is an essential component of chlorophyllcomponent of chlorophyll

Magnesium in ChlorophyllMagnesium in Chlorophyll

MagnesiumMagnesium• Most of the magnesium in the soil Most of the magnesium in the soil

exists in forms which are not directly exists in forms which are not directly available to plantsavailable to plants

• Magnesium is taken up by plants as Magnesium is taken up by plants as magnesium ions (Mgmagnesium ions (Mg2+2+))

• Magnesium is an essential component Magnesium is an essential component of chlorophyllof chlorophyll

• Magnesium also plays a role in Magnesium also plays a role in enzymes activation, protein synthesis, enzymes activation, protein synthesis, etc.etc.

Magnesium DeficiencyMagnesium Deficiency

A deficiency in magnesium will A deficiency in magnesium will result in:result in:

• ChlorosisChlorosis• Growth can be reduced alsoGrowth can be reduced also

Magnesium DeficiencyMagnesium Deficiency

MineralsMinerals

SoilSoil PlantPlant

Minerals in soil are taken up by plants, Minerals in soil are taken up by plants, and can be released back into the soil and can be released back into the soil by by decompositiondecomposition

MineralsMinerals

• Crops take up minerals from soilCrops take up minerals from soil• When crops are harvested, minerals are When crops are harvested, minerals are

removed from soilremoved from soil• Soil can also be washed away by rain Soil can also be washed away by rain

waterwater• If there is a lack of minerals in soil, the If there is a lack of minerals in soil, the

production of crops might be affectedproduction of crops might be affected• How can farmers prevent the depletion How can farmers prevent the depletion

of minerals in soil?of minerals in soil?

FertilizersFertilizers

• Fertilizers are added to soil to Fertilizers are added to soil to replace the loss of mineralsreplace the loss of minerals

• Two kinds of fertilizers can be used:Two kinds of fertilizers can be used:

- Natural fertilizers- Natural fertilizers

- Chemical fertilizers- Chemical fertilizers

Natural FertilizersNatural Fertilizers

• Organic fertilizersOrganic fertilizers• Made from organic substances, such Made from organic substances, such

as manure (animal wastes) and dead as manure (animal wastes) and dead bodies of plants and animalsbodies of plants and animals

• Organic compounds in it are Organic compounds in it are decomposed by the bacteria in soil to decomposed by the bacteria in soil to form mineral saltsform mineral salts

Chemical FertilizersChemical Fertilizers

• ““Man-made” fertilizersMan-made” fertilizers• Made with inorganic compoundsMade with inorganic compounds• Can result in pollution of the Can result in pollution of the

environment, such as algal bloomenvironment, such as algal bloom

Comparison between Comparison between natural and chemical natural and chemical

fertilizersfertilizers

Natural fertilizersNatural fertilizers

Contain humus which Contain humus which can improve soil texturecan improve soil texture

Chemical fertilizersChemical fertilizers

No humus so cannot No humus so cannot improve soil textureimprove soil texture

HumusHumus

• Humus is the organic portion of soil, Humus is the organic portion of soil, brown or black in color, consisting of brown or black in color, consisting of partially or wholly decayed plant and partially or wholly decayed plant and animal matter that provides nutrients animal matter that provides nutrients to plants and increases the ability of to plants and increases the ability of soil to retain watersoil to retain water




Contain humus which Contain humus which can improve soil texturecan improve soil textureLess soluble in water so Less soluble in water so less likely to be washed less likely to be washed

awayaway


No humus so cannot No humus so cannot improve soil textureimprove soil texture

Very soluble in water so Very soluble in water so more likely to be more likely to be

washed awaywashed away




Less soluble in water so Less soluble in water so more difficult to be more difficult to be

absorbedabsorbedTime is needed for the Time is needed for the

decomposition to decomposition to complete before complete before

nutrients are available to nutrients are available to plantsplants

Much cheaperMuch cheaper


Very expensive Very expensive

Very soluble in water so Very soluble in water so easier to be absorbedeasier to be absorbed

More readily to be used More readily to be used by the plantsby the plants

Documents

YUMMY!!! Sigh, I wish its time for dinner already. I am so hungry! Hmmm, I wonder what we are having tonight!?