Plant Nutrition and Plant Nutrition and PhotosynthesisPhotosynthesis

Reading QuizReading Quiz•Get out a small sheet of paper and write your name at Get out a small sheet of paper and write your name at

the top. Answer the following questions the top. Answer the following questions in silencein silence

1)1)What is the chemical process that plants use to make What is the chemical process that plants use to make

energy from sunlight?energy from sunlight?

2) What reactants do plants need to do this reaction?2) What reactants do plants need to do this reaction?

3) Why are plants green?3) Why are plants green?

4)What is the organelle that absorbs sunlight?4)What is the organelle that absorbs sunlight?

6CO2+6H2O+sunlightC6H12O6+6O2

CO2, H2O, and sunlight

Only color they don’t absorb well

Chloroplasts

ATP: The Energy unit of the Cell

ATP (adenosine triphosphate,三磷酸腺苷）

O O O O CH2

H

OH OH

H

N

H H

O

NC

HC

N CC

N

NH2Adenine

RibosePhosphate groups

O

O O

O

O

O

-

- - -

CH

Cell Energy use in Active Transport

• Energy is released from ATP (-30.54 kJ/mol)– When the 3rd phosphate bond is broken

Trapping Energy from Sunlight

• The process that uses the sun’s energy to make simple sugars is called photosynthesis

• Bases of all ecosystems on Earth

6 CO2 + 6 H2O + Light energy C6H12O6 + 6 O2

Tissue of a LeafTissue of a Leaf•Plant tissue:Plant tissue:

•Upper epidermisUpper epidermis water proof outer water proof outer

covering; covered with covering; covered with cuticlecuticle

•Palisade mesophyllPalisade mesophyll photosynthetic cells; photosynthetic cells;

lots of chloroplastslots of chloroplasts

•Spongy mesophyllSpongy mesophyll space for CO space for CO22/O/O22

circulationcirculation

•PhloemPhloem transport solutes transport solutes

•XylemXylem transport water and salts transport water and salts

•Lower epidermisLower epidermis stomata for gas stomata for gas

exchangeexchange

Vein

Leaf cross section

Mesophyll

CO2 O2

Stomata

Where Does CO2 come from?•Enters leafs through the stomata

Where does H2O come from?•Absorbed by roots and pulled up to the leaves by cohesion and adhesion

(transpiration)

The Problem with Gas Exchange• How does CO2 and O2

get in and out of a plant?– Stromata under the

leaves• What else can escape

through a stromata that the plant needs?– H2O

• What problems must plants in dry, hot climates deal with?– The plant needs to

take in CO2 and release O2, but the open stromata will also release H2O

H2O out

Where does Light Energy come from?

• Energy from the sun must be absorbed by pigments, light absorbing molecules (chlorophyll)

• Inside a chloroplasts are thylakoids and inside their membranes are pigments

• What wavelength of light do the pigments not absorb?– Green; reason why plants

are green

Photosynthesis: 2 Reaction Set

1) Light-dependent reactions chemical reactions driven by light energy absorbed by pigments

2) Light-independent reactions chemical reactions that use ATP and NADPH to create sugars out of CO2

H2O CO2

Light

LIGHT REACTIONSCALVINCYCLE

Chloroplast

[CH2O](sugar)

NADPH

NADP

ADP

+ P

O2

ATP

The Light-Dependent reactions

LightReflectedLight

Chloroplast

Absorbedlight

Granum

Transmittedlight

Pigments- light absorbing moleculesChlorophyll main light absorbing pigment

Light-dependent reactions use chlorophyll to trap light energy. This energy produces ATP, NADPH, and O2

The Light-Dependent reactions

Photolysis

H2O CO2

Light

LIGHT REACTIONSCALVINCYCLE

Chloroplast

[CH2O](sugar)

NADPH

NADP

ADP

+ P

O2

ATP

The Light-Independent reactions

Final NumbersUse Produce

Light-Dependent Reactions

Sunlight NADPH

H2O ATP

O2

Use Produce

Light-Independent Reactions

(Calvin Cycle)

NADPH

RuBP

RuBP (recycled to keep

cycle going)

ATP PGAL (Which form sugars)

CO2

Photosynthetic RatesPhotosynthetic Rates

Structure of a Leaf• If photosynthesis occurs

mostly in the leaf, what factors must be considered when designing a leaf?

1)Amount of sun exposure– More surface area = more

photosynthesis

2)Movement of CO2 and O2– Space for exchange

3)Movement of H2O and products of photosynthesis– Water from the roots and

organic molecules to other areas

Photosynthetic Rates: Light• What factors could affect

photosynthetic rate?– Light intensity– Amount of CO2 / H2O– Too much O2 – Temperature

• Increase Light Intensity = Higher Photosynthetic rate

– BUT there is a max. limit; Why?

• Limit to how fast enzymes can work

Photosynthetic Rates: Temperature• If just temperature is increased,

rates go up Why?– More kinetic energy = faster

enzymatic rates

• Why is there only a small increase in rate?

– Light-dependent stage is limited by light intensity

• What would be create the best photosynthetic rate?

– High temperature and high light intensity

• Why do rates drop after raising the temperature too high?

– Enzymes (proteins) denature

Photosynthetic Rates: Limiting Factors• Even with high temps

and high light intensity, what factors must be considered?

– Availability of CO2 and H2O

– Too much O2 (limits enzymes in high conc.)

• Limiting factor the factor least available or having the strongest affect on reactions rates

– Can be light, temperature, CO2, H2O, or O2 depending on the situation

Limiting Factors Practice• What is the limiting factor for :1) Plants in the rain forest?

– Light intensity; Rain forests have plenty of rainfall and humidity but limited space; plants fight for sunlight

2) Plants in the deserts?– Water; Deserts have plenty of sun and

open space but very little rain3) Plants underwater?

– CO2/Sunlight; Dissolved CO2 harder to access and sunlight loses strength as it passes through water

4) Plants in the arctic?– Temp/Sunlight; Cold temperatures

and little direct sunlight limits growth

Limiting Factors on Growth• We have plant that gets

plenty of sunlight, water, and CO2. However it seems to grow very slowly and looks unhealthy. Why?

– Missing other nutrients– Soil does not contain enough

mineral salts

• Mineral salt plant nutrients needed for growth and repair

– Nitrates– Phosphates– Ions like Mg and K

Mineral Salts• Nitrates nitrogen based

compounds like NH3, NO2-, and

NO3- which are used to build

amino acids– Most nitrogen is N2 which is

unusable– Nitrogen fixation by bacteria

make nitrates – Animal urine has urea which is

similar to NH3

• Phosphates PO43- which is

used to build DNA and RNA• Magnesium ions Mg2+ which

is used to build chlorophyll• Potassium ions K+ which is

used to make stable cells all over the plant

Getting Mineral Salts• Mineral salts must be present in

the soil for plants to grow. How can we add mineral salts?

1) NPK fertilizers mix of material containing NPK ions which are absorbed by the roots

– Can wash away and cause algae blooms rapid growth of algae in lakes that causes the ecosystem to crash

2) Humus natural decomposition of material (compost) that slowly added mineral salts to soil

– Farms can never be sure if enough of each Ion is present in compost