Nutrition in plants

Nutrition in plants (I)

Chapter 7

Learning ObjectivesPart I

• Why is photosynthesis important? Pg 127

• Photosynthesis overall Equation pg 120

• Fate of glucose formed pg 125-126

• Leaf structure & function Chap 7.2 pg 128-130

• How do CO2 & H2O enter the plant? pg132

• What are the conditions necessary for photosynthesis? Pg 118

Part II

• Testing for starch investigation 7.1

• Factors affecting the rate of photosynthesis (ICT) pg 123-124

• Limiting factors pg 121

Why is photosynthesis important?

• Converts light to chemical energy

• “Purifies” air

• Fossil fuel: Coal

7.1 pg 127 Why photosynthesis?

– Sunlight is the ultimate source of energy– Light chemical energy stored as carbohydrate– Proteins, fats and other organic compounds can be derived from carbohydrates

–Removes CO2; – Provides O2 for cellular respiration

– Coal formed from dead plant matter over 400 MYA

Photosynthesis

• Photosynthesis is the process by which light energy absorbed by chlorophyll is transformed into chemical energy used to make carbohydrates from water & carbon dioxide. Oxygen is released during the process.

7.1 pg 119 What is photosynthesis?

Photosynthesis

• Photosynthesis consists of

2 stages: Light stage

- Light independent stage


Light stage of photosynthesis

• Light energy is absorbed by chlorophyll and converted into chemical energy.

• Light energy used for photolysis of water

• Photolysis = light + spliting

• 12 H2O molecules spilt to yield 6 O2 molecules + 24 H atoms

• Glucose is the first stable form of carbohydrate formed.


Q. Why does the volume of oxygen produced indicate the rate of photosynthesis?

Light-independent stage of Photosynthesis

• H atoms from light stage help reduce 6 carbon dioxide molecules to glucose.

Overall Equation for Photosynthesis

7.1 pg 120 Equation

glucose

Chlorophyll

Word equation:

Chemical equation:

Fate of glucose formed

7.1 pg 125-126 Fate of glucose

Glucose

Sucrose

Energy

Used

Used

Used

Stored

StarchFats

a.a

Proteins

Cellulose cell wall

Fate of glucose formed during photosynthesis

Glucose is used

- immediately for Energy via respiration

- To make cell wall

- To make fats

- To make amino acids & proteins

Use of glucose

•Glucose is first used by cells during tissue respiration to provide energy for cellular activity

•Glucose react with nitrates & minerals to form amino acids.•Amino acids form proteins which are used to build new cell protoplasm.

•In leaves & storage organs

Fate of glucose formed during photosynthesis

Glucose can be stored as starch- Excess glucose sucrose which is

transported to storage organs e.g. stem tubers & root tubers.

Storage of glucose

-Temporally stored as starch in leaf in the -day (high rate photosynthesis)-Starch is reconverted by enzymes into -glucose/sucrose at night

Leaf Structure & Function

7.2 pg 128 Leaf Structure & function

Leaf Structure7.2 pg 128 Leaf Structure & function

External Internal

•Vein network •Upper epidermis

•Mesophyll a) palisade

b) spongy

•Lower epidermis

•Stoma

•Lamina

•Petiole (leaf stalk)

•Leaf arrangement

External Structure of Leaf

Internal Structure of Leaf

Internal Structure of Leaf

Mesophyll

Palisademesophyll

Spongymesophyll

Upper Epidermis• Cuticle

- Waxy

- protects leaf tissue

- prevents excessive water evaporation

- Is transparent

• 1 layer of closely packed cells

Mesophyll• Layer between upper and lower epidermis• Consists of Palisade Mesophyll Spongy Mesophylllong, cylindrical cells

(1-2 layers)closely packed

Cells here has many chloroplasts

Irregular cells

Loosely packed; many intercellular air spacesFewer chloroplasts than palisade mesophyll cells

Mesophyll cells

• All mesophyll cells have a thin film of moisture for

• CO2 to dissolve in• Xylem & Phloem found here.• X+ Y = vascular bundles (more in chap 9)

• Xylem transports water & dissolved materials from roots to rest of plants

• Phloem transports sugars from leaf to rest of plant

Lower Epidermis

• Similar to upper epidermis

• Contains stomata

Leaf Structural adaptations to Function7.2 pg 133 Leaf Structure to function

Structure Function

Petiole (leaf stalk) Position leaf for max light absorption

Thin lamina Max absorption & penetration of light to reach mesophyll

Max diffusion for CO2

Waxy cuticle Reduce water loss due to evaporation

Stomata Gaseous exchange

chloroplasts Absorbs, converts light chemical energy stored in glucose

More chloroplasts in upper palisade tissue

More sunlight reaches top half of leaf

Many intercellular air spaces Rapid diffusion of gases

Veins with xylem & phloem Xylem transports water; phloem transports sugar

Q. How do CO2 & H2O enters the leaf?

• Via stomata • Via roots• Xylem • Veins • Cell to cell in leaf

(osmosis)

In the day, CO2 is used for photosynthesis. The CO2 concentration in leaf is lower than that of the atmosphere.CO2 diffuses from surrounding air through stomata into leaf’s air spaces down a concentration gradient.

Q. What are the conditions necessary for photosynthesis?

• Sunlight

• Chlorophyll (green pigment)

• CO2

• Water

• Suitable temperature

7.1 pg 118 Photosynthesis conditions

Sunlight, Chlorophyll & CO2 are essential for photosynthesis. Other conditions needed are a suitable temperature and water.

Investigation on conditions necessary for photosynthesis 7.2-7.4Exp 7.2 Sunlight Exp 7.3 Chlorophyll Exp 7.4 CO2

1. Destarch

2. Remove leaf

3. Cover parts of leaf with black paper

4. Remove leaf after a few hours

5. Test for starch

1. Destarch variegated leaf

2. Expose leaf to sunlight for a few hours

3. Remove leaf; note parts with chlorophyll

4. Decolourise the leaf with ethanol

5. Test for starch

1. Destarch 2 potted plants

2. Enclose pots & parts of plants excluding leaves in polythene bags;

3. Place 1 pot in bell jar with soda lime or KI; the other without

4. Expose plants in sunlight

5. Remove a leaf from each pot test for starch.

Q. Why do we test for starch as an indicator of photosynthesis?

• Excess glucose made by leaves are stored as starch

Q. How do we “de-starch” plants?

• By placing the plant in darkness for 2 days. In darkness, no photosynthesis occurs. Glucose is used up for respiration. Some starch will be converted back to glucose for cellular respiration.

SummaryPart I


• Photosynthesis Overall Equation pg 120





Part II




Nutrition in plants (II)

Chapter 7

Learning ObjectivesPart I







Part II




Recap

How do CO2 & H2O enter the plant? pg132

Pathway of CO2 from

atmosphere through

Stomata to rest of the

plant.

Recap:

Pathway of water

from roots through

plant & out of stomata

Starch Test(Recap of Activity 20.1 in sec 2 practical)

How can we test for starch in a leaf?

• Remove green leaf

• Submerge leaf in boiling water for 2 min

• Place leaf in ethanol in boiling tube in a hot water for 10minutes

• Remove the leaf, dip it in hot water

• add a few drops of iodine solution and test for starch

We can show that photosynthesis has taken place by testing for presence of starch in leaves.

7.1 pg 115 Photosynthesis

Factors affecting Photosynthetic Rate

7.1 pg 123-124 Photosynthesis

-Light intensity-temperature

- Carbon dioxide concentration

- Chlorophyll concentration

- Water

- pollution



Light intensity (investigation 7.6)

Q. How can we investigate the effect of different light intensities on the rate of photosynthesis?

1. Set up apparatus2. Allow plant to adapt till bubbles produced at a steady rate 3. Count bubbles over a period of 5 minutes. Repeat to get

average4. Repeat step 3 with different distance from light source. E.g.

10, 25, 50,75,100cm (shorter distance= higher intensity)5. Record results in table. Plot rate of bubbling per min against

distance between lamp & the plant. 6. Conclusion

Suggested Table

Set up

Distance of light source from plant (cm)

1st reading

2nd reading

3rd reading

Aver-age

Rate of bubbles/min

1 10 100 103 110 104.3 20.9

2 25 80 89 85 84.7 16.9

3 50 60 58 63 60.3 12.1

4 75 40 39 39 39.3 7.9

5 100 20 18 16 18.0 3.6

Graph of Rate of bubbles per min (1/min) against distance of light source from plant

(cm)

05

1015

2025

0 50 100 150

Distance of light source from plant (cm)

Rat

e o

f b

ub

ble

s/m

in

As distance increases, light intensity decreases.

0

B

▲Fig 1 Effect of increasing light intensity on the rate of photosynthesis at 0.03% CO2 at 20°C

From A to B, even though light intensity increases, rate of photosynthesis remains constant. Light intensity is no longer a limiting factor.

From 0 to A, as light intensity increases, rate of photosynthesis increases. Light intensity is a limiting factor during this stage

A



Temperature (investigation 7.7)

Q. How can we investigate the effect of different temperatures on the rate of photosynthesis?

1. Set up2. Place lamp (e.g. 60W) 10cm away from plant. Keep this

distance constant. 3. Add ice-cube to make the water bath 5°C temperature.

Allow plant to adapt till bubbles produced at a steady rate 4. Count bubbles over a period of 5 minutes. Repeat to get

average5. Repeat step 3 at different temperatures. E.g. 15°C, 20°C,

35°C,50°C. Record results in table. Plot rate of bubbling per min against temperature.

6. Conclusion

Effect of increasing temperature on rate of photosynthesis

a) As temperature increases, rate of photosynthesis increases

b) optimum temperature; max rate of photosynthesis

c) beyond point B, photosynthesis decreases as temperature increased

Carbon dioxide Concentration(investigation 7.8)

Q. How can we investigate the effect of different carbon dioxide concentration on the rate of photosynthesis?


• Refer to TB pg124 investigation 7.8 for details of experiment

Limiting factors

• Any factor that directly affects a process if its quantity is changed.

• Rate of photosynthesis is affected by:

- Light intensity

- temperature

- CO2 concentration

7.1 pg 121 Photosynthesis

If there is not enough chairs , time taken will be longer.

If there are many chairs – time taken would still be the same as in the case of having 5 chairs only.

0

B

▲Fig 1 Effect of increasing light intensity on the rate of photosynthesis at 0.03% CO2 at 20°C

From A to B, even though light intensity increases, rate of photosynthesis remains constant. Light intensity is no longer a limiting factor.

From 0 to A, as light intensity increases, rate of photosynthesis increases. Light intensity is a limiting factor during this stage

A

Light intensity as a limiting factor

Effect of increasing temperature on the rate of photosynthesis

Increasing light intensity (photons/m/s)

Rat

e of

pho

tosy

nthe

sis

(bub

bles

/min

)Temperature as a limiting factor

FE

• As temperature increases, rate of photosynthesis increases significantly

• From graph, every 10°C increase in temperature, rate of photosynthesis ≈ doubles.

• Therefore temperature of surroundings is the limiting factor.

Temperature as a limiting factor

Carbon dioxide concentration as a limiting factor

DC

Carbon dioxide concentration as a limiting factor

Usually CO2 is an important limiting factor in the atmosphere.

As CO2 increases, rate of photosynthesis significantly increases.

This indicates CO2 concentration is the limiting factor in CD.

SummaryPart I







Part II




Nutrition in plants

Technology

Transcript of Nutrition in plants