How do plants make food?

Can plants make their own food?

Autotrophs/ Autotrophic organism

Heterotrophs/ Heterotrophic organism

Overview

What is photosynthesis?How does photosynthesis

take place?Conditions needed for

photosynthesisImportance of

photosynthesis

Q: What would the world be like if there were no green plants on earth??

1) Eventually no oxygen

2) No primary producer thus animals starve to death.

blue black

Water Carbon Dioxide

Glucose Oxygen

Light,Chlorophyll,Suitable temperature

+

+

WORD EQUATION FOR PHOTOSYNTHESIS

6H2O 6CO2

C6H12O6 6O2

Light,Chlorophyll,Suitable temperature

+

+

CHEMICAL EQUATION FOR PHOTOSYNTHESIS

Process where light energy is absorbed by chlorophyll and converted to chemical energy, which is used to synthesise glucose from water and carbon dioxide, liberating oxygen during the process.

How do we tell if Photosynthesis has taken

place?Test for Starch

Glucose + Oxygen

Light energy

chlorophyll

(stored as

starch)

Carbon dioxide + Water

Use Iodine test

To Test for Starch in a Leaf1.Place leaf in boiling water.

To stop chemical reactions in the leaf so that enzymes will stop converting starch to glucose.

2.Place leaf in hot alcohol /ethanol. To remove the green chlorophyll

(decolourisation) so the final results can be clearly seen.

           

Bunsen burner

turned off

Alcohol

turned green

3. Dip leaf into warm water

To remove the alcohol on the leaf/ to soften the leaf

4. Spread leaf evenly on white tile. Cover leaf with iodine solution to test for the presence of starch.

5. Leaf turns blue-black if starch is present.

Leaf turns light brown, starch is absent

test_for_starch_in_leaf.flv

MY_FAVE_SONG__THE_PHOTOSYNTHESIS_SONG_[www.keepvid.com].flv

Conditions Essential for Photosynthesis

Sunlight

Chlorophyll

Carbon dioxide

WaterRaw materials

Blue Red

Best absorbedby chlorophyll

Violet Indigo Blue Green Yellow Orange Red

Green

Least absorbed/Best

reflected by chlorophyll

That’s why a leaf

appears

green!

Light Intensit

yCarbonDioxide

Concentration

Temperature

Factors affecting Rate of Photosynthesis

• Keep in a dark place for 24-48 hours (1 to 2 days)

- any stored starch will be converted to sugars which are transported to other parts of the plant

How to destarch a plant?

• To ensure that starch is absent from the leaves at the beginning of an experiment, so that if any starch is formed, then photosynthesis must have taken place

Why destarch a plant?

To find out whether sunlight is necessary for photosynthesis

white

green

brown

Blue-black

To find out whether chlorophyll is essential for photosynthesisVariegated leaf

To find out whether carbon dioxide is necessary for photosynthesis

Soda lime to absorb

CO2

Sodium hydroxide to absorb CO2

To find out what gas is given off during photosynthesis

Oxygen gas released from the cut end of

the stem

To find out what gas is given off during photosynthesis

To provide CO2

Why is Photosynthesis important?

Provides food and energy for animals (primary producers).

Produces oxygen and removes carbon dioxide from the air.

RESPIRATION

Oxygen taken in, Carbon dioxide given out Takes place all the time in living organisms.

DIFFERENCES BETWEEN PHOTOSYNTHESIS RESPIRATION

Can you differentiate between

photosynthesis & respiration?

PHOTOSYNTHESIS- Takes place only in

green plants.- Carbon dioxide taken

in, - Oxygen given out.

- Glucose produced.

RESPIRATION

- Takes place in ALL living organisms.

- Oxygen taken in,

- Carbon dioxide given out.

- Glucose required.- Energy produced.

Net uptake/release of gases

Rate of photosynthesis > rate of respirationNet uptake of CO2 > Net release of CO2

Net release of oxygen > Net uptake of oxygen

Rate of respiration > rate of photosynthesisNet release of CO2 > Net uptake of CO2

Net uptake of oxygen > Net release of oxygen

Photosynthesis/ RespirationN

et

rele

ase o

f oxyg

en

Net

up

take o

f oxyg

en

6 am midday

6 pm midnight

X

Time of day

rate of photosynthesis=rate of respiration X

Yrate of photosynthesis>rate of respiration

Zrate of respiration > rate of photosynthesis

20-

15-

10-

5 -

0

5 -

10-

15-

20-

Q: Why should you not have any green plants in your bedroom at night?

At night, green plants do not photosynthesize due to the absence of light. Respiration takes place and the green plants will compete with you for oxygen.