PHOTOSYNTHESIS

TOPIC

3.8 and 8.2

3.8: Objectives• State that photosynthesis involves the conversion of light energy into

chemical energy.

• State that light from the Sun is composed of a range of wavelengths (colours).

• State that chlorophyll is the main photosynthetic pigment.

• Outline the differences in absorption of red, blue and green light by chlorophyll.

• State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.

• State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.

• Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.

• Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis.

Photosynthesis:

General formula of photosynthesis. 3.8.1

What is light?

Which of these colors does chlorohyll absorb and use for photosynthesis?

Where does photosynthesis take place in eukaryotic cell? 3.8.3 SL-HL

Where does photosynthesis take place in prokaryotic cell?

Chlorophyll SL-HL 3.8.3

SL-HL

ENGELMAN’S EXPERIMENT

• Which wavelengths are used in photosynthesis?

• He used filamentous algae in a fresh water pond.

• He shone fine beams of white light and light of different wavelengths onto different parts of of the algae.

• He used aerobic bacteria as oxygen indicator.• Where algal cells produce oxygen, bacteria

migrated to certain of the illuminated regions.• Bacteria accumulated around red and blue light

region but not around green light.

ENGELMAN’S EXPERIMENT 1882

What happens in photosynthesis?

Two main steps in photosynthesis

1- Light dependent reactions:Light is used to produce ATP by phophosphorylation. At the same time light is used to split water into oxygen and hydrogen (photolysis). These hydrogen protons are used in the second step to make sugar. Oxygen is given out.

Oxygen is the waste product of the photosynthesis.

2- Sugars are built up from carbon dioxide.Carbon dioxide from atmosphere and ATP and hydrogen from light dependent reactions are used to make sugar.

How can we measure the rate of photosynthesis?

Factors Affect Rate of Photosynthesis 3.8.8

a) CO2 concentration:

b) Light Intensity:

c) Temperature:Changes in the temperature has little effect on the light dependent reaction, WHY?

TOPIC 8.2 HL PHOTOSYNTHESIS

1- Draw and label a diagram showing the structure of a chloroplast as seen in electron micrographs.2- State that photosynthesis consists of light-dependent and light-independentreactions.3- Explain the light-dependent reactions.4- Explain photophosphorylation in terms of chemiosmosis.5- Explain the light-independent reactions.6- Explain the relationship between the structure of the chloroplast and its function.7- Explain the relationship between the action spectrum and the absorption spectrum of photosynthetic pigments in green plants.8- Explain the concept of limiting factors in photosynthesis, with reference to light intensity, temperature and concentration of carbon dioxide.

8.2: Objectives

8.2.1

8.2.2

SL-HL

WHAT IS THE SOURCE OF OXYGEN ?

Redox in photosynthesis HL

8.2.3

LIGHT DEPENDENT REACTIONS

a.Cyclic photophosphorylation

b.Non-cyclic photophosphorylation

8.2.3

Light dependent reactions

Cyclic photophosphorylation

Non-cyclic photophosphorylation

CHEMIOSMOSIS 8.2.4

CHEMIOSMOSIS 8.2.4

During transfer of electrons of chl a and b on ETS energy is released. This energy is used to accumulate H ions in the thylokoid space. As a result a H ion concentration gradient is generated (thylokoid side has more H+ than stroma site. These H ions try to diffuse the stroma site. While they diffuse to the stroma site through a protein called ATP synthase ATP is produced.

RELATIONSHIP BETWEEN STRUCTURE OF CHLOROPLAST PHOTOSYNTHESIS 8.2.6

LIGHT INDEPENDENT REACTIONSCALVIN CYCLE 8.2.5

ACTION SPECTRUM and ABSORPTION SPECTRUM

1-

2-

3-

4-

WHAT ARE THE LIMITING FACTORS IN PHOTOSYNTHEIS?

• Temperature

• Carbon dioxide

• Light intensity

• Water

• Number of stomata

• Surface area of the leaf