Photosynthesis: the basis…

1. Photosynthesis: the basis… Mrs.JAckie

2. State the photosynthesis involves the conversion of light energy into chemical energy • Light is converted into chemical energy. • The substances needed for photosynthesis are carbon dioxide and water • In the presence of sunlight and chlorophyll these substances can produced glucose and oxygen

3. State that white light from the sun is composed of a range of wavelenghts (colors) • The most usual light for photosynthesis is sunlight • Is white light made of all color together. • Different colors are actually different wavelengths of light.

4. Chlorophyll is the main photosynthetic pigment • Most plants are green • The green color is caused by the presence of the pigment chlorophyll. • It reflects green light and absorbs all other colors. • Different types of chlorophyll exist, each with their own specific absorption spectrum

5. Outline the differences in absorption of red, blue and green light by chlorophyll • Orange-red light and blue light are mostly absorbed while green light is reflected. • Not all pigments contribute efficiently to photosynthesis

7. State that light energy is used to split water molecules to give oxygen and to produced ATP • During photosynthesis light energy is used to split water molecules (photolysis) into hydrogen ion H+, oxygen and electrons producing ATP. • This is called the light dependent stage.

8. ATP and hydrogen are used to fix carbon dioxide to make organic molecules • The H+ and ATP produced drive the formation of glucose from CO2 • Water is formed • This is called the light independent stage

9. Two stages of Photosynthesis Used in forming 6O2 12 H2O + light 24H+ + 24electrons 18 ATP + 12 NADPH2 Light dependent Calvin Cycle 6CO2 18ADP + 18Pi 12NADP+ Used in forming C6H12O6 + H2O Light Independent Stage

10. Rate of photosynthesis can me measured directly by the production of oxygen or the uptake of CO2 or by the increase of biomass • It is possible to allow the carbon dioxide to interact with water, producing bicarbonate and hydrogen ions. • The acidity of the solution will indicate the amount of CO2 • Or it is possible to measure how much oxygen the plant produces over time • Or possible to measure change in organic matter that is the weight of the plant afer dehydration occurs.

11. Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis • To allow photosynthesis to take place the following criteria need to be fulfilled • Presence of chlorophyll • Light • Carbon dioxide • Water • temperature

12. Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis • In practical work it is possible to determine if all the factors are required for photosynthesis by observing • The glucose during photosynthesis is turned to starch • A plant can be destarched by placing it in a dark cupboard for 2 days • During the experiment photosynthesis may or may no take place • Presence of starch can be tested for in a simple test involving the use of iodine

13. Effects of temp, light and CO2 • Chlorophyll requirement • Using a destarched plant with variegated leaves (green and white) and placing it in the light will show that the white parts contain no starch a day later • Showing the need for chlorophyll in the process

14. Effects of … • Temperature • The enzymes involved in photosynthesis have temperature ranges in which they are most effective • These vary from enzyme to enzyme • The rate is higher at the optimum temperature and lower at both low and high temperature

15. Effect of…. • CO2 requirement • If two destarched plants are placed in the light but covered with a transparent plastic bag, one with soda-lime (NAOH) • When the plants are tested for starch the plant with soda lime will have had no photosynthesis • The other plant will show starch • This indicate the need for photosynthesis