8.2 Photosynthesis

How do plants get energy?

What factors affect photosynthesis?

Objectives12a) I can describe the role of ATP in cellular activities.

12b) I can explain where plants get the energy they need to produce food.

13a) I can explain the role of light, pigments, and electron carrier molecules in

photosynthesis.

13b) I can state the overall equation for photosynthesis.

14a) I can describe what happens during the light-dependent and light-independent

reactions.

14b) I can identify factors that affect the rate at which photosynthesis occurs.

15a) I can explain where organisms get the energy they need for life processes.

15b) I can define cellular respiration and compare it to photosynthesis.

16a) I can describe what happens during glycolysis and the Krebs cycle.

16b) I can explain how high energy electrons are used by the electron transport chain

An Overview of Photosynthesis

Photosynthesis uses the energy of sunlight to convert water and carbon

dioxide into high-energy sugars and oxygen.

Overview of Cellular Respiration

If oxygen is available, organisms can obtain energy from food

by a process called cellular respiration. The summary of

cellular respiration is presented below.

In symbols:

6 O2 + C6H12O6 → 6 CO2 + 6 H2O + Energy

In words:

Oxygen + Glucose → Carbon dioxide + Water +

Energy

Lactic Acid Fermentation

● A breakdown of glucose

that creates ATP. Does not

need oxygen.

Ways to break down energy ● Aerobic Respiration- the process of producing cellular

energy involving oxygen.

● Anaerobic Respiration- the process of producing cellular

energy without oxygen.

● Fermentation- a partial breakdown of organic molecules to

produce energy, usually without oxygen.

Lesson Overview Leaves

Stomata - small openings that allow carbon dioxide, water, and oxygen exchange.

Photosynthesis

Lesson Overview Leaves

Guard cells - regulate the movement of gases into and out of leaf tissues.

Chloroplasts

● Chloroplast - organelle where photosynthesis occurs.

● Thylakoid - a photosynthetic structure within the chloroplast.

● Grana - stacks of thylakoids

● Stroma - fluid portion outside of thylakoid

High-Energy Electrons

● NADP+ (nicotinamide adenine

dinucleotide phosphate) is an

energy carrier molecule.

● NADP+ accepts and holds two

high-energy electrons, along with

a hydrogen ion (H+). In this way, it

is converted into NADPH.

● NADPH can then carry the high-

energy electrons to chemical

reactions elsewhere in the cell.

Lets Draw!What is really going on in a chloroplast? (p. 111)

Energy Collection

Because light is a form of energy, any compound that absorbs light absorbs

energy. Chlorophyll absorbs visible light especially well.

When chlorophyll absorbs light, a large fraction of the light energy is transferred

to electrons. These high-energy electrons make photosynthesis work.

Light-Dependent Reactions

● Photosynthesis involves two sets of reactions.

● The first set of reactions is known as the light-dependent reactions

because they require the direct involvement of light and light-absorbing

pigments.

Light-Dependent Reactions

● Light-dependent reactions use energy from sunlight to produce ATP and NADPH.

● These reactions take place within the thylakoid membranes of the chloroplast.

● Water is required as a source of electrons and hydrogen ions. Oxygen is released

as a byproduct.

Light-Independent Reactions

Plants absorb carbon dioxide from the atmosphere and complete the process of

photosynthesis by producing sugars and other carbohydrates.

● Light-independent reactions - ATP and NADPH molecules produced in

the light-dependent reactions are used to produce high-energy sugars from

carbon dioxide.