Photosynthesis

Chapter 8

8-1: Energy & Life

What is energy?

The ability to do work.

What is the difference between autotrophs & heterotrophs?

Autotrophs = make their own food

Heterotrophs = can’t make their own food; must eat other organisms

-LEARNING TARGETS: Define energy.- Why is energy so important to living things?- Explain the difference between autotrophs and heterotrophs.- Draw and label the basic structure of an ATP molecule.- Demonstrate how ATP energy releases energy.

8-1: Energy & Life

Living things use chemical energy to do work.

Chemical energy is found in two places:

A. Electrons (changing energy levels is how light is

produced)

B. Chemical Bonds

- make a bond = store energy

- break a bond = release

energy

8-1: Energy & Life

Adenosine triphosphate (ATP) is the primary energy molecule used by living things.

It is a special nucleotide with three parts:

1. The 5-carbon sugar called ribose

2. The nitrogenous base called adenine

3. 3 phosphate groups (this where the energy is stored)

8-1: Energy & Life

The ADP/ATP Cycle:

* This reaction is reversible!

8.2: Overview of Photosynthesis

The Basic Reaction:

LEARNING TARGETS:- Write the overall reaction

(unbalanced) for photosynthesis using chemical symbols for reactants and products.

- Identify the reactants and products for each stage in a photosynthesis diagram. Explain their functions.

8.2: Overview of PhotosynthesisThe steps of photosynthesis are

placed into groups:1. Light-dependent Reactions

– releases O2 & creates products that will be used in the next step

2. Light-independent Reactions – Uses the products of

the L-D reactions & CO2 to make sugars

* The light-independent reactions are also known as the Calvin Cycle.

8.2: Overview of PhotosynthesisWhat is NADPH & NADP+?

NADP+ is an e- carrier. It is called NADPH when it is carrying an e-. These electrons will help power the Calvin Cycle

NADPH

Light-Dependent Ractions

Calvin Cycle (Light-Independent Reactions)

NADP+

8.2: Overview of Photosynthesis

How do plants capture the energy in light?

They use pigments like chlorophyll.

What does chlorophyll look like?

A phospholipid with a magnesium atom instead of P.

MgPolar Head

Nonpolar TailsChlorophyll molecules are found in clusters called photosystems.

8.2: Overview of PhotosynthesisWhat happens to chlorophyll

when light hits it?An electron gets excited (jumps up an energy level or two) & pops off!

How is the electron replaced?A H2O molecule is split by light in a process called photolysis. This process donates an e- to the chlorophyll molecule & creates the waste product of O2.

H2O

e-

O2 (waste)H+ (to be used later)

Mg

e- (to be used later)

e-

8.2: Overview of PhotosynthesisWhat is a pigment?

A substance that absorbs some colors of light, but reflects others.

Why is chlorophyll green?

It reflects green light.

What colors does chlorophyll absorb best?

Blues, Reds & Violets

8-3: The Details

Review of Chloroplast Structure:

1. Thylakoid Membranes

- the light-dependent reactions occur

here

2. Stroma

- the Calvin Cycle occurs here

LEARNINNG TARGETS:- Label the primary components, or thylakoid and stroma in a chloroplast.- Explain why the pigment chlorophyll captures so much light energy.- Label the 2 stages (reactions) of photosynthesis given a diagram of a chloroplast. - Fill in the reactants and products for each stage in a photosynthesis diagram.

8-3: The DetailsWhat happens during the light-dependent

reactions?1. Water is split (a.k.a. photolysis)2. O2 is made as a waste product during

photolysis.3. Some of the H+ is used to make ATP by an

electron transport chain4. High energy e- & some H+ are picked up by

an electron carrier called NADP+ (NADPH). 5. The NADPH & ATP will be used to power the

Calvin Cycle (light-independent reactions).

8-3: The Details

What happens during the light-independent reactions (Calvin Cycle)?

With the help of the energy stored in the ATP & the NADPH made during the light-dependent reactions, CO2 from the air is used to make sugars.

8-3: The DetailsWhat factors can affect photosynthesis?1. Amount of water

- plants have developed ways to conserve water like waxy coatings on

their leaves2. Temperature

- warmer is better, but if it gets too hot, the enzymes used during photosynthesis will denature

3. Light intensity- brighter is better, but once the

saturation point is met, the rate of photosynthesis is unaffected by increased light intensity

8-3: The Details

Saturation Point

Enzymes denatured past this point.