Powers Unit 4 Photosynthesis

Photosynthesis Notes

Unit 3: Cellular Energy

How do plants convert light
energy into chemical energy

(glucose)? What is the difference

between light dependent and
light independent reactions?

Carbohydrates

● Carbohydrates are made up of carbon, hydrogen,

and oxygen, abbreviated as CHO.

● They are usually found in a 1:2:1 ratio in their

formulas.
○ Ex: glucose = C6H12O6 = 1:2:1 x 6 = 6:12:6
○ This will help you tell carbohydrates from lipids.

● They can be small like glucose or large like starch.

Carbohydrates

● These are used as the primary source of fuel for all

organisms and for short term energy storage.

● Cells receive energy when complex carbohydrates

are broken down into simple sugars.

● These simple sugars are used as fuel during

cellular respiration, releasing energy that is stored
in the form of ATP.

Carbohydrates

● They are also used for structure, such as plants

using cellulose in their cell walls.
○ Also known as fiber, which stimulates the

digestive system in animals.

● Lastly, they are used as raw materials for the cells

to synthesize other molecules needed, such as
fatty acids and amino acids.

Types of Carbohydrates

Monosaccharides

● The monomer of carbohydrates are

monosaccharides, or simple sugars (C6H12O6)

● Ex: glucose (green plants), galactose (milk), and

fructose (fruit)

Disaccharides

● Disaccharides are made of two monosaccharides.
● Ex: sucrose (glucose + fructose), lactose (galactose

+ glucose), and maltose (glucose + glucose)

Polysaccharides

● Polysaccharides are made up of more than two

monosaccharides and are often quite large.

● Ex: Cellulose (used for structure in plant cell walls),

starch (excess sugar storage in plants), glycogen
(excess sugar storage in animals), and chitin
(exoskeleton of insects and crustaceans)

Polysaccharides

Carbohydrate Facts

● Carbs are soluble in water
● You receive 4 kCal/g of energy
● Their names typically end in

-ose

● Cellulose is the most

abundant macromolecule
on earth

“This is how I cut carbs on

the weekend…”

Food Examples

Cellular
Examples

Photosynthesis
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Overview of Photosynthesis

★ Producers make their own source of chemical energy.

• Plants use photosynthesis and are producers.

• Photosynthesis captures energy from sunlight to make

sugars.

Photosynthesis
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Overview of Photosynthesis

• The absorption of lightis the first step in

photosynthesis.

• Chlorophyll is a pigment molecule that absorbs

light energy.

• In plants, chlorophyll is found in organelles

called chloroplasts.

➔

We see plants as green because green light rays from the sun
are reflected. During the time of the year when there is less
daylight (fall, winter), we see leaves as orange and red
because the green chlorophyll pigments no longer dominate
in the cooler months, which allow other pigments to be seen

Photosynthesis
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Overview of Photosynthesis

Chloroplasts

• Organelles that capture light energy because they contain

chlorophyll

• Contain two main compartments:

• Thylakoids: flattened saclike membranes

• Stacks of thylakoids are called grana.

• The fluid filled space outside the grana called the stroma.

Chloroplast Structure

Thylakoid
Granum

Thylakoid membrane

Stroma

Photosynthesis
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★ Photosynthesis in plants occurs in the chloroplasts
• Photosynthesis is all about converting energy from one form

(sunlight) into another, more useable form (glucose)

• Photosynthesis includes 2 main reactions that take place in

two parts of chloroplasts.

1. Light-Dependent
2. Light-Independent (Calvin Cycle)

Photosynthesis
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Stages of Photosynthesis

1. Light-Dependent reactions

Overview:

● solar energy is absorbed by chloroplast and two

energy-storing molecules (ATP and NADPH) are produced

● solar energy is used to split water molecules which results

in the release of oxygen as a waste product

Photosynthesis
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Stages of Photosynthesis

1. Light-Dependent reactions

In detail:

●

1. Chlorophyll in the thylakoids inside the chloroplast absorb light

●

2. Water is split into H+, electrons (e ), and O2 gas.

●

3. Electrons (e ) are excited by light and become energized

●

4. Excited electrons enter an electron transport chain (ETC) in the
thylakoids where they are used to make ATP (energy!)

●

5. An electron acceptor called NADP+ combines with the H+ and
electrons to become NADPH, an energy rich molecule

Photosynthesis
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Light-Dependent Reaction Review

1. Light-Dependent Reaction

Goal: Capture energy from sunlight

Where: Grana (thylakoid membranes)

Needs: H2O, sunlight & chlorophyll (chlorophyll absorbs
sun energy)

What happens: Light energy is transferred along thylakoid
membrane and then to light-independent reactions

Released: Oxygen

Photosynthesis
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Stages of Photosynthesis
2. Light-Independent (also known as the Calvin Cycle)
Overview:
● Carbon dioxide from the atmosphere and

energy carried by ATP and NADPH is used to
make simple sugars (such as glucose)

● These simple sugars store chemical energy

Photosynthesis
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Stages of Photosynthesis
2. Light-Independent (Calvin Cycle)

●

In Detail:

●

1. NADPH and ATP made in the light reactions move to the stroma inside
the chloroplast

●

2. CO2 from the air also enters the stroma through the stomata (stomates)
and combines with a 5 carbon molecule there to make a 6 carbon sugar

●

3. A cycle of reactions begins where NADPH and ATP give off (donate)
their energy to the molecules being made

●

4. Glucose is produced in the cycle, and everything else left over
recombines into the 5 carbon molecule we started with (and the cycle
starts over again)

Photosynthesis
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What is it? Where it happens? What does it needs to
start? What does it produces?

2. Light-Independent (Calvin Cycle) reaction

Goal: make sugars

Where: Stroma

Needs: carbon dioxide from atmosphere and energy from
the light reactions

What happens: use energy to build sugar in a cycle of
chemical reactions

Released: sugars (glucose)

Photosynthesis
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Photosynthesis

●

The equation for the overall process is:

6CO2 + 6H2O → C6H12O6 + 6O2