1. Energy in a Cell
The Need for Energy (9.1)
Photosynthesis (9.2)
Respiration and Fermentation (9.3)

2. The Need for Energy
Why does a cell need energy?
How does a cell store energy?
Active Transport (moving
materials against the
concentration gradient)


Cell Division


Movement (flagella or cilia)

Production, transport, and
storage of proteins

Other Examples?

First, how does a cell get
energy?

So, how does a cell store
energy?


Breaking bonds
Forming bonds
Energy is stores in the bonds of
adenosine triphosphateor ATP

3. How ATP stores energy

Phosphate groups are negatively charged


Bonding them together requires a lot of energy
Therefore, the bonds store a lot of energy

5. How is the energy in ATP used?

ATP binds to a cell at a specific site

The phosphate bond is broken
 ATP  ADP

The energy from the bond is appropriated to the process that requires the
energy

The ADP can be “recharged” by adding another phosphate

6. Obtaining Energy
Autotroph vs. Heterotroph
Photosynthesis
vs.
Respiration

Food synthesized

Food broken down

Energy from sun stored in
glucose

Energy of glucose released

Carbon dioxide given off

Oxygen taken in

Produces carbon dioxide and
water


Carbon dioxide taken in
Oxygen given off

Produces sugars

Requires light

Does not require light

Occurs only in the presence of
chlorophyll

Occurs in all living cells

7. Photosynthesis

The process by which organisms that contain the pigment chlorophyll convert
light energy into chemical energystored in the molecular bonds of organic
molecules (e.g., sugars)

Chlorophyll absorbs most wavelengths of light (except what?)

9. Photosynthesis

The chlorophyll is found in the thylakoid discs of chloroplasts

10. Photosynthesis

6CO2+ 6H2O +light energy  C6H12O6 + 6O2

Photosynthesis occurs in 2 phases



Light-dependent – occurs in thylakoid discs
Light-independent – occurs in stroma
Photosynthesis is not a very efficient process. Of the sunlight reaching the
surface of a leaf, approximately:





75% is evaporated (heats up water in the leaf)
15% is reflected
5% is transmitted through the leaf
4% is converted to heat energy
1% is used in photosynthesis

11. Photosynthesis
Light-dependent Reactions
Light-independent Reactions

Electron Transport Chain

Calvin Cycle

Put in:

Put in:





Water (H2O)
NADP
NADPH
ATP
Carbon dioxide (CO2)
ADP
Get out:






Sunlight (energy)
Oxygen (O2)
NADPH
ATP

Get out:



NADP
ADP
Glucose (C6H12O6)

13. Light-dependent Reactions:
The Electron Transport Chain

One molecule of chlorophyll absorbs one photon of light and looses one electron.

This electron is passed down through a chain of molecules ultimately leading to the
reduction of NADP to NADPH

ATP is also formed in the process

The chlorophyll regains the lost electron from a water molecule



H2O is split with photons (photolysis)
O2 is released
2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2

14. Light-independent Reactions:
The Calvin Cycle

CO2 is captured from the atmosphere, and with the energy from ATP and the
hydrogen from NADPH, 3-carbon molecules are formed that will later be used
to make sugars (e.g., glucose)

3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi +6
NADP+ + 3 H2O

Why make sugar for energy instead of just using ATP?

16. Respiration

The process by which mitochondria break down food molecules (like glucose)
to produce ATP

There are several possible metabolic pathways by which cells can obtain the
energy stored in chemical bonds:



Glycolysis
Cellular respiration
Fermentation

17. Glycolysis

No oxygen is required (anaerobic)

Glycolysis occurs in the cytoplasm of cells, not in organelles, and occurs
in all kinds of living organisms.

Prokaryote cells use glycolysis and the first living cells most likely used
glycolysis.

Glucose Pyruvic acid + 2 ATP

18. Cellular Respiration:
The Citric Acid Cycle (Krebs Cycle)
The Electron Transport Chain

Oxygen is required (aerobic)

The products of glycolysis (pyruvic acid + 2 ATP) are transferred into
the mitochondria…

…and are used in the citric acid cycle and electron transport chain to
accomplish the reaction below:

C6H12O6+6O2 6CO2+6H2O+36ATP

20. Fermentation

No oxygen required (anaerobic)

Lactic acid fermentation



Glucose pyruvic acid (glycolysis) lactic acid + 2 ATP
Occurs in muscles when oxygen deprived
Alcoholic fermentation


Glucose pyruvic acid (glycolysis) carbon dioxide + alcohol + 2 ATP
What is this used for?

22. Fermentation vs. Cellular Respiration