Cell Energy:
Photosynthesis & Respiration
Chapter 5, Section 1




In plants, chlorophyll (found in chloroplasts) captures energy from the sun in order to make food during photosynthesis
Cells release energy from food through either cellular respiration or fermentation
Why it matters: Understanding how plants & animals get energy to grow & develop is an important part of biology.

How Does a Plant Make It’s Own
Food?


Plants use carbon dioxide ( CO
2 sun’s energy to make food.
), water ( H
2
O ), and
This is called “ photosynthesis
”
 The food gives plants energy
 Animals get the energy stored in plants when they eat them.

How Do Plants Get Energy From Sun?
 Plants have pigments that absorb energy from light
 Chlorophyll (found in chloroplasts) is the pigment used in photosynthesis



The “food” plants make is a sugar called glucose
(C
6
H
12
O
6
).
Glucose and oxygen
(O
2
) are made during photosynthesis.

How Do Organisms Get Energy
From Food?
 Animals cannot make their own food like plants can.
 But, BOTH plants and animals must break down
(digest) food in order to get energy from it (so they can live, grow, & develop)
 Cells do this 2 ways: cellular respiration and fermentation

Cellular Respiration & Fermentation


Cellular Respiration uses oxygen (O
2
) to break down food
Fermentation does not use oxygen
 Cellular respiration releases more energy from food than
Fermentation.
 So most eukaryotes
(ex: plants & animals) get their energy through cellular respiration

 Cellular Respiration = chemical process that happens in cells
 In prokaryotes, it happens in the cell membranes
 In eukaryotes, it happens mostly in the mitochondria




Food (glucose) is broken down into CO
2 energy is released and H
2
O and
C
6
H
12
O
6
+ 6 O
2

6 CO
2
+ 6 H
2
O + energy (ATP)
This energy can be used for:
 Keeping a constant body temperature
 Storage (ATP) - to be used later for things like growth

 Did you notice that cellular respiration is just the opposite of photosynthesis?




Happens when cells cannot get the oxygen they need for cellular respiration
Fermentation is a way to get energy when oxygen isn’t available
Ex: In short, fast races you might get a burning feeling in you leg muscles because of a build up of lactic acid (made during fermentation)

1) Plants use carbon dioxide (____), water (____), and the sun’s energy to make food.
CO
2 and H
2
O
2) What type of cell has chloroplasts?
PLANT CELL
3) BOTH plants and animals must break down food in order to get ________from it.
ENERGY
4) How are respiration and photosynthesis related?
THEY ARE THE REVERSE (OPPOSITE) OF EACH
OTHER.
5) Fermentation is a way to get energy when ______ isn’t available.
OXYGEN




In plants, chloroplasts capture energy from the sun in order to make food during photosynthesis
Cells release energy from food through either cellular respiration of fermentation
Why it matters: Understanding how plants & animals get energy to grow & develop is an important part of biology.