Photosynthesis & Cellular Respiration

Chapter 9

Energy: the ability to do work

In cells, energy is in the chemical form

The stored chemical energy in cells is called ATP, or adenosine triphosphate

Energy is released when ATP is converted into ADP + a phosphate group

Chemical Energy

Plants and animals obtain energy in different ways:

◦Plants ONLY: make their own energy through the process of photosynthesis

◦Plants and Animals: get ATP by breaking down organic compounds (proteins, carbs, etc.) through the process of cellular respiration

Photosynthesis: the conversion of light energy into chemical energy◦Occurs in chloroplasts◦Reactants (IN): CO2, H2O, and energy

◦Products (OUT): O2 and glucose (C6H12O6)

◦6CO2 + 6H2O + light energy → C6H12O6 + 6O2

Photosynthesis Overview

1) Light Reactions (“photo”)◦ Occurs in thylakoid◦ Light from sun excites

electrons◦ O2 is released

2) Calvin Cycle (“synthesis”)◦ Occurs in stroma◦ CO2 is used to make glucose

(C6H12O6)

Phases of Photosynthesis

Plant and animal cells make ATP by breaking down organic molecules (sugars, fats, etc.)

This process is called Cellular Respiration◦ Occurs in the mitochondria◦ Reactants (IN): C6H12O6 (glucose) & O2

◦ Products (OUT): CO2 & H2O & ATP (energy)

◦ C6H12O6 + 6O2 → 6CO2 + 6 H2O + 36 ATP

Cellular Respiration Overview

Begins with Glycolysis◦ 1 molecule glucose is split in half into 2 pyruvate

molecules

If O2 is present → Citric Acid (Kreb’s) Cycle & Electron Transport Chain

If O2 is NOT present → Fermentation

Cell Respiration Overview

Occurs when no O2 is present 2 Types:

◦ 1. Lactic Acid Fermentation: Converts pyruvate → lactic acid Helps make yogurt & cheese Creates burning sensation in muscles during exercise

◦ 2. Alcoholic Fermentation: Converts pyruvate → ethyl alcohol Helps make bread, wine & beer

Fermentation

Occurs when O2 is present Breaks down pyruvate molecules (from

glycolysis) into smaller molecules As chemical bonds form and break,

electrons get moved around & CO2 is released

This releases energy, thus making ATP!

Citric Acid (Kreb’s) Cycle & Electron Transport Chain