Chapter 8

Energy is the ability to do work

All living organisms require energy To be active (play sports) Even while resting (cells require energy at all

times!)

Without the ability to obtain and utilize energy, life would stop!

Where does energy come from? The energy to create most food comes from the sun

Autotrophs – organisms that can produce their own food Plants and some other types of organisms can use

light energy from the sun to produce their own food

Heterotrophs – organisms that cannot produce their own food, but must consume other organisms Animals, bacteria, fungi

Energy comes in many forms Light, heat, electricity

Living organisms use chemical fuel One of the main chemical compounds used for

energy is ATP (adenosine triphosphate) ATP is exceptionally useful as the basic source of

energy of all cells

ATP is made of adenine, ribose, and 3 phosphate groups The phosphate groups allow ATP to store and

release energy

ADP (adenine diphosphate) is similar to ATP, except it only has 2 phosphate groups

When a cell has energy available, it adds another phosphate group to ADP which produces ATP ADP = ½ charged battery : ATP = fully charged

battery

When the cell needs energy, the 3rd phosphate group breaks away from the ATP molecule Remember energy is created when bonds are

broken

Enough energy is released to power cell activities

The molecule then becomes ADP again

Cells use ATP energy for different functions:

1. Transport across cell membranes Active Transport - the movement of

molecules across the cell membrane from low to high concentration

2. Protein synthesis Energy is used to respond to chemical

signal to produce proteins

3. Muscle contraction Requires energy from the cell with the use

of a sodium/potassium pump

Even though ATP is an excellent source of energy, cells are not packed with it

Most cells have only a small amount of ATP Only enough to last a few seconds of

activity

ATP is good for transferring energy, but not storing energy Energy storage is best in carb’s (glucose

can store 90 times the chemical energy of an ATP molecule)

One of the key processes involved with energy production is photosynthesis

Photosynthesis – the process that uses the sun’s energy to convert carbon dioxide and water into oxygen and carbohydrates

There has been much research on photosynthesis Early research investigated the overall

process Later research investigated the

chemical pathways

In addition to CO2 and H2O, plants require light (to energize the reaction) and chlorophyll for photosynthesis to occur

Plants gather the sun’s energy with light absorbing molecules called pigments

The main pigment of plants is called chlorophyll

Chlorophyll absorbs light very well in some spectrums (blue-violet and red) and not in others (green) Green light is reflected, so plants

appear green

Since light is a form of energy, any compound that absorbs light also absorbs energy When chlorophyll absorbs light, it is

directed to its electrons which raises their energy levels

These high energy electrons make photosynthesis work

The requirements for photosynthesis were discovered in the 1800’s

It wasn’t until the mid to late 1900’s that scientists understood the complex chemical reactions of photosynthesis

Photosynthesis takes place inside organelles called chloroplasts

Chloroplasts contain saclike photosynthetic membranes called thylakoids

Within the thylakoids are proteins called photosystems which organize chlorophyll They are the light-collecting units of the

chloroplast

There are 2 different types of reactions that take place in order for photosynthesis to happen

1. Light-Dependent Reactions – take place in the thylakoid

2. Light-Independent Reactions – take place in the stroma (the region outside the thylakoid membranes)

Is represented with the Calvin Cycle

When sunlight excites electrons in chlorophyll, these electrons gain a great deal of energy These electrons require a special carrier

A carrier molecule is a compound that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule

This process is called electon transport and the carriers are known as the electron transport chain

One of the electron carriers is NADP+

When an electron needs to be transported, NADP+ accepts 2 high energy electrons and 1 hydrogen ion (H +)

This converts NADP+ into NAPDH one way sunlight can be trapped into a

chemical form

NADPH carries the electrons to elsewhere in the cell, releases them and returns to the NADP+ form

Light-Dependent Reactions require light

These reactions use energy from light to produce ATP and NADPH and oxygen

The ATP and NADPH formed by light-dependent reactions contains an abundant amount of chemical energy These compounds are not stable

enough to store that energy for more than a few minutes

The Calvin Cycle uses the ATP and NADPH to produce high-energy sugars which can store energy for long periods of time

Remember, photosynthesis is possible because of the back and forth relationships of the light-dependent and light-independent (Calvin Cycle) reactions

Light-Dependent traps energy

Calvin Cycle converts energy into sugars

Water shortage Why plants that live in dry climates have a

waxy covering on their leaves

Temperature Photosynthesis happens best between 0 C

and 35 C (32 F and 95 F) Anything above or below can damage

enzymes which can slow or stop photosynthesis

Light intensity Photosynthesis happens best only at

certain intensity levels