1

Biology 3

Ch 4 Photosynthesis and

Respiration

Dr. Terence Lee

Enzymes

2

Why do some adults get sick when they drink milk?

3

Energy Conversions

� All life depends on capturing energy from the sun and converting it into a form that living organisms can use.

� Two key processes

Take-home message 4.1

� The sun is the source of the energy that powers all living organisms and other “machines.”

What is energy?

� The capacity to do work

�Work

4

Kinetic Energy

� The energy of moving objects

Potential Energy

� A capacity to do work that results from the location or position of an object

5

Energy Conversions� Only ~1% of the energy released by the sun that earth receives is captured and converted by plants.

• Converted into chemical bond energy

First Law of Thermodynamics

� Energy can never be created or destroyed.

ATP Molecules

� Cells cannot use light energy directly to do work.

6

Photosynthesis

• The process in green plants and certain other

organisms by which …

Photosynthesis: The Big Picture

7

“Photo” and “Synthesis”

Light Energy

� Different photons carry different amounts of energy, carried as waves.

� Length of the wave = amount of energy the photon contains.

Electromagnetic Spectrum

� Range of energy that is organized into waves of different lengths.

� Shorter the wavelength, higher the energy.

8

Visible Spectrum

�Range of energy humans see as light

� Pigments

Chlorophyll

� Plant pigment

� Absorbs certain wavelengths of energy (photons) from the sun

Plant Pigments

� Plant pigments can only absorb specific wavelengths of energy

9

10

Where does oxygen come from?

An Electron Transport Chain

Connects the two photosystems

11

The Second Photosystem

� Follow the electrons

The Calvin Cycle

� Series of chemical reactions

� Occurs in stroma

The Processes in the Calvin Cycle Occur in Three Steps:

12

• Cellular Respiration – control the release of

chemical-bond energy from large, organic

molecules and use the energy for the many

activities to sustain life.

Cellular Respiration

� Requires (1) fuel and (2) oxygen.

� Potential energy stored in chemical bonds of sugar, protein, and fat molecules.

4.13 The first step of cellular respiration: glycolysis is the universal energy-releasing pathway.

Glycolysis:

13

Glycolysis

Three of the ten steps yield energy

– quickly harnessed to make ATP.

High-energy electrons are transferred to NADH.

Net result:

�each glucose molecule broken down into two

molecules of pyruvate

The Preparatory Phase to the Krebs Cycle

14

The “bag-within-a-bag”

Follow the Electrons, as We Did in Photosynthesis

#2) This proton concentration gradient represents a significant

source of potential energy!

15

16

17