Energy for Cells

A look at Photosynthesis

• Every muscle cell in a person’s body, every cell in your brain, eyes, intestines and skin, must have energy to function and stay alive.

• The cells of the body obtain their energy from the food that we eat.

• Plants need energy much like people do.

• Every cell making up a plant’s roots, stems, and leaves must have energy to function.

Where do plants get their energy from?

Fossilized plants

• Forests of plants from ancient times store

great amounts of solar energy as organic matter. Buried beneath layer upon layer of sediment, great pressure over many years changed the plant matter into the coal and oil we use today.

• How do cells of living things make use of molecules to obtain the energy needed to run their chemical processes?

• We have seen organelles, and the molecules of life that they require to function. We are now going to focus on ENERGY.

Goals for today

• To become familiar with mechanisms that allow cells to make use of energy.

• To explore technologies that humans have developed to make use of these biological processes.

Cells, Matter, and Energy

• All cells, both plant and animal need energy and matter for growth and reproduction.

• Organisms that PHOTOSYNTHESIZE obtain their energy directly from the Sun.

• What about other organisms? What is the source of their energy?

Photosynthesis• Method of converting sun energy into

chemical energy usable by cells• Autotrophs: self feeders, organisms

capable of making their own food– Photoautotrophs: use sun energy e.g. plants

photosynthesis-makes organic compounds (glucose) from light

– Chemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

Food Webs

• Herbivores – directly from the plants they eat.

• Carnivores - obtain energy from the herbivores that they eat.

• Top Carnivores – obtain energy from the herbivores and other carnivores they eat.

• Not all energy the photosynthesizers obtain from the Sun is passed on to the herbivores that eat them.

e.g. Energy for a Dog

• Everyday processes – walking, running, catching a stick, blinking.

• Some energy is emitted as sound – barking

• Thermal energy – Uses some fuel to keep his body warm.

• Some energy escapes from the food chain at each of the feeding levels.

PHOTOSYNTHESIS

HERBIVORES

CARNIVORES

SOLAR ENERGY

2% of SOLAR ENERGY REACHES

THE EARTH’S ATMOSPHERE

DECOMPOSERS

DEATH

Thinking About Energy

• Energy = Capacity to do work• Light energy, sound energy, electrical energy.• Potential Energy = Stored energy (the energy

must be released for it to do any work) e.g. apple hanging by a stem.

• Kinetic Energy = The energy of motion (apple falls to the ground)

• Chemical Energy = Energy stored in the bonds broken

• Chemical bonds store potential energy.

• Once the chemical bonds are broken, the atoms have extra kinetic energy. The atoms can move, do work, make things happen!

Metabolism

• All of the chemical reactions that occur inside a cell.

• Includes all of the building up and breaking down of substances in a cell as well as the energy changes that occur simultaneously.

• In the cell, relies on chemical energy.

The CARBON CYCLE

Essential Energy Transformations

1. Photosynthesis = light energy from the Sun is used to transform carbon dioxide and water into energy-rich food molecules.

6CO2 + 6H2O C6H12O6 + 6O2

Carbon Dioxide

Water

Light Energy

Glucose Oxygen

Essential Energy Transformations

2. Cellular Respiration = all of the chemical reactions needed to break down (metabolize) carbohydrates and other molecules to transfer chemical energy to ATP.

C6H12O6 + 6O2 6H2O + 6CO2 + ATPCarbon Dioxide

Water

Energy

Glucose Oxygen Energy Storage

Molecule

• Both photosynthesis and cellular respiration are series of complex chemical reactions.

• All chemical reactions involve the absorption or the release of energy.

What is Photosynthesis?

• Involves over 100 chemical reactions.

• The overall process happens in two main stages:

–1. PHOTO stage

–2. SYNTHESIS stage.

Photo stage• Supplied the chemical energy needed to

drive the synthesis reactions forward.

• Also known as the light dependant stage.

• Chemical energy in the bonds of glucose are stored for use.

• Light independent stage.

Synthesis stage

What is light?

• Review of Natural light.

• Visible and Invisible radiation from the Sun and other sources of radiant energy.

• TV signals, microwaves, x-rays.

• Visible radiation is usually simply called LIGHT.

• Radiation has waves of electrical and magnetic properties.

• Regular pulses of waves move forwards away from the light source.

Electromagnetic Spectrum

• The entire range of radiation produced by natural or human-made sources.

• All forms of electromagnetic radiation travel at an amazing speed of

300 000 000 m/s

• The frequency of light is different according to how the light waves pulse, or vibrate.

Light Frequency• Different frequency of light is perceived as

different colours.

• The highest or greatest frequency of light is violet, while the light with the lowest frequency is seen as red.

• A combination of all of the frequencies is interpreted as White light.

• Human eyes cannot detect wavelengths longer than 770 nm.

• We cannot see infrared radiation, but heat receptors in our skin can detect it as “heat rays”.

• We cannot see wavelengths showers than 400 nm and we cannot feel this light wavelength but we know ultraviolet rays from our exposure to the sun.

• Our body in turn produces extra melanin in the presence of ultraviolet rays.

Photon Model of Light • Light travels through space in the form

of individual energy “packets” called photons.

• These photon packets travel at 300 000 000m/s• The amount of energy in a photon

depends on the frequency of light. The higher the frequency the more energy the photon is able to deliver.

• Violet is higher than Red.• More energy in a photon of violet

than in red.

The Chemistry of Pigments

• To use the energy of light for photosynthesis, a plant must first absorb photons of light.

• Absorption is only one of three possible outcomes when light strikes a surface.– The other two are reflection and transmission

Which colours reflect off the leaf and return to the eye?

• Molecules that absorb specific colours (wavelengths) of light are called Pigments.

• Most plant leaves contain chlorophyll pigments which give leaves their green colour.

Photosynthesis

• Photosynthesis takes place in specialized structures inside plant cells called chloroplasts– Light absorbing pigment molecules e.g.

chlorophyll

Two Chlorophylls

• 2 types of chlorophyll

• 1 chlorophyll is yellow-green and reflects yellow and green photons of light.

• 1 chlorophyll is blue-green and reflects green and some shades of blue photons.

Chlorophyll’s Role

1. Chlorophyll absorbs red light, violet light, and shades of blue.

2. Converts the absorbed energy into a form that the synthesis reaction can use.

Chlorophyll can only work when it is in an

enzyme filled membrane organelle known as

the chloroplast!

Chloroplast Structure

• Very small – 40 chloroplasts in 1mm.

• Yet, very powerful performing hundreds of reactions in just 1 second.

• Watery substance called STROMA

• Increased surface area – from the many-folded thylakoid membrane inside the chloroplast helps these reactions occur.

Enzymes• Proteins that promote or speed up

chemical reactions without being used up themselves.

• Chlorophyll is not an enzyme but it can be recycled over and over again.

• The chlorophyll molecule absorbs light photons and then passes the energy onto other molecules.

Photosystem

Bucket Model

• Light enters photosystem > Pigment acts as a collection area allowing light to combine in the reaction centre where a continuous supply of water is present.

• Two chlorophyll molecules breakdown the water into oxygen and hydrogen.

• Producing more oxygen.

Photosynthesis

Carbon dioxide and water plus light energy are the raw materials of photosynthesis.

Enzymes and chlorophyll are accessories

that needed to make photosynthesis occur.

• Oxygen molecules produced from photosynthesis pass out the chloroplast membrane into the cell’s cytoplasm.

• Most of the oxygen that is produced is waste product, but the plant’s own cells use some of the waste oxygen to carry out cellular respiration that is needed to release the energy the plant needs from glucose.

Light-dependent Reactions

• Recap: light energy is absorbed by chlorophyll molecules-this light energy excites electrons and powers them to higher energy levels. They are trapped by an electron acceptor that begins start of a an electron transport system.

• The electrons “fall” to a lower energy state, releasing energy that is harnessed to make ATP

Energy Shuttling

• Recall ATP: cellular energy-

• 3 phosphate groups bonded to it when removing the third phosphate group, lots of energy given off

• An EXCELLENT molecule for shuttling energy around within cells.

• Photosystem reactions need light energy

• Synthesis reactions need chemical energy (ATP)

Photosynthesis Part 2

Synthesis Stage

• Thylakoid enzymes break down hydrogen atoms into protons and electrons.

• The energy released from this process is used in ATP (adenosine triphosphate).

Photorespiration

In hot weather, stomates close to save

water; CO2 concentration decrease in

leaves; O2 increases.