Transcript Energy for Cells A look at Photosynthesis

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.
SOLAR ENERGY
2% of SOLAR ENERGY REACHES
THE EARTH’S ATMOSPHERE
CARNIVORES
DEATH
PHOTOSYNTHESIS
HERBIVORES
DECOMPOSERS
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.
Light
Energy
6CO2 + 6H2O
Carbon
Dioxide
Water
C6H12O6 + 6O2
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.
Energy
C6H12O6 + 6O2
Glucose
Oxygen
6H2O + 6CO2 + ATP
Water
Carbon
Dioxide
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.
Synthesis stage
• Chemical energy in the bonds of glucose are
stored for use.
• Light independent 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 manyfolded 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.