1. Chapter Seven (7): Autotrophic Nutrition-Photosynthesis
Mrs. Clayton-Bridges

2. What is Nutrition?
A process in animals and plants
involving the intake of nutrient
materials and their subsequent
assimilation into the tissues in
order to acquire energy.

3. Why do living organisms
need energy?

4. Energy Source
There are two main energy sources for
living organisms:
1. Light energy (phototrophic)
2. Chemical energy (chemotrophic)

5. Objective
Overview :
•What is photosynthesis
•The importance of photosynthesis
•The structure of the leaf

6. What is
photosynthesis?
Photosynthesis is
the process by which
plants, some bacteria,
and some protistans
use the energy from
sunlight to produce
sugar .

7. photosynthesis Product(S)
The primary product of photosynthesis is glucose -
the source of carbohydrates like
cellulose, starches, etc.
The process of photosynthesis also leads to the
production of fats, proteins, and water soluble
sugars such as maltose and sucrose. The plants
depend on this glucose for their growth and energy.

8. Importance of photosynthesis
1. The level of carbon-dioxide in the environment largely
depends on the process of photosynthesis.
 Photosynthesis consumes atmospheric CO2 and yields
carbohydrates and atmospheric oxygen, vital to
respiration – which allows living organisms to
breathe.
 CO2 helps in keeping our planet warm and live-able.
However, too much may cause us to over heat and too
little may cause us to freeze.

9. Importance of photosynthesis
 Photosynthesis replaces CO2 with O2
which allows living organisms to
breathe.
2. Photosynthesis supplies food and energy
to all living organisms whether direct or
indirect.

10. The structure of the Leaf
Leaves are the powerhouse External Features
of plants. In most plants
leaves are the major site of
food production for the
plant. Structures within
the leaf convert the energy
in sunlight in to chemical
energy that the plant can
use as food.

11. The structure of the Leaf
 The epidermis secretes a waxy
substance called the cuticle. These
layers protect the leaf from pests.
Internal Features
Among the epidermal cells are pairs of
guard cells. Each pair of guards cells
forms a pore called or stoma.
 Gases enter and exit the leaf
through the stomata.
 Most food production takes place in
the cells of the Palisade Mesophyll.
 Gas exchange occurs in the air spaces
between the cells of the spongy
mesophyll.
 Veins support the leaf and are filled
with vessels that support food, water,
and minerals toe the plant.

12. TS OF A TYPICAL DICOTYLEDON

13. Objective
Overview :
•What are plastids?
•Discuss the common types of plastids
•Explain the structure/function of chloroplast
•What are pigments and their role in photosynthesis
•Explain using a graph common photosynthetic pigments and
their absorption and action spectra

14. Plastids
Plastids are organelles that specialize in photosynthesis
function in storage.
Three (3) types common in different parts of the plants are:
1. Chromoplast – lacks chlorophylls but have an abundance of
carotenoids. They reflect yellow, orange and red colours of
many flowers, autumn leaves, ripening fruits, and carrots and
other roots.
2. Amyloplast - Lacks pigment. They are responsible for the
synthesis and storage of starch granules. It also convert starch
back to sugar when the plant needs it. Also, found in fruits
and underground storage tissues of some plants such as
potato tuber

15. Autumn Leaves

16. Plastids (con’t)
3. Chloroplast – contained only in eukaryotic cells that are
photosynthetic. They reflect or transmit green light.
These organelles convert sunlight energy into chemical
energy of ATP, which is used to make sugars and other
organics compounds.
 Chloroplast are commonly oval or disk shaped. Their semi-
fluid interior the stroma is enclosed by two outer
membrane layers. In the stroma is a double membrane
organelle called the thylakoid membrane.
The thylakoid membrane is a folded system of
interconnecting, disc-shaped compartments. In many
chloroplasts, these compartments stack, one atop the other.

17. The structure of chloroplast

18. Pigments
A pigment is a material that changes the
colour of reflected or transmitted light as a
result of wavelength-selective absorption.
Most pigments absorb only some wavelengths
and transmit the rest.
A few, such as melanins in animals, absorb so
many wavelengths they appear dark or black.

19. Types of photosynthetic Pigments
Chlorophyll a – grass green pigment that absorbs blue-
violet and red wavelengths- as key player in the light
dependent reactions
Chlorophyll b – a bluish pigment occurs in plants, green
algae and a
few photoautotrophic bacteria's.
Absorbs blue, red and orange wavelengths, in
chloroplasts, it is one of several accessory pigments,
busily harvesting wavelengths that chlorophyll misses
Carotenoids - contained in all photoautotrophs bacteria. These
are accessory pigments absorb blue-violet and blue-green
wavelengths that chlorophylls miss.

20. Absorption of Spectra

21. Excitation of Electrons
Many reactions in Chemistry involve the gain and loss of
reactions. These are called oxidation/reduction reactions.
Oxidation is LOSS of electrons
Reduction is GAIN of electrons
You can use the acronym OILRIG to help remember this.
Lithium loses an electron to become a positively charged ion

22. Excitation of Chlorophyll by light
Chlorophyll has a light-catching array of
atoms, which often are joined by
alternating single and double bonds.
When an atom's electrons absorb
energy, they move to a higher energy
level.
Chlorophyll molecule, an input of
energy destabilizes the electron orbits.
Within 10 -15 of a second, excited
electrons return to a lower energy
level, the electron distribution
stabilizes, and energy is emitted in the
form of light.
All destabilized molecules emits light as
it reverts to its more stable
configuration, this is called
fluorescence.

23. Photosystems
Pigment molecules organized intophotosystems capture sunlight in the
`
chloroplast.
Photosystems (or Reaction Center) are enzyme which uses light to
reduce molecules with clusters of light-absorbing pigments

24. Photosystem [con’t]
 Each photosystem is comprised of chlorophyll and carotenoids
pigments. In the reaction center of the photosystem, the energy of
sunlight is converted to chemical energy. The center is sometimes called a
light-harvesting antenna.
 There are two photosystems within the thylakoid membranes, designated
photosystem I and photosystem II.
 The reaction centers of these photosystems are P700 and
P680, respectively.
 The energy captured in these reaction centers drives
chemiosmosis, and the energy of chemiosmosis stimulates ATP
production in the chloroplasts.
Chemiosmosis is the diffusion of ions across a selectively-permeable
membrane. More specifically, it relates to the generation of ATP by the
movement of hydrogen ions across a membrane during cellular respiration.

25. Photophosphorylation
Photophosphorylation - the process in
photosynthesis that converts light energy into
stored energy – ATP, in plants and bacteria.
There are two types:
cyclic phosphorylation
non-cyclic phosphorylation.

26. Non-Cyclic Photophosphorylation
Non-cyclic photophosphorylation, is a two-stage
process involving two different chlorophyll photosystems.
First, a photon is absorbed by the chlorophyll core of
photosystem II, exciting four electrons which are
transferred to the primary acceptor protein. The deficit
of electrons is made up for by taking electrons from a
molecule of water, splitting it into O2 and 4H+.
The electrons transfer from the primary acceptor to
plastoquinone, then to plastocyanin, producing
proton-motive force as with cyclic electron flow and
driving ATP synthase.

27. Non-Cyclic Photophosphorylation (con’t)
 The photosystem II complex replaced its lost electrons from an
external source, however, these electrons are not returned to
photosystem II as they would in the cyclic pathway. Instead, the still-
excited electrons are transferred to a photosystem I complex, which
boosts their energy level to a higher level using a second solar photon
capturing array.
 The highly excited electrons are transferred to the primary acceptor
protein, but this time are passed on to ferredoxin, and then to an
enzyme called NADP+ reductase which uses the electrons to drive the
reaction
NADP+ + H+ + 2e- → NADPH
 This consumes the H+ ions produced by the splitting of water, leading to
a net production of O2, ATP, and NADPH with the consumption of solar
photons and water.

28. Photosystems in action

29. Cyclic Photophosphorylation
 In cyclic phosphorylation, an electron originates
from a pigment complex called photosystem I, passes
from the primary acceptor to ferrodoxin, then to a
complex of two cytochromes , and then to
plastocyanin before returning to chlorophyll.
 This transport chain produces a proton-motive
force, pumping H+ ions across the membrane; this
produces a concentration gradient which can be used
to power ATP synthase.

30. Photosystems in action

31. Light dependent stage of photosynthesis

32. Comparing the two Photosystem
Similarities :
 Both photosystems consist of a complex of molecules embedded in
thylakoid membranes of the chloroplast.
 Photosystem I and photosystem II are similar in that they both contain
chlorophyll molecules, which can convert light energy into chemical
energy.
 In both photosystems, a photon causes an electron to reach a high
energy level.
 In both photosystems, the energized electron must be passed to a
chlorophyll molecule in the reaction center before it can leave the
photosystem.
 Both contain carotenoid molecules.

33. Contrasting the two Photosystem
Differences
 The chlorophyll molecules in the reaction center of photosystem II are P680
(sensitive to wavelengths up to about 680 nm), whereas those in
photosystem I are P700, which can therefore respond to slighter longer
wavelengths.
 Photosystem II, unlike photosystem I, contains plastoquinone, which
passes the energetic electron to cytochromes b6 and f, but photosystem I
passes the electron to ferredoxin.
 In non-cyclic photophosphorylation, photosystem II is associated with the
photolysis of water and subsequent synthesis of ATP; photosystem I is
associated with the conversion of NADP+ to NADPH.
 In cyclic photophosphorylation, only photosystem I produces an energized
electron on receipt of a photon. Instead of producing NADPH, this
electron travels to plastoquinone, and then to cytochromes b6 and f, as
in the non-cyclic process.

34. Adenosine Triphosphate (ATP)
ATPs consist of
adenine, sugar
(ribose), and three
phosphates.
An ATP energy is
used when one of
the phosphate
bonds are broken,
becoming ADPs.

35. Importance ATP
 ATP is needed for the heart to beat, it is needed for muscular
effort, in fact everything we do requires ATP as energy. The
body cannot function without it. That is why ATP is known
as the “energy currency” of each cell in your body and your
body must be supplied with energy continuously if it is to
function.
 The harder the body works, for example during exercise, or
during recovery from illness or injury, the greater then
requirement is for additional energy, and potentially
additional ATP.
 At rest, the body is able to produce all the ATP it needs to
maintain a healthy existence.

36. Nicotinamide adenine dinucleotide
phosphate (NADP)
NADP (Nicotinamide adenine dinucleotide phosphate):
a co enzyme which acts as a hydrogen carrier.
The role of NADP is to carry the hydrogen atom from the light dependent
stage, which comes from the water molecule ( water molecule splits to
form 2H+, 2electrons & oxygen, which is a waste gas).
NADP carries this hydrogen atom and gets reduced. The reducing power
of reduced NADPH reduces the 3 Carbon acid that has the group ( -
COOH ) to a 3 Carbon sugar that has an aldehyde group ( -CHO ) known
as Glyceraldehyde phosphate (GP), which is a triose phosphate (TP). This
is the first carbohydrate in photosynthesis. The reason for the conversion
of GP to TP is because TP contains more chemical energy.

37. “when a chemical process is affected by more than one
factor, its rate is limited by that factor which is nearest its
minimum value: it is the factor which directly affects a
process if its quantity is changed.”
first establish by Frederick Blackman, 1905

38. The Variables of Photosynthesis
There are many factors limiting photosynthesis.
However, the principal factors are:
light intensity
carbon dioxide concentration
temperature.

39. Light Intensity
 In low light intensities the rate of photosynthesis
increases linearly with increasing light intensity.
 Except for shaded plants, light is not normally a major
limiting factor.
 Very high light intensities may bleach chlorophyll and
slow down photosynthesis, but plants normally
exposed to such conditions are usually protected by
devices such as thick cuticles and hairy leaves.

40. Light Intensity
A. Represents a linear increase of a limiting
factor.
Meaning an increase in the input results
in a direct proportional increase in the
output.
B. Levelling off demonstrates that this factor
is becoming saturated and further
increase yields diminishing returns on
output.
C. Factor is no longer the limiting factor.
Increases have no effect on output.
D. Point at which factor is saturated.
Factor has reached maximum level of
benefit for process.
E. Maximum or ideal output for the input
when it is no longer a limiting factor.

41. Carbon Dioxide Concentration
Carbon dioxide is needed in the light-independant
stages where it is needed to make sugar. Under
normal conditions, carbon dioxide is the major
limiting factor in photosynthesis.
Its concentration in the atmosphere varies between
0.03% and 0.04%, but increases in the photosynthetic
rate can be achieved by increasing this percentage.

42. Temperature
The light-independent reactions and, to a certain
extent, the light-dependent reactions are enzyme
controlled and therefore temperature sensitive.
For temperate plants the optimum temperature is
usually about 25 °C. The rate of reaction doubles for
every 10 °C rise up to about 35 °C, although other
factors mean that the plant grows better at 25 °C.

43. Other Factors Limiting
Photosynthesis
 Chlorophyll concentration is not normally a limiting
factor, but reduction in chlorophyll levels can be
induced by several factors:
 disease (such as mildews, rusts, and virus diseases)
 mineral deficiency
 normal ageing processes (senescence).
 If the leave becomes yellow is is said to be
chlorotic, the yellowing process being known as
chlorosis.

44. Specific Inhibitors
 An obvious way of killing a plant is to inhibit
photosynthesis, and various herbicides have been
introduced to do this.
 A notable example is DCMU (dichlorophenyl dimethyl
urea) which short circuits non-cyclic electron flow in
chloroplasts and thus inhibits the light-independant
reactions. DCMU has been useful in research on the
light-dependent reactions.

45. Water
 Water is a raw material in photosynthesis, but so many
cell processes are affected by a lack of water that it is
impossible to measure the direct effect of water on
photosynthesis. Nevertheless, by studying the yields
(amounts of organic matter synthesized) of water
deficient plants, it can be shown that periods of
temporary wilting can lead to severe yield losses.

46. Pollution
 Low levels of certain gases of industrial origin, notably
ozone and sulphur dioxide, are very damaging to the
leaves of some plants, although the exact reasons are
still being investigated.
 It is estimated, for example, that cereal crop losses as
high as 15% may occur in badly polluted
areas, particularly during dry summers.