The document discusses photosynthesis and how it is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of glucose. It explains that chloroplasts are the sites of photosynthesis and contain chlorophyll, which absorbs sunlight that is converted to chemical energy. The light reactions use sunlight to make ATP and NADPH, while the dark reactions, such as the Calvin Cycle, use this energy to fix carbon from carbon dioxide into organic molecules like glucose. Photosynthesis is essential as it produces oxygen and feeds the base of the food chain.

2. 2
This
presentation is
re-purposed
from various
sources, which
will be
referenced.

3. 3
LIFE ON
EARTH
ULTIMATELY
DEPENDS
ON ENERGY

4. 4
THE SUN IS THE MAIN SOURCE
OF ENERGY FOR LIFE ON EARTH

5. What is ENERGY?
 Some define it as the ability to
work.
 In physics it is the capacity of
the body or a system to do work.
e.g. Growth and repair, active transport
across membranes, reproduction,
synthesis, etc.

6. PHOTOSYNTESIS
 Photosynthesis is the
process by which
autotrophic organisms use
light energy to make sugar
and oxygen gas from carbon
dioxide and water.

7. 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

8.  Almost all plants are
photosynthetic
autotrophs, as are some
bacteria and protists.

9. Cyanobacteria
Euglena
Kelp
Mosses, ferns, and
flowering plants

10. Sites of Photosynthesis
 Photosynthesis occurs in
chloroplasts, organelles in
certain plants.

11.  All green plant parts have
chloroplasts and carry out
photosynthesis.
The leaves have the most chloroplasts
The green color comes from chlorophyll in
the chloroplasts
The pigments absorb light energy

12. Chloroplasts
 10 to 100 chloroplasts
 Enclosed by a double membrane
phospholipid inner and outer
membrane.
Outer and inner membranes: protective
coverings that keep chloroplast structures
enclosed.

13.  Intermembrane space between
them inside the membrane is the
stroma.
Stroma: Site of conversion of carbon
dioxide to sugar.
 Stroma contains stacks (grana)
of thylakoids.

14. Thylakoid: Site of conversion of
light energy to chemical energy.
Grana: Dense layered stacks of
thylakoid sacs.
Sites of conversion of light
energy to chemical energy.

15. Chloroplasts

17. LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Inner
membrane
Granum
Grana Stroma
Stroma Thylakoid
Thylakoid
compartment
Chloroplast

19.  The chlorophyll in the
chloroplasts in green plants
absorbs the sunlight.
 The sunlight is combined with
water, Carbon Dioxide and
nutrients from the soil.

20.  The chlorophyll processes the
ingredients and makes sugar
(plant food) and oxygen.
 Cellular respiration converts
sugar into ATP.

21. PHOTOSYNTESIS
PROCESS
 Involves:
Light reaction - photosystem 1 & 2
Dark reaction - calvin cycle

22. Light Reactions (H2O
O2 + ATP + NADPH2)
 Water splits, giving off oxygen.
 Dependent on sunlight for
activation.

23.  Light is absorbed by chlorophyll a
and “excites” the electrons in the
chlorophyll molecule.
 Electrons are passed through a
series of carriers and ATP is
produced.
 Takes place in thylakoids.

25. Dark Reactions (ATP +
NADPH2 + CO2 C6H12O6)
 Carbon dioxide is split,
providing carbon to make
sugars.
 Glucose is the final product.

26.  Does not require light
energy.
 Includes the Calvin Cycle.
 Takes place in the stroma.

27. The Calvin Cycle
 STEP 1
 CO2 is diffused into the stroma.
 An enzyme combines CO2 with a five-
carbon carbohydrate called RuBP.
 The resulting six-carbon molecule splits
into a pair of three-carbon molecules
called PGA.

28.  STEP 2
 Each PGA molecule receives a
phosphate group from ATP.
 It also receives a proton from
NADPH and releases a phosphate
group producing PGAL.
 This produces ADP, NADP+, and
phosphate which are used in Light
Reactions.

29.  STEP 3
 Some PGAL is converted to RuBP
to continue the cycle.
 Some PGAL leaves the cycle to
create organic compounds.
 Each turn of the cycle fixes one
CO2 molecule and it takes six turns
to make one glucose molecule.

30. CHLOROPLAST

32. Why is Photosynthesis
important?
 It makes organic molecules (glucose)
out of inorganic materials (carbon
dioxide and water).
 It begins all food chains/webs. Thus all
life is supported by this process.
 It also makes oxygen gas!!

33. Photosynthesis starts ecological food webs

35. Rate of Photosynthesis
 Light intensity – as intensity increases the
rate increases and eventually levels off into
a plateau.
 Temperature
 Water shortage
 Increasing amount of CO2 increases rate of
photosynthesis.

36. WATER SHORTAGE
 Water is one of the raw
materials of photosynthesis, a
shortage of water can slow or
even stop photosynthesis.

37.  Plants that live in dry conditions,
such as desert plants and
conifers, have a waxy coating on
their leaves that reduces water
loss.

38. TEMPERATURE
 Temperatures above or below
0 C and 35 C may damage
enzymes, slowing down the
rate of photosynthesis.

39.  Very low temperatures -
photosynthesis may stop entirely.
 Very high temperatures -
enzymes are denatured.
 Optimum temperature: 25oC to
35oC

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