The document summarizes key discoveries and experiments in the history of understanding photosynthesis. It describes Jan Van Helmont's early experiment in the 1640s that showed plant mass comes from water, not soil. Later experiments by Priestley, Ingenhousz, Senebier, and others identified carbon dioxide as the source of plant mass and showed plants release oxygen during photosynthesis. The structure and functions of plant leaves and their adaptations are also outlined, followed by descriptions of the light and dark reactions of photosynthesis and factors like light, carbon dioxide, and temperature that affect the rate.

1. Photosynthesis
• The discovery of
photosynthesis
started when Jan
Van Helmont
began the research
of this process in
the mind-1640s.

2. • He had measured the mass of the soil used
by a plant and the mass of the plant as it
grew.
• After noticing that the soil mass was almost
the same, he hypothesised that the mass or
the growing plant must have come from the
water, the only substance he added to the
potted plant.

3. • In 1772, Joseph
Priestley, then
discovered that when he
isolated a volume of air
in an inverted jar and
burn a candle in it, the
candle would extinguish
very quickly

4. • He further discovered that a mouse could
similarly “injure” air. He then showed that
the air that had been “injured” by the
candle and also by the mouse could be
restored by a plant.

5. • In 1778, Jan Ingenhousz, repeated
Priestley’s experiments. He discovered
that it was the influence of the sun and
light on the plant that causes it to restore
the air that saves the mouse.

6. • In 1780, Jean Senebier, showed that
carbon dioxide was the “fixed” or “injured”
air, and that it was taken up by plant in
photosynthesis.

7. • Nicolas-Theodore de Saussure showed
that the increase in mass of the plant as it
grows is not only due to the carbon
dioxide, but also to the intake of water.
Thus the basic reaction by which
photosynthesis is used to produce glucose
was outlined.

8. • In 1845, Robert Mayer discovered that
plants convert solar energy into chemical
energy during photosynthesis.

9. • In 1905, Blackman discovered that
photosynthesis involves two principal
reactions- photochemical reaction (light-
dependent) and biochemical reaction
(light-independent)

10. • The first experiment to prove that the oxygen
released during the photosynthesis of green
plant comes from water performed by Robet
Hill in 1937.

11. Leaf structure and function

12. • Cuticle – it prevents excessive water loss

13. • Palisade mesophyll
– These cells are arranged
close together and
located near the surface
of the leaf.
– This is to receive
maximum amount of
light.
– It contains a lot of
chloroplasts and are able
to move about and
arrange themselves to
carry out maximum light
absorption.

14. • Spongy mesophyll
– Spongy mesophyll is made of
irregular shaped cells and
contains fewer chloroplasts
than palisade cells.
– They are arranged loosely and
there are air spaces between
them that connect the
mesophyll with the stomata.
– These spaces allow water and
carbon dioxide to diffuse
through the leaf to the palisade
cell.
– The irregular shape of the cells
increase the internal surface
area for gaseous exchange.

15. • Stomata
– Carbon dioxide
diffuses into the leaf
through the
stomata. While
oxygen diffuses out
of the leaf via the
same route.
– Each stomata has
two guard cells
which controls the
size of the pore.

16. • Xylem
– Water is
transported from
the roots to the
leaf through
xylem.

17. • Phloem
– Organic products
from the leaf are
transported to the
other parts of the
plant through phloem.

18. Adaptation of plant

19. • Lamina or leaf blade
– It is usually thin, flat and wide to allow the leaf
to absorb light.
– It is also to allow more gas exchange involved
in photosynthesis
• Vein
– It consists of vascular tissues, xylem and
phloem
– Xylem transports mineral ions and water to
leaf to be used during photosynthesis.
– Phloem transports products of photosynthesis
to other parts of the plant.

20. • Petiole or leaf stalk
– It makes sure that the leaf is held up to allow
maximum exposure to sunlight.

22. • Upper epidermis
– it is thin and transparent, and is generally lack of
chloroplast.
• Palisade mesophyll
– They are tightly packed cells and have a large
number of chloroplasts.
– This is to trap as much light that comes through
the epidermis.
• Spongy mesophyll
– They are loosely packed cells and have large air
spaces between them.
– This is to allow water and carbon dioxide to be
diffused easily into the cell.

23. • Lower epidermis
– It contains guard cells to allow the opening and
closing of stomata.
• Stomata
– Stomata can be found more in the lower epidermis
than in the upper epidermis.
– This is where carbon dioxide move in and out of
the leaf.
• Waxy cuticle
– It is waterproof to ensure not much water is lost
during photosynthesis.
– It is also transparent enough to let enough sunlight
in.

24. • The chloroplasts of the cactus are mostly
found in the stems.

25. • This is because some of the cacti do not
have leaves and some only grow small
seasonal leaves that grow after it rains.

26. • Leaves with hairs help reduce water loss.

27. • Some plants such as Hakea sp. have
sunken stomata in their leaves to reduce
water loss during transpiration.

28. • For these kinds of plants, gaseous
exchange occurs during night time.
• This is because it is hot during the day.
This also helps in preventing too much
water being lost during transpiration.
• The carbon dioxide is absorbed and
stored during the night for these kinds of
cacti. The carbon dioxide is used during
the day when there is sunlight.

31. • Thorns on cactus reduce transpiration
rate.

32. • The waxy coating on their stems and
leaves help reduce water loss.

33. • Hibiscus is an example of plants living in
this tropical weather.
• In order to allow maximum absorption of
sunlight for the plants to carry out
photosynthesis.
• A large number of chloroplasts are found
on the palisade and spongy mesophyll
cells.
• To allow maximum absorption of carbon
dioxide, a large number of stomata are
found in the lower epidermis of the leaf.

34. • Even so, not many stomata are found in
the upper epidermis.
• This is because of its direct exposure to
sunlight that can lead to too much water
loss during transpiration.

35. • The duckweeds and water lilies are
examples of floating aquatic plants.
• The leaves of duckweeds and water lilies
are covered with thick and waxy cuticle.
• The function of cuticle is to repel water.
• The thick and waxy cuticle also allows the
stomata to stay open.
• Chloroplasts can only be found in the
upper epidermis to allow maximum
absorption of sunlight.

37. The Mechanism of Photosynthesis

38. • The chloroplast consists of several structures
which are related to photosynthesis.
• The structures are thylakoids, outer
membranes, inner membranes and stroma.
• Thylakoid (grana) contains membranes that
are important for photosynthesis.
• Thylakoid also contains chlorophyll which
traps solar energy during photosynthesis.
• Thylakoid are arranged in stacks and they
are called granum.
• Stroma is a gel-like matrix. The enzymes
responsible for photosynthesis are found
here.

39. • Photosynthesis happens in two stages.
• The first stage is light reaction which
occurs only in the presence of light.
• The next stage is dark reaction where light
is not needed but it can also occur in the
presence of light.

40. • The light reaction takes place in the
membrane of grana.
• During the light reaction, chlorophyll in the
thylakoid captures light energy.
• Light energy, to split the water molecules
into hydrogen ions (H+
) and hydroxyl ions
(OH-
). The reaction is known as photolysis
of water.
24H2
O → 24H+
+ 24OH-

42. • The hydrogen ions then combine with the
electrons released by chlorophyll to from
hydrogen atom
• The energy released from the excited
electrons is used to from energy-rice
molecules of ATP.
24H+
+ 24e-
→ 24H

44. • The hydroxyl ion loses an electron to from
a hydroxyl group.
• This electron is received by chlorophyll.
• The hydroxyl group then combine to from
water and gaseous oxygen.
• Oxygen is released into the atmosphere
and later used for cellular respiration.
24OH-
→ 24OH + 24e-
24OH → 12H2O + 6O2

46. • The ATP molecules and hydrogen atoms
then move to the stroma to provide energy
and reducing power.
• During the dark reaction, the hydrogen
atoms are used to fix carbon dioxide in a
series of reactions catalysed by
photosynthetic enzymes.
• The overall reaction results in the reduction
of carbon dioxide into glucose
6CO2 + 24H → 6(CH2O) + 6H2O
6(CH2O) → C6H12O6

48. • [CH2O] is the basic unit of glucose.
• Six units of [CH2O] combine to from one
molecule of glucose.
• The glucose monomers then undergo
condensation to from starch which is
temporarily stored as starch granules in
the chloroplasts.
6H2O + 6CO2 → C6H12O6 + 6O2

50. Comparing and contrasting the light
reaction and dark reaction

52. The Factors Affecting
Photosynthesis
• The rate of photosynthesis is affected by
carbon dioxide, temperature, light intensity
and water.

53. • Light intensity
– Light intensity is the limiting factor at AB.
– This is because between A and B, increasing
the light intensity increases the rate of
photosynthesis.
– Between B and C, the rate of photosynthesis
is constant (maximum).
– Between BC, either CO2 concentration or
temperature is the limiting factor.

54. A
B
C

55. • Concentration of carbon dioxide
– Between DE, CO2 concentration is the the
limiting factor.
– This is because between D and E, increasing
the CO2 concentration increases the rate of
photosynthesis.
– Between EF, the rate of photosynthesis is
constant (maximum rate).
– Between EF, either light intensity or
temperature is the limiting factor.

56. D
E
F

57. • Temperature
– From 10o
C to 35o
C, the number of gas bubbles
released increases, but when the temperature
increases from 35o
C the number of bubbles
released decreases until it became 0 at 50o
C.
– Photosynthesis is catalysed by the
photosynthetic enzymes and therefore changes
in temperature will affect the rate of
photosynthesis.
– The optimum temperature varies from the
different species of plants, but most plants have
an optimum temperature of between 25o
C and
30o
C.

58. – However, when the temperature is too high, the
photosynthetic enzymes are destroyed and
photosynthesis stops altogether.

59. A Caring Attitude towards
Plants
• Plants are the primary producers that sustain
all other life forms.
• Humans are in capable of making their own
food.
• We depend directly or indirectly on plant for
food supply.
• Through photosynthesis, plants absorb
energy from the sun, carbon dioxide, water
and minerals.
• They then give off water and oxygen.
• Oxygen is the most important part of the air.

61. • Animals and other non-producers take
part in this cycle through respiration.
• The cycles of photosynthesis and
respiration help maintain the earth’s
natural balance of oxygen, carbon dioxide
and water.

64. • Latex, pigment and resin
– Plant like Brazilian carnauba palm also
produce resin or wax that is an ingredient in
car wax and candles so they look shiny.

65. – Colour pigment from parts of plants are used
such as onion peel to get shade of light
brown, tumeric to get shade of yellow and
berries to get shade of pink and red.

66. • Oil palm
– Palm oil comes from oil palm trees. Cooking
oil, soap and margarine are products that
come from palm oil.

67. • Drug
– Aspirin that is used in painkillers comes from the
bark of the white willow tree.
– Quinine that comes from the quinine tree is used to
treat Malaria.
– In Malaysia, there are lots of medicinal plants such
as Misai Kucing that is used traditionally to cure
diabetes and Hempedu Bumi that can be used to
cure high blood pressure.

68. • Fibre
– Most of our clothes are made out of cotton.
Cotton fibre comes from the cotton plant. The
fibre that comes from the jute plant is used to
make ropes and sacks.

69. • Petroleum oil
– Petroleum is formed from the decayed remains of
prehistoric marine animals and terrestrial plant.
– It takes millions of years for petroleum to develop.
– From petroleum, we can get gasoline, fuel, diesel
and tar.
– Petroleum is also used to make plastic products
and synthetic rubber.

70. • Wood and wood products
– Some furniture and wood products are made
out of wood that comes from trees.
– Common trees that are used to make furniture
are Jati, Merbau and also rubber tree.

71. • Add aesthetic value
– Plants make our surrounding more beautiful
with its flowers and green leaves.

72. • Reduce greenhouse effect
– Plants control the quality of our air by
supplying oxygen. It lessens the greenhouse
effect caused from the burning of fossil fuels.

73. • Prevent soil erosion
– The plant’s roots help stabilise soil and
prevent erosion.
– That’s why grass is often planted at the
slopes of hills.

74. • Water reservoirs
– Forests act as water reservoirs and oxygen
tank, supplying water and oxygen to living
things.

75. Technology Used in Food
Production
• The rapid increase in Malaysia’s
population imposes a greater demand on
food supply.
• Because of this, greater supply of quality
food needs to be provided.
• Although agriculture is an important sector
in Malaysia, the production of certain
foods is still not sufficient to support the
greater demand.

76. • The government encourages consumption
of food from diverse sources as well as
developing new methods and techniques
to improve the quantity and quality of food.

78. • Plant breeding
– Plant breeding or cross breeding is a
technique which involves selective crossing of
different varieties of plants to produce new
varieties with beneficial characteristics.
– The new variety of plant inherits the beneficial
characteristics of both parent plants.
– New plant varieties have increased nutritional
value, higher yields and show greater
resistance to diseases and climatic changes.
– For example, the most widely planted variety
of oil palm is the Tenera hybrid variety

79. – It is bred by crossing the Dura variety with the
Pisifera variety.
– Tenera hybrid variety produces fruits with thick
mesocarp and more oil content.

80. • Animal breeding
– Animal breeding is a method that involves the
cross-breeding of two different breeds of
animals.
– Animals such as cows have been cross bred to
enhance the yield of milk, meat and other
products.
– The hybrid cattle called Mafriwal is a cross
between Fresian cow and Sahiwal bull.
– Mafriwal produces more milk with low fat content.
– Many breeds of goat, sheep, chicken and ducks
have also been crossbred in Malaysia.

82. • Biotechnology and tissue culture
– Biotechnology has opened up new possibilities in
food production.
– One of the branches of biotechnology is plant
tissue culture.
– Plant tissue culture or micro propagation is an
important alternative to the more conventional
method of plant propagation.
– It involves production of plants from very small
plant parts.
– The propagated plants are exactly identical to their
parent plant.
– In Malaysia, rubber, banana, oil palm, pineapple,
papaya and orchid are also propagated by tissue
culture.

84. • Soil management
– Good soil will ensure continuous production of
crops well into the future.
– In order to retain the nutrients in the soil, the crop
should be cultivated in a sustainable manner.
– Sustainable soil management includes:
• Crop rotation to maintain and improve soil fertility
• Ploughing to help increase aeration of the soil
• Regular addition of fertilizers to return nutrients to the
soil
• Adding organic matter to promote humus formation and
improves soil structure
• Reducing soil erosion and leaching of nutrients from
the soil

85. • Direct seeding
– Most farmers in Malaysia use the direct seeding
technique to plant paddy.
– Using machines, seeds are sown directly into the
soil.
– This technique is easier, faster to plant and it
requires less labour.
– The product matures earlier by more than ten
days compared to the conventional transplanted
paddy.
– Therefore, increasing the production of paddy.

87. • Biological control
– Biological control is an approach of using natural
enemies of a pest or parasite to reduce its
population.
– This programme is an alternative method to
reduce and stop the use of chemicals such as
pesticides, herbicides and insecticides.
– This method is safer to the environment.
– Examples of successful biological control are
putting snakes and owls to control the rat
population in oil palm plantation.

89. • Genetic engineering
– Genetic engineering is a technique to enable the
characteristics of an organism to be altered by
changing its genetic composition.
– This is a very useful and advanced way to
increase the quantity and quality of food products.
– For example, beneficial genes from plant can be
inserted into the DNA of animals and vice versa.
– The genetically modified organism otherwise
known as GMO, is called a transgenic organism.

91. • Diverse protein sources
– To diversify the sources of protein, the
consumption of rabbit meat, ostrich meat, quail
meat, freshwater fish and prawns is encouraged.
– Rabbit meat is low in cholesterol and fat but high
in protein.
– Freshwater fish like tilapia, jelawat and haruan
are low in cholesterol.
– Fish protein are easy to digest and is important
for growing child’s healthy development.
– Meanwhile, ostrich meat is very nutritious, low in
fat and rich in protein.

93. • Different food sources
– ‘Ulam’ is rich in vitamins, fibres and mineral ions.
– Some of these ‘ulam’ are vital ingredients in
traditional and herbal medicines.
– Examples of ‘ulam’ are pegaga, kacang botor and
petai
– The efforts include the campaign of consuming
‘ulam’.
– ‘Ulam’ is a vegetable salad that is eaten raw.
– It consists of fresh leaves, fruits and other plant
parts.

95. • Hydroponics & aeroponics
– Vegetables are important in our daily food intake/
– An alternative method of planting vegetables is the
hydroponics method.
– Hydroponics is a method of growing plants without
using soil.
– First, the root of the plant is put in a solution.
– This solution contains all the macronutrients and
micronutrients required for the plant to grow
healthy.
– These plants are supported by a medium such as
pebbles in a special container.

96. – The culture solution is aerated to provide enough
oxygen for respiration.
– The water used in this method can be used again
as it is less prone to evaporation.

97. Technological Development in
Food Processing
• Food has to be processed so that it can last
longer and safe for us to eat.
• The main purpose of food processing is to
preserve food by overcoming the factors that
cause food spoilage.
• There are a many things that can make good
food turn bad, sometimes faster than usual.

98. • Among the two khown causes of food
spoilage are:
– Actions of microorganisms on food
– The oxidation of food

99. • Actions of microorganisms
– Decomposing bacteria and fungi act on
carbohydrates and proteins in food.
– The actions will result in producing substances
like carbon dioxide, water, ammonia, hydrogen
sulphide and other organic compounds.
– The presence of these substances
subsequently spoils the food, making it toxic
and poisonous for us to eat

101. • The oxidation
– As for oily types of food, they become rancid
and start smelling and tasting differently as a
result of oxidation.
– Spoiled food is harmful to the body and can
cause food poisoning.

102. • Food is processed to diversify the uses of
food substances.
• The production of food from raw materials
can be diversified.
• Milk is a good example of how food
processing has increased the various
assortments of dairy products.
• Milk can be made into chocolate, cheese,
yogurt and butter.
• Soya bean can be made into bean curd,
tempe and soya souce.

106. • Cooking
– Cooking is probably the easiest way to prevent
or delay food spoilage.
– Heating food at high temperature can kill
microorganisms and denature the enzymes that
cause the breakdown of food.

107. • Fermentation
– Fermentation is the use of biological processes
to make food products, for instance,
microorganisms are used to make yogurt and
cheese.
– Fermentation of fruit juices produces ethanol
which, at high concentrations, prevents the
spoilage of juices.
– At the same time, the ethanol produces has a
great commercial value.
– Traditional food such as tapai, is produces by the
fermentation of glutinous rice or tapioca.

109. • Drying
– Drying is one of the oldest methods of food
preservation.
– This method involves removing enough moisture
from food to prevent its decay and spoilage.
– Water content of properly dried food varies from
5 to 25 percent depending on the food.
– Successful food drying depends on:
• Enough amount of heat to remove moisture, without
cooking the food.
• Dry air to absorb the released moisture.
• Adequate air circulation to remove the moisture.

110. • Pickling
– Pickling vegetables and fruits with vinegar
prevents the growth of microorganisms.
– This is because when food is kept in a low pH
solution, microorganisms cannot grow.

111. • Treating food with salt or sugar
– Food is soaked in a concentrated salt solution or
boiled with sugar.
– In this way, microorganisms lose water through
osmosis in a hypertonic solution and therefore,
food is preserved.

112. • Pasteurisation is the process of killing most
food-spoiling and pathogenic substances.
• This is done by heating the food to 63o
C for
30 minutes or 72o
C for 15 minutes, following
by rapid cooling to below 10o
C.
• Milk is preserved by pasteurisation to destroy
bacteria such as Streptococcus lactis, which
convert lactose in milk to lactic acid.
• This method of preservation retains the
natural flavour of milk and nutrients like
vitamin B.

113. • The pasteurized milk can then be refrigerated
to last for a few days.
• Fruit juices and soups can also be preserved
this way.

114. • Canning
– Canning is an important, safe method for
preserving food by keeping foods in jars or
similar containers.
– After that, they are heated to a temperature that
destroys microorganisms that cause food
spoilage.
– During the heating process of canning, air is
driven out of the jar and as it cools off, a vacuum
seal is formed.
– This vacuum seal prevents air from getting into
the product, thus preventing the entry of the
microorganisms.

116. • Refrigeration
– Refrigeration is a common method employed at
home to keep food such as meat and fish from
turning bad quickly.
– Food stored at the temperature below 0o
C can
remain fresh for a long period of time.
– The extremely low temperature prevents the
growth of microorganisms such as bacteria, or
germination of spores, thus preventing the food
from spoilage.