Van Helmont conducted an experiment where he planted a willow sapling in soil and measured the soil weight before and after 5 years of growth. He found that the tree had gained 74kg in weight but the soil had only lost 52g. This showed that the tree's food came from water alone, not the soil. However, he overlooked the role of carbon dioxide from the air, which plants use along with water during photosynthesis to produce their own food in the form of glucose.

1. How Plants Get Their Food

2. How do plants get their food ?
The soil was watered but nothing else was added. After 5 years, the
tree had gained 74kg in weight but the soil had lost only 52g.
van Helmont concluded that the tree had made 74kg of new growth
from water alone
2
90.72kg soil
In the 17th Century, A Belgian physician, van Helmont, set up an
experiment in which he planted a willow sapling in a weighed
amount of soil.
90.20kg
soil

3. Van Helmont’s experiment was effective in
showing that the plant’s food did not come
from the soil.
But he had overlooked the fact that air was
available to the plant as well as water.
Could it be that the plant made 74kg ofCould it be that the plant made 74kg of
material from justmaterial from just airair andand waterwater??
3

4. Review QuestionReview Question
• Which mode of nutrition do the green
plants carry out?
A. Autotrophic nutrition
B. Heterotrophic nutrition

5. Sorry! You’re wrong!Sorry! You’re wrong!
• Heterotrophic nutrition is the mode of
nutrition in which organisms have to depend
on other organisms or dead organic matters
as their food sources. Green plants, however,
can make organic food by themselves using
simple inorganic substances.

6. Very Good!Very Good!
• Autotrophic nutrition is the mode of
nutrition in which organisms can make
organic food by themselves using simple
inorganic substances.
• The process by which the green plants
obtain nutrients is called :
Photosynthesis

7. Feeding
Plants make their own food
They combine carbon dioxide from the air with water
and dissolved salts from the soil
Plants do NOTNOT get their food from the soil
The first stage by which plants make food is
called PHOTOSYNTHESIS
4
Animals get their food by eating
*plants,
*plant products
*other animals
Carnivores eat animals
Herbivores eat plants

8. Photosynthesis
6
from the air (DIFFUSION)
(OSMOSIS)
a by-product(DIFFUSION)
glucose (C6H12O6)

9. C6H12O6
CO2
CO2
CO2
CO2
CO2
CO2
H2O
H2O
H2O
H2O
H2O
H2O
6O2
+
7
6CO6CO22 + 6H+ 6H22O = CO = C66HH1212OO66 + 6O+ 6O22

10. CHLOROPLASTS
Only plants have
It stores CHLOROPHYLL
It absorbs photons from the
sun and converts them in ATP
(Green plastids)
Chlorophyll is a green
coloured chemical, present in
the leaves of green plants

11. Leaf cells with chloroplasts
cell wall
nucleus
chloroplast
cytoplasm vacuole
11

12. All the reactions to combine CO2 and H2O take
place in the chloroplast
sunlight
water
carbon dioxide
in the chloroplast,
carbon dioxide and
water combine to
make sugar
12
palisade cell
of leaf

13. Cell structure of a leaf
The palisade cells are in the
uppermost layers of the leaf
epidermis
palisade cell ( photosynthesis)
vessel (carries water)
stoma (admits air)
13

14. CO2
Stoma
Air Space
Spongy Mesophyll
Cell
Chloroplast
Route of Carbon Dioxide for
Photosynthesis

15. CO2
Chloroplast
Palisade Mesophyll
Cell
Stoma
Air Space

16. =
Calvin Cycle
Light
independent
stage
Light
dependent
stage
by DIFFUSION (Stomata)
by OSMOSIS

17.  Light energy is trapped by chlorophyll in
chloroplast
 Light energy absorbed by chlorophyll splits
water molecules into hydrogen and oxygen
 Oxygen is released as a gas through stoma
to outside
 Hydrogen is fed into dark reaction
Light reactionLight reaction

18. Oxygen is produce as the by-product of photosynthesis.

19. Dark reactionDark reaction
 No light is required; can take place either
in light or darkness
 Hydrogen produced in light reaction
combines with CO2 to form carbohydrates
 Water is formed as a by-product

20. Dark Reaction
Water
Oxygen Glucose
(C6H12O6)
Light Reaction
H
Summary of PhotosynthesisSummary of Photosynthesis
6 CO2 + 6 H20 C6H12O6 + 6 O2
Light Carbon Dioxide
absorbed and used by a substance called
chlorophyll

21. This is what you missed on…
9
PLANT NUTRITIONPLANT NUTRITION

22. GaseousGaseous
ExchangeExchange
RESPIRATION
PHOTOSYNTHESIS
COCO22
OO22 COCO22
PHOTOSYNTHESIS
OO22
RESPIRATION
COCO22
Compensation point
NO photosynthesis
OO22
RESPIRATION
COCO22

23. The leaf is thin
decrease diffusion
distance for gases &
light
The leaf is broad &
flattened
increase surface area to
absorb more sunlight
Adaptation of leaf toAdaptation of leaf to
photosynthesisphotosynthesis

24. Cuticle exists in
upper epidermis and
is transparent
Allows most light to
pass into
photosynthetic
mesophyll tissues

25. Palisade mesophyll
cells are closely
packed and contain
many chloroplasts
To carry out
photosynthesis more
efficiently

26. Spongy mesophyll cells
are loosely packed with
numerous large air
spaces
To allow rapid
diffusion of gases
throughout the leaf

27. Numerous stomata
on lower epidermis
To allow rapid
gaseous exchange
with the atmosphere

28. Extensive vein system
• Allow sufficient
water to reach the
cells in the leaf
• To carry food away
to other parts of the
plant

29. What happens to the glucose?
The glucose made by the chloroplast is either
(a) used to provide energy for the chemical
processes in the cell (by respiration)
(b) turned into sucrosesucrose and transportedtransported to
other parts of the plant
or
(c) turned into starchstarch and storedstored in the cell
as starch grains
In darkness the starch is changed back into
glucose and transported out of the cell
15

30. Other Food
Glucose and starch are carbohydratescarbohydrates
Carbohydrates can be oxidised during
respiration to produce energy
Plants need more than carbohydrates
They need proteinsproteins for making new
cytoplasm and cells for growth
To make proteins plants combine glucose
with compounds of nitrogennitrogen (nitrates)
17

31. GLUCOSE
storage e.g. starch in potato
starch
fruitsother sugars
e.g. seed germination
energy
cytoplasm
protein
cell walls
cellulose
18

32. Nitrates
Nitrate ions are present in the soil, dissolved in
water
The plants take up nitrate ions in the soil water
The nitrate ions are conducted through the
roots to the stem and then to the leaves
In the leaves, the nitrate ions and glucose are
combined to make PROTEINS
This process is called assimilation
19

33. Mineral ions
Nitrates are not the only ions that plants need
to take in from the soil
They need phosphate  DNA
sulphate  Sulfur (proteins)
magnesiummagnesium  Chlorophyll
iron, potassium ions
This is the reason why farmers and gardeners
add fertiliser to the soil
20

34. • “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
(limiting the action of the others)”
Limiting Factors of
Photosynthesis

35. Limiting Factors
Temperature
Carbon dioxide concentration
Amount of sunlight
Amount of water

36. Limiting Factors
• 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.
Light Intensity

37. 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.

38. 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.

39. 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.

40. 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).
Other Factors Limiting
Photosynthesis

41. *Plants combine carbon dioxide from the air, and water
from the soil to make glucose.
* The energy needed for this process comes from sunlight
* The sunlight is absorbed by chlorophyll contained in the
chloroplasts of the leaf.
* The glucose can be used for energy or to make other
substances.
* To make other substances, the glucose must be combined
with other chemical elements such as nitrogen and
potassium.
These chemical elements are present as ions in the soil and
are taken up in solution by the roots.
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TO SUM UP