1. Life Processes in Plants
and Animals
Photosynthesis

2. Introduction
 Green plants – have chloroplast containing chlorophyll.
 Chlorophyll – enables plant to produce food through photosynthesis.
 Some bacteria contains chlorophyll and can photosynthesize
 Other bacteria have no chlorophyll, but use energy from chemical processes to make food -
chemosynthesis
 Producers – organisms able to manufacture their own organic compounds using energy form the sun
or chemical reactions
 Consumers – organisms who obtain their food by eating other organisms
 Decomposers – organisms that cause the decay of dead organisms (Ex: fungi)
 Producers can be called autotroph – being able to manufacture their own food
 Consumers and decomposers can be called heterotroph- obtain their food from other
organisms/sources.

3. A history of photosynthesis
• Aristotle, who lived more than 2300 years ago, was the first person to suggest that
plants get their food from the soil.
• Jan Von Helmont planted a tree, he weighed the tree and the soil before hand.
• After a few days he weighed the soil and the tree again, the soil was the same but the
tree was much heavier thus concluding that it was in fact the water in the soil that fed
the plant.
• In the 1750’s the people thought that plants only needed water to grow.
• In 1771 Joseph Priestly put a sprig of mint in a bell jar for a week, then placed a
burning candle in it. The candle continued to burn, thus plants use carbon dioxide and
produce oxygen as the candle needed oxygen to burn.
• In 1773 Jan Ingenhousz showed that plants need light to change the air so that the
candle could burn. H also showed that it was green plants who changed the air and that
the plants roots also needed air.
• In 1782 Jean Senebier showed that carbon dioxide was used by the plants to “restore”
the air.
• In 1804 Nicolas de Saussure showed that plants needed water to make their own food.
• Only in 1950’s did Melvin Calvin discover the biochemical pathway of plants making
food.

4. Process of photosynthesis
Chlorophyll
Light
energy
from the
sun
Water from the
soil
Carbon dioxide
from the air
Oxygen
(waste or
by-
product)
Organic food
for plant
(glucose)
1)Requirements for photosynthesis:
2) Products:

5. Equation of photosynthesis
chlorophyll
 6CO2 + 6H2O + light ——————> C6H12O6 + 6O2
enzymes
(catalyst)
chlorophyll
 Carbon dioxide + water + light ——————> glucose + oxygen
enzymes

6. Where does photosynthesis take place? (1)
 The leaf is the main site for photosynthesis, particularly in the CHLOROPLASTS (p125)

7. Chloroplast structure

8. Where does photosynthesis take place? (2)

9. Where does photosynthesis take place? (3)
 The leaf is the main site for photosynthesis
 Particularly in the CHLOROPLASTS
 2 Phases involved in photosynthesis:
 Light reaction/phase
 Takes place in the grana of chloroplasts
 The chlorophyll molecule absorbs light energy
 The light energy is used to form the energy-carrier ATP (Adenosine
Triphosphate)
 The light energy is used to split water molecules to release high
energy hydrogen atoms and oxygen.
 The hydrogen atoms combine with coenzymes which take them
into the dark phase
 The oxygen is released into the atmosphere as a by-product
(waste)
 Dark reaction/phase
 Take place in the stoma of chloroplasts
 Carbon and oxygen from CO2 combines with high-energy hydrogen
atoms to form energy-rich carbohydrates (glucose and starch)
 The hydrogen and ATP provide the energy for this process
 All the reactions of the dark phase is controlled by enzymes

10. The rate of photosynthesis (1) : Internal
factors
 Internal factors:
 The structure of the leaves
 Increased rate of photosynthesis in leaves with:
 Large and many stomata
 Large intercellular spaces (air spaces)
 Many mesophyll cells with many chloroplasts
 Thin cuticle
 Absence/reduced amount of epidermal hairs
 Leaves have various adaptations for improved photosynthesis
(p131)

11. The rate of photosynthesis (2): External factors
 A) Light intensity
 Increase in light intensity =
increase in photosynthesis
 When optimum intensity is
reached, rate of
photosynthesis levels off
because of other factors
(not enough water or CO2)
 C) Temperature
 Optimum temperature = 25˚C
in mesophytic plants
 As the temperature rises to
25˚C, the rate of
photosynthesis increases
 Any further increase in
temperature (above 25˚C),
results in a decrease in
photosynthesis because the
enzymes become denatured.
 B) The carbon dioxide concentration
 CO2 concentration in atmosphere –
0.03%
 Decrease in CO2 = decrease in
photosynthesis
 CO2 increase = increase in
photosynthesis
 High CO2 over long period – decrease
in photosynthesis – toxic levels
 Water and light may also be limiting
factors
A B C

12. The role of photosynthesis
(Importance of photosynthesis)
 Most important process on earth. Why?
 Primary source of food for all organisms, forms the
base of all food chains.
 Animals that eat plants are called herbivores.
 Provides oxygen for respiration in all living things.
 Uses up vast quantities of carbon dioxide produced
during respiration, burning of fuels and
decomposition
 Fossil fuels e.g. coal and oil are derived from plants.
Energy stored in these fuels originally trapped from
the sun during photosynthesis.

13. The role of ATP
 Adenosine Triphosphate (ATP) is a nucleotide that performs many
important roles in the cell:
 It is the major energy carrier of the cell, providing energy for all the
energy-consuming processes in the cell
 It is used in the synthesis of DNA and RNA.
 It regulates many biochemical pathways.
 It is synthesised in chloroplasts during photosynthesis.
 It is also used during the formation of polysaccharides such as starch.

14. Greenhouses
 A greenhouse is a special building used for growing
plants in areas (or seasons) where they would not
normally grow well.
 They have see-through walls and ceilings (polyethylene)
 Sunlight passes through the clear walls and ceilings for
photosynthesis
 It keeps bugs, cold air and birds out.
 The plants are watered and fertilised.
 A good air flow is also kept flowing (for O2 and CO2).
 In commercial greenhouses, trained staff and special
equipment monitor and control CO2 levels and humidity.

15. The role of CO2-enrichment, optimal light and
optimal temperature in greenhouse systems
 CO2 concentration, light intensity and temperature affect the rate of
photosynthesis.
 In greenhouses, all these external factors can be increased, decreased or kept
constant.
 They can use artificial lights or shade cloth to control light intensity.
 They can use heaters or fans and shade cloth to control temperature.
 They can pump in compressed CO2 to increase the concentration inside the
greenhouse.
 In this way, special plants can be grown and crop yields can be improved.

16. Definitions
 Photosynthesis
 Chlorophyll
 Chloroplast
 Producer
 Autotrophic
 Consumer
 Heterotrophic
 Chemosynthesis
 Decomposer
 Destarch
 Hypothesis
 Experiment
 Control
 Stroma
 Lamella
 Granum
 Light phase
 Dark phase
 ATP
 NADP
 Petiole
 Stomata
 Mesophyll
 Palisade mesophyll
 Spongy mesophyll
 Cuticle
 Xylem
 Phloem
 Greenhouse