2. Types of
organisms
based on how
they acquire
their food
Based on
how
organisms
acquire
their food,
they can
be
classified
into:
Autotrophs – They synthesize their
own food. They make use of simple
inorganic substances like carbon
dioxide and water and convert them
into complex substances.
Eg: Green plants, bacteria
Heterotrophs – They cannot
synthesize their own food. They
take up complex substances and
break them down to simpler ones.
To break down food, they need
biocatalysts which are also called
enzymes.
Eg: Animals, fungi
3. Autotrophic nutrition
+Autotrophs synthesize food through photosynthesis.
+Here, carbon dioxide and water are converted to carbohydrates in
the presence of sunlight and chlorophyll.
+The synthesized carbohydrates are used to provide energy to plants.
+Plants may not use all of the carbohydrates which are synthesized.
+ Excess carbohydrates are stored in the form of starch.
+Starch acts as internal energy reserve, which is used when required
by plant.
6. Events in
Photosynthesis
1. Absorption of light energy by chlorophyll
2. Conversion of light energy to chemical energy;
Splitting of water into hydrogen and oxygen.
3. Reduction of carbon dioxide to carbohydrates
7. Photosynthesis
in desert plants
To avoid loss of water, desert plants :
1. Take carbon dioxide at night
2. Synthesize an intermediate(they do not
make glucose immediately)
3. Absorb sunlight during day
4. Using the absorbed light energy, the
intermediate is finally converted to glucose.
8. Raw materials for
photosynthesis
+ Chlorophyll:
+ It is found in leaves.
+ Below the upper epidermis of leaves, cells called
mesophyll are present which contain green dots in
them.
+ These green dots are chloroplasts within which
chlorophyll is present.
9. Experiment to prove that chlorophyll is
essential for photosynthesis
1. Take a plant with
variegated leaves- money
plant or crotons
10. + Keep the plant in dark- because it does not
receive sunlight anymore, it will use up all
the stored starch(destarching)
11. + Keep the plant in sunlight for six hours(it begins to
synthesise new food)
12. + Pick a leaf from the plant. Mark the green
areas in it. Also trace the regions in a
paper.
13. + Dip the leaf in boiling water(it stops all the
metabolic activities of the leaf)
14. + Immerse the leaf in boiling alcohol(this removes all
pigments from the leaf. The leaf becomes
colorless).
15. + Dip the leaf in iodine solution. Rinse off the
iodine after sometime.
16. + When you compare colourless leaf and the
paper, you will find that only those regions
which contained chlorophyll have turned blue
black in colour. This is because only the
regions with chlorophyll have the ability to
produce food.
17. Related questions
1.How is the nutrition of autotrophs different from that of heterotrophs?
2. What are enzymes otherwise known as and why?(important)
3. What is internal energy reserve? How is it different in plants and
animals?(important)
4. What are the raw materials required for photosynthesis? State the
products obtained.(important)
5. What is the source of oxygen in photosynthesis? .(important)
6. State the events of photosynthesis.(important)
18. 7. Draw the cross section of a leaf.
8. How is photosynthesis of desert plants different from that of normal
plants? .(important)
9. Mr. X was observing the cross section of a leaf through microscope
when he noticed a few green dots in some cells. What are they? What
do they contain? .(important)
10. Why are plants kept in dark for starch test?
11. State the significance of dropping leaves in the following during
starch test:
a) Boiling water
b) Boiling alcohol
19. 12.
a) What do a) and b) represent?
b) What do the marked regions in b indicate?
c) What do you understand from the observations?
