For B.Sc. I (Medical) students

1. Dr Jasmine Brar
Email : drjasmine1807@gmail.com

2. Plastids: Haeckel, 1866
They are semi-autonomous organelles having DNA &
double membrane envelope which store or synthesize
various types of organic compounds like fatty acids,
amino acids, purines, pyrimidines etc.
Proplastids
Small spherical colourless structures, 1 µm in diameter
which occur in meristematic cells. It is double membrane,
Its internal membrane develops lamellae

3. Chloroplasts has 3 parts
a. Envelope: 2 memberane separated by
intermembrane space.
b. Matrix: ground substance (stroma). They have
special starch storing structures called
pyrenoids.
c. Thylakoids: flattened sacs run throughout the
stroma & called structural elements of
chloroplasts. Thylakoids are stacked to form
grana. Each granum has 20-50 thylakoids.

4. Proplastids

6. Leucoplasts
Internal structure
of a leucoplasts
a developing
amyloplasts

7. Cell containing
chromoplasts
of various shapes
Chromoplast showing
degenerating lamellae
of parent plastid

8. Ultra structure of Chloroplasts

9. 3-dimensional structure of chloroplasts

10. Arrangement of
Thylakoids in granum
Distribution of pigment
System, cyt b6/f & coupling factors in
Thylakoid membranes

11. An algal chloroplast (lamellar chloroplasts) showing
pyrenoid & eye spot (found in motile algae which
have photoreceptors)

12. Functions of Chloroplasts
They are centre of photosynthesis.
They are able to trap sun energy & change it into
chemical energy which is used by all living
organisms.
Percentage of CO2 balanced in atmosphere which is
constantly being added through combustion &
respiration.
It liberates O2 which is passed into the atmosphere

13. They store starch either temporary (higher plants),
permanently in algae.
Chloroplasts of some algae provide photosensitivity
due to presence of stigma (eye spot).
The reducing power produced during the light
reaction (NADPH) is used in reduction of nitrates &
synthesis of amino acids.
Murphy & Leech (1978) have reported the synthesis
of fatty acids in Spinach chloroplasts.

14. They store fat in the form of plastogloubli.
They can be changed into chromoplasts to provide colour
to many flowers & fruits for attracting animals.
Biogenesis
Schimper & Meyer (1883) found that plastids seldom
arise de novo but originate by division of pre-existing
Plastids.

15. Origin of chloroplasts
from
proplastid

16. 1. Division of pre-existing chloroplasts: Lower plants
eg Spirogyra, Funaria
2. Development from proplastids: DNA of proplastids
replicates, other contents also multiply.
The proplastids enlarges & constricts inn the middle
to form 2 daughter proplastids.
By repeated divisions large number of proplastids
are formed.

17. Differentiation phase: proplastids get changed into
etioplasts in dark grown plants. On exposure to light for
5 min. prolamellar body (lattice of tubules in etioplasts)
opens out & form chloroplasts.
Maturation phase: Plastids grow in size, lamellae increase
in number & develop grana, pigments like chlorophyll are
Synthesized & proplastid turn into chloroplast.