Chloroplasts are double membranous organelles within plant cells where photosynthesis occurs, absorbing sunlight to convert it into sugar molecules and free energy stored as ATP and NADPH. They consist of a stroma containing DNA and ribosomes, and a thylakoid system where the light reactions of photosynthesis take place. The overall process supports life on Earth by producing oxygen and carbohydrates, essential for both plants and animals.

1. PHOTOSYNTHESIS AND
CHLOROPLAST
AMRITHA S R
BSC
BIOTECHNOLOGY
JSS UNIVERSITY
MYSURU

2. Introduction
 Chloroplasts are double membranous organelles
with thylakoid system present in plant cells & some
eukaryotic organism . It is the structure in a green
plant cell in which photosynthesis occurs. Animal
cells do not contain chloroplasts.

3. The distribution of chloroplasts is homogenous in
the cytoplasm of the cells & in certain cells
chloroplasts become concentrated around the
nucleus or just beneath the plasma membrane. A
typical plant cell might contain about 50
chloroplasts per cell.

4.  Chloroplast absorb sunlight & convert into sugar
molecules & also produce free energy which is
stored in the form of ATP & NADPH through
photosynthesis.
 Chloroplasts are said to have originated from
endosymbiotic bacteria.

5. Chloroplast structure
 They are generally biconvex or Plano convex shaped.
 Size varies from 4-6µ in diameter & 1-3µ in
thickness.

6.  Double membranous
structure with the inner
& outer membrane.
 Outer membrane- semi-
porous & is permeable to
small molecules & ions, which
diffuse easily.
 Inner membrane –regulates
passage of materials in & out
of the chloroplast.
 Stroma-alkaline ,aqueous
protein rich fluid .The
chloroplast DNA ,ribosomes &
thylakoid system are found
floating in stroma.

7.  Granum & Thylakoid system-is
suspended in the stroma. It is a
collection of membranous sacks called
thylakoids. Chlorophyll is found in the
thylakoids & is the sight for the process
of light reaction of photosynthesis.
Each granum contains around 10-20
thylakoids.
 Thylakoids are of two types
1. Granal thylakoids
2. Stromal thylakoids
 Stroma lamellae -granum is
interconnected by stroma lamellae.

8. Chloroplast Pigments
chlorophyll a
chlorophyll b
carotenoids
xanthophyll

10. Chloroplast function
 Participate in plant immune system.
 Site of photosynthesis
 Light reaction takes place on the membranes of thylakoids.
 Dark reaction / Calvin cycle takes place in the stroma.
 Production of NADPH₂ & O₂.

11. PHOTOSYNTHESIS

12. Photosynthesis
 Photosynthesis is a physio-chemical process by which autotrophic organisms use
light energy to make sugar & O₂ gas from CO₂ & H₂O in the presence of
chlorophyll.
6CO₂ + 6H₂O ――――――> C₆H₁₂O₆ + 6O₂

13. Function of photosynthesis
 Evolves molecular oxygen ,for use by other living
organisms.
 Maintains the level of atmospheric oxygen.
 Produces carbohydrates that are used by the plants &
animals.
 It is the only process ,which produces huge quantities of
organic matter for sustaining life on earth . For e.g.:
natural fibers, drugs ,vitamins, gums, rubber ,furniture
etc.

14. Steps in photosynthesis
1. In all green plants ,this process occurs in
leaves .
2. CO₂ & O₂ enter & exit the leaves from the
leaves through pores called stomata.
3. Water gets delivered to the leaves from the
roots through a vascular system.
4. The chlorophyll ,present in the chloroplasts
of the leaf cells helps in absorbing sunlight.
5. Chlorophyll & other carotenoids help in
transferring light energy.
6. Photosynthesis is carried out in two phases.
7. The light reactions produce carbohydrates by
using ATP & NADPH.
8. The dark reaction synthesizes sugar from
CO₂ with the help of ATP & NADPH.

15. Phases of Photosynthesis
1) Light Reaction
2) Dark reaction

16. Light reaction
 Requires light energy & occurs in thylakoids membranes.

17. Dark reaction
 It takes place in the stroma region of the chloroplast .