Download Chloroplast

Chapter 4.8
Specialized Plant Organelles
AP Biology
Fall 2010
Objective
• Describe the structure and function of the
chloroplast
• Understand the differences between
chloroplasts, chromoplasts, and amyloplasts
• Describe the structure and function of the
central vacuole
Chloroplasts and Plastids
• Plastids: organelles that function in
photosynthesis or storage in plants
• Three types:
– Chloroplasts
– Chromoplasts
– Amyloplasts
Chloroplasts
• Chloroplast: oval or disk shaped organelles,
bounded by a double membrane, and
specialized for photosynthesis
Chloroplasts
• Structure:
– Two outer membranes enclose their semifluid
interior, the stroma
– In the stroma, third membrane forms a single
compartment that is commonly folded in intricate
ways
– Fold resemble stack of flattened disks, called
granum
– Photosynthesis occurs in thylakoid membrane
Chlorplasts
• In simpler terms:
– Stroma: semifluid
interior
– Thylakoid: contains
chlorophyll and other
pigments, individual
units
– Granum: stacks of
thylakoids
Chloroplasts
• In the innermost membrane, stacked disks
(thylakoids), pigments, and enzymes trap
sunlight energy to form ATP and NADPH
• Sugars and starches are formed in the fluid
substance (stroma) surrounding the stacks
• Pigments such as chlorophyll (green) confer
distinctive colours to the chloroplasts
Chloroplasts
• Chlorophyll reflect green light
• Many kinds of accessory pigments assist
chlorophyll in capturing light
• Energy drives reactions
– ATP and NADPH form
– ATP and NADPH used at sites in stroma where
sugars, starches assembled
– Starch grains: new starch molecules that
accumulate in stroma
Chloroplasts
• Chloroplasts are like photosynthetic bacteria
and may have evolved through endosymbiosis
like mitochondria
Chromoplasts
• Chromoplasts: store red and brown pigments
(carotenoids) that give colour to flowers,
autumn leaves, fruits, and roots
• Have no chlorophyll
• Attract animals
Amyloplasts
• Amyloplasts: colourless, lack pigments
– Store starch grains, and are abundant in stem
cells, tubers, and seeds
– Found in stems, potato tubers (underground
stems), and seeds
Comparison
Central Vacuoles
• Central Vacuoles:
– Fluid filled vacuoles
– In a mature plant, the central vacuole may occupy
50 to 90% of the cell interior
– Store amino acids, sugars, ions, and wastes
– Vacuole enlarges during growth and greatly
increases the cell’s outer surface area
• Enlarged cell, with more surface area, has an
enhanced ability to absorb nutrients
Central Vacuole
Review
1. Describe differences between amyloplasts,
chloroplasts, and chromoplasts
2. What are the main structural components of
the chloroplasts?
Answers
1. Amyloplasts are pigment free, store starch
grains. Chromoplasts have no chlorophyll, have
abundance of carotenoids, colours attract
animals. Chloroplasts are specialized organelles
for photosynthesis, contain chlorophyll.
2. Clorplasts:
– Stroma: semifluid interior
– Thylakoid: contains chlorophyll and other pigments,
individual units
– Granum: stacks of thylakoids