Chloroplast

This deck will help you learn detailed concepts of the chloroplast

What is a chloroplast?

A food-making organelle in plant and algal cells where photosynthesis converts light to chemical energy.

In what kinds of organisms are chloroplasts found?

In the cells of plants and certain algae, especially in photosynthetic tissues.

Where in a typical plant leaf are chloroplasts especially concentrated?

In the parenchyma cells of the leaf mesophyll (internal layers).

Why are chloroplasts green?

They contain chlorophyll pigments, mainly chlorophyll a and chlorophyll b.

What type of cell structure is a chloroplast classified as?

A plastid, which is a double-membrane organelle involved in food synthesis and storage.

What is the main function of chlorophyll in chloroplasts?

Chlorophyll absorbs light energy and helps start the reactions of photosynthesis.

Besides chlorophyll, what other pigments are present in chloroplasts and what is their role?

Carotenoids act as accessory pigments that capture light and transfer energy to chlorophyll.

What is the general size of a chloroplast?

About 1-2 micrometers thick and 5-7 micrometers in diameter.

What is the stroma of a chloroplast?

The fluid matrix inside the inner membrane containing enzymes, starch granules, and DNA.

What is the chloroplast envelope?

The double outer membrane, made of outer and inner membranes with an intermembrane space.

What are thylakoids?

Membrane-bound sacs inside the chloroplast where light reactions of photosynthesis take place.

What is a granum (plural: grana)?

A stack of thylakoid disks found in most higher plant chloroplasts.

What connects grana to each other?

Stromal lamellae, which are membrane extensions that link grana across the stroma.

What is the thylakoid lumen?

The aqueous space inside each thylakoid sac.

What key complexes are located in the thylakoid membrane for the light reactions?

Photosystem I, photosystem II, and ATP synthase are embedded in the membrane.

In which part of the chloroplast do the light-dependent reactions of photosynthesis occur?

In the thylakoid membranes.

In which part of the chloroplast do the light-independent (dark) reactions occur?

The stroma

What two main energy-rich products are made by the light reactions?

ATP and NADPH are produced by the light reactions.

What enzyme in the stroma starts carbon fixation in the Calvin cycle?

Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the first step of carbon fixation.

What are C4 plants in terms of chloroplast function?

Plants that separate initial carbon fixation (mesophyll) and Calvin cycle (bundle-sheath) in space.

What is CAM photosynthesis in terms of timing?

Plants separate PEP carboxylation (at night) and the Calvin cycle (during the day) in time.

Do chloroplasts have their own DNA?

Yes, they have circular extranuclear DNA encoding genes for photosynthesis and chloroplast functions.

What evolutionary theory explains the origin of chloroplasts?

Endosymbiotic theory suggests they evolved from free-living cyanobacteria inside early eukaryotic cells.

How has the chloroplast genome changed over evolution?

Many genes moved to the nucleus, so nuclear-encoded proteins must be imported.

How permeable is the outer chloroplast membrane?

Freely permeable to small molecules; has channels for importing larger proteins.

How permeable is the inner chloroplast membrane?

Highly selective; allows passage mainly of specific targeted proteins and certain solutes.

What are plastoquinones and where are they found?

Small, lipid-soluble molecules in thylakoid membranes that carry electrons in light reactions.