page_title: Chloroplast
section_title: Thylakoid system
hierarchical_section_title: Chloroplast / Structure / Thylakoid system
caption_attribution_description: English: (Top) 10-nm-thick STEM tomographic slice of a lettuce chloroplast. Grana stacks are interconnected by unstacked stromal thylakoids, called “stroma lamellae”. Round inclusions associated with the thylakoids are plastoglobules. Scalebar = 200 nm. See &#91;1&#93;. (Bottom) Large-scale 3D model generated from segmentation of tomographic reconstructions by STEM. grana = yellow; stroma lamellae = green; plastoglobules = purple; chloroplast envelope = blue. See &#91;1&#93;.
context_page_description: Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water in plant and algal cells. They then use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of other functions, including fatty acid synthesis, much amino acid synthesis, and the immune response in plants. The number of chloroplasts per cell varies from one, in unicellular algae, up to 100 in plants like Arabidopsis and wheat.
  A chloroplast is a type of organelle known as a plastid, characterized by its two membranes and a high concentration of chlorophyll. Other plastid types, such as the leucoplast and the chromoplast, contain little chlorophyll and do not carry out photosynthesis.
  Chloroplasts are highly dynamic—they circulate and are moved around within plant cells, and occasionally pinch in two to reproduce. Their behavior is strongly influenced by environmental factors like light color and intensity.
context_section_description: Thylakoids (sometimes spelled thylakoïds), are small interconnected sacks which contain the membranes that the light reactions of photosynthesis take place on. The word thylakoid comes from the Greek word thylakos which means "sack".
  Suspended within the chloroplast stroma is the thylakoid system, a highly dynamic collection of membranous sacks called thylakoids where chlorophyll is found and the light reactions of photosynthesis happen.
  In most vascular plant chloroplasts, the thylakoids are arranged in stacks called grana, though in certain C₄ plant chloroplasts and some algal chloroplasts, the thylakoids are free floating.
caption: Scanning transmission electron microscope imaging of a chloroplast
  (Top) 10-nm-thick STEM tomographic slice of a lettuce chloroplast. Grana stacks are interconnected by unstacked stromal thylakoids, called “stroma lamellae”. Round inclusions associated with the thylakoids are plastoglobules. Scalebar = 200 nm. See [123]. 
  (Bottom) Large-scale 3D model generated from segmentation of tomographic reconstructions by STEM. grana = yellow; stroma lamellae = green; plastoglobules = purple; chloroplast envelope = blue. See [123].
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