Vacuole

• Vacuoles are very simple yet versatile organelles. Consisting of a single membrane that surrounds its contents and isolates them from the cell's cytoplasm, a vacuole can contain water, digestive products, waste or food. A food vacuole may contain another unicellular organism that was eaten by a predatory species such as an amoeba, or sugars and amino acids that have already been broken down elsewhere in the cell. Vacuoles typically occupy 30 percent to 90 percent of a cell's volume.
  
  

Chloroplast

• Chloroplasts act as storage sites for chlorophyll and contain the structures that allow plants and some bacteria to convert sunlight into energy. The chloroplast has outer and inner membranes wrapped around stacks of even smaller structures called thykaloids, hollow disks that actually contain the embedded chlorophyll molecules. The chlorophyll molecules absorb photons from light and emit electrons, which power the process of ATP formation and provide energy for the rest of the cell.
  
  

Sarcoplasmic Reticulum

• The sarcoplasmic reticulum is a structure found in muscle cells. Structurally similar to the endoplasmic reticulum that synthesizes proteins and lipids in most types of cells, its function is to store and transport calcium ions. Calcium is important to the process of muscle contraction and relaxation. When the muscle is relaxed, calcium is transported actively into the sarcoplasmic reticulum. When a nerve impulse activates the muscles, gates in the sarcoplasmic reticulum open and allow the calcium ions to flood out into the rest of the cell.
  
  

Melanosome

• Melanosomes are specialized organelles present in some cells that produce and store the pigment called melanin. The location, composition and number of melanosomes determine the skin, hair and iris color of mammals. Some melanosomes can produce increased melanin levels in response to ultraviolet light exposure. Abnormal melanin production within pigment cells is connected with diseases and conditions ranging from albinism to malignant melanoma, a life-threatening form of cancer.