The Observer's 20 photographs of the week

A protester throws a cobblestone at police during a demonstration against same-sex marriage in Paris. Police say that the protest drew about 150,000 people Photograph: Etienne Laurent/EPA

An aerial view of the world's largest algae farm, in Kalbarri, Western Australia. The micro-organisms in the salt lake produce tonnes of beta-carotene, a versatile pigment used in everything from ice-cream to nutritional supplements Photograph: Steve Back/Barcroft Media

Mohammed Al-Shaikh, a regular contributor to this gallery, continues his excellent work on the unrest in Bahrain. Here, a girl is carried by her mother during the funeral of Sayed Omran Sayed Hameed who died after reportedly developing respiratory complications. His relatives claim that his death was due to the inhalation of teargas that riot police used during a protest Photograph: Mohammed Al-Shaikh/AFP

Schoolchildren get a close view of Inuka, the first polar bear born in the tropics, during the launch of the Frozen Tundra exhibit at the Singapore zoo Photograph: Tom White/EPA

The Mexican synchronised divers German Sanchez and Ivan Garcia perform in the men's 10-metre platform synchronised finals at the Fina Midea Diving World Series 2013 in Guadalajara, Mexico Photograph: Hector Vivas/LatinContent/Getty

Friends and family gather at the graveside of fallen soldier Ronald George Luce Jr, on Memorial Day at Arlington National Cemetery, Virginia. Luce died in Afghanistan. Barack Obama laid a wreath at the Tomb of the Unknowns, paying tribute to veterans past and present Photograph: Mark Wilson/Getty

A Brazilian navy sniper takes part in a hostage rescue drill, near Rio de Janeiro, Brazil. The Brazilian navy conducted the exercise in preparation for the Confederation Cup football tournament that takes place in Brazil later this month Photograph: Victor R Caivano/AP

A tree frog eyes its prey on a branch of tree in Costa Rica Photograph: Nicolas Reusens/Barcroft Media

Comic fan Wayne Adams at the MCM London Comic Con 2013, a comic magazine convention, held at the Excel centre in the city Photograph: Leon Neal/AFP

Anti-government protesters clash with police in Lome, Togo. Authorities have banned all protests in the capital after violent clashes during the week Photograph: Daniel Hayduk/AFP

The installation Bang by the Chinese artist Ai Weiwei is assembled in the German Pavilion at the Venice Biennale 2013. The installation is made up of 886 three-legged wooden stools
Photograph: David Levene/The Guardian

A farmer on the Shangbao terrace in Chongyi county, China Photograph: Wang Song/Corbis

Israeli soldiers of the Home Front Command rescue unit work in protective clothing during a drill in Azur, Israel. The country has launched a national civil defence exercise focusing on the threat of unconventional weapons, at a time of growing regional tension Photograph: Ariel Schalit/AP

Memorial day fireworks explode far above a house damaged by a tornado in Moore, Oklahoma. The tornado was the strongest in the US in nearly two years and created a trail of destruction 27km long and 2km wide Photograph: Lucas Jackson/Reuters

At the end of the week another series of tornadoes rolled in from the prairie and hit Oklahoma City and its suburbs. Here, high winds snap an electricity pylon on Highway 81 just south El Reno, Oklahoma Photograph: Chris Machian/AP

A Turkish riot police officer uses teargas against demonstrators protesting against the destruction of trees in a park in Taksim Square, Istanbul Photograph: Osman Orsal/Reuters

The demonstrations in Istanbul increased through the week. Here, again in Taksim Square, riot police fire more teargas to disperse crowds during an anti-government protest Photograph: Murad Sezer/Reuters

A Soyuz spacecraft is transported to a launch pad at the Baikonur cosmodrome, in Kazakhstan, before being launched to the International Space Station Photograph: Shamil Zhumatov/Reuters

A Palestinian worker holds a pot made out of kneaded mud, at a large pottery workshop in Gaza. More than 50 pottery workshops in Gaza are said to have closed in recent years, because of the growing availability of cheaper plastic containers Photograph: Ali Ali/EPA

Circus performer Hans Klose and his wife hold a rope for their performing dog to balance on, as they train for the show Dragons in Mexico City Photograph: Eduardo Verdugo/AP