Confidence votes 9.4K. Animal cells do not have cell walls, they only have cell membranes. The cell membrane mainly consists of a phospholipid bilayer, and also contains embedded proteins and cholesterol. Plant cell walls are mainly made of cellulose, bacterial cell walls are mainly made of peptidoglycan.
In the Northern Hemisphere, the official summer season begins with the June solstice, which takes place on June 20th, 21st or 22nd each year, and ends with the September equinox, which takes place on September 22nd or 23rd each year; the exact duration of summer depends on when the solstice and equinox will take place and can range from 92 to 95 ...
Therefore, in the meteorological calendar, summer includes the months of June, July and August - always starting on 1 June and ending on 31 August. Confusingly, British Summer Time (BST) lasts for 7 months - the time in the year when the UK is one hour ahead of Greenwich Mean Time (GMT). The clocks go forward on the last Sunday on March, going to back to GMT on the last Sunday of October.