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 ...
Summer 2017 begins on Wednesday, June 21, 2017 at 04:24 UTC, or 12:24 am EDT. For the other United States time zones, summer will begin on Tuesday June 20th at 11:24 pm CDT, 10:24 pm MDT, and 9:24 pm PDT. 1  2016: 93 days, 15 hours, and 47 minutes.  2017: 93 days, 15 hours, and 38 minutes.