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 ...
Did you ever wonder why the days are so long in the summer and so short in the winter? The length changes throughout the year. In the summer, around June 20 or 21, we experience the summer solstice, which is the longest day of the year. And in the winter, December 21 or 22 is the winter solstice, or shortest day. But wait! If you live in Australia, you experience the oppositeâthe longest day is in December and the shortest is in June.