If CO2 was in very small amounts then it would be the limiting factor of photosynthesis, this means the process will take place at a much slower rate because it is lacking one of the raw materials it needs for the process to occur. To find the optimum light intensity you really need all other factors to be at optimum levels or in abundance.
Summer
, for the northern hemisphere, summer is the warmest time of year. It's not because the planet is that much closer to the Sun, it's because the top part of the Earth is facing the Sun for a amount of time.
The Sun is directly over the Equator during the autumnal equinox, and heating the northern and southern hemispheres equally. As the northern hemisphere is moving towards shorter days and the cold winter, the southern hemisphere is watching the snows melt and the flowers bloom during their spring.
Summer is the season where the Earth is tilted way from the Sun and the South Pole is getting all of the light
Spring is a bit of a mirror image to our position in autumn. The Sun is directly over the Equator during the equinox and the northern and southern hemispheres
They are called prokaryotic cells
