If there was no Jupiter in the solar system, Saturn would indeed be the largest planet in the solar system. Here's an explanation of why this would be the case:

1. The role of Jupiter:
Jupiter is the largest planet in our solar system and exerts a significant gravitational force on other celestial bodies. Its presence has played a crucial role in shaping the solar system as we know it today.

2. Influence on Saturn:
Jupiter's gravitational pull has a profound effect on Saturn. It helps to stabilize Saturn's orbit and prevents it from getting too close to the Sun or other planets. Without Jupiter, Saturn's orbit would be more chaotic, leading to potential collisions or disturbances in its path.

3. Impact on size:
Jupiter's massive size also affects the distribution of matter in the solar system. Its strong gravity has prevented smaller objects from coalescing into a larger planet between Mars and Jupiter. This is why we have the asteroid belt in that region instead of a single large planet. However, if Jupiter were not present, it is likely that these smaller objects would have accumulated over time to form a larger planet. Consequently, Saturn would not be the largest planet in the solar system.

4. Other planets:
The absence of Jupiter would not directly impact the size of other planets. However, it may have secondary effects on their orbits and interactions with other celestial bodies.

5. Cold Mars:
The absence of Jupiter would not make Mars the coldest planet in the solar system. The cold temperatures on Mars are primarily due to its distance from the Sun, thin atmosphere, and lack of a significant greenhouse effect. These factors would remain unchanged even without Jupiter's presence.

6. Life on Venus:
The absence of Jupiter would not directly lead to the growth of life on Venus. Venus is an inhospitable planet with a dense atmosphere, extreme temperatures, and a highly corrosive environment. These conditions are unrelated to Jupiter's presence or absence.

In conclusion, if there was no Jupiter in the solar system, Saturn would not automatically become the largest planet. The absence of Jupiter would have complex effects on the dynamics and structure of the solar system, but it would not directly impact the size of other planets or the conditions on Venus or Mars.