El ciclo del agua | Ecología | Biología | Khan Academy en Español

Summary

This video explains the water cycle, highlighting the continuous movement of water through various stages: evaporation, condensation, precipitation, and runoff. It delves into the roles of oceans, rivers, lakes, glaciers, and groundwater in the cycle, and the processes of transpiration and sublimation. It also emphasizes the limited availability of fresh water, with most of Earth's water being salty or locked in glaciers. The video further explores how water molecules can remain in different parts of the cycle for varying periods, from a week in the atmosphere to thousands of years in glaciers and oceans.

Takeaways

• 😀 Water is an essential part of the water cycle, and we are all part of it every moment, even if we don't realize it.
• 😀 Evaporation occurs when water molecules on the surface of oceans, rivers, and lakes gain enough energy to transform from liquid to gas, forming water vapor.
• 😀 Water vapor rises with warm air and cools as it ascends, eventually condensing into tiny droplets that form clouds.
• 😀 Clouds are formed when water vapor condenses around particles of dust and air, and can sometimes form ice crystals when temperatures are low enough.
• 😀 Water in clouds moves with the air, and when droplets become heavy enough, they precipitate, falling as rain or snow depending on the temperature.
• 😀 Precipitated water can return to the oceans or fall on mountains, where it may melt and contribute to runoff or groundwater.
• 😀 Groundwater, including water in aquifers, flows into rivers and lakes, where it can be stored or accessed through wells.
• 😀 Plants play a role in the water cycle by absorbing water from the soil and using it in processes like photosynthesis, with much of it being transpired through leaves.
• 😀 Sublimation is the direct conversion of ice or snow into water vapor, occurring under conditions of low temperature, low humidity, and low pressure.
• 😀 Freshwater, which is essential for human life, constitutes only 2.5% of the total water on Earth, with most of it locked in glaciers and ice sheets, not easily accessible.
• 😀 The residence time of water molecules varies depending on their location: oceans (up to 4,000 years), glaciers (up to 10,000 years), and the atmosphere (about 1.5 weeks on average).

Q & A

What is the first step of the water cycle described in the video?

The first step of the water cycle is evaporation. Water evaporates from the surface of oceans, rivers, and lakes, where some liquid water molecules gain enough energy to escape into the gas phase as water vapor.

How do clouds form in the water cycle?

Clouds form when water vapor rises into the atmosphere, cools, and condenses into tiny water droplets. These droplets cluster around microscopic particles like dust and air particles, forming visible clouds.

What is the role of plants in the water cycle?

Plants absorb water from the ground through their roots and use it to transport nutrients to their leaves. The water is also used in photosynthesis, and a significant amount is transpired, meaning it evaporates from the leaves back into the atmosphere.

What is sublimation, and when does it occur?

Sublimation is the process where water changes directly from a solid (ice) to a gas (water vapor) without passing through the liquid phase. This typically occurs in very cold, dry environments with low pressure.

How does water return to the Earth's surface from clouds?

Water returns to the Earth's surface from clouds through precipitation, where the water droplets in the clouds grow heavy enough to fall as rain, snow, or other forms of precipitation, depending on the temperature.

What happens to water when it precipitates in mountainous regions?

In mountainous regions, precipitation may fall as snow or ice due to the cold temperatures. Over time, some of this snow will melt and contribute to runoff, eventually reaching rivers and lakes.

How does water become part of underground aquifers?

Water from precipitation, such as rain, filters through the soil and accumulates in underground aquifers. These aquifers can hold water for extended periods, and people often access this water by digging wells.

What is the difference between fresh water and saline water in terms of global distribution?

Only about 2.5% of Earth's water is fresh water, with most of it locked in glaciers, ice caps, and underground aquifers. The remaining 97.5% of Earth's water is saline, mostly found in the oceans.

How long can water stay in different parts of the water cycle?

Water can stay in different parts of the water cycle for varying amounts of time. For example, water can remain in glaciers for up to 10,000 years, while it can stay in oceans for up to 4,000 years. In the atmosphere as water vapor, it can stay for about a week and a half, and in living organisms, it typically stays for up to a week.

Why is the small percentage of fresh water on Earth significant for human survival?

The small percentage of fresh water on Earth is crucial for human survival because it is the water we use for drinking, agriculture, and other essential activities. However, it is limited and not evenly distributed across the planet, making access to fresh water a critical issue.