OCR A Level ELSS - 2. OCR A Level ELSS 4.1 The importance of water and carbon to life on Earth

Question 1

What characteristic about water is key to understanding its importance in the development of life on Earth?

Answer 1

Water allows organic molecules to mix and form more complex structures.

Question 2

Why is liquid water found around ubiquitously (everywhere) on Earth?

Answer 2

Earth is found in the ‘Goldilocks zone’ in terms of distance from the Sun, allowing water to exist in all 3 states, especially in liquid form.

Question 3

How does water help create ideal temperatures on Earth for life to thrive?

Answer 3

1. Oceans, which occupy 71% of Earth’s surface, moderate temperatures by absorbing heat, storing it and releasing it slowly. 2. Clouds reflect around 1/5th of incoming solar radiation and so lower surface temperatures. 3. Water vapour, a greenhouse gas, absorbs long-wave radiation from Earth, maintaining average global temperatures almost 15 degrees C higher than they would be otherwise

Question 4

What percentage of all living organisms are made of water?

Answer 4

between 65-95%

Question 5

How is water important to living organisms?

Answer 5

Water is crucial in living organisms for: 1. Growth - e.g. plants manufacture food using photosynthesis, respiration and transpiration, all of which require water. Photosynthesis is the mechanism by which carbon enters the food chain. 2. Reproduction 3. Metabolic functions including: Respiration e.g. all chemical reactions in the bodies of all animals and humans take place in water, especially for circulating oxygen and nutrients around the body. Transpiration e.g. plants use this to cool plants, sweating is a similar cooling process in humans and panting in animals with fur.

Question 6

How is water used as an economic activity?

Answer 6

1. Generate Electricity - Hydro-electric power, Tidal and Wave energy 2. Irrigating crops - a key element of food production 3. Domestic use - drinking, labour-saving devices such as dishwashers and washing machines. 4. Manufacturing - for food, brewing, paper and steel making.

Question 7

How is carbon considered to be a building block for life on Earth?

Answer 7

All life on Earth is carbon based. In particular, carbon is a key element in more complex organic molecules such as 1. Proteins 2. Carbohydrates and 3. Nucleic acids

Question 8

Where is carbon found on Earth?

Answer 8

1. Carbonate rocks - limestone, 2. Sea-floor sediments - 3. Ocean water (as dissolved carbon dioxide) 4. Atmosphere - as carbon dioxide and methane 5. Biosphere - in all living organisms

Question 9

Why are carbon dioxide and methane in the atmosphere needed to support life on Earth?

Answer 9

Carbon dioxide and methane are key gases in the natural greenhouse effect which make Earth’s climate warm enough for life to exist. (The mean global surface temperature would be around -15 degrees C without the natural greenhouse effect).

Question 10

How is carbon used as an economic resource?

Answer 10

1. Fossil Fuels - coal, oil and natural gas currently power the global economy. 2. Oil derivatives - plastics, paint and synthetic fabrics are all derived from oil making many of the world’s products. 3. Agriculture - crops store large amounts of carbon for human and animal use. 4. Forestry - timber, paper and textiles use wood