1. Natural Sciences Grade 7
Term 1: Life and Living
The biosphere
(PPT 4)

2. Requirements for sustaining life
Topic 1 The Biosphere
Requirements for sustaining life
Gr 7 Natural Sciences – Term 1, Topic 1

3. Factors needed for survival
5 Main factors –
Energy
Gases
Water
Soil
Favourable temperatures
Living organisms are found in the biosphere. What do the three parts of the biosphere have that living things need to survive?
Gr 7 Natural Sciences – Term 1, Topic 1

4. Gr 7 Natural Sciences – Term 1, Topic 1
Energy
The sun releases heat energy and light energy.
Heat energy in the sun’s rays warms up the lithosphere, hydrosphere and the atmosphere.
Light energy is used by green plants to –
make food for living
make food to grow
store food for future use
The sun is like an enormous nuclear power station which releases a huge amount of energy. The energy radiates into space. As the earth moves around the sun, some of the energy from the sun will fall on earth.
Gr 7 Natural Sciences – Term 1, Topic 1

5. Gr 7 Natural Sciences – Term 1, Topic 1
Energy
Animals eat the plants and use the stored energy to build their own bodies and to live.
Gr 7 Natural Sciences – Term 1, Topic 1

6. Gr 7 Natural Sciences – Term 1, Topic 1
Energy
Gr 7 Natural Sciences – Term 1, Topic 1

7. Gr 7 Natural Sciences – Term 1, Topic 1
Gases
The atmosphere contains air.
Air is not a gas, but a mixture of several gases.
Three of these gases are important for life:
carbon dioxide
nitrogen
oxygen
The atmosphere is the region of gas around the earth. It contains air.
Gr 7 Natural Sciences – Term 1, Topic 1

8. The main gases in the atmosphere
Whether you know it or not, you are breathing argon right now. But there is no need to be worried: This colourless, odourless gas makes up only 0.94 percent of the air around you, and it has no effect on living organisms. This tiny amount of argon is not very important to biology or to the Earth's climate, but it is useful to scientists.
Gr 7 Natural Sciences – Term 1, Topic 1

9. Gr 7 Natural Sciences – Term 1, Topic 1
Carbon dioxide (CO2)
Carbon (not carbon dioxide) is found in foods like sugars, fats and meat.
Carbon is present in the atmosphere as a gas called carbon dioxide.
Carbon dioxide is the waste product of respiration in animals.
Humans get rid of carbon dioxide by breathing it into the air.
During photosynthesis, plants take in carbon dioxide and release oxygen.
Plant material and the amount of combustion influence the amount of carbon dioxide on Earth. The Amazon jungle covers 5% of Earth’s surface, but because of it’s dense forests it absorbs 10% of the carbon dioxide in the atmosphere. On average, the amount of carbon dioxide in the atmosphere is 0,04%.
Gr 7 Natural Sciences – Term 1, Topic 1

10. Gr 7 Natural Sciences – Term 1, Topic 1
Oxygen (O2)
Oxygen is released during the process of photosynthesis.
Oxygen is present in the air that we breath, in other words, it is important for respiration.
Our cells use the oxygen to release the energy from the food that we eat so that it can be used by our bodies.
It makes up 21% of the air.
The amount of oxygen in the Earth’s atmosphere is in perfect proportion. Any more oxygen on Earth, would mean that fires would start very easily and burn out of control. Any less oxygen would mean that we would be gasping for breath.
Gr 7 Natural Sciences – Term 1, Topic 1

11. Gr 7 Natural Sciences – Term 1, Topic 1
Nitrogen
Nitrogen makes up 78% of the atmosphere.
It is used by organisms to make protein.
The human body needs protein to develop muscles, brain tissue, hair and skin.
Most living things cannot use nitrogen as a gas; plants make protein using the nitrogen in the soil.
Animals get their proteins from the food that they eat.
Gr 7 Natural Sciences – Term 1, Topic 1

12. Gr 7 Natural Sciences – Term 1, Topic 1
Water
Nutrients dissolve in water and gets taken up by the roots of plants in the soil.
Animals get nutrients when they eat plants.
When drinking water, the animals’ bodies absorb the vitamins, minerals and other nutrients contained in their food.
Plants will wilt without sufficient water.
Humans will dehydrate without sufficient water.
Water is important for photosynthesis, which is the only way that food can be made.
Water is vital to all life on Earth. Humans can live without food for a month or more, but only a few days without water.
Gr 7 Natural Sciences – Term 1, Topic 1

13. Gr 7 Natural Sciences – Term 1, Topic 1
Soil
Plants need soil to grow.
Soil provides plants with water, it contains nutrients and it anchors the plants.
Soil contains living organisms and non-living elements, but the soil itself is non-living.
Animals need plants to make their food.
Soil is also important for the welfare of humans.
Soil is abiotic, which means that it is non-living. Animals depend directly or indirectly on plants for food: herbivores and omnivores eat food
produced by plants (directly); carnivores eat animals that survive on plants (indirectly).
Gr 7 Natural Sciences – Term 1, Topic 1

14. Favourable temperature
Living things need a favourable temperature range in which to live.
Earth’s temperature ranges between -50 degrees celsius to about 50 degrees celsius.
The temperature will affect the phases of water in an area, for example – frozen water in the Arctic and Antarctic.
Hot areas will have high humidity (Durban) and high evaporation of water from dams and lakes.
Gr 7 Natural Sciences – Term 1, Topic 1

15. Gr 7 Natural Sciences – Term 1, Topic 1.
Gr 7 Natural Sciences – Term 1, Topic 1