Course 29.1Lesson 1 of 3
An organism lives in a place with its own temperature, water, light and soil. These abiotic factors decide which organisms can live there. This lesson names the four levels of ecology, gives the numbers that NCERT states for temperature and salinity, and explains the words eurythermal, stenothermal, euryhaline and stenohaline.
Try the code and the simulations beside the lesson.
Look at the plants and animals around your school. Now think of a place with snow all year. Different living things live there. Why?
Every organism lives in a habitat, which is the place where it is found. The place has a climate and a soil, and it has other living things. Ecology is the study of how organisms relate to their surroundings and to each other.
NCERT names four levels of biological organisation that ecology studies.
This chapter goes from the first level to the second. The next chapters in the book go on to the ecosystem. The temperature and the rainfall of a region decide which biome grows there.
The surroundings of an organism have two kinds of parts.
Each factor decides where an organism can live and how well it does. Let us take them one by one.
Temperature is the most important abiotic factor for most organisms. It changes the working of enzymes, and so it changes the metabolism, the activity and the other body functions of the organism.
NCERT gives these facts about temperature.
A few organisms can live in a wide range of temperatures. They are called eurythermal. Most organisms live in only a narrow range. They are called stenothermal. The range of temperature that a species can bear is one of the main reasons for its geographical distribution.
The standard atmosphere falls about 6.5 °C for each kilometre that you climb. NCERT does not give this number, but it shows why high mountains are cold.
Life cannot go on without water. The growth of plants and their spread over the Earth depend very much on the rainfall. In a desert, water is so short that only special adaptations make life possible.
For organisms that live in water, the quality of the water matters. Two things count: its chemical make-up and its pH. The most important is the salinity, the amount of salt in the water. It is measured in parts per thousand, which is the grams of salt in each kilogram of water.
Some organisms bear a wide range of salinity. They are euryhaline. Others live only in a narrow range. They are stenohaline. Many freshwater animals cannot stay long in sea water, and sea animals cannot stay long in fresh water. The problem is osmosis, the movement of water across the body surface.
A note on the print. NCERT writes these three numbers with the words per cent. The sea is about 3.5 per cent salt, and that is 35 parts per thousand. So the unit is parts per thousand, as in every standard book on oceans, and this course uses it.
Plants need sunlight for photosynthesis. Many small plants of a forest floor, the herbs and the shrubs, are always in the shade of tall trees. They do their photosynthesis best in very weak light.
Light matters in other ways too. Many plants flower only when the days have the right length. The length of the day and of the night is called the photoperiod. Many animals use the changes in the light to decide when to feed, to breed and to migrate. The quality of the light matters as well. The ultraviolet part of the sun's light harms many organisms, and the colours of the visible light do not all reach the plants that live deep in the sea.
On land, light and temperature go together, because the Sun gives both. Deep in the ocean, below about 500 m, there is no sunlight at all.
The soil differs from place to place. It depends on the climate, on the weathering of rocks, and on how the soil formed. The size of the soil grains and the way they stick together decide how water passes through the soil and how much it holds. The pH and the minerals of the soil, and the slope of the land, together decide to a large extent which plants grow in an area. In water, the sediment on the bottom decides which animals can live there.
You should find that a wide curve gives a wide range of temperature, and a narrow curve gives a narrow one. The best temperature moves the whole range up or down, and it does not change its width.
The program works out the salinity of three samples of water and names each kind.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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