Quest Subject: EVS Our Surroundings Grade: 3 What is life? What does it mean to be alive? Although biology is the study of life, even biologists don't agree on what 'life' actually is. However, it’s hard to come up with a precise definition of life. Because of this, many definitions of life are operational definitions describing life with a list of properties based on what life has or what life does. We use a list of properties that are, as a group, uniquely characteristic of living organisms. We can only say that ‘Life’ is the condition that distinguishes living things from nonliving ones. Is non – living the same as dead? In science, living is used to describe anything that is or has ever been alive. Nonliving means anything that is not now nor has ever been alive (rock, mountain, glass, wristwatch etc.) Non-living is not the same as being dead because non-living things were never alive and therefore cannot die. Remember that ‘dead means that it was once living’ and ‘nonliving means that it never lived’. All living things are made up of cells. How? Observe the picture of a brick wall. It is made of bricks. Bricks are the building blocks/ units of the wall. The bricks may vary in size. Similarly, living things are also composed of building blocks, called cells which are not visible to the naked eye. A cell is the basic unit of life and the smallest (microscopic) unit of all living things. A living thing, small or big, whether made of one cell (like bacteria) or many cells (like a human), is called an organism. Compare both plants and animals regarding their response to stimuli. Like all organisms, plants detect and respond to stimuli in their environment. Unlike animals, plants can’t run, fly, or swim toward food or away from danger. Instead, a plant’s primary means of response is to change how it is growing (growth toward or away from a stimulus). How are living and nonliving depend on each other (interdependence)? Can you think of any non-living things that you need every single day? What about water for drinking? How about air for breathing? Certain non-living things are necessary for living things to survive. Let us take the example of aquarium In this aquarium green plants and fish are living things. Soil, water and air are non – living things. Fish breathe in oxygen in water and release carbon dioxide which green plants need to make their food. The droppings of the fish make soil fertile which helps plants grow. Difference between the environment and ecosystem. The environment is everything around us including living and non – living things. It is the surroundings or area where an organism lives. Ecosystem is group of organisms (producers, consumers and decomposers) which interact among themselves and also with non – living things in their environment. An ecosystem can be of any size from a small puddle to a vast desert. Aquarium is the best example an artificial ecosystem.
