All living things are made up of cells. Cell is the basic unit of life. Living organisms that are made up of only one cell are called unicellular such as Amoeba, Chlamydomonas, bacteria, etc. Those made up of many cells are called multicellular. A complex multicellular organism is made up of trillions of cells. All living things require food for growth and development. It also gives them energy for sustaining life processes. For example, plants manufacture their own food by the process of photosynthesis. Such organisms are called autotrophs. Animals, on the other hand, depend on plants and other animals for their food. They are called heterotrophs. All living things grow. Growth can be easily observed in all plants and animals. Living things either produce new cells or their pre-existing cells increase in size and hence they grow. In animals, growth stops as they reach their adult stage while the plants keep on growing throughout their life. All living things respire. Respiration is a process that includes breathing. The movement of air in and out of the body and vice-versa is known as breathing. For example, animals such as earthworms breathe through their skin; fish use gills for breathing; and plants exchange gases through tiny pores called stomata, which are present mainly on the surface of leaves. Respiration is a two stage process. It has two stages: External respiration − This is the process of breathing i.e., taking in oxygen and giving out carbon dioxide. Internal respiration − In this stage, oxygen taken in is utilised to produce energy. All living organisms respond to stimuli. Do you know what stimulus is?
Stimuli are certain changes in the surroundings that cause an organism to respond to them. For example, animals such as cockroaches hide as soon as the light is switched on.
Plants such as Mimosa pudica (touch-me-not) close their leaves when touched.
Let us now perform the following activity to understand how plants respond to stimuli.
Take a potted plant and keep it in a room at a slight distance from the window. Sunlight must enter through the window during the day time. Water this plant regularly for a few days.
You will observe that the stem of the plant bends towards the sunlight.
This proves that living organisms react to stimuli.
All living organisms excrete. What is excretion?
A part of the food we eat is utilised by the body while the rest is removed from the body.
The process of getting rid of waste materials from the body is known as excretion. This process occurs in both plants and animals. In animals, waste products such as urea are excreted in urine; and carbon dioxide, which is also a waste product, is excreted by lungs. In plants, the wastes are converted into harmless substances such as gum, resins, etc.
All living organisms reproduce. Some animals produce eggs while others give birth to young ones. Plants, on the other hand, reproduce by producing spores or seeds. Do you know?
Mammals such as humans, cats, dogs etc., which give birth to young ones, are called viviparous animals. Animals such as hens, crocodiles, insects, etc., which produce eggs, are called oviparous animals. All living organisms can move. It should be noted that all living organisms can move. While animals can move from one place to another with the help of special locomotory organs such as limbs, plants show movement in the form of movement of root towards earth, bending of flowers in sunflower plant towards light, etc. The energy for movement comes from within the organism. All living organisms have a definite life span. All organisms have a definite life span. Organisms are born; they grow, and finally die. Some organisms have a short life span such as bacteria that live for only 20 to 25 minutes while some organisms have a longer life span such as tortoise that live up to 150 years. We can now distinguish between living and non-living things.
They are made up of cells. They are not made up of cells. They show movement, but the energy for movement comes from within the organism. They show movement by taking external force or energy. They require food. They do not require food. Growth in them is irreversible. Growth is reversible. Respiration occurs in them for oxidising food to release energy. They do not require respiration. Reproduction occurs in living things. Non-living things do not reproduce. Differences between plants and animals
They can make their own food by the process of photosynthesis. They are autotrophs. They cannot make their own food. They are heterotrophs. They show movement, but cannot show locomotion i.e., they cannot change their position from one place to another. They show movement as well as locomotion. They show response to stimuli, but lack sense organs. They also show response to stimuli and have well-developed sense organs. They grow throughout their life. They stop growing once they reach their adult form.