Class 6 Science Chapter 10 Notes Living Creatures: Exploring their Characteristics
There are numerous entities around us that can be categorized as living or non-living. For instance, dogs, plants, people, birds, and snails are living, while fans and windows are non-living. The distinction between these two categories is based on specific characteristics that define their nature. Understanding these differences helps us to appreciate the diverse nature of our world.
Characteristics of Living Organisms
All living things share certain unique characteristics that set them apart from non-living things. These features not only distinguish them but also highlight the processes that are essential for life. Some of the features of living organisms are as follows.
- They need food, water, and air to survive.
- They can grow.
- They can move on their own.
- They respond to stimuli.
- They reproduce themselves.
- They respire and utilize energy from food.
- They excrete and get rid of waste materials from their body.
- They have a definite lifespan.
- They are made up of living cells.
Non-living things do not perform any of the above functions.
Let us discuss a few important characteristics of living beings in detail.
1. Growth
All living things (plants and animals) show growth by increase in size and weight. When living things grow, they become taller and bigger on their own. For example,
- A baby grows into an adult.
- A small puppy grows and becomes a dog.
- A chicken hatched from an egg grows and becomes a hen or a cock.
- Similarly, a small plant grows and becomes a big tree.
2. Movement
It is one of the most important signs of life in an organism. All living things move by themselves. Animals can move from one place to another.
Plants are generally anchored in soil so they do not move from one place to another. Instead, they exhibit movement by moving their body parts. For example,
- Opening of petals in a flower.
- Winding of climbers around any object placed close to them.
- Eating of insects by insectivorous plants, such as Drosera, by showing movement in their leaves. Drosera relies on insects for its nutrition. It has saucer-shaped leaves with many hair-like projections of unequal length having sticky ends. Whenever an insect enters the saucer, the hairs move inward and trap the insect with the help of their sticky ends.
3. Food
All living beings need food (nutrition) for their growth and development. Plants make their own food with the help of sunlight, air, and water, through the process known as photosynthesis. Whereas, animals and humans depend on plants, other animals, and their products for their survival.
4. Respiration
It is a vital process carried out by all living organisms. It is through respiration that the body finally obtains energy from the food it takes. Breathing is a part of respiration. When we inhale, the air moves from the outside to the inside of the body. When we breathe out, we expel the air which was inhaled. This process can also be observed in other animals, such as dogs, cats, cows, and buffaloes, through the movement of their abdomen while they are at rest. All living organisms breathe in oxygen, which is used by their body and gives out carbon dioxide produced in the process. The mechanism for the exchange of gases is different in different organisms. Some examples are given below.
- Fishes use gills to obtain dissolved oxygen from water.
- Plants also exchange gases through tiny pores present on the surface of leaves called stomata.
5. Excretion
The process of removal of waste from the body is called excretion. All living things take food, but not all food that is eaten is used. A part of it, which is not used is removed as a waste. Our body also produces waste products during various life processes. These waste products are harmful to our body and need to be removed. Thus, excretion becomes a necessary process that is carried out by all living organisms. In animals, excess water and salts are removed from the body in the form of sweat and urine. Similarly, plants, such as grasses and roses, excrete excess water and minerals in the form of small droplets on their leaves.
Some plant removes waste through secretions such as gums and resins, which are used as adhesives and for making varnishes, respectively.
6. Response to Stimuli
All living things respond to changes around them. The changes in our surroundings that make us respond to them are called stimuli. A few examples are given below.
- On touching a hot plate, our hand withdraws suddenly from its surface to avoid burning.
- We close our eyes, when a sudden bright light is flashed or when we suddenly move from a dark place to bright sunlight.
- Shoots of plants grow upward and exhibit movement toward sunlight, while roots grow downward in response to gravity.
- In some plants like Mimosa, commonly known as ‘touch-me-not’ chhui-mui, or lajjalu leaves close or fold when someone touches them.
- Similarly, the sleeping leaves of the gooseberry (amla) tree that are facing each other tend to come together after sunset.
Jagadish Chandra Bose (1858-1937) was an Indian scientist, who is known for his interesting experiments with plants. He built a machine called a crescograph to record how plants respond to stimuli like light, heat, electricity, and gravity. This machine, allowed him to measure how fast plants grow. He also showed that plants can sense and respond to stimuli.
7. Reproduction
It is the process by which living things produce more of their kind. It is necessary for the continuity of life. Reproduction takes place in many different ways in different organisms. Some modes of reproduction are given below.
- Animals like insects, fishes, and birds lay eggs and when these eggs hatch, the young ones come out and grow into adults.
- Some animals like cats, dogs, cows, and human beings give birth to their young ones.
- Plants also reproduce. Many plants produce seeds which can germinate and grow into new plants.
When a living being is not able to exhibit all of the above-mentioned characteristics, despite the availability of all resources (like food, air, and water) needed for being alive, it is said to be dead.
Some Exceptions of Living Characteristics
We can conclude that living things may have all the characteristics that we have discussed, while non-living things may not show all these characteristics at the same time.
- Non-living things like cars, bicycles, clocks, and water in the river move. The moon moves in the sky and a cloud grows in size.
- Sometimes living things may also not show all the characteristics of the living. For example, seeds stay in a shop for months and do not show any growth or some of the other signs of life. However, when we bring the same seed, plant it in the soil, and water it, it begins to sprout and grow into a whole plant.
Germination of a Seed
In this process, a seed takes in water and starts to swell. As it absorbs moisture, it activates the growth inside the seed. The first thing that happens is the development of roots that grow downward into the soil. At the same time, a shoot begins to grow upward, which will eventually develop into the stem and leaves of the new plant. This growth allows the seed to become a seedling and ultimately a fully-grown plant.
Essential Conditions for Seed Germination
The germination of seeds marks the beginning of a plant’s life cycle and depends on the right amount of water and air. These conditions work together and aid in seed germination in the following ways.
- Water: It enables the seed to carry out the processes necessary for its growth. Water softens the outer covering of the seed called the seed coat and helps the tiny embryo inside it to develop into a plant.
- Air: Seeds use the air available in the spaces between soil particles. Moreover, spaces between the soil particles allow roots to grow easily.
Most seeds do not need light for germination. However, once germination is complete, sunlight becomes necessary for the seedlings to continue their growth and development. Some flowering plant seeds, such as Coleus and Petunia, need light to germinate. Covering these seeds with soil can prevent them from sprouting. In contrast, seeds of flowering plants like Calendula and Zinnia require darkness to germinate and should be covered with an appropriate amount of soil.
Life Cycle of a Plant
The life cycle of a plant outlines its various stages of development. This process begins with a seed growing into a young plant. As the plant matures, it produces flowers and fruits. The fruit contains seeds that give rise to a new generation of plants. The entire process, from a seed to a plant and then, to the next generation of seeds is called the life cycle of a plant. For a better understanding, the life cycle of a bean plant is illustrated below.
When a plant stops growing and all activities of life gradually come to an end, even after the availably of all the necessary conditions, the plant is considered dead.
Life Cycle of Animals
Just like plants, animals also undergo many changes throughout their life cycle. These changes can be quite different depending on the type of animal. The life cycles of the mosquitoes and frogs are discussed below.
Life Cycle of a Mosquito
Mosquitoes are small, flying insects often found near stagnant water sources. They undergo four stages in their life cycle, which are described below.
- Stage 1 (Egg): The female mosquito lays eggs on or near water, which then hatch into larvae.
- Stage 2 (Larva): It develops from the eggs and grows into pupae.
- Stage 3 (Pupa): The pupae transform and eventually become adult mosquitoes.
- Stage 4 (Adult): The adult mosquitoes that emerge from the pupa rest briefly on the water’s surface and then fly away. They typically live for 10 to 15 days.
Throughout these stages, the mosquito undergoes significant changes in appearance, body shape, and structure. The shape of the egg differs greatly from that of the larva; the larva looks distinct from the pupa and the pupa is markedly different from the adult mosquito.
How to Stop Mosquitoes from Breeding?
Female mosquitoes are bloodsucking insects that transmit diseases such as malaria, dengue, and chikungunya to humans. Therefore, it is important to prevent their breeding. This can be done by eliminating common places, where water is likely to stagnate, as the larval and pupal stages of mosquitoes require water for their development. Another method to prevent mosquito breeding is to spray kerosene oil on stagnant water. The oil forms a thin layer on the surface of water separating it from the air. This prevents larvae and pupae from getting air, when they move to the surface to breathe, ultimately causing their death.
The silk moth also goes through four life stages: egg, larva, pupa, and adult. Eggs hatch into larvae, which then grow in size. The larvae produce thread-like material that they wrap around themselves to form a cocoon before transitioning into pupae. These fibers are used to make silk fabric. In India, the Khadi and Village Industries Commission (KVIC) has established several centers for silk production.
Life Cycle of a Frog
Frogs are amphibians that are commonly found near small water bodies and are particularly abundant during the rainy season. They undergo four stages which are described below.
- Stage 1 (Spawn): An adult frog lays a cluster of jelly-like eggs called spawn on the surface of the water, usually near the edge of a pond. The eggs develop into embryos, which then transform into tadpoles.
- Stage 2 (Tadpole): In the early tadpole stage, they are characterized by having a tail and no legs, which aids their swimming in the water. As they advance to the later stage, they begin to develop hind legs.
- Stage 3 (Froglet): In this stage, they still live in water but begin to spend some time on the land. Eventually, they lose their tails and their legs become strong, allowing them to jump on land effectively.
- Stage 4 (Adult Frog): In this stage, froglets mature into fully developed adult frogs, capable of living both in water and on land.
The transformation of a larva into an adult, involving a series of sudden and continuous changes in the body or an animal during its life cycle, is called metamorphosis.
→ Breathing: Process in which air moves in and out of the body.
→ Death: It is the end of life.
→ Excretion: Removal of waste products from the body.
→ Froglet: Stage in the cycle of frogs marked by eventual loss of their tail.
→ Germination: The process by which a plant grows from a seed into a seedling.
→ Growth: The process of increase in size.
→ Larva: It is an early stage in the life cycle of some animals, such as insects.
→ Life Cycle: The series of stages an organism goes through from birth to reproduction and eventually to death.
→ Living: Organisms that interact with their environment to sustain themselves.
→ Movement: The process of changing the position of a body part or the whole body from one place to another.
→ Non-living: Things that do not have life.
→ Nutrition: The process of obtaining and using food to support growth, maintenance, and overall health.
→ Pupa: The life stage in the development of some insects that occurs between the larval and adult stages.
→ Reproduction: The process of producing new ones of its kind.
→ Respiration: The process by which living organisms take in oxygen and release carbon dioxide to release energy.
→ Response: A reaction to a question, experience, or some other type of stimulus.
→ Stimulus: Anything or any event that prompts living beings to respond.
→ Tadpole: The aquatic stage in the life cycle of a frog.