The Living World: Adaptations and Classification Class 7 Science Notes Maharashtra State Board
A great variety of plants is found on the earth. Some plants have colorful flowers. Some plants grow in water whereas some are to be found in deserts which have a scarcity of water. Some plants are found only in snowy regions. Some plants cannot be seen without a microscope whereas some are huge. Like plants, animals too show diversity. Some are unicellular, others, multicellular. Some are vertebrates whereas others are invertebrates. This world is full of a variety of animals – aquatic, terrestrial, amphibian, reptilian, aerial, etc. These observations give rise to the question – How did this great diversity come into being?
Are the plants and animals from Kashmir and Rajasthan of the same type? Can you elaborate on any differences between the two? Coniferous trees like pine and deodar flourish in snowy regions like Kashmir. However, in the deserts of Rajasthan, plants like cactus and acacia (babhul) are to be found. The camel, a desert animal, is not found in Kashmir. What is the reason for these differences?
Adaptation
Gradual changes occur in the body parts and also in the behaviour of organisms which help them to adjust to their surroundings. Such changes are called adaptations. They take place over a long period.
Adaptation in Plants
Adaptation in Aquatic Plants
Some of the aquatic plants are firmly rooted in the soil at the bottom of the water bodies. Their stems are submerged, while leaves and flowers float on the surface. However, some plants are entirely afloat. Their roots are not anchored in the soil.
The surfaces of the leaves and stems of many aquatic plants are covered with a waxy layer. Leaves of some aquatic plants are thin and slender like a ribbon. This shape helps them to withstand fast currents of water. Air spaces in stems and petioles of aquatic plants are useful for floating in water.
Adaptation in Desert Plants
Desert plants are either leafless or their leaves are like small needles or have been modified into thorns. As a result, they lose very little water by evaporation. The stem stores water and food and is therefore fleshy. The stems are green as they perform photosynthesis in the absence of leaves. Their roots penetrate deep into the soil in search of water. There is a thick layer of a waxy substance on the stems of these plants, too.
Adaptation in Plants of Snowy Regions
Plants of snowy regions mainly include conifers like deodar and pine. These trees are conical in shape due to their sloping branches. In the heavy snowfall and extreme cold in these regions, their conical shape prevents the snow from accumulating on the tree and the thick bark helps the tree to withstand the cold.
Adaptation in Plants of Forest Regions
A variety of plants – trees, shrubs, and herbs – are found in forests. These plants compete amongst themselves for sunlight. Hence, trees grow tall to get sunlight, and climbers and vines grow to a great height with the support of trees. Spring-like tendrils on the stems of some climbers is an example of adaptation.
Adaptation in Grassland Plants
Diverse types of bushes and grasses are found in the grasslands. Fibrous roots of grasses prevent soil erosion. Grasses in the equatorial region are very tall. Animals like tigers, elephants, and deer can remain hidden in these grasses. However, grasses in cold regions are very short. Animals like the rabbit are found in such grasses. Vast meadows are found in hilly areas as well as plains.
Adaptation for Ingestion of Food in Plants
Most of the plants are anchored in the ground and are autotrophic. However, plants like dodder (cuscuta) are parasitic. The plant body of the dodder consists of yellow wire-like stems. It is leafless and cannot perform photosynthesis. However, it has haustorial (sucking) roots for absorbing nutrients from the host plant. These roots penetrate upto the conducting vessels of the host plant to absorb water and food.
Fungi do not have chlorophyll and cannot perform photosynthesis. They obtain food from starchy foodstuffs like bhakri and bread. They have root-like fibers for the absorption of food. Plants need nitrogen, phosphorus, and potassium for growth. Plants that grow in soil that is deficient in nitrogen, like drosera (sundew), Venus flytrap, pitcher plant, etc. fulfill their need for nitrogen by consuming insects. Adaptations are seen in these plants which serve to attract insects and hold them captive.
Adaptation in Animals
Make a list of animals in your surroundings. Compare the diversity of animals listed by your friends, with your list. Discuss the habitats, food habits, characteristics of body structures like vertebral columns, wings, gills, tails, etc., and prepare a chart. What differences do you see between terrestrial and aquatic animals?
As compared to terrestrial animals, the skin and body shape of aquatic animals appear to have changed. Fishes have scales on the skin and fins on the body. Their body tapers towards both ends, like a spindle. Fish breathe with gills instead of a nose. Their eyes have transparent eyelids. They have air bladders within the body to help them to float. Observe the bodies of the frog, duck, and tortoise.
- Of what use are their legs to these animals?
- What helps frogs to breathe underwater?
- Of what use are the long hind legs of a frog?
- Why doesn’t a duck get wet in water?
As the frog and ducks have webbed toes, they can use their legs like oars. Water flows off the waxy feathers of birds like ducks and waterhen. Webbed toes, slippery, smooth skin, and a triangular head help frogs to swim easily through the water. They can live on land as well as in water due to their ability to breathe through the skin in water and using the nose and lungs on land. The typical colors of a frog’s back help it to hide among grasses.
Adaptation in Forest and Grassland Animals
Carnivorous animals like wild dogs, foxes, tigers, and lions have strong legs to run fast and capture their prey. They have claws and their canine teeth are sharp and pointed. What is the function of such teeth? Tigers have padded paws. This enables them to silently stalk their prey and capture it easily. The eyes of predatory carnivores are located in the front of their head. It helps them to spot their prey from a long distance.
The eyes of herbivores are below the forehead, on either side of the head. This gives them wide-angle vision which helps to protect them from predators. Their legs are long and tapering with strong hooves, which enables them to run fast taking long leaps. Their long and freely moving ears can receive sounds from long distances and in different directions. Deer and blackbucks have colors that merge with their surroundings. Their teeth are strong for chewing tough plant material.
Adaptation in Desert Animals
Deserts are characterized by severe scarcity of water. Hence, desert animals have thick skin to prevent loss of water from the body. Their legs are long with flat and cushioned soles. The nostrils are protected by folds of skin. The eyelashes are long and thick. Rats, snakes, spiders, and lizards in deserts live in deep burrows during the daytime and are active at night.
Adaptation in Animals of Snowy Regions
From the internet, download images of animals like yak, polar bears, white foxes, silver foxes, mountain goats, Siberian husky dogs, and snow leopards. Compare these images with those of similar animals from tropical forests. A white or silver body color, and long, thick hair on the skin are typical characteristics of animals of snowy regions. How are these useful to them?
Adaptation in Aerial Animals
What is the main difference between vehicles on the road and airplanes? The spindle-shaped body of birds also minimizes the resistance of air while flying. With hollow bones, a body covering of feathers, and modification of forelegs into wings, their body is light in weight and adapted for flying. The body of insects also is light in weight and tapers at both ends. They can fly with two pairs of wings and also walk with six stick-like legs. Bats can fly with the help of the patagium, a thin fold of skin between their forelegs and hind legs. Observe the various birds and insects in your area.
Adaptation in Reptiles
Observe, from a distance, how snakes and earthworms creep. Which organs do they use for creeping? Are there any special changes for that purpose? Note any such changes. Animals like house lizards, garden lizards, and crocodile use their muscles for creeping. Similarly, they show adaptations in the skin, soles of feet, body color, etc. For example, the house lizard and monitor lizards have clawed toes and thin soles, whereas snakes have scaly skin.
Adaptation for Food in Animals
We can categorize animals as herbivores and carnivores. Special adaptations are seen in each category to make the process of feeding easy. We will discuss this in greater detail in the chapter on Nutrition. Watch the programs on channels like National Geographic Wild, Discovery, etc. to learn about the feeding habits of animals like frogs, snakes, birds, mosquitoes, butterflies, etc.
Adaptation for Blending with the Surroundings
We cannot easily spot colorful butterflies, lizards, and grasshoppers. They get camouflaged amidst grasses, and parts of plants like stems, leaves, flowers, etc. That is because their colors blend with those of their surroundings. Changes that take place in the various organs and life processes of organisms, that enable them to live, feed, reproduce to perpetuate themselves, and protect themselves from their enemies in specific surroundings, depending upon the habitat and its geographical conditions, are called adaptations. Adaptation is not a sudden process. It is gradual and continuous. Differences in the structure and appearance of present-day animals and animals of thousands of years ago are the adaptations that occurred according to prevailing conditions. We must conserve this diversity.
Darwin’s Theory of Evolution
Charles Darwin, a biologist, studied numerous types of plants and animals and suggested that only those organisms are likely to survive and can best adapt themselves to a changing environment. This is called the theory of survival of the fittest. This is Darwin’s first principle. If an organism is born with a new beneficial characteristic and can survive, this change is preserved in the next generation. This is Darwin’s second principle and is called the theory of ‘natural selection’.
Classification of Living Organisms
It is difficult to study and remember all the organisms in this diverse living world at the same time. Classification helps in this respect. Different scientists have used different criteria and independently classified plants and animals. A hierarchy is formed in the classification that starts with Kingdom Animalia or Kingdom Plantae; further groups and sub-groups are formed depending upon basic similarities and differences. This is called the ‘hierarchy of classification’.
| Hierarchy | Mango | Human |
| Kingdom | Plantae | Animalia |
| Phylum | Anthophyla | Chordata |
| Class | Dicotyledonae | Mammalia |
| Order | Sapindales | Primates |
| Family | Anacardiaceae | Hominidae |
| Genus | Mangifera | Homo |
| Species | Indica | Sapiens |
Binomial Nomenclature by Carl Linnaeus
Imagine that there are four students with the name ‘Kabir’ or ‘Kiran’ in a classroom. If you are talking about any one of them, how would you ensure that others know which one of them you are talking about, without any confusion? We would tell the full name i.e., the first name and the last name. This is similar to binomial nomenclature.
Binomial nomenclature is used to identify each organism. Accordingly, a scientific name has been assigned to each organism. It consists of two parts – the first part is ‘genus’ and the second, is ‘species’. All identified organisms have been assigned a binomial name as per the guidelines of the International Code of Nomenclature.
All the organisms of a species are so similar that irrespective of differences in color, height, habitats, and habits, they can reproduce among themselves and form new individuals like themselves. For example, all domestic cats in the world belong to the same species. The same is true in the case of animals like hens, cows, dogs, etc. and plants like mango, wheat, maize, etc.
Following are some examples of organisms from Kingdom Plantae and Animalia classified by the binomial method of nomenclature:
| Living Things | Scientific Name |
| Dog | Canis lupus familiaris |
| Cow | Bos Taurus |
| Hibiscus | Hibiscus rosa-sinensis |
| Jowar | Sorghum bicolor |
29th April is observed as ‘World Frog Protection Day’. Killing or harming frogs is prohibited by the Wild Life Protection Act.
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