(ক) কোষের সাইটোপ্লাজমের কাঠামো দান করা

(খ) স্নেহ বিপাকে সাহায্য করা

(গ) হরমোন নিঃসরণে সাহায্য করা

(ঘ) পানির সাম্যতা বজায় রাখা

 

 

 

 

উত্তর (ক) কোষের সাইটোপ্লাজমের কাঠামো দান করা

(ক) গুয়ানিন      

(খ) সাইটোসিন  

(গ) ইউরাসিল     

(ঘ) থাইমিন

 

 

 

 

উত্তর (গ) ইউরাসিল     

(ক) ১        

(খ) ২          

(গ) ৩        

(ঘ) ৫

 

উত্তর (ক) ১        

Differences in shape and behavior between different members of the same species is called variation. Variation is permanent and heritable. Only those variations that are able to adapt to the adverse environment survive. Nature selects those species or varieties that are able to easily adapt to changing and adverse environments. They reproduce at high rates. Nature re-selects them through inheritance. Thus over the ages they are selected by nature and new species are created.

No difference is seen in the embryonic stage of different animals. But the difference is seen in the transformed state. The embryos of fish, frog, chicken, cow, goat, monkey, human etc. are almost exactly the same. The embryos of monkeys, gorillas, humans etc. are almost identical.

According to the scientist Von Baer, ​​the set of general characteristics arose before the emergence of special characteristics. From general characteristics eventually special characteristics emerge. In the embryonic stage each animal quickly sheds the structure of other animals. A baby animal looks like a fetus.

Animals whose embryos are similar derive from the same ancestor. Due to variation their structural differences have arisen. As a result, different species have been created.

The propositions of Lamarckism are mentioned.

(i) Growth of Organs: The organism can grow and nourish the organs under the influence of its own vital energy on demand.

(ii) Formation of new organs on the demand of the environment: Changes in the body depend on the environment. Changes in the environment can cause changes in the nature and physical properties of organisms. Organisms change their organs and produce new organs in a changing environment.

(iii) Use and disuse of organs: The organs which the organism uses are active and nourished. Organs that are not used become inactive and ineffective.

(iv) Inheritance of Acquired Traits: The traits acquired by an organism during its life cycle are heritable.

The basic conclusions of Darwin’s theory of natural selection are briefly mentioned.

1. High rate of reproduction: High rate of reproduction is an inherent characteristic of organisms. It increases the number of organisms at a geometric and mathematical rate. A salmon fish lays 30 million eggs per season, a hilsa fish lays about 20 lakh eggs.
2. Habitat and food limitation: With the increase in the number of organisms there are habitat and food limitations. Natural resources like light, air, water, food etc. are less than the number of living beings. So the food and habitat of the organism is limited.
3. Life Struggle: The competition of organisms for food, water, shelter and other beneficial elements is called life struggle. Life struggles are of three types.

(i) Intra-species struggle: Struggle between members of the same species is called intra-species struggle. Deer-deer struggle, buffalo-buffalo struggle, tiger-tiger struggle etc. intra-species struggle.

(ii) Interspecies struggle: Struggle between members of different species is called interspecies struggle. Interspecies struggle like tiger and deer struggle, snake and frog struggle, lion and buffalo struggle.

(iii) Environmental Struggle: The struggle to survive and save life in a hostile environment is called ecological struggle. The struggle to protect against floods, droughts, storms, heavy rains, cold currents, epidemics, floods, cyclones, earthquakes, eruptions, fires is an environmental struggle.

4. Variation or Parivritti: Variation is the difference in shape and character among different members of the same species. Variation is permanent and heritable. Only those variations that are able to adapt to the unfavorable environment survive.
5. Victory of the fittest: Favorable variants are able to adapt to adverse environments and survive in competition. The fittest varieties survive well. It is called the victory of the fittest. Organisms that lose the competition gradually become extinct. Because of this, dinosaurs became extinct.
6. Natural selection and creation of new species: Nature selects those species or varieties which are able to easily adapt to changing and adverse environment. They reproduce at high rates. Nature re-selects them through inheritance. Thus over the ages they are selected by nature and new species are created.

Archeopteryx appeared 14.7 million years ago. It has features of both bird and reptile classes. Its features are-

1. Reptilian traits

(i) Archeopteryx 20 vertebrae long like reptiles.

(ii) Their bones are thick and heavy.

(iii) They have teeth in their jaws.

(iv) Their bodies consist of dry scales.

(v) They have claws on their wings.

 

2. Characteristics of birds

(i) Body structure of Archeopteryx is similar to bird.

(ii) Their bone structure is similar to that of birds.

(iii) They have wings like birds.

(iv) Their bodies have bird-like tails and feathers.

(v) Their lips have turned into bird-like beaks.

The characteristics of Archeopteryx show that it has characteristics of the Reptilia and Avis classes. Archeopteryx is therefore said to be the link connecting the two classes.

A living organism is called a living fossil if the characteristics of a fossil animal of the past match the characteristics of a living animal of the present. Fossil organisms survive on Earth in morphologically and physiologically unchanged forms.

Characteristics of Platypus

(i) Body of platypus is covered with hair.

(ii) They lay eggs containing yolk and the eggs hatch.

(iii) They have active mammary glands.

(iv) Their cubs drink mother’s milk.

(v) T-shaped thoracic skeleton of platypus.

The features of the platypus are very similar to those of past fossil animals. Hence the platypus is called a living fossil.

(i) Vertebrate brain: The brain of vertebrates has evolved. Brains are enlarged in fish, amphibians, reptiles, avius ​​and mammals. The structure of the cerebral hemispheres and cerebellum is complex.

(ii) Vertebrate heart: The heart of vertebrates has undergone gradual evolution. The heart of fish is two-chambered, the heart of amphibians is three-chambered, the heart of reptiles is partially four-chambered, and the heart of birds and mammals is fully four-chambered. The heart has progressed from simple to complex.

(iii) Homologous organs: Organs which are similar in function but different in structure and origin are called homologous organs. For example, the wing of a bird and the wing of a butterfly are symmetrical organs.

(iv) Homologous Organs: Organs which are structurally similar are called homologous organs. Wings of birds and bats, hands of humans, front legs of horses and flippers of whales are related organs.

(v) Peripheral organs: Organs which are not functional are called peripheral organs. Such as ear muscles, pineal gland, coccyx and body hair.