All questions of Heredity and Evolution for Class 10 Exam

Trilobite: An Arthropod

Trilobites are extinct marine arthropods that lived during the Paleozoic era, for over 270 million years. They are considered to be one of the earliest known groups of arthropods, making them a crucial part of the evolutionary history of this diverse phylum.

Characteristics of Arthropods

Arthropods are characterized by having a segmented body, an exoskeleton made of chitin, jointed appendages, and a well-developed nervous system. Trilobites possessed all these features, placing them firmly within the arthropod group.

Physical Characteristics of Trilobites

Trilobites had a hard exoskeleton that was divided into three distinct sections: the cephalon (head), the thorax (body), and the pygidium (tail). They also had multiple pairs of legs attached to their body segments, which is a key characteristic of arthropods.

Fossil Evidence

The fossil record provides ample evidence of trilobites being arthropods. Their body structure, appendages, and overall morphology closely resemble that of modern arthropods, further supporting their classification within this group.

Conclusion

In conclusion, trilobites were not reptiles, birds, or mammals but instead belonged to the diverse group of arthropods. Their unique characteristics and fossil evidence make it clear that they were an important part of the evolutionary history of arthropods.

Explanation:

When studying the layers of the Earth, scientists have noticed that the deeper layers are older than the upper layers. This is because new layers of sediment are continuously being deposited on top of older layers over time.

Relation between Fossils and Earth Layers:

Fossils are the remains or traces of organisms that lived in the past. When an organism dies, its remains can be preserved in sedimentary rock layers over time. The position of a fossil in the layers of the Earth can provide valuable information about the age of the fossil and the time of extinction of the organism.

Deeper Layer and Extinction Time:

If a fossil is found in a deeper layer of the Earth, it indicates that the organism became extinct a long time ago, as it is buried under several layers of sediment. The deeper the layer, the older the fossil is likely to be. This means that option 'C' is the correct answer - the extinction of the organism has occurred thousands of years ago.

Why Other Options are Incorrect:

Option 'A' states that the extinction of the organism has occurred recently, but this is contradictory to the fact that the fossil is found in a deeper layer. If the extinction was recent, the fossil would be found in a more shallow layer.

Option 'B' suggests that the position of the fossil in the layers of the Earth is not related to its time of extinction. However, this contradicts the principle of superposition, which states that deeper layers are older than upper layers. The position of the fossil in the layers provides important chronological information.

Option 'D' claims that the time of extinction cannot be determined. While it may be challenging to determine the exact time of extinction, the relative age can be estimated based on the position of the fossil in the layers of the Earth.

Conclusion:

In conclusion, when a fossil is found in a deeper layer of the Earth, it indicates that the organism became extinct thousands of years ago. The position of the fossil in the layers provides valuable information about the relative age of the fossil and can help scientists understand the history of life on Earth.

Explanation:

The palisade cells of a plant contain 28 chromosomes. Chromosomes are the structures that carry genetic information in the form of genes. During the process of sexual reproduction, gametes are produced, which are the reproductive cells that combine during fertilization to form a new organism.

Chromosomes in gametes:
Gametes are formed through a process called meiosis. Meiosis is a type of cell division that reduces the number of chromosomes in a cell by half. In plants, meiosis occurs in the reproductive organs, such as the flowers.

During meiosis, the diploid cells (cells with two sets of chromosomes) undergo two rounds of division, resulting in the formation of four haploid cells (cells with one set of chromosomes). These haploid cells are the gametes.

Chromosome number in gametes:
Since the plant's palisade cells contain 28 chromosomes, which are diploid cells, the gametes produced by the plant will have a haploid number of chromosomes.

The haploid number of chromosomes is half the diploid number. Therefore, the number of chromosomes in each gamete will be:

28 chromosomes / 2 = 14 chromosomes

Therefore, the correct answer is option B) 14. Each gamete produced by the plant will contain 14 chromosomes.

Summary:
The palisade cells of a plant species contain 28 chromosomes. During the process of meiosis, which is involved in gamete formation, the chromosome number is reduced by half. Therefore, each gamete produced by the plant will have 14 chromosomes.