Problem 3 - Campbell Biology

Question

In angiosperms, which of the following is correctly paired with its chromosome count? (A) microspore-n (B) zygote-n (C) egg-2n (D) megaspore- \(2 n\)

Step-by-Step Solution

Answer

The correct pair is (A) microspore-n.

Step 1: Understand the Components

Read and understand the terms: microspore, zygote, egg, and megaspore. Recognize that 'n' refers to the haploid number of chromosomes, while '2n' refers to the diploid number.

Step 2: Microspore Chromosome Count

Microspores are haploid cells in angiosperms formed through meiosis. Thus, their chromosome count is 'n'.

Step 3: Zygote Chromosome Count

A zygote is formed by the fusion of two haploid gametes, making it diploid. Therefore, its chromosome count is '2n'.

Step 4: Egg Chromosome Count

An egg cell in angiosperms is a gamete, hence it is haploid. Its chromosome count is 'n'.

Step 5: Megaspore Chromosome Count

Megaspores are produced through meiosis and are haploid. Therefore, the chromosome count is 'n'.

Step 6: Select the Correct Pair

Compare each option to the detailed information above: (A) microspore-n is correct based on the definition.

Key Concepts

Microspore

A microspore is a type of haploid (n) cell found in angiosperms, the group of plants that produces flowers. These cells are created through a process known as meiosis. The main function of microspores is to form pollen grains. These grains are critical for plant reproduction as they transport male genetic material to the female parts of a flower.

Meiosis ensures that each microspore contains half the number of chromosomes compared to the parent cell. For example, if the parent cell has 2n chromosomes, each microspore will have n chromosomes. This reduction is essential for maintaining genetic stability across generations.

Zygote

In angiosperm plants, the zygote represents the early stage of a new organism. It is produced through the fusion of two haploid (n) cells called gametes. One gamete comes from the pollen (male), and another from the ovule (female).

When these gametes combine, they create a diploid (2n) zygote containing a full set of chromosomes.
This is because each haploid parent cell contributes half of the genetic material. The zygote will undergo multiple rounds of cell division to develop into a mature plant.

Haploid

A haploid cell contains a single set of chromosomes, denoted as 'n'. In the context of flowering plants (angiosperms), this term applies to gametes such as eggs and sperm, as well as microspores and megaspores.

Haploid cells are vital for sexual reproduction in plants. They ensure genetic diversity by recombining genetic material from two different organisms during fertilization. This also prevents the chromosome number from doubling with each generation.

Diploid

A diploid cell is one that has two sets of chromosomes, referred to as '2n'. Diploid cells in angiosperms include most of the cells in the adult plant, as well as the zygote.

These cells are a result of the fusion of two haploid cells during fertilization. The balance between haploid and diploid stages in the plant life cycle ensures that the chromosome number remains stable over generations. This is crucial for the proper functioning and development of organisms.

Meiosis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in the production of haploid cells from diploid parent cells. This process is essential in the reproductive cycle of angiosperms.

During meiosis, one diploid cell goes through two rounds of cell division, ultimately forming four haploid cells. In angiosperms, this leads to the creation of microspores (male) and megaspores (female), which are essential for sexual reproduction. Meiosis increases genetic variability through the recombination of genetic material, enhancing the adaptability of species.