Cell Cycle and Cell Division (VSAQs)
Botany-1 | 11. Cell Cycle And Cell Division – VSAQs:
Welcome to VSAQs in Chapter 11: Cell Cycle And Cell Division. This page includes the most important FAQs from previous exams. Each question is answered in a concise format to help you understand quickly and aim for top marks in your final exams.
VSAQ-1: Among prokaryotes and eukaryotes, which one has a shorter duration of cell cycle?
Prokaryotes, such as bacteria, have a shorter cell cycle compared to eukaryotes. Imagine bacteria as tiny, fast-growing organisms. Their cell cycle, which includes all the steps from replication to division, can be completed in as little as 20 minutes. This quick cycle helps them multiply rapidly. On the other hand, eukaryotic cells, like those in plants and animals, have a much longer cell cycle. It usually takes around 24 hours or more for a complete cycle, depending on the type of cell and organism. Think of it like comparing a speedy scooter (prokaryotes) to a car with a longer journey (eukaryotes); the scooter can get from one place to another much faster.
VSAQ-2: Which of the phases of the cell cycle is of longest duration?
The G1 (Gap 1) Phase is typically the longest part of the cell cycle in eukaryotic cells. During this phase, the cell grows, makes proteins, and prepares for DNA replication. It’s like a busy preparation period before a big event. Just as you might spend more time preparing for an important exam or party, the cell spends a significant amount of time getting ready for the next steps in the cycle.
VSAQ-3: Which tissue of animals and plants exhibits meiosis?
In animals, meiosis happens in the germ cells, which are the cells that make sperm and eggs. This process helps in producing haploid gametes, which are crucial for reproduction. In plants, meiosis occurs in specialized structures called sporangia or spore cases. For example, in ferns, this happens in the sporophylls, and in flowering plants (angiosperms) and gymnosperms (like pine trees), it takes place in the anthers, ovaries, and cones. These structures produce haploid spores that eventually develop into gametophytes, continuing the cycle of reproduction.
VSAQ-4: Given that the average duplication time of E. coli is 20 minutes, how much time will two E. coli cells take to become 32 cells?
If you start with two E. coli cells, they will take 80 minutes to grow into 32 cells. Here’s why: Each time the cells divide, the number doubles. So, in 20 minutes you get 4 cells (2 cells × 2). In another 20 minutes (40 minutes total), you have 8 cells, and so on. After four such doubling periods, or 80 minutes, you end up with 32 cells. It’s like planting a tree that grows and branches out rapidly—each branch quickly produces more branches, leading to a large number of trees in a short amount of time.
VSAQ-5: Which of the four chromatids of a bivalent at prophase I of meiosis can involve in crossover?
During prophase I of meiosis, a key event is the crossover, which happens between non-sister chromatids of a bivalent. A bivalent consists of two homologous chromosomes, and each chromosome has two chromatids. Imagine two pairs of chromosomes lined up next to each other, with each chromosome having a pair of chromatids. Crossover occurs when the non-sister chromatids (the chromatids from different chromosomes of the same pair) exchange sections. This swapping of genetic material is like two friends trading parts of their favorite stories, leading to new and diverse combinations of traits in the resulting gametes.
VSAQ-6: If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single cell undergone?
If a tissue has 1024 cells, it means the original single cell has gone through 10 cycles of mitosis. Here’s how it works: Each cycle of mitosis doubles the number of cells. Starting with one cell, after one cycle you have 2 cells, after two cycles you have 4 cells, and so on. To reach 1024 cells, you need to double the number of cells 10 times (2^10 = 1024). It’s like a plant that doubles in size every day; after 10 days, it grows to be 1024 times its original size.
VSAQ-7: An anther has 1200 pollen grains. How many pollen mother cells must have been there to produce them?
To produce 1200 pollen grains, there must have been 300 pollen mother cells. Each pollen mother cell undergoes meiosis, which results in four pollen grains. Therefore, to get 1200 pollen grains, you divide 1200 by 4, which gives you 300 pollen mother cells. It’s like making 1200 cookies where each batch of dough yields 4 cookies; you’d need 300 batches to bake all the cookies.
VSAQ-8: At what stage of the cell cycle does DNA synthesis occur?
DNA synthesis happens during the S-phase (Synthesis phase) of the cell cycle. This phase is part of interphase, the period when the cell is preparing for division. During the S-phase, the cell copies its entire DNA so that each new cell will have a complete set of genetic instructions. It’s similar to making copies of an important document before distributing it; each new cell gets a complete set of the genetic material.
VSAQ-9: Name the stage of meiosis in which actual reduction in chromosome number occurs.
The actual reduction in chromosome number occurs during Anaphase I of meiosis. At this stage, the homologous chromosomes (each made of two sister chromatids) are pulled to opposite sides of the cell. This separation cuts the chromosome number in half in the daughter cells compared to the parent cell. It’s like dividing a deck of cards between two players; each player ends up with half of the original deck, reflecting a reduction in the total number of cards.