Section 6: Cell Division And Cellular Organisation Flashcards
What happens during interphase in mitosis?
During interphase the cell carries out normal functions, but also prepares to divide. The cell’s DNA is unravelled and replicated, to double its genetic content. The organelles are also replicated so it has spare ones, and its ATP content is increased (ATP provides energy needed for cell division).
What are the two types of cell division?
There are two types of cell division - mitosis and meiosis.
What is mitosis?
Mitosis is the form of cell division that occurs during the cell cycle. It’s needed for the growth of multicellular organisms and for repairing damaged tissues. Some animals, plants and fungi also use it to reproduce asexually. Mitosis is really one continuous process, but it’s described as a series of division stages - prophase, metaphase, anaphase and telophase.
What is the structure of chromosomes like in mitosis?
As mitosis begins, the chromosomes are made of two strands joined in the middle by a centromere. The separate strands are called chromatids. Two strands on the same chromosome are called sister chromatids. There are to strands because each chromosome has already made an identical copy of itself during interphase. When mitosis is over, the chromatids end up as one-strand chromosomes in the new daughter cells.
What happens during prophase in mitosis?
During prophase l, the chromosomes condense, getting shorter and fatter. Tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle. The nuclear envelope (the membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm.
What happens during Metaphase in mitosis?
During Metaphase I, the chromosomes (each with two chromatids) line up along the middle of the cell (at the spindle equator) and become attached to the spindle by their centromere. At the metaphase checkpoint, the cell checks that all of the chromosomes are attached to the spindle before mitosis can continue.
What happens during Anaphase in mitosis?
During Anaphase I, the centromeres divide, separating each pair of sister chromatids. The spindles contract, pulling chromatids to opposite ends of the cell, centromere first.
What happens during Telophase in mitosis?
During Telophase I, the chromatids reach the opposite poles on the spindle. They uncoil and become long and thin again. They’re now called chromosomes again. A nuclear envelope forms around each group of chromosomes, so there are now two nuclei.
What happens during cytokinesis?
During cytokinesis, the cytoplasm divides. In animal cells, a cleavage furrow forms to divide the cell membrane. There are now two daughter cells that are genetically identical to the original cell an to each other. Cytokinesis usually begins in Anaphase and ends in Telophase. It’s a separate process to mitosis.
Explain and state what the cell cycle is and the steps it involves.
The cell cycle is the process that all body cells in multicellular organisms use to grow ad divide. It starts when a cell has been produced by cell division and ends with the cell dividing to produce two identical cells.
The cell cycle consists of a period of cell growth and DNA replication, called interphase, and a period of cell division, called M phase. M phase involves mitosis and cytokinesis. Interphase is subdivided into three separate growth stages. These are called G1, S and G2
The cell cycle is regulated by checkpoints. Checkpoint occur at key points during the cycle to make sure it’s okay for the process to continue.
What happens at the G1 checkpoint?
At the G1 checkpoint, the cell checks that the chemicals needed for replication are present and for any damage to the DNA before entering S-phase.
What happens during the G2 checkpoint?
At the G2 checkpoint, the cell checks whether all the DNA has been replicated without any damage. If it has, the cell can enter mitosis.
How do you investigate mitosis?
You can stain chromosomes so you can see them under a microscope. This means you can watch what happens to them during mitosis. To do this, you need to stain the specimen, put it on a microscope slide and examine it under a microscope. Figure 7(on page 141 of the textbook) shows some plant root tip cells on a ‘squash’ microscope slide, viewed under a light microscope. Squashes like this can be made by treating the very tips of growing roots in hydrochloric acid, then breaking them open and spreading the cells thinly on a microscope slide using a mounted needle. A few drops of stain are then added to the spread out cells before they are physically squashed beneath a coverslip. When you look at the slide under he light microscope, you should be able to see cells at different stages of mitosis.
What is and what happens during sexual reproduction?
Gametes are the sperm cells in males and egg cells in females. In sexual reproduction two gametes join together at fertilisation to form a zygote, which divides and develops into a new organism.
Normal body cells have the diploid number (2N) of chromosomes – meaning each cell contains two of each chromosome (a pair), one from the mum and one from the dad. The chromosomes that make up each pair are the same size and have the same genes, although they could have different versions of those genes (called alleles). These pairs of matching chromosomes are called homologous chromosomes.
Gametes have a haploid (n) number of chromosomes – there’s only one copy of each chromosome. At fertilisation, a haploid sperm fuses with a haploid egg, making a cell with the normal diploid number of chromosomes. Half of these chromosomes are from the father (the sperm) and half are from the mother (the egg).The diploid cell produced by fertilisation is called a zygote.
What is meiosis?
Meiosis is the type of cell division that happens in the reproductive organs to produce gametes. Meiosis involves a reduction division. Cells that divide by meiosis are diploid to start with, but the cells that are formed from meiosis are haploid – the chromosome number halves. Cells formed by meiosis are all genetically different because each new cell ends up with a different combination of chromosomes.
What happens during interphase in meiosis?
The whole of meiosis begins with interphase. During interphase, the cell’s DNA unravels and replicates to produce double-armed chromosomes called sister chromatids.
What is meiosis 1?
Meiosis involves two divisions – meiosis 1 and meiosis 2. After interphase, the cells enter meiosis 1. Meiosis 1 is the reduction division (it halves the chromosome number). There are four similar stages to each division in meiosis called prophase, metaphase, anaphase and telophase.
What happens in prophase 1?
In prophase one, the chromosomes condense, getting shorter and fatter. Homologous chromosomes pair up – number 1 with number 1, 2 with 2, 3 with 3, etc.
