Cell Division Flashcards
Why does cell division occur in multicellular organisms?
Cell division allows them to grow and replace damaged or worn out cells.
What are the types of cell division in eukaryotic cells?
Mitosis and meiosis are the two types of cell division.
What is meiosis?
It is a type of cell division that produces 4 identical haploid (1 complete set of chromosomes) daughter cells (gametes). It takes place in reproductive organs for sexual reproduction.
What is mitosis?
It is a type of cell division that produces 2 genetically identical diploid (2 complete sets of chromosomes) daughter cells. It is used to grow tissues, replace cells, repair damaged tissue, form clones of white blood cells and form cancerous tumours.
What is the cell cycle?
It is a process cells go through in order to divide and multiply.
What are the stages of the cell cycle?
- Interphase (includes G1, S and G2 phases)
- Mitosis (includes prophase, metaphase, anaphase and telophase)
- Cytokinesis
What happens during interphase?
Interphase takes up 90% of the cell cycle. In this phase, the cell grows and DNA is uncondensed and doubled. Organelles are replicated and also, the amount of ATP is increased to produce enough energy for cell division.
What happens in each stage of interphase?
- G1 - the cell elongates and new organelles and proteins are made.
- S (synthesis) - the cell replicates its DNA
- G2 - the cell keeps elongating and proteins needed for cell division are made.
What is cytokinesis?
This is the final stage of the cell cycle where the cytoplasm divides and two separate, identical cells are formed.
What is the structure of chromosomes?
Chromosomes are made of one (during mitosis) or two chromatids joined in the middle by a centromere.
What order are the stages of mitosis?
The stages can be remembered by IPMAT.
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
What happens during prophase?
While the DNA is uncondensed in interphase, the chromosomes condense in prophase (DNA is tightly coiled around proteins called histones) and become visible. The nucleolus disappears and nuclear envelope begins to break down. The centrioles begin to produce spindle fibres.
What happens during metaphase?
By now, the nuclear membrane has disappeared and spindle fibres attach to the centromere of the chromosomes. The chromosomes are pulled to the equator (middle) of the cell and line up there.
What happens during anaphase?
The spindle fibres contract and the centromere of each chromosome splits in half, pulling its chromatids to opposite poles.
What happens during telophase?
The nuclear envelope begins to reform around each group of new chromosomes. The spindle fibres disappear and the chromosomes begin to uncoil.
How do you calculate the time taken for stages of mitosis to occur?
- To calculate this, you need the number of cells undergoing mitosis, the total number of cells and how long the cell cycle takes.
- Calculate the proportion of cells in a specific phase of mitosis.
- Convert the cell cycle time to units required for the answer.
- Calculate the proportion of time spent in this phase compared to the whole cycle.
Where is mitosis observed in root tips?
Mitosis occurs in meristems at the root and shoot tips because there are undifferentiated cells here in order to grow the roots and stems.
Why is toluidine blue stain used in the mitosis practical?
The blue stain binds to the chromatin DNA to stain it and make the chromosomes in mitosis visible.
Why are the root tips suspended in a drop of distilled water?
The water helps to elongate the cells as osmosis causes the cells to swell. This separates the chromosomes to make them easier to see.
What is the main hazard in the observing mitosis practical?
It is the use of acid as if it gets into eyes, it will sting. It is necessary to break down cell walls and make them permeable but it is dangerous.
Why does the coverslip need to be pressed and not slid to squash the cells?
It is necessary to produce a layer that is one cell thick so enough light can travel through. It cannot be slid so the layer of cells doesn’t roll on top of each other, which would obscure the view of the chromosomes and possibly damage them.
What is the method of the mitosis in garlic root tips practical?
- Submerge the garlic roots in warm hydrochloric acid and leave in the 40 degree waterbath for 5-10 minutes.
- Remove the garlic clove from the acid and rinse the roots in water in the sink.
- Cut of the last 3mm of the root tips using scissors and allow them to drop into a small watch glass.
- Add a few drops of 1% toluidine blue stain and leave for 2 minutes.
- Remove the excess stain with a paper towel and add distilled water to the watch glass.
- Transfer the root tips to a slide using a mounted needle, add a drop of water and spread the root tips out.
- Place a coverslip on top of the root tips and place a paper towel on top in order to press down on it firmly, without sliding the coverslip.
- View the cells under the microscope.
How do you calculate the mitotic index?
Mitotic index = number of cells undergoing cell division in the field of view / total number of cells in the field of view
What causes cancer?
Mutations are changes in the base sequence of DNA, caused by mutagens (environmental factors such as UV rays or carcinogenic chemicals) and when they are in genes that control cell division, they can cause cells to grow out of control, which is cancer.
