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Description
Flashcards by eliza lander, updated more than 1 year ago
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Created by eliza lander
over 7 years ago
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| Question | Answer |
| What is MITOSIS? | By mitosis a cell splits to create two identical copies of the original cell. |
| What is MEIOSIS? | In meiosis cells split to form new cells with half the usual number of chromosomes, to produce gametes for sexual reproduction. |
| What is DNA? | DNA is a very large molecule shaped like a twisted ladder. The shape is a double helix. |
| What is DNA and where is it found? | Long strands of DNA make up chromosomes. These are found in the nucleus of a cell. |
| Why is MITOSIS done? | Mitosis is a type of cell division. Mitosis occurs wherever more cells are needed. It produces two new cells that are identical to each other, and to the parent cell. The process of growth and division is called the cell cycle. |
| How does MITOSIS work? | The cycle starts as the number of organelles - the different parts of the cell - increases. This is to ensure that each of the two new cells receives copies of all the organelles.Before a cell divides, its chromosomes are copied exactly. The DNA molecule is made of two strands. As each of the two strands separate, new strands are made alongside each of them, thereby making two new copies. |
| What are the stages of MITOSIS? | |
| Why is MEIOSIS done? | Meiosis is a different kind of cell division. It is used to produce male and female gametes. A human body cell contains 46 chromosomes arranged in 23 pairs. The gametes are sperm or eggs, and only contain half as many chromosomes (23). This is why meiosis is sometimes called reduction division. |
| What happens at fertilisation? | At fertilisation, the nuclei of the sperm and an egg join to form the zygote. The zygote contains 23 pairs of chromosomes - 23 single chromosomes from the sperm, and 23 single chromosomes from the egg, thereby creating the correct number of 46 chromosomes for all body cells. It also means the zygote contains a complete set of chromosomes from each parent. |
| What ae the stages of MEIOSIS? | |
| What is a gene? | Genes are sections of DNA. Each gene is a set of coded instructions for making a particular protein. |
| What does DNA do? | DNA is a chemical code, or set of instructions. Our bodies need proteins for growth and development, and the DNA controls which proteins are made. The code consists of four different chemicals, or bases, that always pair up in the same way. |
| What base pairs always go together? | T always pairs with A G always pairs with C |
| Where are proteins made? | The genetic code of the DNA always remains safe inside the nucleus. But the proteins are made outside the nucleus in the cytoplasm of the cell. For this to happen, a copy of the genetic code of a gene is made. This copy then passes out of the nucleus into the cytoplasm where the protein is made. |
| What is an unspecialised cell? | 'Unspecialised' stem cells can develop into any other type of cell. Unspecialised stem cells are found in human embryos, animal zygotes (very young embryos), and in plants of all ages. |
| Cell Specialisation | The zygote then divides many times by mitosis to form an embryo. The first division of the zygote forms two cells, the next four, the next eight, and so on. Up to the eight-cell stage, all of the cells are identical. They are called embryonic stem cells. It is possible for embryonic stem cells to develop into any other specialised type of cell that the growing embryo needs - for example, nerve cells, blood cells and muscle cells. However, once the embryonic stem cells become specialised, they can't change into any other type of cell. |
| Switching genes on and off | Cells become specialised because the genes that are not required are switched off. Only the genes needed to make a particular type of cell work are switched on. So muscle cells only have the genes needed to make muscle cell proteins switched on. All the other genes, such as those needed to make blood cell proteins and nerve cell proteins, are switched off. |
| Cloning plants | Cuttings develop much bigger root systems if they are dipped in hormone rooting powder or planted in rooting compound containing growth hormone. These hormones cause unspecialised stem cells to grow and develop. They turn into tissues such as xylem and phloem, and organs such as roots, leaves and flowers, thereby forming a complete new plant. This makes it possible to clone plants quickly and cheaply. |
| What is phototropism? | Phototropism is a plant's growth response to light. When the stem grows towards the light, the plant can photosynthesise more. More food is produced, so the plant can grow faster. This increases the plant's chances of survival. |
| What is meristem? | Plants cells are different to animal cells in another way. Unspecialised stem cells in plants are grouped together in structures called meristems. Cells produced by meristems ensure that plants continue to grow in height and width throughout their life. Animals stop growing in size once they become adults. Plant meristems divide to produce cells that increase the height of the plant, length of the roots and girth of the stem. They also produce cells that develop into leaves and flowers. |
| How can you switch genes back on? | This is done by changing the genetic material in a human egg cell, by changing its nucleus. |
| What are the steps in turning genes back on? | 1.nucleus taken out of a human egg cell 2. nucleus from a patient's cell put into the egg cell 3.egg cell stimulated to develop into an embryo 4.stem cells taken from the embryo 5. stem cells grown in a container of warm nutrients 6.stem cells treated to develop into required cell types |
| What are auxins? | Auxins are plant hormones that make some parts of a plant stem grow faster than others. The result is that the plant stem bends towards the light. |
| Which side will speed up/slow down due to auxin? | You may have noticed that a houseplant grows towards the window and turns its leaves towards the light. It does this because light coming from the window side of the plant destroys the auxin in that side of the stem. So growth on that side slows down. On the shaded side of the plant there is more auxin. So growth on this side speeds up. The result is that the shoots and leaves are turned towards the light for photosynthesis. |
| Where is auxin produced? | Auxin is produced in the tip of growing shoots. |
| What happens if the tip of the growing shoots is cut off or covered? | If the tips are removed, they cannot produce auxin, so phototropism cannot occur. If the tips are covered, light cannot break down the auxin, so phototropism cannot then occur either. |
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