cell division-b2

Question 1

What does the nucleus contain?

Answer 1

The nucleus contains genetic information in the form of chromosomes.

Question 2

What are chromosomes?

Answer 2

Chromosomes are coiled up lengths of DNA molecules. Each chromosome carries a large number of genes.

Question 3

What is a gene?

Answer 3

A gene is a small packet of information that controls a characteristic of your body. It is a section of DNA.

Question 4

How many chromosomes are there in the nucleus?

Answer 4

46 chromosomes. arranged in 23 pairs.

In each pair of chromosome, one chromosome is inherited from the father and one from the mother.

Question 5

How many chromosomes do gametes have?

Answer 5

Gametes are sex cells and have 23 chromosome bc in each pair there is only one chromosome.

Question 6

What is the cell cycle?

Answer 6

Body cells divide in a series of stages, this is the cell cycle

Question 7

What is mitosis?

Answer 7

The stage of the cell cycle when the cell divides is called mitosis. The end of the cycle results in two new cells identical to the original cell, with the same number of chromosomes.

Question 8

Why is mitosis important?

Answer 8

Mitosis is important and multi cellular organisms use mitosis to grow or replace cells that have been damaged. The additional cells can be used for growth and development.

Question 9

How long is the cell cycle?

Answer 9

The length of the cell cycle varies considerably. It can take less than 24 hours, or it can take several years, depending on the cells involved and the stage of life of the organism.

Question 10

Does the cell cycle vary in different age groups?

Answer 10

Yes, the cell cycle is short as a baby develops before it is born, when new cells are being made all the time. It remains fairly rapid during childhood, but the cell cycle slows down once puberty is over and the body is adult. However even in adults, there are regions where there is continued growth or a regular replacement of cells.

Question 11

What cells that continue having a rapid cell cycle in adulthood?

Answer 11

Hair follicles, the skin, the blood, and the lining of the digestive system.

Question 12

How many stages are there in the cell cycle?

Answer 12

3

Question 13

What happens in stage 1?

Answer 13

Stage 1 is the longest stage in the cell cycle. The cells grow bigger, increase their mass, and carry out normal cell activities. Most importantly they replicate their DNA to form two copies of each chromosome ready for cell division. They also increase the number of sub-cellular structures such as mitochondria ,ribosomes and chloroplasts ready for the cell to divide.

Question 14

What happens in stage 2?

Answer 14

One set of chromosomes is pulled to each end of the divided cell and the nucleus divides.

Question 15

What happens in stage 3?

Answer 15

This is the stage where the cytoplasm and the cell membranes also divide to form identical daughter cells. The cell divides in two.

Question 16

What is interphase?

Answer 16

The cell spends most of its time in this phase. The DNA in the chromosome copies itself ready for mitosis. This phase is part of stage 1.

Question 17

What is prophase?

Answer 17

The DNA in chromosomes and their copies condenses to become more visible. The membrane around the nucleus disappears. This is stage 1.

Question 18

What is metaphase?

Answer 18

Chromosomes and their copies line up in the middle of the cell. This is stage 1

Question 19

What is anaphase?

Answer 19

Chromosomes and their copies are pulled to different ends of the cell. This is stage 2.

Question 20

What is telophase?

Answer 20

New membranes form around the chromosomes at each end of the cell.

Question 21

What is cytokinesis?

Answer 21

The cell divides into two daughter cells

Question 22

Read some info about mitosis and cell cycle, i don’t think it’s that important but read it :) also keep it up with revision, im proud of you for starting, you got this.

Answer 22

In some parts of an animal or plant, mitotic cell division carries on rapidly all the time. For example you lose cells from the skin’s surface and make new cells to replace them. In fact, about 300 million of your body cells die every minute, so cell division by mitosis is very important. In a child, mitotic division produces new cells faster than the old ones die. As an adult, cell death and mitosis keep more or less in balance. When you get very old, mitosis slows down and you show the typical signs of aging.

Question 23

What is differentiation?

Answer 23

Differentiation is the process by which a cell changes to become specialised for its job.

Question 24

What are stem cells?

Answer 24

Undifferentiated cells

Question 25

How does differentiation work in humans?

Answer 25

In humans and animals, many types of cells become specialised very early in life. By the time a human baby is born, most of its cell are specialsied to carry out a particular job, such as nerve cells,skin cells or muscle cells. They have differentiated. Some of their genes have been switched on and others have been switched off. As a result, different types of specialised cells have different sub cellular structures to carry out specific functions

Question 26

Do specialised cells divide by mitosis?

Answer 26

Most specialsied cells can divide by mitosis, but they can only form the same sort of cell. Muscle cells divide to produce more muscle cells. Some differentiated cells, such as red blood cells and skin cells cannot divide at all so adult stem cells replace dead or damaged cells. Nerve cells do not divide once they have differentiated and they are not replaced by stem cells.

Question 27

How does differentiation work in plants?

Answer 27

In contrast to animal cells, most plant cells are able to differentiate all through their lives. Undifferentiated cells are formed at active regions of the stems and roots, known as meristems. In these areas, mitosis takes place all the time, The cells then elongate and grow before they finally differentiate. Plants keep growing all through their lives at these growing points. The plant cells produced do not differentiate until they are in their final position in the plant. Even then, the differentiation is not permanent. You can move a plant cell from one part of the plant to another. There it can re differentiate and become a completely different type of cell. You cannot do that with animal cells- once a muscle cell, always a muscle cell.

Question 28

What is cloning?

Answer 28

Producing identical offspring

Question 29

How can you clone plants?

Answer 29

Huge numbers of identical plant clones can be produced from a tiny piece of leaf tissue. This is because, in the right conditions, a plant cell will become unspecialsied and undergo mitosis many times. Each of these undifferentiated cells will produce more cells by mitosis. These will then differentiate to form tissues such as xylem, phloem, photosynthetic cells, and root hair cells that are needed to form a new plant. The new plant will be identical to the original parent.

Question 30

Why is it difficult to clone animals?

Answer 30

Most animal cells differentiate permanently early in embroyo development. These cells cannot change back.

Question 31

How do embroyonic stem cells form?

Answer 31

An egg and sperm cell fuse to form a zygote, a single new cell. That cell divides and becomes a hollow ball of cells- the embryo. The inner cells of this ball are the embryonic stem cells that differentiate to form all of the specialised cells of your body.

Question 32

What are adult stem cells?

Answer 32

Even when you are adult, some of your stem cells remain. An adult stem cell is an undifferentiated cell of an organism that can give rise to many more cells of the same type. The bone marrow is a good source of adult stem cells.

Question 33

How can you use stem cells to cure diseases?

Answer 33

Medicine already uses stem cells to treat diseases for example stem cells trasnferred from the bone marrow of an healthy person can replace faulty blood cells. Embryonic stem cells could also be used to replace faulty cells in sick people- you could make insulin producing cells for people with diabetes, nerve cells for people paralysed by spinal injuries, or transporting stem cells in blind people's eyes.

Question 34

What is therapeutic cloning?

Answer 34

An embryo could be made to have the same genetic information as the patient This means that the stem cells produced from it would also contain the same genes and so wouldn't be rejected by the patients body.

Question 35

What are the risks with using stem cells grown in the lab?

Answer 35

Stem cells grown in the lab could become contaminated with a virus which could be passed on to the patient and make them sicker.

Question 36

What are the uses of making clones of plants from stem cells?

Answer 36

The stem cells from plant meristems can be used to make clones of the mature parent plant very quickly and economically. This is important as it gives us a way of producing large numbers of rare plants reliably and safely. We may be able to save some rare plants from extinction in this way. Plant cloning also gives us a way of producing large populations of identical plants for research. This is important as scientists can change variables and observe the effects on genetically identical individuals. Cloning large numbers of identical plants from the stem cells in plant meristems is also widely used in horticulture producing large numbers of plants such as orchids for sale. In agriculture it is used to produce large numbers of identical crop plants with special features, such as disease resistance.

Question 37

What are the ethical problems with using stem cells?

Answer 37

Some people are against stem cell research because they feel that human embryos shouldn't be used for experiments since each one is a potential human life and it is a violation of human rights. Some religious people also have this viewpoint. Others think that curing patients who already exist and who are suffering is more important than the rights of embryo. And embryos used in the research are usually unwanted ones from fertility clinics which would be destroyed anyways. But other people believe scientists should focus on other areas of medicine.