Cell division-mocks

Question 1

In the body cells of diploid organisms, chromosomes are

Answer 1

normally found in pairs

-one chromosome from each pair is inherited from the mother and the other from the father

Question 2

Humans chromosomes

Answer 2

-They have 46 chromosomes in the nucleus of all their body cells, found in 23 pairs

Question 3

Horses chromosomes

Answer 3

They have 64 chromosomes in 32 pairs

Question 4

Red blood cells

Answer 4

-exception: they lose their nuclei therefore have no chromosomes

Question 5

What happens during the growth phase of the cell cycle?

Answer 5

The genetic material of the cell (chromosomes) are doubled.

-the number of subcellular structures also increases

Question 6

Describe what happens in each of the three stages of the cell cycle.

Answer 6

In stage 1, which is the longest, the DNA replicates to form two copies of chromosomes and there is an increase in the number of subcellular structures (ribosomes,mitochondria). In Stage 2, the nucleus divides and one set of chromosomes moves to each end of the cell. In stage 3, which is cytokinesis, the cell membrane splits into two to form two genetically identical daughter cells.

Question 7

Human cell dividing by mitosis

Answer 7

• Its 46 chromosomes are doubled, so that there are two copies of each of the 46 chromosomes (or 92 chromatids) in total in the cell
• The number of ribosomes and mitochondria subcellular structures also increases
• During mitosis, the chromatids are pulled apart, with a complete set of 46 chromosomes in 23 pairs moving to each end of the cell
• The cytoplasm and cell membrane divide, forming two new daughter cells

Question 8

The Role of Mitosis

Answer 8

• Cell division by mitosis is important in the growth and development of multicellular organisms
• When a sperm cell fertilises an egg cell in human reproduction, the resulting zygote cell that forms divides by mitosis, with each subsequent cell produced dividing in the same way to form an embryo
• As the embryo continues to grow in size, with the cells dividing by mitosis (and differentiating), a fetus forms
• Therefore, for a multicellular organism to grow, cells have to divide by mitosis to produce an increase in cell number

Question 9

Meiosis

Answer 9

-Cells in reproductive organs divide by meiosis to form gametes (sex cells)
-The number of chromosomes must be halved when the gametes are formed
-Otherwise, there would be double the number of chromosomes after they join at fertilisation in the zygote (fertilized egg)
-This halving occurs during meiosis, and so it is described as a reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells
-It starts with chromosomes doubling themselves as in mitosis and lining up in the centre of the cell
After this has happened the cells divide twice so that only one copy of each chromosome passes to each gamete

Question 10

Meiosis process

Answer 10

• Each chromosome is duplicated (makes identical copies of itself), forming X-shaped chromosomes
• First division: the chromosome pairs line up along the centre of the cell and are then pulled apart so that each new cell only has one copy of each chromosome
• Second division: the chromosomes line up along the centre of the cell and the arms of the chromosomes are pulled apart
• A total of four haploid daughter cells will be produced

Question 11

Importance of meiosis

Answer 11

• Produces gametes eg. sperm cells and egg cells in animals, pollen grains and ovum cells in plants
• Increases genetic variation of offspring
• Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others