1.6 cell cycle and division

Question 1

What is interphase?

Answer 1

• Longest stage of eukryotik cell cycle
• Cells grow and synthesise new organelles, proteins and DNA in preperation for mitosis.

Question 2

What is mitosis?

Answer 2

• Forms of cell division.
• Produces two genetically identical diploid daughter cells.

Question 3

Why is mitosis important?

Answer 3

Important for the growth of tissue and repair and replacement of cells.

Question 4

Name the stages of mitosis

Answer 4

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 5

Summarise the processes of mitosis

Answer 5

• Prophase= nuclear envolope breaks down, chromosomes condese, centrioles move to opposite poles of the cell.
• Metaphase = sister chromosomes line up at the equator, centrosomes attach to the spindle fibres.
• Anaphase = sister chromatids eperated and pulled part to opposite poles
• Telophase = nuclear envolope forms, spindle fibres break down, chromosomes uncoil.

Question 6

What are sister chromatids?

Answer 6

A pair of identical chromatids formed by DNA Replication, joined by a centromere

Question 7

What is cytokenesis?

Answer 7

The division of the cytoplasm at the end of miitosis to produce to new daughter cells.

Question 8

Compare mitosis in plant and animal cells.

Answer 8

• A= occurs in most tissues, P= occurs in meristemic cells only.
• A= before mitosis, cells become rounded. P = cell does not chnge shape.
• A= involes centrioles, P= does not.
• A= involves microfilaments, P= no microfilaments involved.
• A = spindle fibres disappear prior to cytokenesis, P= some spindle fibres remain during cytokenesis.

Question 9

What may unrestricted mitosis lead to?

Answer 9

Cancerous growths.

Question 10

What is meiosis?

Answer 10

• Form of cell division
• Produces 4 geneticlly differnt daughter cells (gametes) with a haploid number of chromosomes.
• Involves 2 divisions.

Question 11

What is the significsnce of meiosis in reproduction?

Answer 11

Gametes must be haploid so that when they combine during fererlisation, the full number of chromosomes is present within the resulting zygote. It also creates genetic variation.

Question 12

What is meiosis I?

Answer 12

• First stage of meiosis
• Homologus chromosomes spereated to form two haploid cells.

Question 13

draw diagrams to show the stages in meiosis I

Question 14

Describe what happens during meiosos I

Answer 14

1. Homologus chromosomes pair to form bivalents.
2. Crossing over occurs at chismeta.
3. Cell divides into two; independent segration of homologus chromosomes, each cell contains either a meternal or paternal copy.

Question 15

What are homologus chromosomes?

Answer 15

• Pair of chromosomes with genes at the same locus.
• One maternal and one paternal
• Some alleles may be the same while others may be differnt.

Question 16

Define crossing over.

Answer 16

• Process in meiosis 1.
• Homologus pairs pair up, their chromatids wrap around one another and their alleles are exchanged at equivelent portions of chromatids.
• Creates genetic variation.

Question 17

What is independent segregation?

Answer 17

• The random seperation of homologus chromosomes in meiosis I that produces genetic variation.

Question 18

what is meiosis II?

Answer 18

• Second stage of meiosis
• Sister chromatids seperated to form 4 haploid gametes.

Question 19

Draw diagrams to illussrtae the stages of meiosis II

Question 20

Describe what happens during meiosis II

Answer 20

1. Independent segration of sister chromatids.
2. each sell divides again producing 4 haploid cells.

Question 21

How does meiosis produce genetic variation?

Answer 21

• Crossing over during meiosis I
• Independent assortment of homologus chromosomes and sister chromatids
• Results in a new combinatio of alleles.

Question 22

Draw a diagram to show cells after each stage in meiosis.