Mitosis

Question 1

What are chromatids?

Answer 1

Replicates of chromosomes

Question 2

What is cytokinesis?

Answer 2

Division of cytoplasm of a cell following mitosis

Question 3

What is mitosis?

Answer 3

• Type of nuclear division maintaining chromosome number
• Each new daughter cell contains same genetic information as parent cell, genetically identical to each other

Question 4

Why do all living organisms need to produce genetically identical daughter cells by mitosis?

Answer 4

Asexual reproduction
• Single-celled protoctists divide by mitosis to produce new individuals • Some plants reproduce asexually by forming new plantlets on ends of stolons (runners)
• Fungi can reproduce asexually by mitosis.

Question 5

When can asexual reproduction occur in animals?

Answer 5

• Rarer but some female sharks kept in captivity without any males have produced female offspring, genetically identical to themselves • Aphids may sometimes produce eggs, by mitosis, that don’t need fertilising

Question 6

What is meant by growth?

Answer 6

All multicellular organisms grow by producing more cells genetically identical to each other and to parent cell they arose by mitosis

Question 7

What is meant by tissue repair?

Answer 7

Wounds heal when growth factors, secreted by platelets and macrophages (white blood cells) and damaged cells of blood-vessel walls, stimulate proliferation of endothelial and smooth muscle cells to repair damaged blood vessels

Question 8

What happens during prophase?

Answer 8

• Chromosomes replicated during S phase of interphase and consist of two identical sister chromatids now shorten and thicken as DNA supercoils
• Nuclear envelope breaks down
• Centriole in animal cells (normally found in centrosome) divides and 2 new daughter centrioles move to opposite poles of cell
• Cytoskeleton protein (tubulin) threads form spindle between centrioles
• In plant cells, tubulin threads are formed from cytoplasm

Question 9

What happens during metaphase?

Answer 9

• Pairs of chromatids attach to spindle threads at equator region
• Attach by centromeres

Question 10

What happens during anaphase?

Answer 10

• Centromere of each pair of chromatids splits
• Motor proteins, walking along tubulin threads, pull each sister chromatid of pair, in opposite directions, towards opposite poles
• Because centromere goes first, chromatids, now called chromosomes, assume V shape

Question 11

What happens during telophase?

Answer 11

• Separated chromosomes reach the poles
• New nuclear envelope forms around each set of chromosomes
• Cell now contains 2 nuclei each genetically identical to each other and to parent cell from which they arose

Question 12

What is the process of cytokinesis?

Answer 12

• Once mitosis is complete, cell splits in 2, so each new cell contains a nucleus
• In animal cells, plasma membrane folds inwards and ‘nips in’ cytoplasm
• In plant cells, an end plate forms where equator of spindle was, and new plasma membrane and cellulose cell-wall material are laid down on either side along this end plate
• 2 new daughter cells are now formed, genetically identical to each other and to parent cell