Cell division.

Question 1

interphase steps of the cell cycle

Answer 1

• Made up of the G1, S and G2 phases
• G1 - cell grows, respires, proteins made and organelles replicated
• S - DNA replication occurs, chromosomes become sister chromatids joined by a centromere
• G2 - DNA replication is checked for mistakes, organelle replicated Mitosis

Question 2

MITOSIS stages

Answer 2

Prophase - sister chromatids supercoil, nuclear envelope breaks down, spider fibres form.
Metaphase - sister chromatids line up at the equator and spindle fibres attach to the centromere
Anaphase - spindle fibres shorten and pull sister chromatids apart towards opposite poles
Telophase - chromosomes uncoil, nuclear envelope reforms cytokinesis
Cytoplasm cleaves down furrow to split cytoplasm
produces 2 genetically identical daughter cells (both identical to the parent cell).

Question 3

Meiosis in detail

Answer 3

sister chromatids supercoil to shorten and thicken
sister chromatids consist of sister chromatids joined by a centromere
they are now visible under a light microscope
the nuclear envelope breaks down
centriole divides in 2 and each daughter centriole goes to the opposite side of the cell
spindle fibres (microtubuals) begin to form metaphase

sister chromatids line up along equator
the spindle fibres attach to the centromeres anaphase

centromere splits 
chromatids separator 
spindle fibres shorten 
pull identical chromatids move to opposite poles 
with the centromere leading

Question 4

telophase

Answer 4

chromosomes uncoil
nuclear envelope reforms
spindle fibres break down

Question 5

difference between mitosis and meiosis

Answer 5

• Mitosis produces genetically identical diploid daughter cells used for growth and repair. it occurs in the body cells and involves only one division.
• Meiosis produces 4 genetically different haploid daughter cells and is used for producing gametes. it occurs only in the testes and involves 2 divisions.

Question 6

cell division and budding in yeast cells

Answer 6

- nuclei divided by mitosis 
bulge in surface of the cell
nucleus moves into bulge 
bulge nips/ pinches off
- this leaves an uneven distribution of cytoplasm in the two cells

Question 7

red blood cells (erythrocytes)

Answer 7

• No nucleus or many other organelles e.g. Golgi, mitochondria and ER - provides maximum space for haemoglobin to increase the oxygen carrying capacity.
• No nucleus and organelles also makes it more flexible to fit through the capillaries
• Filled with haemoglobin which can bind with the oxygen to form oxyhemoglobin to transport it round to the aerobically respiring cells
• Shape is biconcave disc in order to provide a larger s.a. to volume ratio for oxygen exchange for more efficient uptake of oxygen into the red blood cells.

Question 8

Root hair cells

Answer 8

the hair like projections into the soil provides a larger surface area for osmosis and mineral uptake (active transport) into the roots
they also have a thin wall for short diffusion path
many mitochondria to provide energy for the active transport of minerals
many channel proteins for the uptake of water via osmosis

Question 9

neutrophils (phagocytes)

Answer 9

Contain a lot of lysosomes containing lysin enzymes to digest pathogens
multi lobed nucleus to fit between gaps in the endothelial cells of the capillaries to leave the blood
contain many mitochondria to move lysosomes and phagosomes though cell along microtubules.

Question 10

sperm

Answer 10

haploid nucleus so when it fertilises an egg the zygote is diploid
many mitochondria provide energy for movement of flagellum
shape: long and thin - ease of movement

Question 11

sperm

Answer 11

haploid nucleus so when it fertilises an egg the zygote is diploid
many mitochondria provide energy for movement of flagellum
shape: long and thin - ease of movement
enzyme contained in acrosome so when the sperm meets the egg it can penetrate it to fertilise.