Biology Stupied Questions part 5

Question 1

Question 1 - approximate duration of cells in S phase

Answer 1

8 hours

Question 2

Epithelial cells lining the intestine divide two or three times a day , liver cells divide once a year, which parts of their cell cycle will liver cells differ from intestine epithelial cells

Answer 2

Epithelial cells have a shorter cell cycle as they do not have a gap phase 0 - they do not undergo apoptosis or remain in this phase,
whereas liver cells do have a gap phase 0 this is a resting phase which means they only divide once a year and stay in this phase for a long period of time, this resting phase is triggered during gap phase 1 at the restriction point by a checkpoint chemical

Question 3

List the purpose of checkpoints to control the cell cycle

Answer 3

to prevent uncontrolled division that would lead to tumours
to detect and repair damage to DNA
cell cycle can not be reversed
the DNA is only duplicated once during each cell cycle

Question 4

Whys is it crucial that each new cell receives the same amount of DNA

Answer 4

It is crucial that new cells receives the same amount of DNA to stop spontaneous mutations from happening, if the amount of DNA differs then the DNA code will be wrong this means the primary structure of any molecular created will be wrong so when folded in to its tertiary structure it will not fold correctly and will not be able to carry out its function, this could result in a disorder or death

Question 5

In which phase of the eukaryotic cell cycle do the following happen
A) replication of chloroplasts and mitochondria
B) condensation of Chromatin
C) replication of DNA
D) differentiation
E) Apoptosis
F) Growth of the cell

Answer 5

A) Gap phase 1 
B)  M phase 
C) S phase 
D) Gap phase 0
E) Gap phase 0
F) Gap phase 1

Question 6

In a cell in the root of a black nightshade plant, solanum nigrum there are 72 chromosomes. How many chromosomes are in this cell during 
A) Gap phase 2 interphase
B) Gap phase 1 interphase
C) Prophase of mitosis
D) Telophase of mitosis 
E) After cytokinesis

Answer 6

A) 144 
B) 72
C) 72
D) 144
E) 72

Question 7

Explain why plant palisade mesophyll cells cannot undergo mitosis

Answer 7

Palisade mesophyll cells cannot undergo mitosis because once they have differentiated and have a vacuole and a rigid cellulose cell wall they cannot divide

Question 8

Distinguish - explain there meanings - between these terms: 
centriole
centrosome
chromosome
centromere

Answer 8

Centriole - a pair of cylindrical organelles in the cell involved in the development of spindle fibres in cell division
Centrosome - an organelle which contains the centrioles of which spindle fibres develop in cell division
Chromosome - condensed DNA
Centromere-the part of the chromosome which the microtubules of the spindle attach during cell division

Question 9

State 4 reasons why mitosis is necessary in the cell cycle of living organisms

Answer 9

• Asexual reproduction - single celled protoctists divide by mitosis to produce new individuals as well as fungi
• growth - all multicellular organisms grow by producing cells that are genetically identical to each other - this results by mitosis
• tissue repair - wounds need to heal - secreted by platelets and macrophages and damaged cells of the blood-vessel walls - stimulate the proliferation of endothelial and smooth muscle cells to repair damaged blood vessels
• cell replacement - to replace cells that need replacing

Question 10

Male honey bees develop from unfertilised eggs, and each of their cells is a haploid containing only one set of chromosomes
the function of the males in the hive is for some of them to fertilise the new queen, suggest what type of cell division is used to make the bee spermatozoa

Answer 10

Mitosis

- asexual reproduction

Question 11

Explain why sexual reproduction involves meiosis

Answer 11

• it involves meiosis as it is the combining of genetic material from two unrelated individuals of the same species
• results in the formation of cells containing half the number of chromosomes of the parent cell - gametes

Question 12

Describe how meiosis produces genetic variation in the gametes produced

Answer 12

This happens during prophase 1, the chromatin condenses and each chromosome supercoils, they can be stained and see with a light microscope
- the nuclear envelope breaks down and spindle threads of tubulin proteins form the centriole in animal cells, the chromosomes come together in homologous pairs and each member of the pair consists of two chromatids, the crossing over occurs where non sister chromatids wrap around each other and may swap sections so that alleles are shuffled
this leads to random distribution of genetic material and genetic variation in gametes

Question 13

Explain how fertilisation produces genetic variation in a new individual

Answer 13

• combines genetic material from two unrelated individuals of the same species, by fertilisation the gametes combine and there is one maternal set of chromosomes and one paternal set of chromosomes these match up and form homologous chromosomes,

Question 14

Why is genetic variation good for populations of living organisms

Answer 14

• genetic variation within a population increases its chances of survival when the environment changes as some individuals will have characteristics that enable them to be better adapted to change, therefore they ware able to quickly select the best characteristics for survival and survive the new environment

Question 15

in which stage of meiosis is the chromosome number halved

Answer 15

Telophase 2

Question 16

what are the products of meiosis

Answer 16

• 4 haploid daughter cells that are genetically varied