cell division

Question 1

How are mammalian eggs adapted for function

Answer 1

• Zona pellucida to prevent polyspermy

- Haploid nucleus to restore chromosomes at fertillisation

Question 2

How is the sperm adapted to its function

Answer 2

• Contains lots of mitochondria for energy required to move

- Acrosome contains digestive enzymes which break down the zona pellucida of the egg

Question 3

Describe process of fertilisation

Answer 3

• Acrosome reaction= enzymes in acrosome digest the zona pellucida. Sperm nucleus enters the egg cell
• Cortical reaction =causes zona pellucida to harden, preventing polyspermy
• Nucleic Fusion= restoring full set of chromosomes forming a diploid zygote

Question 4

What is a locus?

Answer 4

The fixed position on a chromosome occupied by a gene

Question 5

What is meant by autosomal linkage?

Answer 5

Where two or more genes located on the same chromosome, so are inherited almost as if they were the same gene

Question 6

What is meant by sex-linkage?

Answer 6

Where an allele is located on one of the sex chromosomes, meaning its expression is dependent on the sex of the individual

Question 7

What is meant by polygenic inheritance?

Answer 7

Where a characteristic is determined by different genes as different loci

Question 8

Describe the two types of phenotypic variation

Answer 8

• Continuous=variation exists as gradual changes over a range e.g. height
• Discontinuous=variation exists as distinct categories e.g. blood group

Question 9

Suggest factors that cause a phenotype to show continuous variation

Answer 9

1. If the characteristic is determined by more than one gene

2. If the environment has an effect on the phenotype

Question 10

In which ways does meiosis ensure genetic variation?

Answer 10

Produces non-identical gametes through;

1. Crossing over of alleles between chromatids
2. Independent assortment of chromosomes

Question 11

Explain the role of Mitosis

Answer 11

Produces genetically identical daughter cells. Useful for growth, repair and(in prokaryotic cells) asexual reproduction.

Question 12

Give an example of cells sharing common features

Answer 12

All eukaryotic cells have a nucleus and membrane-bound organelles

Question 13

Describe the structure and function of the nucleus

Answer 13

Structure=surrounded by a double membrane, with pores that allow molecules to enter and leave
Function=stores DNA and coordinates cell activities

Question 14

Describe the structure and function of the nucleolus

Answer 14

Structure=found within the nucleus, made of proteins and RNA

Function=produces ribosomes

Question 15

describe the structure and function of the RER

Answer 15

Structure=a series of flattened sacs, with large numbers of ribosomes on the surface
Function=protein synthesis and folding

Question 16

Describe the structure and function of the SER

Answer 16

structure= a series of membrane-bound sacs, without ribosome on the surface
Function=Produces and processes lipids

Question 17

Describe the structure and function of the Golgi apparatus

Answer 17

Structure= flat, curved, fluid-filled sacs surrounded by vesicles
Function= processes and packages proteins and lipids, produces lysosomes

Question 18

Describe the structure of the mitochondria

Answer 18

Structure=bound by a double outer membrane, inner membrane folded to increase SA
Function=Site of respiration and therefore ATP production

Question 19

Describe the structure and function of centrioles

Answer 19

Structure=hollow cylinders containing microtubules

Function=involved in cell division

Question 20

Describe the structure and function of ribosomes

Answer 20

Structure=composed of two subunits, maybe either be membrane-bound or free in the cytoplasm
Function=site of protein synthesis

Question 21

Describe the structure and function of lysosomes

Answer 21

Structure=vesicles filled with digestive enzymes, bound by a membrane
Function=breakdown any of the cell’s waste, destroy disease-causing organisms that enter the cell

Question 22

Outline the role of the RER and Golgi apparatus in transporting proteins

Answer 22

1. Proteins produced on the ribosomes of RER, and are then folded and processed
2. Transported in vesicles to the Golgi body
3. Modified and repackaged to be transported around the cell, or to leave the cell by exocytosis (extracellular enzymes)

Question 23

What is meant by a stem cells?

Answer 23

An unspecialised cell
that gives rise to other types of cell
with no limit to the number of times it can divide

Question 24

what is meant by pluripotent and totipotent stem cells?

Answer 24

Totipotent=can develop into any cell type including the placenta and embryonic cells
Pluripotent=can develop into any cell type excluding the placental cells.

Question 25

What are some uses of stem cells?

Answer 25

Treat diseases

replace damaged tissues, such as spinal cods

Question 26

Why is use of stem cells controversial?

Answer 26

There is risk of infection

Involves the killing of embryos

Question 27

How do cells become specialised?

Answer 27

1. Some genes become switched on while others are switched off
2. The active ‘switched on’ genes are transcribed and translated into proteins, which are then used for the specific function of that cell

Question 28

What is a phenotype?

Answer 28

The expression of an organism’s genes combines with its interaction with the environment

Question 29

what is epigenetics?

Answer 29

A heritable change in gene function without change to the base of sequence of DNA

Question 30

How does DNA methylation affect gene transcription?

Answer 30

Involves addition of a CH3 group to one of the bases. Prevents transcription factors from binding. Therefore gene transcription is suppressed.

Question 31

How are epigenetic changes passed on?

Answer 31

Because the changes affect cell division, all cells that arise form the altered cells will possess the modification. This includes gametes, meaning the changes are heritable.