Topic 3- Cells, Reproduction, and Differentiation

Question 1

What is the RER and its function?

Answer 1

• fluid filled membranes covered with ribosomes
• folds and processes proteins made at ribosomes

Question 2

What is the SER and its function?

Answer 2

• fluid filled sacs with no ribosomes
• processes and synthesises lipids

Question 3

What is the Golgi Apparatus and its function?

Answer 3

• group of fluid filled membrane bound, flattened sacs/ vesicles seen around them
• processes and packages proteins and lipids (sugar chains trimmed or added)
• makes lysosomes

Question 4

What is the function of pili?

Answer 4

• help prokaryotes stick to other cells
• can be used to transfer genetic material between cells

Question 5

What are plasmids?

Answer 5

• small loops of DNA that aren’t part of main circular DNA
• contains genes coding for antibiotic resistance
• can be passed onto other prokaryotes

Question 6

What are the differences between prokaryotic and eukaryotic DNA? (3)

Answer 6

1. prokaryotic has curcular DNA while eukaryotic has linear
2. eukaryotic DNA is enclosed in a nucleus whereas prokaryotic DNA free floats in cytoplasm
3. prokaryotic DNA is not attached to histone proteins

Question 7

What are prokaryotic cell walls made of and their function?

Answer 7

• made up of the glycoprotein, murein
• suuports cell and prevents it changing shape

Question 8

Compare light and electron microscopes (5)

Answer 8

1. light uses light to form an image whereas electron microscopes use electrons
2. electron microscopes have higher resolution so give a more detailed image (1000x)
3. can’t use light microscopes to view organelles like ribosomes, ER but both can see nuclei
4. maximum magnification for a light microscope is x1500 whereas electron microscope is x1,500,000
5. specimens must be dead when using an electron microscope

Question 9

How to measure the size of a specimen by calibration?

Answer 9

• fit an eyepiece graticule onto eyepiece and place stage micrometer onto stage
• divide the eyepiece divisions by the distance of 1 division on stage micrometer

Question 10

What is a tissue?

Answer 10

a group of similar cells adapted to work together to carry out a particular function

Question 11

What is an organ?

Answer 11

a group of different tissues that work together to perform a particular function

Question 12

Decribe the crossing over of chromatids (4)

Answer 12

1. homologous pairs of chromosomes pair up
2. non sister chromatids cross over and get entangles at the chiasmata
3. entanglement places stress on the DNA and a section of a chromatid from one chromosome breaks and rejoins with the other chromatid
4. forms a new combo of alleles on the 2 chromosomes

Question 13

Describe independent assortment (3)

Answer 13

1. each homologous pair can be arranged with either chromosome on top (random)
2. the combo of alleles that end up in each daughter cell after the chromosomes separate depends on how they line up
3. production of diff combos of allels in daughter cells due to random alignment of homologous pairs along equator of cell during meiosis 1

Question 14

What is polygenetic inheritance?

Answer 14

• when we inherit more than 1 gene and alleles which affect a single characteristic
• shows continuous variation

Question 15

What is a linked trait and autosomal linkage?

Answer 15

• when genes are very close together on a chromosome, they are crossed over together
• it is very unlikely that the chiasma will split these genes apart
• autosomal linkage= occurs in non sex chromosomes

Question 16

Define an operon

Answer 16

a section of DNA that contains a cluster of structural genes that are transcribed together

Question 17

What is the regulatory gene for?

Answer 17

codes for an activator or repressor

Question 18

What are epigenetic changes?

Answer 18

• they occur when chemical hgroups are added are removed from DNA
• doesn’t alter base sequence but does determine what genes are expressed
• histone modification (acetylation) and DNA methylation

Question 19

How may epigenetic changes be passed onto offspring? Why may this be advantageous?

Answer 19

• when cell replicates and divided, epigentic changes may be passed onto resulting daughter cells eg methyl group not being removed when producing gametes
• if epigentic change occured in response to change in environment, offspring will be equipped to deal with changed environment

Question 20

Outline the process of gene expression/ specialisation

Answer 20

1. stimulus (chemical/hormone) activates gene
2. sequence of DNA bases are unzipped and transcribed using RNA polymerase
   - this is where epigenetics affect gene expression
3. mRNA produced and translated at ribosome
4. polypeptide is folded in RER and modified in GA
5. fibrous/globular protein produced
6. final phenotype/ specialisation of a cell is achieved

Question 21

How do stem cells become specialised?

Answer 21

• by differential gene expression where only certain genes in DNA are activated and expressed

Question 22

What is a stem cell?

Answer 22

• a cell that has the potential to differentiate into a specialised cell or remain as a stem cell
• can divide an unlimited amount of times

Question 23

What are the risks of using stem cells in medicine?

Answer 23

• low no. stem cell donors
• cultured stem cells could accumulate mutations + lead to cancer
• is it right to create an embryo for the sole purpose of therapy/ destroy after
• people aren’t educated on what they can’t do

Question 24

Give the structure of the lac operon

Answer 24

• regulatory gene= codes for the repressor protein that controls transcription
• promotor region= section of dNA that initiates transcription
• operator region= section of DNA that repressor binds to to regulate transcription
• structural genes= work together to enable digestion of lactose for energy

Question 25

Give the similarities and fifferences between mitosis and meiosis

Answer 25

• both increase the number of cells
• mitosis creates 2 genetically identical, diploid daughter cells
• meiosis creates 4 genetically different, haploid daughter cells