Cell structure and division

Question 1

What are eukaryotic cells?

Answer 1

complex cells containing a nucleus and membrane bound organelles eg animal cells, plant cells, algal cells and fungal cells
80s ribosomes
dna associated with histones + linear
larger than pro
no cell wall

Question 2

Cell surface membrane

Answer 2

plasma membrane
membrane found on the surface of animal cells and just inside the cell wall of other cells
mainly made of lipids and proteins
regulates the movement of substances in and out of the cell
has receptor molecules which respond to chemicals

Question 3

Nucleus

Answer 3

large organelle surrounded by a nuclear envelope which contains pores
nucleus contains chromosomes in nucleolus
nucleolus makes ribosomes
nucleus controls cells activities (transcription)
pores allow substances to move between nucleus and cytoplasm

Question 4

Mitochondria

Answer 4

oval shaped
double membrane- inner is folded to form cristae which increases surface area for enzymes (to act)/respiration- oxidative phosphorylation
inside is matrix which contains enzymes and DNA
matrix stores substrates
site of aerobic respiration (produces ATP)
found in cells that are active and require energy

Question 5

Chloroplasts

Answer 5

flattened structure found in plant and algal cells
surrounded by double membrane
has membranes inside called thylakoid membranes which are stacked up to form grana
grana are linked by lamellae
where photosynthesis takes place (grana or stroma)

Question 6

Golgi apparatus

Answer 6

fluid filled membrane bound flattened sacs
vesicles are found on edge of sacs
processes and packages new lipids and proteins and makes lysosomes
transports proteins out of cells

Question 7

Golgi vesicle

Answer 7

small fluid filled sac in cytoplasm
produces by golgi apparatus
stores lipids and proteins from golgi apparatus
transports them out of the cell by fusing with cell surface membrane

Question 8

Lysosome

Answer 8

round organelle surrounded by a membrane- type of golgi vesicle
contains digestive enzymes called lysozymes
can be used to digest invading cells

Question 9

Ribosome

Answer 9

small organelle made up of proteins and RNA with no outer membrane
site where proteins are made

Question 10

Rough endoplasmic reticulum

Answer 10

system of membranes enclosing a fluid filled space
surface is covered with ribosomes
folds and processes proteins that have been made at ribosomes

Question 11

Smooth endoplasmic reticulum

Answer 11

same as above but with no ribosomes

synthesises and processes lipids

Question 12

Cell wall

Answer 12

rigid structure surrounding cells (plants, algae, fungi)
made of cellulose or chitin in fungi
supports cell and prevents them from changing shape

Question 13

Cell vacuole (plants)

Answer 13

membrane (tonoplast) bound organelle found in cytoplasm
contains cell sap
helps to maintain pressure in cell and keep it rigid which stops plants wilting

Question 14

What are prokaryotic cells?

Answer 14

small, simple, single celled organisms with no nucleus and no membrane bound organelles
70s ribosomes
dna not associated with histones / no chromosomes
replicate by binary fission
eg bacteria
cell wall of murien/ glycoprotein

Question 15

Flagellum

Answer 15

long, hair like structure that helps the cell move

Question 16

DNA

Answer 16

cells have single circular DNA molecule that floats freely in cytoplasm

Question 17

Cell wall

Answer 17

supports cell, prevents cell from changing shape

made from glycoprotein

Question 18

Capsule

Answer 18

made up of secreted slime

helps protect bacteria from attack

Question 19

Plasmid

Answer 19

small loops of DNA that aren’t part of the main DNA molecule

contain genes for antibiotic resistance

Question 20

How do prokaryotic cells replicate?

Answer 20

by binary fission- cell replicates its genetic material then splits into two daughter cells
1-circular DNA and plasmids replicate
2-cell gets bigger and DNA moves to opposite poles
3-cytoplasm divides
4-producing 2 daughter cells containing a copy of DNA
RODD
replicate, opposite poles, divide, daughter cells DNA

Question 21

What are viruses?

Answer 21

they are acellular (not cells) and non living
they are nucleic acid surrounded by proteins
invade and reproduce inside host cells

Question 22

What is the structure of viruses?

Answer 22

they havent got a membrane, cytoplasm or ribosomes
they have a lipid envelope
attachment proteins which allow them to cling onto a host cell
capsid which protect the nucleic acid from digestion

Question 23

How does viral replication occur?

Answer 23

the virus attaches to the host cell surface using attachment proteins
they release their genetic material into the cell
the genetic material is replicated by host cell machinery
the viral components assemble
the replicated virus is released from the host cell

Question 24

What is cell fractionation?

Answer 24

separating organelles in cells
homogenisation
filtration
ultracentrifugation

Question 25

What is homogenisation?

Answer 25

breaking open of cells with a homogeniser to release organelles
solution must be ice cold to reduce activity of enzymes
solution must be isotonic to prevent organelles bursting or shrinking
a buffer solution should be added to prevent pH from fluctuating

Question 26

Why is the homogenate filtered?

Answer 26

to remove large cell or tissue debris

organelles are much smaller so can pass through

Question 27

What is ultracentrifugation?

Answer 27

the process used to separate organelle
filtered solution is poured into a tube and spun in a centrifuge
the heaviest organelles (nuclei) go to the bottom
the rest of the organelles stay suspended in the supernatant
this supernatant is drained off and spun again and the process is repeated at higher and higher speeds until all the organelles are separated out

Question 28

How are the organelles separated?

Answer 28

through ultracentrifugation
they are separated in order of mass (heavy to light)
nucleus-(chloroplasts)- mitochondria- lysosymes - RER- ribosomes
the speed is faster for each round of centrifugation

Question 29

mitosis

Answer 29

produces two genetically identical daughter cells

allows damaged tissues to be repaired and new tissue can grow

Question 30

interphase

Answer 30

cell increases in mass and size, replicates DNA
g1 phase- growth phase
s phase- synthesis of DNA by dna replication
g2 phase- another growth phase, cell increases in size, cell replicates its organelles
become chromatids due to dna replication

Question 31

prophase

Answer 31

chromosomes become short and fat (can be seen with microscope)
chromosomes are sister chromatids joined by centromere
nuclear envelope disappears
protein fibres form spindle in cell

Question 32

metaphase

Answer 32

spindle fibres attach to centromere

chromatids line up on the equator of the cell

Question 33

anaphase

Answer 33

centromere divides
spindle fibres shorten
chromatids move to opposite poles of the cell

Question 34

telophase

Answer 34

chromosomes collect at opposite ends
new nuclear envelope forms around chromosomes
chromosomes become long and thin

Question 35

cytokinesis

Answer 35

cytoplasm divides to form 2 daughter cells
genetically identical to eachother and parent
23 pairs of chromosomes

Question 36

homologous chromosomes

Answer 36

chromosomes with same size/appearance

same genes at same loci present

Question 37

mitotic index

Answer 37

number of cells undergoing mitosis/total number of cells
can be used to calculated time spent in certain stage
number of cells in stage x time / total number of cells

Question 38

mass/number of dna and chromosomes

Answer 38

number of chromosomes= count no of centromere
m-4 a- 8 cy- 4
number of dna= count no of chromatids
m- 8 a- 8 cy- 4
dna increases in s phase due to replication
dna decreases when cell divides
chromosome number changes when sister chromatids separate
mitosis- anaphase
meiosis- anaphase 2

Question 39

chromatids

Answer 39

homologous chromosomes ( one maternal and one paternal) divide and form sister chromatids
each chromosome is a chromatid and when they join by centromere they are sister chromatids
when mitosis ends, the chromatids end up as single chromosomes
1 paternal and 1 maternal chromosome in each cell

Question 40

euk vs pro dna

Answer 40

similar- same nucleotide structure, joined by pd bonds
different- linear vs circular
associated with histones vs not 
in nucleus vs free floating 
plasmids vs no plasmids
introns vs no introns

Question 41

accurate calculations

Answer 41

repeat to calculate a mean
take a large sample to ensure it is representative
repeat to ensure there are no errors

Question 42

bacteria

Answer 42

produce dipeptidases
to digest proteins
to use amino acids for growth/ protein synthesis
or to destroy a damaging protein

Question 43

cancerous cells mitosis

Answer 43

more cells will be in mitosis stages eg PMAT
less cells will be in interphase
cells are dividing more rapidly, more mitosis is occurring

Question 44

mitosis large number of cells

Answer 44

ensure sample is representative