TOPIC 2A-CELL STRUCTURE AND DIVISION

Question 1

A) Outline what “prokaryotes” and “euakryotes” are and state some examples

Answer 1

A)-prokaryotic organisms are prokaryotic cells which are smaller + simpler (i.e: single celled organisms)

• ->E.G: bacteria
• euakaryotic organisms are made of eukaryotic cells they are more complex
• ->E.G: include all animal + plant cells as well as all cells in algae + fungi

Question 2

B) What are “organelles”?

Answer 2

B)-parts of cells–>each has specific function

-both eukaryotes + prokaryotes contain organelles.

Question 3

A) State all of the different parts of an ANIMAL CELL

Answer 3

A)-nucleus/nucleolus/nuclear envelope/rough endoplasmic reticulum(RER)/golgi apparatus/cytoplasm/mitochondrion/ smooth endoplasmic reticulum (SER)/lysosome/plasma (cell surface) membrane/ribosome

Question 4

B) What are the different parts of a PLANT CELL?

Answer 4

B)-all have same organelles as animal cells + some extra parts:
1-cellulose cell wall with plasmodesmata (channels for exchanging substances with adjacent cells)
2-vacuole (compartment containing cell sap)
3-chloroplasts

Question 5

C) Outline the composition of ALGAL CELLS

D) How are FUNGAL CELLS made up?

Answer 5

C)-are a lot like plant cells–>have same organelles including cell wall + chloroplasts
D)-are also a lot like plant cells BUT 2 key differences:
–>cell walls made of chitin not cellulose + don’t have chloroplasts (as don’t photosynthesis)

Question 6

For all of the following organelles describe each one and outline their function:

A) CELL-SURFACE (PLASMA) MEMBRANE

Answer 6

A)1-membrane found on surface of animal cells + just inside cell wall of others cells
–>mainly made of proteins + lipids
2-regulates movement of substances in + out of cell
–>also has receptor molecules on it which allow it to respond to chemicals like hormones.

Question 7

B) NUCLEUS

Answer 7

B)1-large organelle surrounded by nuclear envelope (double membrane) that contains many pores
-contains chromosomes that made from protein-bound linear DNA + 1+ structures called a nucleolus
2-nucleus controls cell’s activities (via controlling DNA transcription)
DNA contains instructions to make proteins
-pores let substances (e.g: RNA) to move between nucleus + cytoplasm
-nucleolus makes ribosomes.

Question 8

C) MITOCHONDRION

Answer 8

C)1-usually oval-shaped
-have double membrane–>inner one folded to form cristae–>inside is matrix (contains enzymes involved in respiration)
2-site of aerobic respiration where ATP produced
-found in large numbers in cells that v. active + needs lots energy.

Question 9

D) CHLOROPLASTS

Answer 9

D)1-small +flattened structures found in plant + algal cells
-surrounded by double membrane + membranes inside-thylakoid membranes
–>these membranes stacked in some parts of chloroplasts to form grana
-grana–>linked together via lamellae–>thin flat pieces of thylakoid membrane
2-photosynthesis site–>some parts of photosynthesis occurs in grana and others occur in stroma (thick fluid in chloroplasts)

Question 10

E) GOLGI APPARATUS

Answer 10

E)1-group of fluid-filled membrane bound flattened sacs
-vesicles often found at edges of sacs
2-processes and packages new lipids + proteins
-also makes lysosomes.

Question 11

F) GOLGI VESICLE

Answer 11

F)1-small fluid-fileld sac in cytoplasm surrounded by membrane + produced by golgi apparatus
2-stores lipids + proteins made by golgi apparatus and transports them out of cell (via cell-surface membrane).

Question 12

G) LYSOSOME

Answer 12

G)1-round organelle surrounded by membrane with no clear internal structure
–>is type of golgi apparatus
2-stores lipids + proteins made by golgi apparatus and transports them out of cell (via cell-surface membrane).

Question 13

H) RIBOSOME

Answer 13

H)1-v. small organelle that either floats free in cytoplasm OR attached to RER
–>made up of proteins + RNA
-not surrounded by a membrane
2-site of protein synthesis.

Question 14

I) ROUGH ENDOPLASMIC RETICULUM (RER)

Answer 14

I)1-system of membranes enclosing fluid-filled space
-surface covered with ribosomes
2-folds + processes proteins that have been made at ribosomes.

Question 15

J) SMOOTH ENDOPLASMIC RETICULUM (SER)

Answer 15

J)1-similar to RER but with no ribosomes

2-synthesis + processes lipids

Question 16

K) CELL WALL

Answer 16

K)1-rigid structure surrounds cells in plants/algae + fungi
-in plants + algae its made mainly of carbohydrate cellulose
–>its fungi made of chitin
2-supports cells + prevents them changing shape.

Question 17

A) Briefly explain “cell specialization” in multicellular eukaryotic organisms

B) How may knowledge of organelles be needed to explain why a specialised cell is particularly suited to it’s function?

Answer 17

A)-cells become specialized to carry out particular function
-a cell’s structure (i.e: it’s shape + organelles it contains) helps it to carry out particular function
–>therefore depending on a cell’s job a specialised cell can look v. different to cells shown previously.
B)-will have to think about what organelles cell needs to do it’s job
–>e.g: if cell uses lot’s energy it will need lots mitochondria
–>if it makes lots of proteins it will need lots of ribosomes.

Question 18

B) EXAMPLE: Explain how epithelial cells in the small intestine are specialized to absorb food efficiently

Answer 18

B)1-small intestine walls have lot’s finger-like projections-villi
–>they increase S.A for absorption
2-epithelial cells on villi surface have folds in their cell-surface membranes-microvilli
–>microvilli increase S.A even more
3-also have lots mitochondria–>to provide energy fro digested food molecule’s transport in to cell.

Question 19

A) Outline what the following are in multicellular eukaryotic organisms:
1-tissues
2-organ
3-organ system

B) How does the digestive system form from the basics of an epithelial cell?

Answer 19

A)1-specialised cells grouped together to perform a particular function
2-different tissues work together to form organs
3-different organs work together to form organ system
B)-epithelial cells–>make epithelial tissue
-epithelial tissue + muscular tissue + glandular tissue (secretes chemicals) all work together to form stomach (organ system)
-stomach part of digestive system–> this is organ system made of all organs involved in digestion + absorption of food (including small intestine/large intestine + liver).

Question 20

A) Describe each of the following structures in the following prokaryotic bacterial cell:

1-CYTOPLASM
2-PLASMA MEMBRANE
3-CELL WALL

Answer 20

A)1-no membrane-bound organelle (unlike eukaryotic cell)
-has ribosomes but smaller than those in eukaryotic cells
2-same as eukaryotic cells–>mainly made of lipids + proteins
–>controls movement of substances in + out of cell
3-supports cell + prevents it changing shape
–>it’s mainly made of polymer murein (protein with a carbohydrate attached).

Question 21

4-FLAGELLUM (PLURAL FLAGELLA)

5-NUCLEUS

Answer 21

4-long hair-like structure that rotates to make prokaryotic cell move
-not all prokaryotes have have flagellum some have 1+.
5-prokaryotic cell doesn’t have nucleus
–>instead DNA floats free in cytoplasm
–>it’s circular DNA present as 1 coiled up strand
–>not attached to any histone protein

Question 22

6-PLASMIDS

7-CAPSULE

Answer 22

6-small loops of DNA not part of main circular DNA molecule
-plasmids contain genes for things like antibiotic resistance + can be passed between prokaryotes
-plasmids not always present in prokaryotic cells
–>some prokaryotic cells have several.
7-some prokaryotes like bacteria have this–>it’s made up of secreted slime
–>helps protect bacteria from attack by cells of immune system.

Question 23

A) Briefly explain the what a virus is and outline it’s structures and how they work

B) What are “host cells”?

Answer 23

A)-are nucleic acids surrounded by proteins-not alive
-even smaller than bacteria–>E.G: HVI is about 0.1 micrometers across
-unlike bacteria have no plasma membrane/cytoplasm/ribosomes
B)-a virus is one of them–>they invade + reproduce inside cells of other organisms.

Question 24

A) What is “binary fission”?

Answer 24

A)-prokaryotic cell replicates it’s genetic material before physically splitting in to 2 daughter cells.

Question 25

B) Describe each step of binary fission

Answer 25

B)1-circular DNA + plasmid(s) replicate
–>main DNA loop only replicated once BUT plasmids may be replicated many times
2-cell bigger + DNA loops move to opposite ends of cell
3-cytoplasm begins to divide (and new cell walls begin to form)
4-cytoplasm divides–> 2 daughter cells produced
–>each daughter cell has 1 copy of the circular DNA bu may have variable n.of plasmid(s) copies.

Question 26

A) How do viruses attach to the surface of host cells?

B) Why can some viruses only infect one cell type (but others can infect lots of different cells)?

Answer 26

A)-they use their attachment proteins to bind to complementary receptor proteins on surface of host cells
B)-this is as different viruses have different attachment proteins so require different receptor proteins on host cells

Question 27

A) Define the term “magnification”

B) What is the magnification formula?

C) EXAMPLE: If you have magnified an image that’s 5mm wide and your specimen is 0.05 mm wide work out the magnification

D) When working with the magnification what must you make sure?

Answer 27

A)-is how much bigger image is than the specimen (sample looking at)
B)-magnification=image size/real object size
C)-it will be 5/0.05=x100
D)-if given image size and object size in different units make sure to convert them in to same units before using formula.

Question 28

A) Define the term “resolution”

Answer 28

A)-this is how detailed image is

• ->how well microscope able to distinguish between 2 points that close together
• if microscope lens unable to separate 2 objects–> increasing magnification wont help.

Question 29

A) Explain how optical (light) microscopes work and it’s features

Answer 29

A)-use light to form image

• have max resolution of about 0.2 (um)–>means can’t use optical microscope to view organelles smaller than 0.2um
• ->includes ribosomes/endoplasmic reticulum + lysosomes
• ->may be able to make out mitochondria BUT not perfect detail + can see nucleus
• max useful magnification is x1500.

Question 30

B) Similarly, explain how electron microscopes work and it’s features

C) How do you convert between um and mm?

Answer 30

B)-use electrons to form image
-have higher resolution than light microscopes so produce more detailed image (+ can look at more organelles)
-have max resolution of about 0.0002 um (about 100x higher than optical microscopes)
-max useful magnification of an electron microscope is about x1500000.
C)- 1 um is 3x smaller than 1 mm (1um=0.001mm)
-um to mm–>divide by 1000.

Question 31

A) Explain how “Transmission Electron Microscopes (TEM)” and it’s key features

Answer 31

A)-they use electromagnets to focus electron beam which is then transmitted through specimen

• denser parts of specimen absorb more electrons–>so look darker on image end up with
• TEM’s good as give high resolution images so can see internal structures of organelles like chloroplasts
• -> BUT only able to be used on thin specimens

Question 32

B) Explain the functioning of “Scanning Electron Microscopes (SEM’s)” and outline their features

Answer 32

B)-SEM’s scan beam of electrons across specimen

• ->knocks electrons off from specimen which gathered in cathode ray tube to form image
• images end up with show surface of specimen + can be 3D
• SEM’s good as can be used on thicker specimens
• ->BUT give lower resolution images than TEM’s.

Question 33

A) Outline and explain the steps you would follow to prepare a “temporary mount” of a specimen slide

Answer 33

A)1-pipette small water drop on to slide (clear glass strip)
–>then place thin section of specimen on top of water drop using tweezers
2-add stain drop to highlight objects in a cell–>E.G: eosin used to make cytoplasm show up
–>iodine in potassium iodine solution used to stain starch grains in plant cells
3-finally add cover slip (clear plastic square)
–>to do this stand slip upright on slide next to water droplet and carefully tilt + lower to cover specimen
–>try avoiding any air bubbles getting in as will obstruct view.

Question 34

A) What is “cell fractionation”?

STEP 1: HOMEGENISATION

B) What is homegenisation and how may it be done?

Answer 34

A)-this technique used if want to look at some organelles under electron microscope
–>first need to separate them from rest of cell
B)-it’s breaking up of cells (the plasma membrane) which releases organelles into solution
–>can be done in several ways like vibrating cells/grinding cells up in blender.

Question 35

C) Explain why the following conditions must be kept for homegenisation:
1-ice-cold
2-isotonic
3-buffer solution added

Answer 35

C)1-to redeuce enzyme activity that break organelles down
2-this means it should have same conc of chemicals as cells being broken down to prevent organelle damage via osmosis
3-to maintain pH.

Question 36

STEP 2: FILTRATION

A) What is filtration and it’s purpose?

Answer 36

A)-homogenised solution filtred through gauze to separate large cell debris/tissue debris like conncective tissue from organelles
–>organelles much smaller than debris so pass through gauze.

Question 37

STEP 3: ULTRACENTRIFUGATION

A) Define ultracentrifugation

B) Describe and explain the “first spinning” in the centrifuge

Answer 37

A)-after filtration left with solution containing mixture of organelles
–>ultracentrifugation used to separate particular organelle from all others.
B)-cell fragments poured in to tube–>this then put in to cntrifuge (spinning machine that separates materials) and spun at low speed
–>heaviest organelles like nuclei flung to bottom
–>they form thick sediment at bottom-pellet
–>rest of organelles stay suspended in fluid above sediment–>supernatant.

Question 38

D) What results are produced as the process above is repeated at higher and higher speeds?

A) What is the order of the organelle separation according to size?

Answer 38

D)-eventually all organelles separated out
–>each time pellet at bottom of tube is made up of lighter an lighter organelles.

A)-lysosome–>0.1 um (diameter)

• mitochondrion–>2 um (diameter)
• nuceleus–> 5 um (diameter)
• ribosome–> 0.02 um (diameter)
• vesicle–> 0.05 um (diameter)

Question 39

A) What are the 2 types of cell division in eukaryotes?

B) Define mitosis

C) What is the purpose of mitosis?

D) Is the ability to divide via mitosis kept by all multicelluar organisms?

Answer 39

A)-mitosis and meiosis
B)-a parent cell divides to produce 2 genetically identical daughter cells (contain exact copy of parent cell DNA)
C)-needed for growth of multicellular organisms (like us) + for damaged tissue repair
D)-no–>the ones that do follow the cell cycle

Question 40

E) In brief describe the cell cycle

F) Briefly outline each of the following parts of the cell cycle:

1-MITOSIS
2-GAP PHASE 1
3-SYNTHESIS
4-GAP PHASE 2

Answer 40

E)-it consists of period of cell growth + DNA replication called interphase
–>mitosis occurs after that
-interphase (cell growth) subdivided into 3 separate growth stages called G1/S/G2.
F)1-cell cycle starts here
2-cell grows + new organelles and proteins made
3-cell replicates it’s DNA ready to divide via mitosis
4-cell keeps growing + proteins needed for cell division made.

Question 41

A) Outline the 4 mitosis stage and the phase that comes before it

B) Describe INTERPHASE

Answer 41

A)-mitosis: prophase/metaphase/anaphase/telophase
-before mitosis comes interphase in cell cycle
B)-cell carries out normal functions + prepares to divide
–>cell’s DNA unravels + replicates to double genetic material
-organelles also replicated so it has spare ones + it’s ATP increased
–>ATP provides energy needed for cell division

Question 42

C) What happens during PROPHASE.? Explain in appropriate detail

Answer 42

C)-chromosomes condense + get shorter as well as fatter

• tiny protein bundles (centrioles) start to move to opposite ends cell to form network of protein fibres across it called the spindle
• ->also nuclear envelope (membrane around nucleus) breaks down–>chromosomes free in cytoplasm.

Question 43

D) Define the following terms and state what happens to chromosomes during mitosis:
1-centromere
2-chromatids

Answer 43

D)1-as mitosis begins chromosomes made of 2 strands joined in middle by centromere
2-separate strands called chromatids
-there are 2 strands as each chromosome has already made identical copy of itself during interphase
–>when mitosis over chromatids end up one-strand chromosomes in daughter cell.

Question 44

E) Describe METAPHASE in mitosis

F) Briefly explain the ANAPHASE of mitosis

Answer 44

E)-chromosomes (each with 2 chromatids) line up along middle of cell and become attached to spindle by their centromere
F)-centromeres divide–>separating each sister chromatid pair
–>spindles contract to pull chromatids to opposite poles of spindle via centromere first
–>this makes chromosomes appear V-shaped.

Question 45

G) Outline and explain the final stage of mitosis-TELOPHASE

Answer 45

G)-chromatids reach opposite poles on spindle

• ->they uncoil + become long and thin again–>now called chromosomes again
• ->nuclear envelope forms around each chromosome group of chromosomes–>2 nuclei now
• ->cytoplasm divides (cytokinesis) so now have 2 daughter cells genetically identical to original + each other
• ->mitosis finished + each daughter cell starts interphase part of cell cycle to get ready for next mitosis round.

Question 46

Calculating how long each stage of mitosis lasts:

A)EXAMPLE: A scientist observes section of growing tissue under microscope. He counts 100 cells undergoing mitosis from which 10 are in metaphase. One complete cell cycle of tissue lasts 15 hours. How long does cell spend in metaphase? Give answer in minutes

Answer 46

A)1-scientist has observed 10/100 cells in metaphase–> suggests proportion of cells in metaphase from cell cycle is 10/100
2-told cell cycle lasts 15 hours (1560=)900min
3-so cells spend (10/100)900=90 min in metaphase.

Question 47

A) How is mitosis and the cell cycle controlled?

B) Define a “mutation”

C) Outline how a mutation may affect the cell cycle

D) Consequently, how may this result in cancer?

Answer 47

A)-are controlled by genes
B)-changes in base sequence of an organism’s DNA
C)-normally when cells have divided enough times to make enough new cells they stop
–>a mutation in gene that controls cell division could make cells grow out of control.
D)-therefore, the cell keeps dividing to make more and more cells which forms a tumour
–>cancer is a tumour that invades surrounding tissue.

Question 48

A) Give a brief outline how cancer treatments that target the cell cycle work

Answer 48

A)-they are designed to control rate of cell division in tumour cells by distrupting cell cycle–>kill tumour cells

• ->treatments not distinguish tumour cells from normal cells–>also kill normal body cells that are dividing
• ->but tumour cells divide more frequently than normal cells so treatments more likely to kill tumour cells.

Question 49

B) Explain how the G1 (cell growth and protein production) target of cancer treatment works

Answer 49

B)-some chemical drugs (chemotherapy) prevent synthesis of enzymes needed for DNA replication
–>if these not produced cell unable to enter synthesis phase (S)–>disrupts cell cycle–>forces self-destruction of cell

Question 50

C) Similarly, explain how the S phase (DNA replication) target of cancer treatment works

Answer 50

C)-radiation + some drugs damage DNA

• ->at several points in cell cycle (including just before + during S phase) DNA in the cell checked for damage
• ->if severe damage detected–>cell will kill itself
• ->prevents further tumour growth.

Question 51

The experiment can be carried out using a root tip to observe the stages of mitosis:

A) Outline the steps which must be followed to PREPARE a root tip up to the point to just before staining it

Answer 51

A)1-cut 1 cm from growing root tip (e.g: of an onion)
–>needs to be tip as that’s where growth occurs (and so mitosis occurs) if ethano-orcein used to stain cells tips also need to be fixed in ethanoic acid
2-prepare boiling tube with 1M HCL and place in water bath at 60 degrees C
3-transfer root tip to boiling tube–>incubate for 5 min
4-pipette cold water to rinse root tip well–>leave tip to dry on paper towel
5-place root tip on microscope slide and cut 2mm from tip–>get rid of rest
6-use mounted needle to break tip open + spread cells out thinly.

Question 52

A) Define “mitotic index”

B) What is the mitotic index formula?

Answer 52

A)-proportion of cells undergoing mitosis

B)-mitotic index= n.of cells with visible chromosomes/total n.of cells observed.

Question 53

C) How is information from the mitotic index used?

Answer 53

C)-lets you work out how quickly tissue growing + if there is anything abnormal going on

• a plant root tip is constantly growing so would expect high mitotic index (i.e: lots of cells in mitosis)
• ->in other tissue samples high mitotic index could mean tissue repair taking place OR there is cancerous growth in tissue.

Question 54

A) Outline what an “eyepiece graticule” and “stage micrometer” is

Answer 54

A)-eyepiece graticule: fitted on to eyepiece

• ->its type of transparent ruler with numbers BUT no units
• stage micrometer: placed on stage
• ->its a microscope slide with accurate scale (has units) and is used to work value of divisions on eyepiece graticule at particular magnification

Question 55

B) What is the use of the two experimental equipment described above?

Answer 55

B)-they are used to calculate the size of cells looking at
–>when take stage micrometer away and replace with slide containing your tissue sample you are able to measure size of cells.

Question 56

C) EXAMPLE: Measure the size of the cell given in the diagram (with reference to diagram with this card)

Answer 56

C)1-line up eyepiece graticule + stage micrometer
2-each division on stage micrometer is 0.1mm long
3-at this magnification, 1 division on stage micrometer is same as 4.5 divisions on eyepiece graticule
4-to work out size of 1 division on eyepiece graticule need to divide 0.1/4.5=0.022mm
5-so if look at cell under microscope at this magnification and it’s 4 eyepiece divisions long you know it measures 4*0.022=0.08mm

Question 57

D) If you are given an image if cells under the microscope how may you calculate their actual size?

E) EXAMPLE: If the image of a cell measures 5mm and the magnification is x100 what would the actual size of the cell be?

Answer 57

D)-using magnification formula–>actual size= image size/mangification
E)- using the formula it would be 5/100=0.05mm

Question 58

A) What are artefacts and outline the possibility of what artefacts could be

B) How are artefacts made and how must you avoid them?

Answer 58

A)-are things that you can see down microscope that not part of cell/specimen looking at
–anything from dust bits/ air bubbles/ fingerprints to inaccuracies caused by squashing + staining your sample
B)-made during preparation of slides–>shouldn’t be there so need to prepare root tip cells carefully to avoid creating artefacts.

Question 59

C) Why are artefacts especially common in micrographs?

D) How did scientists that first used electron microscopes struggle with viewing the correct organelles under the microscope?

Answer 59

C)-this is as specimens need lots of preparation before can view them under electron microscope
D)-they could only distinguish between artefacts and organelles by repeatedly preparing specimens in different ways
–>if object could be seen with one preparation technique BUT not other it was more likely to be artefact than organelle.