biology paper 1

Question 1

state the relationship between systems and specialised cells

Answer 1

specialised cells form tissues that perform a specific function which creates organs of a specific tissue type which then forms organ systems

Question 2

describe the structure and function of the cell-surface membrane

Answer 2

• phospholipid bilayers
• fluid mosaic
• extrinsic and intrinsic proteins embedded
• isolates cytoplasm from extracellular environment
• selectively permeable to regulate transport of substances
• involved in cell signalling / recognition

Question 3

explain the role of cholesterol, glycoproteins and glycolipids in the cell-surface membrane

Answer 3

cholesterol : steroid molecules connects phospholipids and reduces fluidity
glycoproteins : cell signalling, cell recognition (antigens) and binding cells together
glycolipids : cell signalling and cell recognition

Question 4

describe the structure of the nucleus

Answer 4

• surrounded by nuclear envelope, a semi-permeable double membrane
• nuclear pores allow substances to enter/exit
• dense nucleolus made of rna and proteins assembles ribosomes

Question 5

describe the function of the nucleus

Answer 5

• contains dna coiled around chromatin into chromosomes
• controls cellular processes : gene expression determines specialisation and site of mRNA transcription, mitosis, semiconservative replication

Question 6

describe the structure of a mitochondrion

Answer 6

• surrounded by double membrane folded inner membrane forms cristae : site of electron transport chain
• fluid matrix : contains mitochondrial dna, respiratory enzymes, lipids, proteins

Question 7

describe the structure of a chloroplast

Answer 7

• vesicular plastid with double membrane
• thylakoids : flattened discs stacked to form grana; contain photosystems with chlorophyll.
• intergranal lamellae : tubes attached by thylakoids in adjacent grana
• stroma : fluid-filled matrix

Question 8

state the function of mitochondria and the chloroplasts

Answer 8

mitochondria : site of aerobic respiration to produce ATP
chloroplasts : site of photosynthesis to convert solar energy to chemical energy

Question 9

describe the structure and function of the golgi apparatus

Answer 9

• modifies and packages proteins for export
• synthesises glycoproteins

Question 10

describe the structure and function of a lysosome

Answer 10

sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes glycoprotein coat protects cell interior:
- digests contents of phagosomes
- exocytosis of digestive enzymes

Question 11

describe the structure and function of a ribosome

Answer 11

formed of protein and rRNA free in cytoplasm or attached to the ER
- site of protein synthesis via translation: large subunit joins amino acids; small subunits: contains mRNA binding site

Question 12

describe the structure and function of the endoplasmic reticulum

Answer 12

cisternae: network of tubules and flattened sacs extends from cell membrane through cytoplasm and connects to nuclear envelope
- rough ER : many ribosomes attached for protein synthesis and transport
- smooth ER : lipid synthesis

Question 13

describe the structure of the cell wall

Answer 13

bacteria: made of the polysaccharide murein
plants: made of cellulose microfibrils plasmodesmata allow molecules to pass between cells, middle lamella acts as boundary between adjacent cell walls

Question 14

state the functions of the cell wall

Answer 14

• mechanical strength and support
• physical barrier against pathogens
• part of apoplast pathway (plants) to enable easy diffusion of water

Question 15

describe the structure and function of the cell vacuole in plants

Answer 15

surrounded by single membrane : tonoplast contains cell sap : mineral ions, water, enzymes, soluble pigments
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm

Question 16

explain some common cell adaptations

Answer 16

• folded membrane or microvilli increase surface area e.g. for diffusion
• many mitochondria : large amounts of ATP for active transport
• walls one cell thick to reduce distance of diffusion pathway

Question 17

state the role of plasmids in prokaryotes

Answer 17

• small of ring of DNA that carries non-essential genes
• can be exchanged between bacterial cells via conjugation

Question 18

state the role of flagella in prokaryotes

Answer 18

rotating tail propels (usually uniceullalr) organism

Question 19

state the role of the capsule

Answer 19

polysaccharide layer:
- prevents dessication
- acts as food reserve
- provides mechanical protection against phagocytosis and external chemicals
- sticks cells together

Question 20

compare eukaryotic and prokaryotic cells

Answer 20

both have:
- cell membrane
- cytoplasm
- ribosomes (don’t count as an organelle since not membrane-bound)

Question 21

contrast eukaryotic and prokaryotic cells

Answer 21

PROKARYOTIC:
- small cells and always unicellular
- no membrane-bound organelles and no nucleus
- circular dna not associated with proteins
- small ribosomes (70s ribosomes)
- binary fission - always asexual reproduction
- murein cell walls
- capsule, sometimes plasmids and cytoskeletons

EUKARYOTIC:
- larger cells and often multicellular
- always have organelles and nucleus
- linear chromosomes associated with histones
- larger ribosomes (80s ribosomes)
- mitosis and meiosis - sexual and/or asexual
- cellulose cell wall (plants) / chitin (fungi)
- no capsule, no plasmids, always cytoskeleton

Question 22

why are viruses referred to as particles rather than cells

Answer 22

• acellular and non-living : no cytoplasm, cannot self-produce, no metabolism

Question 23

describe the structure of a viral particle

Answer 23

• linear genetic material (DNA or RNA) and viral enzymes e.g. reverse transcriptase
• surrounded by capsid (protein coat made of capsomeres)
• no cytoplasm

Question 24

describe the structure of an enveloped virus

Answer 24

• simple virus surrounded by matrix protein
• matrix protein surrounded by envelope derived from cell membrane of host cell
• attachment proteins on surface

Question 25

state the role of the capsid on viral particles

Answer 25

- protect nucleic acid from degradation by restriction endonucleases - surface sites enable viral particle to bind to and enter host cells or inject their genetic material

Question 26

state the role of attachment proteins on viral particles

Answer 26

enable viral particle to bind to complementary sites on host cell : entry via endosymbiosis

Question 27

describe how optical microscopes work

Answer 27

- lenses focus rays of light and magnify the view of a thin slice of specimen - different structures absorb different amounts and wavelengths of light - reflected light is transmitted to the observer via the objective lens and the eyepiece

Question 28

outline how a student could prepare a temporary mounth of tissue for an optical microscope

Answer 28

- obtain thin section of tissue (e.g. ultratome or by maceration) - place plant tissue in drop of water - stain tissue on slide to make structures visible - add coverslip using mounted needle at 45degree to avoid trapping air bubbles

Question 29

suggest the advantages and limitations of using an optical microscope

Answer 29

ADVANTAGES: - colour image - can show living structures - affordable apparatus LIMITATIONS: - 2D image - lower resolution than electron microscopes = cannot see ultrastructure

Question 30

describe how a transmission electron microscope (TEM) works

Answer 30

- pass a high energy beam of electrons through thin slice of specimen - more dense structures appear darker since they absorb more electrons - focus image onto fluorescent screen or photographic plate using magnetic lenses

Question 31

suggest the advantages and limitations of using a TEM

Answer 31

ADVANTAGES: - electrons have shorter wavelength than light = high resolution, so ultrastructure visible - high magnification (x500,000) LIMITATIONS: - 2D image - requires a vacuum - cannot show living structures - extensive preparation may introduce artefacts - no colour image

Question 32

describe how a scanning electron microscope (SEM) works

Answer 32

- focuses a beam of electrons onto a specimen's surface using electromagnetic lenses - reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate

Question 33

suggest the advantages and limitations of using an SEM

Answer 33

ADVANTAGES: - 3D image - electrons have shorter wavelength than light = high resolution LIMITATIONS: - requires a vacuum = cannot show living structures - no colour image - only shows outer surface

Question 34

define magnification and resolution

Answer 34

magnification : factor by which the image is larger than the actual specimen resolution : smallest preparation distance at which 2 separate structures can be distinguished from one another

Question 35

explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure

Answer 35

- place micrometer on stage to calibrate eyepiece graticule - line up scales on graticule and micrometer. count how many graticule divisions are in 100 micrometers on the micrometer - length of one eyepiece division = 100 micrometer / number of divisions - use calibrated values to calculate actual length of structures

Question 37

outline what happens during cell fractionation and ultracentrifugation

Answer 37

- homogenise tissue to break open cells and release organelles - filter homogenate to remove debris - perform differential centrifugation : - spin homogenate in centrifuge - the most dense organelles in the mixture form a pellet - filter off the supernatant and spin again at a higher speed

Question 38

state the order of sedimentation of organelles during differential centrifugation

Answer 38

most dense to least dense nucleus - mitochondria - lysosomes - RER* - plasma membranes - SER* - ribosomes *RER = rough endoplasmic reticulum *SER = smooth endoplasmic reticulum

Question 39

explain why fractionated cells are kept in a cold, buffered, isotonic solution

Answer 39

cold = slow action of hydrolase enzymes buffered = maintain constant pH isotonic = prevent osmotic lysis / shrinking of organelles