2.1 Cell Structure

Question 1

what are the distinguishing features of eukaryotic cells

Answer 1

-cytoplasm containing membrane-bound organelles
-so DNA enclosed in a nucleus

Question 2

which cells have similar structures to plant cells

Answer 2

-algal cells
-fungal cells

Question 3

describe the structure of the cell surface membrane

Answer 3

-hydrophilic phosphate heads that are attracted to water
-hydrophobic fatty acid tails that repel water
-which both make up a phospholipid
-phospholipid bilayer
-proteins

Question 4

describe the function of the cell surface membrane

Answer 4

-selectively permeable → enables control of passage of substances in / out of cell
-molecules / receptors / antigens on surface → allow cell recognition / signalling

Question 5

describe the structure of the nucleus

Answer 5

-nuclear envelope
with double membrane
has nuclear pores
-nucleoplasm
-nucleolus (dense region)
-protein/histone bound, linear DNA
chromatin = condensed
chromosome = highly condensed

Question 6

describe the function of the nucleus

Answer 6

-holds / stores genetic information which codes for polypeptides (proteins)
-site of DNA replication
-site of transcription (part of protein synthesis), producing mRNA
-nucleolus makes ribosomes / rRNA

Question 7

describe the structure of a ribosome

Answer 7

-made of ribosomal RNA and protein (two subunits)
-not a membrane-bound organelle

Question 8

describe the function of a ribosome

Answer 8

-site of protein synthesis (translation)

Question 9

describe the structure of rER and sER

Answer 9

-ribosomes
-systems of membranes

Question 10

describe the function of rER

Answer 10

-ribosomes on surface synthesise proteins
-proteins processed / folded / transported inside rER
-proteins packaged into vesicles for transport eg. to golgi apparatus

Question 11

describe the function of sER

Answer 11

-synthesises and processes lipids
-eg. cholesterol and steroid hormones

Question 12

describe the structure of golgi apparatus and vesicles

Answer 12

golgi apparatus = flattened membrane sacs
golgi vesicle = small membrane sac

Question 13

describe the function of the golgi apparatus

Answer 13

-modifies protein, eg. adds carbohydrates to produce glycoproteins
-modifies lipids, eg. adds carbohydrates to make glycolipids
-packages proteins / lipids into golgi vesicles
-produces lysosomes (a type of golgi vesicle)

Question 14

describe the function of golgi vesicles

Answer 14

-transports proteins / lipids to their required destination
-eg. moves to and fuses with cell-surface membrane

Question 15

describe the structure of lysosomes

Answer 15

-membrane
-hydrolytic enzymes

Question 16

describe the function of lysosomes

Answer 16

-release hydrolytic enzymes (lysozymes)
-to break down / hydrolyse pathogens or worn-out cell components

Question 17

describe the structure of mitochondria

Answer 17

-outer membrane
-cristae -inner membrane fold
-matrix containing 70s ribosomes and circular dna

Question 18

describe the function of mitochondria

Answer 18

-site of aerobic respiration
-to produce ATP for energy release
-eg. for protein synthesis / vesicle movement / active transport

Question 19

describe the structure of chloroplasts in plants and algae

Answer 19

-double membrane
-stroma containing
●thylakoid membrane
●70s ribosomes
●circular dna
●starch granules/lipid droplets
-lamella - thylakoid linking grana
-grana - stacks of thylakoid

Question 20

describe the function of chloroplasts in plants and algae

Answer 20

-absorbs light energy for photosynthesis
-to produce organic substances eg. carbohydrates / lipids

Question 21

describe the structure of the cell wall in plants, algae and fungi

Answer 21

-composed mainly of cellulose (a polysaccharide) in plants / algae
-composed of chitin (a nitrogen-containing polysaccharide) in fungi

Question 22

describe the function of the cell wall in plants, algae and fungi

Answer 22

-provides mechanical strength to cell
-so prevents cell changing shape or bursting under pressure due to osmosis

Question 23

describe the structure of the cell vacuole in plants

Answer 23

-tonoplast membrane
-cell sap

Question 24

describe the function of the cell vacuole in plants

Answer 24

-maintains turgor pressure in cell (stopping plant wilting)
-contains cell sap → stores sugars, amino acids, pigments and any waste chemicals

Question 25

describe how eukaryotic cells are organised in complex multicellular organisms

Answer 25

-specialised for specific functions -tissue -organ -organ system

Question 26

define tissue

Answer 26

-group of specialised cells with a similar structure working together to perform a specific function, often with the same origin

Question 27

define organ

Answer 27

-aggregations of tissues performing specific functions

Question 28

define organ system

Answer 28

-group of organs working together to perform specific functions

Question 29

suggest how you can apply your knowledge of cell features / organelles to explain adaptations of eukaryotic cells

Answer 29

-general answer format: -[Named cell] has many [named organelle, eg. ribosomes] -to [link organelle function to cell function eg. increase rate of protein synthesis, making many antibodies]

Question 30

what are the distinguishing features of prokaryotic cells

Answer 30

-cytoplasm lacking membrane-bound organelles -so genetic material not enclosed in a nucleus

Question 31

examples of prokaryotic cells

Answer 31

-bacteria -archaea

Question 32

describe the general structure of prokaryotic cells

Answer 32

-cell surface membrane -cell wall (containing murein) -cytoplasm -70s ribosomes -circular DNA (free in cytoplasm and not associated with proteins) and sometimes -capsule -plasmids -flagella

Question 33

compare and contrast the structure of eukaryotic and prokaryotic cells

Answer 33

eukaryotic cell -has membrane-bound organelles -has a nucleus containing DNA -DNA is long & linear & associated with histone proteins -larger (80S) ribosomes (in cytoplasm) -cell wall only in plants, algae and fungi containing cellulose or chitin -plasmids / capsule never present (sometimes flagella) -larger overall size prokaryotic cell -no membrane-bound organelles -no nucleus DNA is is free in cytoplasm -DNA is short & circular & not associated with proteins -smaller 70s ribosomes -cell wall in all prokaryotic cells containing murein, a glycoprotein -plasmids, flagella and a capsule sometimes present -much smaller overall size

Question 34

explain why viruses are described as acellular and non-living

Answer 34

-acellular - not made of cells, no cell membrane / cytoplasm / organelles -non-living - have no metabolism, cannot independently move / respire / replicate / excrete

Question 35

describe the general structure of a virus particle

Answer 35

1. nucleic acids (RNA or DNA) surrounded by a capsid (protein coat) 2. attachment proteins allow attachment to specific host cells 3. no cytoplasm, ribosomes, cell wall, cell-surface membrane etc 4. some also surrounded by a lipid envelope eg. HIV