2.1 and 2.2

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

Describe the structure of the cell-surface membrane:

Answer 2

Phospholipid bilayer. Hydrophilic phosphate heads point to/attracted to water and hydrophobic fatty acid tails point away/repelled from water

Question 3

Describe the function of the cell-surface membrane:

Answer 3

Selectively permeable- enables control of passage of substances in/out cell

Molecules/receptors/antigens on surface- allow cell recognition and signalling

Question 4

Describe the structure of the nucleus

Answer 4

Nuclear envelope
- double membrane
- nuclear pores

Nucleoplasm
Nucleolus
Protein/histone bound DNA
- chromatin condensed
Chromosome- highly condensed

Question 5

Describe the function of the nucleus:

Answer 5

Holds/stores genetic info which codes for polypeptides (proteins)
Site of DNA replication
Site of transcription, producing mRNA
Nucleolus makes ribosomes/rRNA

Question 6

Describe the structure of a ribosome:

Answer 6

Made of ribosomal RNA and protein
Not a membrane-bound organelle

Question 7

Describe the function of a ribosome:

Answer 7

Site of protein synthesis (translation)

Question 8

Describe the function of rough (rER) and a smooth endoplasmic reticulum:

Answer 8

rER: ribosomes on surface synthesis proteins
proteins processed/folded/transported inside rER
proteins packaged into vesicles for transport

sER: synthesises and processes lipids e.g. cholesterol and steroid hormones

Question 9

Describe the structure of the golgi apparatus and vesicles:

Answer 9

Flattened membrane sac. Vesicle is small membrane sac

Question 10

Describe the function of the golgi apparatus and golgi vesicles:

Answer 10

Modifies proteins
modifies lipids
packages proteins/lipids into vesicles
produces lysosomes

vesicles transport proteins/lipids to their required destination, moves and fuses with cell membrane

Question 11

Describe the structure and function of lysosomes:

Answer 11

Type of vesicle with hydrolytic enzymes
Release hydrolytic enzymes (lysozymes) to break down/hydrolyse pathogens or worn-out cell components

Question 12

Describe the structure of mitochondria:

Answer 12

Outer membrane, inner folded membrane (cristae), matrix containing 70s ribosomes and circular DNA

Question 13

Describe the function of mitochondria:

Answer 13

SIte of aerobic respiration
To produce ATP for energy release

Question 14

Describe the structure of chloroplasts in plants/algae:

Answer 14

Double membrane
Stroma containing thylakoid membrane, 70s ribosomes, circular DNA, starch granules
Lamella- thylakoid linking grana
Grana- stacks of thylakoid

Question 15

Describe the function of chloroplasts in plants/algae

Answer 15

Absorbs light energy for photosynthesis
To produce organic substances

Question 16

Describe the structure and function of the cell wall in plants, algae and fungi

Answer 16

In plants/algae composed mainly of cellulose
In fungi composed of chitin

provides mechanical strength to cell, so prevents cell changing shape or bursting under pressure

Question 17

Describe the structure and function of cell vacuole:

Answer 17

Tonoplast membrane, contains cell sap

Maintains turgor pressure in cell
Contains cell sap- stores sugars, amino acids, pigments and any waste chemicals

Question 18

Describe how eukaryotic cells are organised in complex multicellular organisms:

Answer 18

Tissue- group of specialised cells with a similar structure, working together to perform a specific function, often with same origin
Organ- aggregations of tissues, performing specific functions
Organ system- group of organs working together to perform specific functions

Question 19

What are the distinguishing features of prokaryotic cells?

Answer 19

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

Question 20

Describe the structure of prokaryotic cells:

Answer 20

ALWAYS: cell surface membrane, murein cell wall, 70s ribosomes, circular DNA

SOMETIMES: Capsule, plasmids and flagella

Question 21

Why are viruses described as acellular and non-living?

Answer 21

Acellular- not made of cells, no cell membrane/cytoplasm/organelles
Non-living - no metabolisms, cannot independently respire/move/replicate/excrete

Question 22

Describe the general structure of a virus particle:

Answer 22

Nucleic acids surrounded by a capsid
Attachment proteins allow attachment to specific host cells
No cytoplasm, ribosome, cell wall, cell membrane etc
Some also surrounded by a lipid envelope

Question 23

Define magnification and resolution:

Answer 23

Magnification= number of times greater image is than size of real object
Magnification=image/actual

Resolution= minimum distance apart 2 objects can be to be distinguished as separate objects

Question 24

How does an optical microscope work?

Answer 24

Light focused using glass lenses, passes through specimen and different structures absorb different amounts and wavelengths
Generates a 2d image of a cross section
Low resolution due to long wavelengths
Can’t see internal structures of organelles or ribosomes
Specimen=thin
Low magnification x1500
Can view living organisms
simple prep
colour

Question 25

How do TEM work?

Answer 25

Electrons focused using electromagnets Pass through specimen, darker parts absorb more and appear darker Generates a 2D image of a cross sections Very high resolution due to short wavelength Can see internal structures of organelles and ribosomes Specimen=very thin High magnification x1000000 Dead/dehydrate specimens as uses a vacuum Complex prep so artefacts often present No colour

Question 26

How does an SEM work?

Answer 26

electrons focused using electromagnets Deflected/bounce off specimen 3D image of surface High resolution due to short wavelength Can't see internal structures No need to be thin High magnification x1000000 Dead/dehydrate specimens as vacuum Complex prep so artefacts No colour

Question 27

Describe how the size of an object viewed with an optical microscope can be meausred:

Answer 27

Line up eyepiece graticule with stage micrometre Calibrate eyepiece graticule- use stage micrometer to calculate size of divisions on eyepiece graticule Take micrometre away and use graticule to measure how many divisions make up object Calculate size of object by multiplying no. divisions by size of division Recalibrate eyepiece graticule at different magnifications

Question 28

Describe and explain the principles of cell fractionation and ultracentrifugation :

Answer 28

1. Homogenise tissue/use blender - disrupts cell membrane, breaking open cells and releasing contents/organelles 2. Place in a cold, isotonic, buffered solution - cold to reduce enzyme activity - isotonic so water doesnt move in/out organelles by osmosis (don't burst) - buffered to keep pH constant so enzymes don't denature 3. Filter homogenate - remove large, unwanted debris 4. Ultracentrifugation separates organelles in order of density/mass - centrifuge at high speed - remove pellet of heaviest and respin supernatant at a higher speed - repeat and increasing speed nuclei, chloroplasts, mitochondria, lysosomes, endoplasmic reticulum, ribosomes

Question 29

Describe the stages of the cell cylce in eukaryotic cells:

Answer 29

1. Interphase - DNA replicates semiconservatively leading to two chromatids joined at a centromere - number of organelles and volume of cytoplasm increases, protein synthesis 2. Mitosis - nucleus divides - to produce 2 identical nuclei 3. Cytokinesis - cytoplasm and cell membrane divide - forms 2 new genetically identical daughter cells

Question 30

Describe the behaviour of chromosomes and the role of spindle fibres in mitosis:

Answer 30

1. Prophase - chromosomes condense, becoming shorter/thicker so appear as 2 sister chromatids joined by a centromere - nuclear envelope breaks down - centrioles move to opposite poles forming spindle network 2. Metaphase - spindle fibres attach to chromosomes by their centromeres - chromosomes align along equator 3. Anaphase - spindle fibres shorten/contract - centromere divides - pulling chromatids to opposite poles of cell 4. Telephase - chromosomes uncoil becoming longer/thinner - nuclear envelopes reform = 2 nuclei - spindle fibres/centrioles break down

Question 31

Why do some eukaryotic cells not undergo the cell cycle?

Answer 31

Within multicellular organisms, some cells lose the ability to divide (e.g neurons) Only cells that do retain this ability go through a cell cycle

Question 32

Explain the importance of mitosis in the life of an organism:

Answer 32

Growth of multicellular organisms Replacing cells to repair damaged tissues Asexual reproduction

Question 33

Describe how tumours and cancers form:

Answer 33

Mutations in DNA/genes controlling mitosis can lead to uncontrolled cell division Tumour formed if this results in mass of abnormal cells - malignant=cancerous, can spread - benign= non-cancerous

Question 34

Suggest how cancer treatments control rate of cell division:

Answer 34

Some disrupt spindle fibre activity/formation - so chromosomes can't attach to spindle by their centromere - so chromatids can't be separated to opposite poles - so prevents/slows mitosis Some prevent DNA replication during interphase - so can't make 2 copies of each chromosme - so prevents/slows mitosis

Question 35

Describe how prokaryotic cells replicate:

Answer 35

Binary fission: Replication of circular DNA Replication of plasmids Division of cytoplasm to produce 2 daughter cells - single copy of circular DNA but variable number of copies of plasmids

Question 36

Describe how viruses replicate:

Answer 36

1. Attachment proteins attach to complementary receptors on host cell 2. Inject viral nucleic acid into host cell 3. Infected cell replicates virus particles - nucleic acid replicated - cell produces viral protein/capsid/enzymes - virus assembled then released