2.1.1 Cell Structure

Question 1

State differences between eukaryotic and prokaryotic cells

Answer 1

• Prokaryotes don’t have a nucleus, eukaryotes do
• Prokaryotes are bacteria, eukaryotes are animal and plant cells

Question 2

Describe a virus

Answer 2

• non-cellular
• contains no cytoplasm or organelles
• no chromosome, just DNA and RNA strands
• enclosed in a protein coat
• depends on cells for metabolism and reproduction

Question 3

Name organelles of an animal cell

Answer 3

• mitochondria
• plasma membrane
• centrioles
• Golgi apparatus
• nucleus
• lysosome
• rough er
• smooth er
• ribosome
• cell surface membrane

Question 4

Describe the structure and function of a nucleus

Answer 4

Structure
Nuclear envelope:
- outer membrane
- inner membrane
- pores in nuclear envelope

• nucleoplasm (made from chromatin)
• nucleolus (dark region of chromatin)
• largest organelle

Function
- stores genetic information in DNA
- DNA replication occurs in the nucleus

Question 5

Describe the structure and function of a ribosome

Answer 5

Structure
- very small
- mostly found on ER (makes it rough)
- made of RNA
- no membrane
- made from two subunits
- 70s (smaller) in prokaryotic cells
- 80s in eukaryotic cells

Function
- carries out protein synthesis

Question 6

Describe the structure and function of the rough endoplasmic reticulum

Answer 6

Structure
- covered in ribosomes
- forms cisternae (flattened sacs)
- membrane made from phospholipid bilayer
- membranes are continuous with nuclear envelope

Function
- transports protein around the cell and the Golgi body
- holds ribosomes responsible for protein synthesis

Question 7

Describe the structure and function of the smooth endoplasmic reticulum

Answer 7

Structure
- forms cisternae (flattened sacs)
- membrane made from phospholipid bilayer

function
- site of production and transport of lipids/steroids

Question 8

Describe the structure and function of the Golgi body/apparatus

Answer 8

Structure
- flatterned membrane-bound sacs

Function
- receives proteins from ribosomes
- proteins and lipids then become modified to produce glycoproteins and glycolipids (carbohydrate is added) then packaged into vesicles
- vesicles transport glycoproteins and glycolipids to the cell membrane, to be secreted by exocytosis
- also produces lysosomes, which contain lytic enzymes which breakdown bacteria and worn out organelles

Question 9

Describe the structure and function of the mitochondria

Answer 9

Structure
- outer + inner membrane
- matrix, where DNA is found (space inside)
- inner membrane is folded to form cristae
- sausage shaped

function
- site of aerobic respiration
- ATP is formed here
- have circular DNA and 70s ribosomes (suggest they could have evolved from bacteria)

Question 10

Describe the structure and function of the cytoskeleton

Answer 10

Structure
- microfilaments of actin
- microtubules made of tublin

Function
- micro filaments move against each other allowing cellular movement
- provides strength
- stabilises, supports, strengthens the cell
- holds organelles in place
- transport within the cell
- make up the spindle fibres and centrioles used in cell devision
- used to move flagella and cilia

Question 11

Describe and explain vesicle and lysosome transport

Answer 11

• cytoskeleton (microtubules) provide a pathway
• 2 motor types- dynein + kinesin, which use ATP
• microtubules can be extended and broken down

Question 12

Suggest processes that rely on the cytoskeleton for movement

Answer 12

• movement of chromosomes in cell division
• movement of cytoplasm in cytokinesis
• movement of organelles
• movement of RNA in protein synthesis
• movement of proteins

Question 13

Describe the structure and function of centrioles

Answer 13

Structure
- small tubes of protein fibres
- found near the nucleus in animal cells
- not found in plant cells

Function
- form spindle fibres for cell division
- move chromosomes during nuclear division

Question 14

Describe the structure and function of flagella and cilia

Answer 14

Structure
- nine microtubules arranged in a circle with two at the centre

Function
- movement caused by ATP
- required mitochondria and cytoskeleton to function
- used by sperm cells and ciliated epithelial cells

Question 15

Describe the structure and function of micro villi

Answer 15

Structure
- folds in the plasma membrane of animals cells

Function
- increases surface area for a faster rate of diffusion

Question 16

Name the organelles of a plant cell

Answer 16

• cell wall
• cell surface membrane
• large permanent vacuole
• nucleus
• chloroplasts
• mitochondria
• cytoplasm
• lysosome
• rough er
• smooth er
• ribosomes
• Golgi body

Question 17

Describe and explain the components of a chloroplast

Answer 17

• outer and inner membrane
• oil droplets contacting lipids used for making/ repairing membranes (as they are made from phospholipids)
• grana made from stacks of disks called thylakoids
• thylakoids contain the pigment chlorophyll
• intergranal lamellae are membranes that link the grana together
• the Stroma is fill with fluid + starch grains
• contains 70s ribosomes and circular DNA (suggests they evolved from bacteria)

Question 18

Name 3 important adaptations of chloroplasts

Answer 18

• grana have a large surface area for attachment of lots of chlorophyll molecules
• chloroplasts have DNA and ribosomes to quickly create protein when needed
• chloroplasts have oil droplets for making more phospholioid membranes

Question 19

Describe the structure and function of the cell wall in plant cells

Answer 19

• made from cellulose (a polysaccharide) which is permeable
• provides strength to the cell, as it has a high tensile strength to stop the cell bursting when water enters
• makes the cell rigid, which prevents wilting

Question 20

Describe the structure and function of the cell vacuole

Answer 20

Structure
- Membrane bound (tonoplast)
- contains cell sap (weak solution of sugar + salts)

Function
- helps maintain pressure inside cell and keep it rigid
- stop the plant wilting
- can isolate unwanted chemicals

Question 21

Name the parts of the cell protein manufacture requires

Answer 21

• DNA and RNA molecules
• rough endoplasmic reticulum
• ribosomes
• vesicles
• Golgi body

Question 22

Explain the production of extracellular proteins

Answer 22

1. Genes in nucleus are copied into mRNA (transcription)
2. mRNA joins with rough ER and ribosome for translation/protein synthesis
3. A protein is built in the ribosome
4. Protein is put into a transport vesicle to be transported to the Golgi body
5. Golgi body process, modifies and packages protein (e.g. makes a glycoprotein)
6. Golgi body packages protein into a secretory vesicle which moves and fuses to the cell membrane, then released by exocytosis (using ATP)
7. Golgi body also makes lysosomes which digest worn out organelles

Question 23

Give examples of extracellular proteins which are excreted (4)

Answer 23

• enzymes - amylase/lipase/protease
• protein hormones - insulin/ADH
• glycoproteins for cell membrane
• antibodies

Question 24

Describe the structure of DNA in eukaryotic and prokaryotic cells

Answer 24

• eukaryotic DNA is linear as chromosomes
• eukaryotic DNA has proteins called histones which organise it into chromosomes
• prokaryotic DNA is circular
• prokaryotic DNA has no histones so does not form chromosomes

Question 25

List similarities of eukaryotic and prokaryotic cells

Answer 25

- plasma membrane which controls substances entering and exiting the cell - cytoplasm where most of the metabolic reactions occur - ribosomes for protein synthesis - DNA containing coded information for protein production

Question 26

List differences of prokaryotic and eukaryotic cells

Answer 26

- Eukaryotic: larger cells (20-100um) - Prokaryotic: extremely small (less than 0.5 - 5um) - Eukaryotic: has membrane bound organelles - Prokaryotic: no membrane bound orangelles - Eukaryotic: nucleus containing DNA - Prokaryotic: no nucleus- DNA free in cytoplasm - Eukaryotic: DNA is linear as chromosomes - wound around histone proteins - Prokaryotic: DNA is circular and not wound around histone proteins - Eukaryotic: small 70s ribosomes (18nm) - Prokaryotic: large 80s ribosomes (22nm) - Eukaryotic: cellulose cell wall in plant cells, chitin fungal cell wall, no cell wall in animal cells - Prokaryotic: peptidiglycan cell wall

Question 27

Explain the makeup of cells, tissues, organs and systems

Answer 27

- cells make up all living things - a tissue is a collection of similar cells that are specialised to work together to a particular function - an organ is a collection of different tissues working together to perform a common function - a system is a group of organs working together to perform a particular function

Question 28

What are the two lenses found in a compound light microscope, and how do they work?

Answer 28

1. Objective lens - placed near the specimen 2. Eyepiece (ocular) lens - lens through which the specimen is viewed Objective lens produces a magnified image, which is magnified again by the eyepiece lens

Question 29

What are dry and wet mounts?

Answer 29

1. Dry mount - solid specimen either cut thin or whole with a cover slip on top 2. Wet mount - specimens suspended in water or oil (with refractive index same as glass), cover slip placed at angle to prevent bubbles

Question 30

What are squash and smear slides?

Answer 30

1. Squash slide - wet mount but using a lens tissue apply pressure to the cover slip to squash specimen 2. Smear slide - edge of slide used to smear a specimen then a cover slip is added

Question 31

List important things to do when preparing an onion cell slide

Answer 31

- use forcepts to obtain thin layer + place on slide - use pipette to place 2 stopds on stain on edge of sample - lower cover slip at angle using a mounted needle - use blotting paper to remove excess stain

Question 32

What rules must be followed when drawing a scientific drawing?

Answer 32

- use a piece of plain paper - use a sharp pencil - use at leasat 50% of space - use correct proportions - continous lines - NO shading - use ruled label lines - labels outside diagram - lables don't cross - include a title + magnification

Question 33

Why is staining used on samples?

Answer 33

- makes cells/organelles visible by increasing contrast - allows recognition of different cell types + different organelles

Question 34

What is the difference between gram negative and gram positive bacteria?

Answer 34

Gram negative: Not killed by penicillin as the less vital peptidoglycan cell wall is thinner and covered by a lipopolysaccharide layer Gram positive: Killed by penicillin as it works by reaking down the vital peptidoglycan cell wall

Question 35

When is a differential stain - gram stain used?

Answer 35

To determine whether bacteria are gram negative or gram positive

Question 36

What is the procedure of gram staining?

Answer 36

1. Crystal violet stain applied 2. Alcohol decolorization - alcohol is used to wash away the stain from gram negative cells, leaving them colorless. Gram-positive cells retain the stain due to their thicker peptidoglycan layer. 3. Counterstaining - counterstain is applied to the smear, staining the decolorized Gram-negative cells pink while maintaining the purple color of the gram positive cells 4. Observation - the slide is observed under a microscope to determine the gram reaction of the bacteria

Question 37

What colour does each bacteria stain and why?

Answer 37

Gram positive: Purple, as the alcohol doesn't remove crystal violet because of the thick peptidoglycan wall Gram negative: Pink, as the alcohol washes out the crystal violet due to the thin peptidoglycan cell wall covered by the lipopolysaccharide cell wall - pink counter-stain bindso the cell wall

Question 38

What is leishman's stain used for?

Answer 38

- provides contrast between the cytoplasm and the nucleus - allows the shape of the nucleus to be seen - allows different white blood cells with different shaped nuclei to be seen - red blooc cells not affected as have no nucleus for stain to bind to

Question 39

Define fixing, sectioning, staining and mounting

Answer 39

Fixing: Chemicals like formaldehyde are used to preserve specimens in as near-natural state as possible Sectioning: Specimens are dehydrated with alcohols and then placed in a mould with wax/resin to form a hard block - thinly sliced with a knife Staining: Specimens treated with multiple coloured chemicals to show different strutures Mounting: Specimens secured to microscope slide and cover slide placed on top

Question 40

What are the advantages and disadvantages of using a light microscope?

Answer 40

**Advantages** - portable - takes up little space - specimens easy to prepare - can see cells and often nucleus - colour visible **Disadvantages** - low resolution (200nm) as wavelength of light too long - cannot see small organelles or details of organelles

Question 41

Define magnification and resolution

Answer 41

Magnification: The degree to which the size of an image is larger than the object itself Resolution: The ability to see two objects tha are close together as separate objects and see in detail

Question 42

How do electron microscopes work and why do they have a higher resolution compared to a light microscopes?

Answer 42

- beam of electrons focused by electromagnets through or onto the surface of a specimen - electron microscopes use electrons to take images, which have a much short wavelength (0.2nm), so have a higher resolution

Question 43

What are the two types of electron microscope, how do they work, and what type of image do they produce

Answer 43

**Transmission electron microscope (TEM)** - a beam of electrons is transmitted through a specimen and focused to produce a 2D image - used to view the ultra structure of cells and organelles **Scanning electron microscope (SEM)** - a beam of electrons is sent across a specimen and reflected electrons are collected to produce a 3D image - used to view the 3D shape of the surface of cels and organelles and their surface features

Question 44

What is the magnification and resolution of each type of electron microscope and a light microscope?

Answer 44

**Transmission electron microscope (TEM)** Magnification: x500,000 Resolution: 0.05 - 2nm **Scanning electron microscope (TEM)** Magnification: x100,000 Resolution: 5 - 50nm **Light microscope** Magnification: x1500 Resolution: 200nm

Question 45

What are the advantages and disadvantages of using an electron microscope?

Answer 45

**Advantages** - higher resolution - higher magnification - shorter wavelength - can see ultra structure **Disadvantages** - cannot view living cells - must be in vacuum - no colour images - specimen must be thin - artefacts may appear (structures produced during preparation process) - have to be treated with metal (lead) salts

Question 46

List units used when measuring smaller specimens, their units and how to convert between them

Answer 46

- milimetre (mm) - 1000μm - micrometre (μm) - 1000nm - nanometre (nm)

Question 47

How is magnification calculated?

Answer 47

Magnification = Image size / real object size

Question 48

What is an eyepiece graticule and stage micrometer?

Answer 48

Eyepiece graticule: Placed into the eyepiece lens - used to measure specimens seen udner the microscope. Will not change size when magnification is changed. Needs to be calibrated Stage micrometer: Goes on the stage of the microscope - a microscope slide with a scale etched into it. Is a known size (e.g. 1mm). Used to calibrate eyepiece graticle