3.2.1 Cell structure

Question 1

Define Eukaryotic

Answer 1

DNA is contained in a nucleus and contains membrane bound specialised organelles

Question 2

Where are Eukaryotic cells found?

Answer 2

• Plants
• Animal
• Fungi
• Protists

Question 3

Details about the Cell surface membrane

Answer 3

‘Fluid mosaic’ phospholipid bilayer in which intrinsic and extrinsic proteins are embedded
- Involved in cell signalling and cell recognition
- Selectively permeable to regulate transport of substances

Question 4

Details about the Endoplasmic reticulum

Answer 4

Flattened membrane bound sacs (cisternae) which are continuous with the outer nuclear membrane
- Rough has ribosomes
- Smooth no ribosomes
- Smooth ER synthesis , stores and transports lipids and carbs
- Rough ER transports proteins made on attached ribosomes

Question 5

Details about the Cell wall (plants/algae/fungi)

Answer 5

Made of cellulose microfibrils , plasmodeta allows molecules to pass between cells , middle lamella acts as boundary between adjacent cell walls
- Mechanical strength and support
- Physical barrier against pathogens
- Part of the apoplast pathway for the easy diffusion of water

Question 6

Details about the Cell vacoule (plants)

Answer 6

Surrounded by single membrane called the tonoplast which contains cell sap
- Controls turgor pressure
- Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm

Question 7

Details about the Mitochondria

Answer 7

Surrounded by a double membrane serrated by a fluid filled space called the matrix which contains lipids , proteins , respiratory enzymes and mitochondrial DNA. Inner membrane is folded to form Cristae which gives a large surface area and is the site of electron transport chain
- Site of aerobic respiration to produce ATP

Question 8

Details about the Golgi apparatus

Answer 8

Consists of a stack of membranes that make up flattened sacs with vesicles
- Forms lysosomes , synthesis glycoproteins and modifies and packages proteins for export

Question 9

Details about Lysosome

Answer 9

Type of golgi vesicle that releases lysozymes and is a sac surrounded by a single membrane. The glycoprotein coat protects cell interior and embedded H+ pump maintains acidic conditions
- Exocytosis of digestive enzymes and digests contents of phagosome

Question 10

Details about Ribosomes

Answer 10

Formed of protein and rRNA and free in cytoplasm or attached to endoplasmic reticulum
- In eukaryotic cells: 80s
- Site of protein synthesis via translation
- Large subunit joins amino acids
- Small subunit contains mRNA binding site

Question 11

Details about Chloroplast (plants/algae)

Answer 11

Vesicular plastid with double membrane , thylakoids are flattened discs stacked to form the grand which contains photosystems with chlorophyll and fluid-filled matrix called the stroma
- Site of photosynthesis
- Converts solar energy to chemical energy

Question 12

Details about the Nucleas

Answer 12

Contains chromosomes consisting of protien bound linear DNA and is a sac surround by a nuclear envelope (double membrane) , nuclear pores allow substances to enter and exit
- Manufactures ribosomal RNA and ribosomes
- Contains DNA coiled around chromatin into chromosomes
- Controls cellular processes

Question 13

Define Prokaryotic

Answer 13

DNA is free in cytoplasm and no organelles e.g. Bactria/archaea

Question 14

What are Plasmids?

Answer 14

Small rings of DNA that carry non essential genes

Question 15

What is a Flagella?

Answer 15

Rotating tail which propels organism

Question 16

What is a Capsule and what is its role?

Answer 16

Polysaccharide layer
- Prevents desiccation
- Acts as a food reserve
- Provides mechanical protection against phagocytosis and external chemicals
- Sticks cells together

Question 17

What do Eukaryotic and Prokaryotic cells have in common?

Answer 17

• Cell membrane
• Ribosomes
• Cytoplasm

Question 18

Contrast Eukaryotic and Prokaryotic cells

Answer 18

Prokaryotic
- unicellular and small
- no membrane bound organelles and no nucleus
- circular DNA not associated with proteins
- small ribosomes = 70s
- murein cells walls
- contains capsule and sometimes plasmids
Eukaryotic
- often multicellular and large
- always have organelles and nucleus
- linear chromosomes associated with histone proteins
- larger ribosomes = 80s
- cellulose cell wall
- no capsule and no plasmids

Question 19

What are Viruses?

Answer 19

• Acellular and non living
• No cytoplasm
• Can’t self reproduce
• No metabolism

Question 20

Structure of a Viral particle

Answer 20

• No cytoplasm
• Surrounded by capsid which is a protein coat made of capsomeres
• Linear genetic material and viral enzymes

Question 21

Structure of an Enveloped virus

Answer 21

• Simple virus surround by matrix protein
• Matrix protein surrounded by envelope
• Attachment proteins on surface

Question 22

Role of the Capsid on viral particles

Answer 22

• Protects nucleic acid from degradation
• Surface sites enable viral particle to bind to and enter host cell or inject their genetic material

Question 23

Role of attachment proteins on viral particles

Answer 23

Enable viral particle to bind to complementary site on host cell

Question 24

Formula for Microscopy

Answer 24

I
A M actual size = image size/magnification

Question 25

State the order of sedimentation of organelles during differential centrifugation

Answer 25

Most dense to least dense - nucleus - mitochondria - lysosomes - rer - plasma membrane - ser - ribosomes

Question 26

Define Magnification

Answer 26

Factor by which the image is larger than the actual specimen

Question 27

Define Resolution

Answer 27

Smallest seperation distance from which 2 separate structures can be distinguished from one another

Question 28

Outline what happens during cell fractionation and ultracentrifugation

Answer 28

- Mince and homegneize 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 supertant and spin again at a higher speed

Question 29

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

Answer 29

Cold: slow action of hydrolyse enzymes Buffered: maintains constant PH Isotonic: Prevents shrinking of organelles

Question 30

Explain how the length of a cell could be estimated

Answer 30

Measure using a graticule and calibrate against a scale of known lengths

Question 31

Describe how a Scanning electron microscope (SEM) works

Answer 31

- Focus a beam of electrons onto specimens surface using electromagnetic lenses - Reflected electrons hit a collective device and are amplified to produce an image on a photographic plate

Question 32

Advantages of using SEM

Answer 32

- 3D image - Electrons have a shorter wavelength than light so a high resolution

Question 33

Disadvantages of using SEM

Answer 33

- Only shows outer surface - No colour image - Requires a vacuum so can't show living structures

Question 34

Describe how a Optical microscope works

Answer 34

- 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 eyepiece

Question 35

Advantages of using Optical

Answer 35

- Colour image - Shows living structures - Affordable apparatus

Question 36

Disadvantages of using Optical

Answer 36

- 2D image - Lower resolution than electron microscopes so can't see ultrastructures

Question 37

Describe how a Transmission electron microscope (TEM) works

Answer 37

- 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 38

Advantages of using TEM

Answer 38

- High magnification as electrons have a shorter wavelength than light so a high resolution so ultrastructure is visible

Question 39

Disadvantages of using TEM

Answer 39

- 2D image - No colour image - Requires a vacuum - Extensive preparation needed