2.1 Cell structure

Question 1

What is a microscope?

Answer 1

Instrument that allows an object to be magnified

Question 2

How does a light microscope work?

Answer 2

Two lenses, objective and eyepiece. Light passes through the specimen

Question 3

What is magnification?

Answer 3

How much bigger the image is than the actual object

Question 4

What is resolution?

Answer 4

The ability to distinguish between two objects

Question 5

What is magnification and resolution of a light microscope?

Answer 5

Magnification up to 2000
Resolution of 200nm

Question 6

What is the equation for magnification?

Answer 6

M = Image size / Actual size

Question 7

What is the difference between dry and wet mounts, examples?

Answer 7

Dry mount - thin small samples are placed on the slide with a coverslip on top. Eg hair/pollen
Wet mount - Specimens are suspended in liquid, coverslip is placed at an angle. Eg aquatic samples

Question 8

What is a squash slide, example?

Answer 8

Wet mount, a soft sample is squashed between two slides, creating a thin layer of cells. Eg Root tips

Question 9

What is a smear slide, example?

Answer 9

A wet mount, the edge of a different slide is used to smear a sample, creating a thin, even layer of cells. Eg blood

Question 10

Why is it important to stain light microscope samples?

Answer 10

Increase contrast between organelles, by being absorbed more or less by different components

Question 11

What are crystal violet and methylene blue attracted to?

Answer 11

Negatively charged materials in cytoplasm

Question 12

What are Congo red and Nigrosin attracted to?

Answer 12

Repelled by negatively charged cytosol, so dye stains outside of cells

Question 13

What does differential staining do?

Answer 13

Distinguishes between two types of organisms that would otherwise be harder to identify

Question 14

What is an eyepiece graticule?

Answer 14

Glass disk with a scale of 1 to 100, which has no units. The relative size of the divisions increase in magnification, but it remains unchanged

Question 15

What is a stage micrometer?

Answer 15

Microscope slide with a scale in micrometers

Question 16

How does a transmission electron microscope work?

Answer 16

A beam of electrons passed through the specimen

Question 17

What is the magnification/resolution of a TEM?

Answer 17

x500,000, 0.5nm

Question 18

How does a scanning electron microscope work?

Answer 18

A beam of electrons is sent across the surface of a specimen

Question 19

What is the magnification/resolution of a SEM?

Answer 19

x500,000, 3-10nm

Question 20

Compare light microscopes and electron microscopes.

Answer 20

Light
Small/portable
Simple sample prep
Up to x2000, 200nm
Specimens are living or dead

Electron
Expensive
Large
Complex sample prep, distorts material
Vacuum needed
Black and white images
x500,000,
Specimens are dead

Question 21

How does a laser scanning confocal microscope work?

Answer 21

Moves a spot of focused light over a specimen, fluorescence from dyed areas, which are filtered through a pinhole aperture. Only light from close is sharp, from far away it is blurry, but these both have the same focal plane, so it is not blurry

Question 22

What is the advantage of laser scanning?

Answer 22

Non invasive, used in development of new drugs

Question 23

What is a cell?

Answer 23

Basic unit of all life

Question 24

What is the difference between prokaryotic and eukaryotic?

Answer 24

Prokaryotic - single celled organisms with no membrane bound organelle
Eukaryotic - multicellular organisms with membrane bound organelle

Question 25

Describe the structure of the nucleus.

Answer 25

● Surrounded by a nuclear envelope ● Nuclear pores allow substances to enter/exit. ● Dense nucleolus

Question 26

Describe the function of the nucleus.

Answer 26

● Contains DNA in the form of chromosomes. ● Controls cellular processes

Question 27

Describe the function of the nucleolus.

Answer 27

Producing ribosomes, composed of proteins and RNA, which is used to make rRNA and combined with proteins to make ribosomes

Question 28

Describe the structure and function of the endoplasmic reticulum (ER).

Answer 28

● Cisternae: network of tubules & flattened sacs extends from cell membrane & connects to nuclear envelope: ● Rough ER: many ribosomes attached for protein synthesis & transport. ● Smooth ER: lipid synthesis.

Question 29

Describe the structure and function of the Golgi apparatus.

Answer 29

● Modifies & packages proteins for export. ● Synthesises glycoproteins.

Question 30

Describe the structure and function of ribosomes.

Answer 30

Formed of protein & rRNA. Have large subunit which joins amino acids & small subunit with mRNA binding site. Protein synthesis.

Question 31

Contrast Eukaryotic and prokaryotic ribosomes

Answer 31

Eukaryotic are larger = 80s Prokaryotic are smaller = 70s

Question 32

Describe the relationship between the organelles involved in the production and synthesis of proteins.

Answer 32

The ribosomes that synthesise proteins are attached to the rER. Vesicles transport proteins to the cis side of the Golgi apparatus, which modifies proteins for secretion via (secretory) vesicles.

Question 33

Describe the structure of a mitochondrion.

Answer 33

● Surrounded by double membrane. ● Folded inner membrane forms cristae ● Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins.

Question 34

Describe the structure of a chloroplast.

Answer 34

● Double membrane. ● Thylakoids: flattened discs stack to form grana, containing chlorophyll ● Lamellae: tubes attach thylakoids in adjacent grana. ● Stroma: fluid-filled matrix.

Question 35

State the function of mitochondria and chloroplasts.

Answer 35

● Mitochondria: site of aerobic respiration to produce ATP. ● Chloroplasts: site of photosynthesis to convert solar energy to chemical energy.

Question 36

describe the structure and function of a lysosome.

Answer 36

contains hydrolytic enzyme removes waste products.

Question 37

Describe the structure and function of a plant cell wall.

Answer 37

● Made of cellulose (support plant) ● Plasmodesmata form pathway to allow molecules to pass between cells. ● Middle lamella separates adjacent cell walls.

Question 38

Describe the function and structure of a permanent vacuole

Answer 38

Selectively permeable membrane called tonoplast, cell sap contained inside Maintains turgor and rigid shape of cell

Question 39

What are bacterial and fungal cell walls made of?

Answer 39

Bacteria: peptidoglycan (murein) Fungi: chitin

Question 40

Describe the structure and function of centrioles.

Answer 40

● Spherical group of 9 microtubules arranged in a 9+2 arrangement ● Located in centrosomes. ● Migrate to opposite poles of cell during prophase & spindle fibres form between them.

Question 41

Describe the structure and function of flagella.

Answer 41

● Made of the protein flagellin. ● Rotates to move (unicellular) organism.

Question 42

Describe the structure and function of pili.

Answer 42

● Protrusions on eukaryotic cells. ● Move back and forth rhythmically to sweep foreign substances / movement.

Question 43

Why is the cytoskeleton important?

Answer 43

● Provides mechanical strength. ● Aids transport within cells. ● Enables cell movement.

Question 44

Compare eukaryotic and prokaryotic cells.

Answer 44

Both have: ● Cell membrane ● Cytoplasm ● Ribosomes

Question 45

Contrast eukaryotic and prokaryotic cells.

Answer 45

Prokaryotic: 0.5-5µm DNA is circular with no proteins, in the cytoplasm Cell division occurs by binary fission - no spindle involved 70s ribosomes No membrane bound organelles Cell wall is made from peptidoglycan and murein Eukaryotic: 100µm DNA is associated with proteins, and formed into proteins (linear) Cell division occurs by mitosis or meiosis involves spindle fibres (Separate chromosomes) 80s ribosomes Membrane bound organelles, and not membrane bound organelles Cell wall is present in plants (cellulose), fungi (chitin)

Question 46

Describe the structure and function of the cell-surface plasma membrane.

Answer 46

‘Fluid mosaic’ phospholipid bilayer with extrinsic & intrinsic proteins embedded. ● Acts as a barrier ● Semi permeable ● Involved in cell signalling / cell recognition.

Question 47

Explain the role of cholesterol, glycoproteins & glycolipids in the cell-surface membrane.

Answer 47

● Cholesterol: steroid molecule connects phospholipids & reduces fluidity. ● Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together. ● Glycolipids: cell signalling & cell recognition.