cell structure

Question 1

what is magnification

Answer 1

the number of times larger an image appears, compared with the size of the object being viewed

Question 2

what is resolution

Answer 2

how clearly we can determine two points, the higher the resolution the greater the detail

Question 3

what is wet mounting

Answer 3

specimens are suspended in a liquid such as water or immersion oil

Question 4

what is dry mounting

Answer 4

solid specimens are viewed whole or cut into very thin slices

Question 5

why must we place a cover slip on at an angle (when placing it onto a wet mount)

Answer 5

this is to prevent air bubbles forming under the cover slip

Question 6

what is the maximum magnification and resolution of a scanning electron microscope (SEM)

Answer 6

• 15 to 200,000 times (magnification range)
• 3-10 Nm (resolution range

Question 7

what is the maximum magnification and resolution of a transition electron microscope (TEM)

Answer 7

• x 2 million (magnification range)
• 0.5nm (resolution range)

Question 8

what are the disadvantages of electron microscopes

Answer 8

• the specimen has to be chemically fixed, by being dehydrated and stained
• vacuum required
• large and needs to be installed
• expensive to buy/operate
• specimens must be dead

Question 9

what is the function of the mitochondrion
mean length = 0.5 to 1 um

Answer 9

• to produce energy in respiration

Question 10

what is the function of chloroplasts
mean length = 3-10 um

Answer 10

uses light energy in photosynthesis
- convert light energy in to stable chemical energy

Question 11

what is the function of the Golgi apparatus
mean length = 0.5 to 2.0 um

Answer 11

to function as a factory in which proteins are processed and transported to the plasma membrane etc.

Question 12

what is the function of the smooth ER
mean length =30nm to 50nm

Answer 12

it synthesis and stores lipids including cholesterol and phospholipids to produce new cellular membranes

Question 13

what is the function of the rough ER
mean length = 20nm to 30nm

Answer 13

to produce proteins that will become part of the Endomembrane system, the plasma or will be secreted
(the endomembrane systems is all of the membranes within the cell)

Question 14

what are centrioles

Answer 14

• centrioles, move to the poles (opposite ends of the cell) of the cell
• froms spindle fibres, which often attach to chromosomes

Question 15

what are flagella

Answer 15

• flagella are prokaryotes/ bacteria
• ## whip like movement

Question 16

what are cilia

Answer 16

• same structure as the flagella, but shorter
• beating movement
• arranged in clusters

Question 17

what are microfilaments

Answer 17

• filaments found in the cytoplasm
• help the cell move
• change shape (endocytosis and exocytosis)

Question 18

what are microtubles

Answer 18

• little tubes (microscopic)
• form the spindle
• make up cilia and undulipodia, so help, with the movement of substances
• motor proteins, allow them to move via ATP

Question 19

what are intermediate fibres

Answer 19

• extended between cells and help to stabilise the tissue

Question 20

what are lysosomes

Answer 20

• Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down)
• Break down waste materials such as worn-out organelles, used extensively by cells of the immune system and in apoptosis (programmed cell death)

Question 21

State some advantages and disadvantages of light microscopes

Answer 21

easy to use, portable, can be used to observe living specimens (tissues) DISADS: Limited magnification and resolution so fine detail cannot be observed

Question 22

State the maximum magnification and resolution for a light microscope

Answer 22

M = 1500 - 2000 times; R = 200nm (0.2µm)

Question 23

Describe reasons why we use staining in microscopy

Answer 23

Coloured chemicals that bind to molecules on the specimen, increasing contrast and making the specimen easier to see; some stains bind to specific cell structures in differential staining, e.g. acetic orcein binds to DNA and stains chromosomes dark red

Question 24

Describe differences in how the image is formed between TEMs, SEMs and LSCMs

Answer 24

• TEM: electrons pass straight through specimen (2D black and white image);
• SEM: electrons bounce off specimen surface and focused (3D black and white image);
• LSCM: laser scans specimen point by point and stacks layers of the image at different depths (3D image)

Question 25

Describe 4 disadvantages of electron microscopy

Answer 25

- Specimen has to be dead (as observed in a vacuum) - requires specialist training to use; heavy metallic salt stains hazardous to human health; - complex preparation process means artefacts may be produced (distorts image); - high energy electron beam can damage the specimen (distorts image)

Question 26

State 5 success criteria that must be considered when making a biological drawing of a specimen

Answer 26

Use a sharp pencil, ensure drawing has a title and a scale bar, make appropriate annotations detailing structure and function, use a ruler to draw label lines which do not overlap (with no arrowheads), ensure all lines in image are clear and continuous (unbroken), NO shading

Question 27

State the formula for calculating magnification

Answer 27

magnification = image size/actual size

Question 28

Describe the structures and functions of the various components of the nucleus

Answer 28

- Nuclear envelope: separates contents of the nucleus from the rest of the cell, contains nuclear pores which allow movement of messenger RNA (mRNA) OUT of the nucleus - nucleolus: contains ribosomal RNA to synthesise ribosomes; nucleoplasm: contains chromatin which is where DNA is stored

Question 29

Describe the structure and function of the rough endoplasmic reticulum (rER)

Answer 29

A system of membranes containing fluid filled cisternae, continuous with nuclear membrane and covered in ribosomes. It acts as both an intracellular transport system and a site of protein synthesis (translation on ribosomes)

Question 30

Describe the structure and function of the smooth endoplasmic reticulum (sER)

Answer 30

Similar to rER but more tubular structure with NO ribosomes. Site of cholesterol, steroid hormone, lipid synthesis

Question 31

Describe the structure and function of the Golgi apparatus

Answer 31

A stack of membrane-flattened sacs; secretory vesicles bring materials to and from the Golgi. It is the site of protein modification (e.g. adding sugar groups to make glycoproteins), protein folding (e.g. into an enzyme/hormone). Modified proteins can then either be stored in the cell or exported via exocytosis at the plasma membrane

Question 32

Describe the structure and function of a mitochondrion

Answer 32

Double membrane with inner membrane folded into cristae (provides a large surface area for electron carrier proteins in aerobic respiration and significant ATP production); contains a fluid filled matrix containing enzymes (for respiration) and mitochondrial DNA (for self-replication and protein synthesis)

Question 33

Describe the structure and function of chloroplasts

Answer 33

Double membrane, inner membrane continuous with stacks of flattened membrane sacs called thylakoids (stacks of thylakoids are called grana) which contain chlorophyll; fluid-filled stroma (contains enzymes for photosynthesis); contains loops of DNA (for protein synthesis) and starch grains (carbohydrate storage)

Question 34

Describe the structure and function of the components of the vacuole

Answer 34

Contains cell sap (water and solutes which maintain cell stability by exerting pressure on the cell wall…turgid); surrounded by a tonoplast (vacuolar membrane)

Question 35

Describe the structure and function of lysosomes

Answer 35

Single-membrane bound vesicles containing hydrolytic enzymes; lysosomes are abundant in phagocytes (neutrophils and macrophages). Lysosomes can engulf dead/damaged organelles and foreign matter and recycle the digested components

Question 36

Describe the structure and function of centrioles

Answer 36

"9 + 3" arrangement of microtubules (made of tubulin); pairs of centrioles are arranged at right angles to each other. Responsible for spindle fibre formation during cell division

Question 37

Describe the structures and function of cilia and flagella

Answer 37

"9 + 2" arrangement of microtubules; cilia can be stationary (sensory role) or mobile (beat rhythmically to move mucus from airways); flagella used for cell motility

Question 38

Outline briefly the structures and functions of three components of the cytoskeleton

Answer 38

Microfilaments (composed of actin protein fibres; responsible for cell movement and contraction during cytokinesis); microtubules (composed of globular tubulin proteins; scaffold shale of cell and important in organelle movement working with motor proteins dynein and kinesin); intermediate fibres (many proteins; mechanical strength, anchor nucleus in cytoplasm)

Question 39

Describe how a protein is synthesised and modified before leaving the cell

Answer 39

Synthesised on ribosome (on rER or free floating), travel through rER in cisternae and pinched off into a vesicle; vesicle moves via microtubules towards Golgi; vesicle fuses with face of Golgi and is modified; modified protein leaves Golgi in vesicle and travels to plasma membrane; vesicle fuses with plasma membrane and exits the cell via exocytosis

Question 40

Describe the main differences between eukaryotes and prokaryotes

Answer 40

Prokaryotes are much smaller, they have no membrane-bound organelles, less well-developed cytoskeleton and no centrioles; cell wall made of murein (not chitin or cellulose); free-floating loop of DNA (and plasmids)

Question 41

Describe the similarities between chloroplasts/mitochondria and prokaryotes

Answer 41

- Contain 70s ribosomes - Contain loops of DNA - contain RNA - divide by binary fission