cell structure and methods of studying cells

Question 1

Define magnification

Answer 1

The ability to make the image of the specimen larger

Question 2

Define resolution

Answer 2

The ability to distinguish between objects that are close together

Question 3

Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure

Answer 3

1. Place micrometer on stage to calibrate eyepiece graticule
2. Line up scales on graticule and micrometer, count how many graticule divisions are in 100um on the micrometer
3. Use calibrated values to calculate actual length of structures

Question 4

State and equation to calculate actual size of a structure from microscopy

Answer 4

Actual size = image size / magnification

Question 5

Outline what happens during cell fractionation and ultracentrifugation

Answer 5

• The sample is homogenised in a cold isotonic buffer solution to release organelles
• Filter homogenate to remove debris
• Ultracentrifuge sample at low speed so the largest organelles form a pellet and the rest stay suspended in the supernatant
• Filter out the pellet and re-centrifuge at a higher speed

Question 6

State the order of sedimentation of organelles during centrifugation (least to most dense)

Answer 6

Lysosome → Ribosome → Mitochondria → Chloroplast → Nucleus

Question 7

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

Answer 7

1. Cold = slow actions of hydrolase enzymes
2. Buffered = maintains constant pH
3. Isotonic = prevent osmotic lysis/shrinking of organelles

Question 8

How do you calculate total magnifications?

Answer 8

Eyepiece lens magnification x objective lens magnification = total magnification

Question 9

Define the terms eukaryotic and prokaryotic cell

Answer 9

Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles

Prokaryotic: DNA is free in cytoplasm, no organelles

Question 10

What are tissues and how do they form?

Answer 10

Tissues are formed by a group of cells working together to perform a particular function

Question 11

What are organs and how do they form?

Answer 11

Organs are made from different tissues working together to perform a particular function.

Question 12

What are organ systems and how do they form?

Answer 12

Organ systems are different organs working together to form organ systems.

Question 13

Describe the structure and function of the cell surface membrane

Answer 13

• Fluid mosaic phospholipid bilayer with extrinsic and intrincsit proteins embedded
• Isolates cytoplasm from extracellular environment
• Selectively permeable to regulate transport of substances
• Involved in cell signalling/cell recognition

Question 14

Describe the structure of the nucleus

Answer 14

• Surrounded by a nuclear envelope, a semi-permeable double membrane
• Nuclear pores allow substances to enter/exit
• Dense nucleolus made of RNA and proteins assembles ribosomes

Question 15

Describe the function of the nucleus

Answer 15

• Contains DNA coiled around chromatin into chromosomes

- Controls cellular processes: site of mRNA transcription, mitosis

Question 16

Describe the structure of a mitochondrion

Answer 16

• Surrounded by a double membrane, folded inner membrane forms cristea a which is the site of the electron transport chain
• Fluid matrix contains mitochondrial DNA, respiratory enzymes, lipids and proteins

Question 17

Describe the structure of a chloroplast

Answer 17

• Double membrane
• Thylakoids: flattened discs stack to form grana, contains chlorophyll
• Stoma: fluid-filled matrix

Question 18

State the function of mitochondria and chloroplasts

Answer 18

Mitochondria: site of anaerobic respiration to produce ATP

Chloroplasts: site of photosynthesis to convert solar energy to chemical energy

Question 19

Describe the structure and function of the Golgi apparatus

Answer 19

• The Golgi apparatus is are flattened sacs of fluid-filled membrane
• Golgi apparatus modifies proteins and lipids before packaging them into the Golgi vesicles

Question 20

Describe the structure and function of the Golgi vesicles

Answer 20

• The vesicle is a membrane-bound sack for transport and storage
• The Golgi vesicles transport the proteins and lipids across the cell

Question 21

Describe the structure and function of a lysosome

Answer 21

• Round organelle surrounded by a membrane with no clear internal structure
• Contain digestive enzymes (hydrolytic enzymes) which digest waste materials such as worn-out organelles or invading cells.

Question 22

Describe the structure and function of a ribsosome

Answer 22

• Formed of protein and RNA, free in the cytoplasm or attached to the rough endoplasmic reticulum
• Site of protein synthesis via translation, the large subunit joins amino acids whereas the small subunit contains mRNA binding site

Question 23

Describe the structure and function of the rough endoplasmic reticulum

Answer 23

• System of fluid-filled membranes with ribosomes covering the surface
• Folds and processes proteins made by the ribosomes

Question 24

Describe the structure and function of the smooth endoplasmic reticulum

Answer 24

• System of fluid-filled membranes with no ribosomes

- Involved in the production, processing and storage of lipids and carbohydrates.

Question 25

Describe the structure of the cell wall

Answer 25

- In bacteria, it is made of polysaccharide murein - In plants and algae its made of cellulose microfibrils - In fungal cells, its made of chitin

Question 26

State the functions of the cell wall

Answer 26

1. Mechanical strength and support 2. Physical barrier against pathogens 3. Part of appoplast pathway to enable easy diffusion of water

Question 27

Describe the structure and function of the cell vacuole in plants

Answer 27

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

Question 28

Explain cell adaptations for efficient diffusion

Answer 28

1. Folded membrane or microvilli to increase surface area for diffusion 2. Many mitochondria so large amounts of ATP are synthesised for active transport 3. Walls are once cell thick to reduce the diffusion pathway distance

Question 29

State the role of plasmids in prokaryotes

Answer 29

- Small ring of DNA that carries non-existential genes | - Can be exchanged between bacterial cells

Question 30

State the role of flagella in prokaryotes

Answer 30

- Rotating tail propels organism

Question 31

State the role of the capsule in prokaryotes

Answer 31

- Acts as a food reserve - Provides mechanical protection against phagocytosis - Sticks cells together

Question 32

What are the similarities between eukaryotic and prokaryotic cells

Answer 32

Both have: - Cell membrane - Cytoplasm - Ribosomes

Question 33

What are the dissimilarities between eukaryotic and prokaryotic cells?

Answer 33

- Prokaryotes are unicellular, and eukaryotes are multicellular - Prokaryotes have no membrane-bound organelles and no nucleus, eukaryotes have organelles and nucleus - Prokaryotes have circular DNA not associated with histone proteins, eukaryotes have linear chromosomes associated with histones - Prokaryotes have smaller ribosomes than eukaryotes - Prokaryotes have a capsule

Question 34

Why are viruses referred to as particles instead of cells

Answer 34

They are acellular and non living

Question 35

Describe the structure of a viral particle

Answer 35

- Linear genetic material (DNA or RNA) - Surrounded by a capsid - No cytoplasm - Attachment protein

Question 36

State the role of attachment proteins on viral particles

Answer 36

Enable viral particles to bind to complementary sites on host cells

Question 37

Describe how optical microscopes work

Answer 37

1. Lenses focus rays of light and magnify the view of a thin slice of a specimen 2. Different structures absorb different amounts of wavelengths of light 3. Reflected light is transmitted to the observer via the objective lens and eyepiece

Question 38

Outline a method how a student could prepare a temporary mount of tissue for an optical microscope

Answer 38

1. Obtain a thin section of tissue 2. Place plant tissue in a drop of water 3. Stain tissue on a slide to make structures visible 4. Add a coverslip using a mounted needle to avoid trapping air bubbles

Question 39

State the advantages of using an optical microscope

Answer 39

1. Colour image | 2. Can show living structures

Question 40

State the disadvantages of using an optical microscope

Answer 40

1. 2D image | 2. Lower resolution than electron microscopes, cannot see ultrastructure

Question 41

Describe how a transmission electron microscope work

Answer 41

1. Pass a high energy beam of electrons through thin slice of specimen 2. More dense structures appear darker since they absorb more electrons

Question 42

Suggest advantages of using a transmission electron microscope

Answer 42

1. Electrons have a shorter wavelength of light giving a high resolution so ultrastructure can be observed 2. High magnification

Question 43

Suggest disadvantages of using a transmission electron microscope

Answer 43

1. 2D image 2. Requires a vacuum so cannot show living structures 3. Extensive preparation may induce artefacts 4. No colour image

Question 44

Describe how a scanning electron microscope works

Answer 44

1. Focus a beam of electrons onto a specimens surface | 2. Reflected electrons hit a collecting device and are amplified to produce an image

Question 45

Suggest the advantages of using a scanning electron microscope

Answer 45

1. 3D image | 2. Electrons have a shorter wavelength than light so high resolution

Question 46

Suggest the disadvantages of using a scanning electron microscope

Answer 46

1. Requires a vacuum so cannot show living structures 2. No colour image 3. Only shows outer surface