T2 - Cells, Viruses and Reproduction of Living Things

Question 1

What is cell theory?

Answer 1

A unifying concept that states that cells are a fundamental unit of structure, function and organisation in all living organisms.

Question 2

How are cells organised in complex organisms?

Answer 2

Tissues, organs, and organ systems.

Question 3

List the organelles found in prokaryotic cells

Answer 3

Nucleoid, plasmids, 70s ribosemes, cell wall, flagellum, pili, slime capsule

Question 4

Describe the structure and function of a Gram positive bacterial cell wall

Answer 4

Thick layer of peptidoglycan, teichoic acids present, no outer lipopolysaccharide layer.
Strength and support - prevents osmotic lysis (stops cell bursting when in water).

Question 5

Describe structure and function of Gram negative bacterial cell wall?

Answer 5

Thin layer of peptidoglycan, teichoic acids not
present, with an outer lippopolysaccharide membrane.
Strength and support - prevents osmotic lysis (stops cell bursting when in water).

Question 6

Describe the structure and function of plasmids in bacteria?

Answer 6

Small circular piece of DNA.
Contain genes that enhance bacterial survival, either by killing other organisms or by defending the host cell by producing toxins / antibiotic resistance.

Question 7

What are plasmids used for in genetic engineering?

Answer 7

Vectors to introduce foreign DNA into a bacterial cell.

Question 8

Describe the structure and function of a bacterium’s flagella?

Answer 8

Made of flagellin (protein) arranged in a helix.
Rotate to move the cell.

Question 9

Describe the structure and function of a bacterial pili?

Answer 9

Hairlike extensions
Facilitate adhesion to surfaces & attachment to host cells, attach to other bacterial cells and allow plasmids to move from cell to cell (-conjugation).

Question 10

Describe the function of the slime layer and capsule?

Answer 10

Protects against phagocytosis as covers cell markers making it easier to be pathogenic.
Helps the cell to retain moisture and adhere to surfaces.

Question 11

What does the nucleoid contain?

Answer 11

Circular chromosomes made of single stranded DNA, no histones

Question 12

What are the main steps of gram staining? (5)

Answer 12

1. Heat fix cells to slide.
2. Primary stain with crystal violet.
3. Fix stain with iodine.
4. Decolourise with alcohol wash.
5. Counterstain with safranin

Question 13

Why do gram positive bacterial cell walls stain purple when gram staining?

Answer 13

Crystal violet-iodine complex adheres to their thick peptiglycan layer. Alcohol dehydrates peptidoglycan layer, which traps crystal violet stain.

Question 14

Give two examples of Gram positive bacteria

Answer 14

Staphylococcus aureus
Clostridium botulinum

Question 15

Give two examples of Gram negative bacteria

Answer 15

Escherichia coli
Vibrio cholerae

Question 16

Why do gram negative bacterial cell walls stain pink when gram staining?

Answer 16

Crystal violet-iodine complex does not adhere to their thin peptiglycan layer, so when alcohol wash dissolves their outer lipopolysaccharide membrane, crystal violet is released.
Safranin counterstain makes cells pink.

Question 17

How do bacteriostatic antibiotics work?

Answer 17

Inhibit growth of bacterial cells.

Question 18

How do bacteriocidal antibiotics work?

Answer 18

Directly destroy bacterial cells.

Question 19

What type of bacteria do beta lactam antibiotics (e.g. penicillin) work against and how do they work?

Answer 19

Both, but more effective against Gram positive.
They inhibit formation of peptiglycan layer during cell division, cell wall becomes weaker, causing cell lysis.

Question 20

What type of bacteria do glycopeptide antibiotics (e.g. vancomycin) work against and how do they work?

Answer 20

Gram positive only, as can’t penetrate out lipopolysaccharide membrane.
They inhibit formation of peptiglycan layer during cell division; cell wall becomes weaker, causing cell lysis.

Question 21

What type of bacteria do polypeptide antibiotics (e.g. polymixins) work against and how do they work?

Answer 21

Gram negative only, as Gram positive don’t have an outer membrane.
They interact with the outer membrane, neutralising their toxicity and causing cell death.

Question 22

List the organelles found in a eukaryotic cell.

Answer 22

nucleus, 80S ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes, Golgi apparatus, cell wall, chloroplasts, vacuole and tonoplast.

Question 23

Describe the structure and function of the nucleus.

Answer 23

Spherical structure surrounded by double membrane - nuclear envelope, which contains pores. Contains chromatin and a dense inner region called the nucleolus.
Stores genetic material (DNA) as chromatin, controls the cells activities by controling the transcription of DNA. Nucleolus is the site of ribosome assembly.

Question 24

Describe the structure and function of the rough endoplasmic reticulum.

Answer 24

A series of membrane bound flattened tubular sacs called cisternea, with ribsomomes bound to the surface.
Folds proteins made on the ribosomes into secondary and tertiary structure and packages in to vesicles to send to Golgi apparatus.

Question 25

Describe the structure and function of the smooth endoplasmic reticulum

Answer 25

A stack of membrane-bound sacs called
with vesicles budding off edges.
Modifies proteins, e.g. adds oligosacharide chains to make glycoproteins, and packages them into vesicles for export.
Produces lysosomes

Question 26

Describe the structure and function of 80S ribsomes.

Answer 26

composed of a large (60S) subunit and a small (40S) subunit,
made of rRNA and proteins.
Site of translation of mRNA (protein synthesis).

Question 27

Conpare free and bound ribosomes.

Answer 27

Free ribosomes are found in the cytoplasm, whereas bound ribosomes are attached to membrane of rER.
Free ribosomes produce intracellular proteins, bound ribosomes produce extracellular proteins.

Question 28

Describe the secretory pathway (how are proteins made and
secreted).

Answer 28

Polypeptides are made by ribosomes on rER.
rER folds them and packages into vesicles.
Vesicles fuse with Golgi apparatus which modfies them and packages them into vesicles.
Vesicles move to and fuse with plasma membrane.
Proteins secreted via exocytosis.

Question 29

Describe the structure and function of mitochondria.

Answer 29

Oval shaped structure surrounded by double membrane.
Inner membrane has folds called cristea. The fluid filled inner space is the matrix which contains ribosomes, enzymes required for the Kreb’s cycle, and mitochondrial DNA.
Produce ATP via aerobic respiration.

Question 30

Where do the aerobic stages of respiration occur within a mitochondrion?

Answer 30

Link reaction and Kreb’s cycle - Matrix
Oxidation phosphorylation - Inner membrane

Question 31

Describe the structure and function of centrioles.

Answer 31

Hollow cylinders containing a ring of microtubules arranged at right angles to each other (in animal cells only).
Produce spindle fibres during cell division.

Question 32

Describe the structure and function of lysosomes.

Answer 32

Small, spherical organelles containing digestive enzymes, bound by a single membrane.
Digest large nutrient molecules and old or damaged parts of organelles.

Question 33

Describe the structure and function of chloroplasts.

Answer 33

Double membrane structure with internal stacks (grana) of thylakoid discs connected by lamella. The fluid filled internal space called the stroma which contains starch, ribosomes, enzymes needed for the Calvin cycle and chloroplast DNA. Site of photosynthesis

Question 34

What is the primary pigment found inside choroplasts?

Answer 34

Chlorophyll (a)

Question 35

Describe the structure and function of the permanent vacuole.

Answer 35

Sac containing cell sap - water with dissolved solutes in it e.g. mineral ions, glucose, etc. surrounded by a selectively permeable membrane called the tonoplast.
Stores nutrients, e.g. mineral ions, and maintains turgidity.

Question 36

Describe the structure and function of amyloplasts in plant cells.

Answer 36

Small, membrane bound organelle containing starch granules.
Storing starch in plants and converting it back to glucose when the plant needs it

Question 37

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

Answer 37

The cell wall is made of different parallel cellulose chains held together by many hydrogen bonds, forming cellulose microfibrils with high tensile strength.
Structural support, prevent cell lysis, resist turgor pressure.

Question 38

What is the middle lamella of a plant cell?

Answer 38

This forms the outermost layer of the plant cell and acts like glue to stick adjacent plant cells together.
It provides stability to the plant.

Question 39

Describe the structure and function of the cell surface membrane.

Answer 39

Lipid bilayer containing phospholipds, proteins, glycoproteins,
glycolipids and cholesterol.
Partially permeable - controls what substances enter and exit.

Question 40

Define magnification

Answer 40

The number of times larger an image is compared with the real size of the object.

Question 41

Define resolution

Answer 41

How far apart two points can be before they are seen as one.

Question 42

Describe how a light microscope works.

Answer 42

A beam of light is shone through the specimen, objective lens and eyepiece lens produce a magnified image.
Max magnification = 1500X.
Max resolution = 200nm.

Question 43

Describe how a transmission electron microscope works.

Answer 43

A beam of electrons focused by electromagnetic coils is transmitted through the specimen inside a vacuum, producing a 2D image of the internal structure of cells/organelles.
A dead specimen is sliced into very thin slices and dehydrated.

Question 44

What is the maximum magnification and resolution of a transmission electron microscope?

Answer 44

Max magnification = 500,000x.
Max resolution = 0.1nm.

Question 45

Describe how a scanning electron microscope works.

Answer 45

The specimen is coated in a very thin layer of metal which reflects the beam of electrons off the surface onto a photographic plate, forming a 3-D image.

Question 46

What is the maximum magnification and resolution of a scanning electron microscope?

Answer 46

Max magnificaiton: x100.
Max resolution: 3nm.

Question 47

Why do electron microscopes have a higher resolution?

Answer 47

Electrons have a shorter wavelength.

Question 48

What is the advantage of electron microscopes?

Answer 48

Higher resolution (so can see more detail) and magnification (so can see smaller objects).

Question 49

What is the disadvantage of electron microscopes?

Answer 49

Sample must be dead as it is placed in a vacuum.
Very expensive and not portable.
Produces only black and white images.

Question 50

Explain the importance of staining specimens in microscopy.

Answer 50

Some stains increase contrast as different components within a cell take up stains to different degrees.
Some stains bind to specific cell structures, and colours them when it reacts with chemicals in it.
Stains make cells and organelles to become visible.