Biology: Cells

Question 1

how do electron microscopes work and what are the conditions they have to be in?

Answer 1

• electrons fire through the sample, the reflected electrons are observed.
• it must be in a vacuum
• TEM microscope: sample is sliced and stained with a heavy metal
• SEM microscope: specimen is coated with a thin layer of gold.

Question 2

how does centrifugation happen in order to obtain a small organelle?

Answer 2

• cell is homogenated (broken up)
• it’s filtered to remove whole cells and membrane debris.
• it’s put in a supernatant, it’s isotonic, ice cold and buffered to prevent pH or temp. change.
• it’s spun at a slow speed, a pellet containing large organelle forms at the bottom.
• it’s spun at a faster speed for a longer time and smaller organelle collect at the bottom.

Question 3

what is an eyepiece graticule?

Answer 3

• it’s a glass disc that rests on the rim of the eyepiece.

- the stage micrometer is used alongside the graticule to measure the size of the sample.

Question 4

how do you find image size?

Answer 4

actual size x magnification

Question 5

what is the structure of the mitochondria?

Answer 5

• the inner membrane is folded into cristae.

- this maximises surface area so there’s more transport over the organelle.

Question 6

what is the structure of the chloroplast?

Answer 6

-the thylakoid membranes are stacked to increase surface area for maximum light absorption.

Question 7

what do the RER and SER do?

Answer 7

RER:

• it’s rough due to ribosomes on its surface.
• it’s used to sythensise proteins

SER

• lacks ribosomes so it’s smooth
• lipid synthesis.

Question 8

what is cell differentiation?

Answer 8

• the cells of an embryo at an early stage are all the same.
• cells become different from each other.
• differentiated cells are specialised so they carry out specific functions.

Question 9

what is a tissue?

Answer 9

a group of cells of the same type.

Question 10

what are the uses of tissues?

Answer 10

• protection of internal organs from damage
• diffusion of substances across the surface of the epithelium
• absorption of materials, such as the products of digestion.
• secretion of substances onto the surface of the epithelium.

Question 11

what are prokaryotic cells?

Answer 11

• cells with no membrane bound organelle.
• no true nucleus.
• DNA is in a strand which is freely floating inside the cell

Question 12

how does the virus invade cells and replicate?

Answer 12

• attachment proteins bind to receptors on the cell.
• it releases a capsid into the cell.
• this releases its RNA into the cell, which changes the DNA of the cell.
• it replicates viruses
• the cell bursts due to overcrowding.

Question 13

describe the process of mitosis

Answer 13

interphase: DNA replicates so there’s 2 chromatid per chromosome.
prophase: the chromosomes ondense and become more visible, the nuclear membrane breaks down.
metaphase: the chromosomes line up along the middle of the cell and attach to spindle fibres at the poles.
anaphase: the spindle fibres shorten, pulling the chromosomes apart to each of the poles.
telophase: it begins so constrict down the middle and new nuclear membrane forms around both groups of chromosomes. chromosomes decondense and become less visible

Question 14

what is the fluid mosaic model?

Answer 14

• it shows the structure of the phospholipid bilayer

- it’s fluid mosaic as it’s flexible and consists of many parts, each of different shapes and sizes.

Question 15

what is the purpose of the phospholipid bilayer?

Answer 15

• the hydrophilic head and hydrophobic tail doesn’t let water in.
• intrinsic proteins allow the passage of certain molecules through

Question 16

what is the purpose of the channel and carrier proteins?

Answer 16

CHANNEL:
-water filled tubes to allow the passage of water-soluble molecules into the cell.

CARRIER:

• used in active transport
• change shape to let larger molecules enter the cell.

Question 17

what is the purpose of cholesterol in the phospholipid bilayer?

Answer 17

• increases resistance to temp. change

- keeps the membrane structurally strong

Question 18

what is diffusion and what factors can affect it?

Answer 18

the movement of a substance from high to low concentration down a concentration gradient until it reaches equilibrium. it’s a passive process as it doesn’t require energy.

factors:

• conc. of substance
• length of diffusion pathway

Question 19

what is facilitated diffusion?

Answer 19

diffusion using the channel proteins. it’s still passive etc.

Question 20

what is osmosis?

Answer 20

the net movement of water molecules through a partially permeable membrane until equilibrium is reached. high to low concentration

Question 21

what is water potential?

Answer 21

the pressure exerted by water molecules. measured in kPa.

Question 22

what is the water potential of pure water?

Answer 22

0

Question 23

what does fick’s law state?

Answer 23

rate of diffusion proportional to:

(surface area x gradient) / length of diffusion pathway

Question 24

how does active transport work?

Answer 24

• molecules go into carrier protein
• a phosphate from ATP phosphorylates the protein and it changes shape.
• this releases the molecules out of the other end of the membrane and into the cell

Question 25

how does the sodium-potassium pump work?

Answer 25

3 sodium out, 2 potassium in

• 3 sodium ions bind using ATP
• phosphate binds, changing the tertiary structure
• 3 sodium released from cell
• higher affinity for potassium
• 2 potassium bind
• phosphate dissocated
• 2 potassium carried into the cell as well as glucose and amino acids etc.

Question 26

what does hypertonic mean?

Answer 26

concentration of solute in a solution surrounding the cell is greater than that inside the cell

Question 27

what does isotonic mean?

Answer 27

solutes in solution = solutes in cell

Question 28

what does hypotonic mean?

Answer 28

conc. of solute in solution surrounding the cell is less than that inside the cell.

Question 29

what happens to a cell in a:

hypertonic solution
hypotonic solution
isotonic solution

Answer 29

hypertonic:
cell deflates as water potential outside the cell is lower so water leaves the cell

hypotonic:
cell lysis as water enters the cell

isotonic:
nothing happens

Question 30

how do barriers prevent us against pathogens?

Answer 30

-prevent pathogens from entering the body

• eyes: tears, eyelashes, blinking
• skin: oily substance called sebum

Question 31

describe the process of phagocytosis

Answer 31

• phagocyte attracted to pathogen by chemoattractants
• it engulfs the pathogen and puts it in a vesicle called a phagosome
• lysosomes line up around the vesicle
• they release lysozyme, a digestive enzyme, into the vesicle
• it hydrolyses the pathogen
• it leaves the phagocyte by exocytosis.

Question 32

what to cytotoxic t-cells do?

Answer 32

• they use an enzyme to break down the membrane of a cell

- water enters the cell, causing cell lysis

Question 33

what do b-cells do in response to phagocytosis?

Answer 33

• divide and produce clones of cells.
• most of these cells are plasma cells and produce monoclonal antibodies
• monoclonal antibodies are complementary to a certain antigen

Question 34

how do antibodies destroy antigens?

Answer 34

agglutination: easier for phagocytes to engulf them
precipitation: facilitates phagocytosis
markers: signal phagocytes

neutralisation of toxins

lysis: breaks down bacteria

Question 35

what’s the difference between artificial and natural immunity?

Answer 35

natural: the body’s response to the antigen
artificial: brought about by vaccinations