Cell structure

Question 1

describe the function and structure of the cell-surface membrane

Answer 1

function is to regulate movement of substances into and out of cell

• phospholipid bilayer - is lipid soluble so allows hydrophobic substances to diffuse through the membrane

Question 2

describe the function and structure of the nucleus

Answer 2

function is to control chemical reactions within the cell, is the site of DNA replication and transcription and contains the genetic code

• has a double membrane and nuclear envelope
• has pores so substances can move in and out
• nucleolus - site of rRNA production and assembles ribosomes
• nucleoplasm - jelly-like material
• contains chromosomes - linear DNA

Question 3

describe the function and structure of the mitochondrion

Answer 3

site of aerobic respiration, site of ATP production and has mitochondrial DNA which codes for enzymes needed in respiration

• has a double membrane
• has a folded inner membrane called cristae
• inner fluid is called matrix
• loop of mitochondrial DNA (similar to prokaryotic DNA)

Question 4

describe the function and structure of the chloroplast

Answer 4

function is to absorb light energy during photosynthesis

• has a double membrane
• folded inner membrane called thylakoid
• proteins such as chlorophyll are embedded within thylakoid
• liquid is called stroma
• thylakoid stack to form grana

Question 5

describe the function and structure of the Golgi apparatus

Answer 5

function:
- adds carbs to proteins to form glycoproteins
- transports, modifies and stores lipids
- produces secretory enzymes for exocytosis
- makes lysosomes

• a stack of fluid-filled membrane-bound sacs

Question 6

describe the function and structure of the lysosomes

Answer 6

function is to hydrolyse unwanted material using hydrolytic enzymes

• a vesicle containing enzymes
• lots in one cell for faster breakdown

Question 7

describe the function and structure of the ribosomes

Answer 7

function is for protein synthesis during translation

• made up of 2 sub-units
• consist of proteins and rRNA
• no membrane so sub-units can move
• 80s in plant cells and 70s in prokaryotic cells

Question 8

describe the function and structure of the RER

Answer 8

function is to transport and package polypeptides, needed for protein synthesis

• a fluid-filled membrane covered in ribosomes, has a large SA

Question 9

describe the function and structure of the SER

Answer 9

function is to process, synthesise and store lipids and carbohydrates

• fluid-filled membrane with a large surface area

Question 10

describe the function and structure of the cell wall

Answer 10

function is to support and maintain shape of cell - structural support

• made from chitin in fungal cells, cellulose in plant cells, and murein in bacteria

Question 11

describe the function and structure of the cell vacuole

Answer 11

function is to maintain the shape and pressure of the cell which makes it turgid, moves chemicals and stores sugars/amino acids

• membrane-bound (tonoplast) within the cytoplasm and contains cell sap

Question 12

describe how a lysosome can break down eg. proteins

Answer 12

• the lysosome will fuse with the faulty protein and the phospholipid biolayers will join together to become 1
• the hydrolytic enzymes within the lysosome are released which will break down the protein into amino acids
• exocytosis then occurs (when the waste molecules leave the cell)

Question 13

name the structures found within prokaryotic cells

Answer 13

• cell wall made from murein
• no membrane bound organelles
• no nucleus - DNA loop instead
• 70s ribosomes

some contain:
- plasmids, flagella, capsules

Question 14

describe how light microscopes work

Answer 14

• light from a mirror is reflected up through the object into the objective lens
• the image produced is magnified by the eyepiece lens

Question 15

describe how an electron microscope works

Answer 15

• a beam of electrons is produced at the top of the microscope by an electron gun
• electrons are focused into a thin beam

Question 16

why can electron microscopes give a higher resolution?

Answer 16

electrons have a shorter wavelength than visible light so produce higher resolution images

Question 17

what are the advantages and disadvantages of light microscopes?

Answer 17

advantages:
- cheap to purchase and operate
- simple and easy sample preparation

disadvantages:
- low magnification
- lower resolution than electron microscopes

Question 18

what are the advantages and disadvantages of SEM microscopes?

Answer 18

advantages:
- higher magnification and resolution than light microscopes
- can look at 3D structures

disadvantages:
- very expensive
- cannot look at live specimens
- produces only black and white images
- lower resolution than TEM’s

Question 19

what are the advantages and disadvantages of TEM microscopes?

Answer 19

advantages:
- high magnification and resolution
- can see internal structures

disadvantages:
- very expensive
- cannot look at live specimens
- produces only black and white images
- can only be used with very thin objects

Question 20

what are artefacts in microscopy and give some examples

Answer 20

they are things that can be seen under the microscope which are not meant to be there

eg. foreign bodies such as eyelashes, clumps of stain/dye

Question 21

what is the formula for magnification

Answer 21

magnification = image size divided by actual size

Question 22

how do you convert from nm to mm

Answer 22

divide by 1,000,000

Question 23

how do you convert from micrometers to mm

Answer 23

divide by 1000

Question 24

what is cell fractionation?

Answer 24

the process of separating different organelles of a cell, so they can be studied in detail

Question 25

What are the steps in ultracentrifugation?

Answer 25

- homogenise tissue to break open cells and release organelles - filter to remove cell debris - use a cold solution to prevent enzyme activity - use a solution with an equivalent water potential to prevent osmosis (isotonic) - buffer solution to stop proteins/enzymes denaturing - centrifuge at a low speed so higher density organelles eg. nucleus sink to the bottom to form a pellet