Cell structure

Question 1

eukaryotic cells

Answer 1

-larger than prokaryotic cells
-DNA contained in a nucleus
- most eukaryotic cells are part of complex multicellular organisms containing a range of specialised cells to perform a variety of functions
-specialized cells with similar structures and functions are organised into tissues
-animals, plants and fungi are all eukaryotic organisms.

Question 2

organisms inside a eukaryotic cell

Answer 2

-cell surface membrane
-nucleus
-mitochondria
-chloroplasts
-golgi apparatus and golgi vesicles
-lysosomes
-ribosomes
-RER (rough endoplasmic reticulum)
-SER ( smooth endoplasmic reticulum)
-cell wall
-cell vacuole

Question 3

cell surface membrane

Answer 3

-found in all cells
-phospholipid bilyaer- molecules embedded within and attached on the outside (proteins carbohydrates, cholesterol)

Question 4

function - cell surface membrane

Answer 4

controls the entrance and exit of molecules

Question 5

nucleus

Answer 5

-nuclear envelope- double membrane
-nuclear pores
-nucleoplasm- granular jelly-like material
-chromosomes- protein bound linear DNA
-nucleolus- smaller sphere in the nucleoplasm which is the site of rRNA production and ribosome synthesis

Question 6

function of the nucleus

Answer 6

-site of DNA replication and transcription (making mRNA)
-contains the genetic code for each cell.

Question 7

mitochondria

Answer 7

-double membrane
-an inner membrane called the cristae
-the fluid centre called the mitochondrial matrix
-contains 70s ribosomes and circular DNA

Question 8

mitochondria function

Answer 8

site of aerobic respiration and ATP production

Question 9

chloroplasts

Answer 9

-surrounded by a double membrane
-contains thylakoids (folded membranes embedded with pigment)
-the fluid filled stroma contains enzymes for photosynthesis
-found in plants
-contains 70s ribosomes
-contains 70s ribosomes and circular DNA

Question 10

chloroplast function

Answer 10

site of photosynthesis

Question 11

golgi apparatus and vesicles

Answer 11

folded membranes making cristernae
-secretory vesicles pinch off from the cisternae

Question 12

function of golgi apparatus and vesicles

Answer 12

-add carbohydrates to proteins to form glycoproteins
-produce secretory enzymes
-secrete carbohydrates
Transport store and modify lipids from lysosomes
molecules are labelled to reach their destination
-finished products are transported to the cell surface in golgi vesicles where they fuse with the membrane and the contents are released via exocytosis.

Question 13

lysosomes

Answer 13

Bags of digestive enzymes- can contain 50 different enzymes

Question 14

function of lysosomes

Answer 14

-hydrolyse pathogens in phagocytosis
-completely break down dead cells (autolysis)
-exocytosis-release enzymes outside of the cell to destroy material
-digest worn-out organelles for reuse of materials

Question 15

ribosome

Answer 15

-small granuels made up of two subunits of protein and rRNA
-80s large ribosomes found in eukaryotic cells
-70s smaller ribosomes found in prokaryotic cells

Question 16

function of ribosome

Answer 16

the site of protein synthesis

Question 17

RER - rough endoplasmic reticulum

Answer 17

• have ribosomes on the cisternae
  -both rer and ser have folded membranes called cisternae

Question 18

function of the RER

Answer 18

protein synthesis

Question 19

smooth endoplasmic reticulum

Answer 19

has ( along with RER ) has folded membranes called cristernae

Question 20

function of the SER

Answer 20

synthesises and stores lipids and carbohydrates

Question 21

cell wall

Answer 21

-in plants and fungal cells
-in plants - made of microfibrils of the cellulose polymer
-fungi- made of chitin, a nitrogen-containing polysaccharide

Question 22

function of the cell wall

Answer 22

provides structural strength to the cell

Question 23

cell vacuole

Answer 23

filled with fluid surrounded by a single membrane called tonoplast

Question 24

function of cell vacuole

Answer 24

-makes cell turgid and therefore provides support
-temporary store of sugars and amino acids
-the pigments are responsible for coloured petals which attract pollinators

Question 25

prokaryotic cells

Answer 25

- smaller than eukaryotic cells -no membrane bound organelles -smaller ribosomes (70s) -no nucleus -a cell wall made of murein

Question 26

bacteria as a prokaryotic cell

Answer 26

-bacteria still contains DNA, but it is not stored in a nucleus ( free floating DNA) instead DNA is found as a single circular molecule in the cytoplasm and is not associated with the histone proteins -prokaryotic cells do have cell walls, but they do not contain cellulose or chitin, instead they are made of a glycoprotein called murein

Question 27

three additional features of bacteria

Answer 27

-contain plasmids, which are rings of DNA containing genes linked to survival such as antibiotic resisitance -some have a capsule surrounding their cell wall, which provides protection from other cells and helps bacteria aggluntinate (stick together) -some have flagella which are used for locomotion (the movements of objects from one place to another)

Question 28

viruses

Answer 28

-non living and cellular -even smaller than bacteria and only contain genetic material, a capsid and attachment proteins e.g HIV is a virus

Question 29

methods of studying cells that allow us to know the internal structure of cells

Answer 29

-microscopes -cell fractionation -ultracentrifugation

Question 30

what are the three key types of microscopes

Answer 30

-optical microscopes -transmission electron microscopes -scanning electron microscopes

Question 31

what is magnification

Answer 31

how many times larger the image is compared to the object

Question 32

what is resolution

Answer 32

the minimum distance between two objects in which they can still be viewed as seperate

Question 33

how the resolution is determined -optical microscope

Answer 33

the wavelength of light

Question 34

how the resolution is determined- -electron microscope

Answer 34

wavelength of the beam of electrons

Question 35

optical (light) microscope

Answer 35

- a beam of light is condensed to create the image -A glass lens is used to condense the beam of light -poorer resolution due to the light having a longer wavelength -lower magnification -coloured images -can view living samples small organelles in a cell are not visible using an optical microscope, but living samples can be examined and a coloured image is obtained

Question 36

electron microscope ( scanning or transmission)

Answer 36

- a beam of electrons is condensed to create an image -electromagnets are used to condense the beam -higher resolving power as electrons have a shorter wavelength -higher magnification -black and white images -the sample must be in a vacuum, and therefore non-living electrons are absorbed by air, which is why samples must be in a vacuum. the image remains in black and white although the samples are stained

Question 37

Transmission electron microscopes

Answer 37

-extremely thin specimens are stained and placed in a vacuum - an electron gun produces a beam of electrons that passes through the specimen -some parts absorb the electrons and appear dark -the image produced is 2D and shows detailed images of the internal structure of cells

Question 38

scanning electron microscopes

Answer 38

-specimens do not need to be thin, as the electrons are not transmitted through, instead the electrons are beamed onto the surface and the electrons are scattered in different ways depending on the contours -this produces a 3D image

Question 39

how to calculate magnification

Answer 39

image size = actual size x magnification I=AM

Question 40

eyepiece graticule

Answer 40

-the scale on the glass disc inside optical microscopes -can be used to measure the size of objects you are viewing under the microscope - however when you change the objective lens, and therefore the magnification, you have to calibrate the eyepiece to work out what the distance is between each division at that magnification

Question 41

what is used to calibrate the eyepiece lens

Answer 41

a stage micrometer -this is a glass slide with a scale on it which you can place on the stage -the scale on the stage micrometer is typically 2mm long and the sub-divisions are 10 um apart

Question 42

calibration steps

Answer 42

1. line up the stage micrometer and the eye piece graticule whilst looking through the eyepiece 2.count how many divisions on the eyepiece graticule fit into one division on the micrometer scale e.g in this example 20 divisions of the eyepiece graticule fit into 10 divisions of the micrometer, meaning two divisions fit into 1 division of the micrometer 3. each division on the micrometer is 10 um, so this can be used to calculate what one division on the eyepiece graticule is at that current magnification now that the graticule is calibrated you can measure the size of cells or organelles

Question 43

cell fractionation

Answer 43

cells are broken down so that the organelles are free to be seperated. this is done using a homogeniser (blender)

Question 44

conditions during homogenisation

Answer 44

- kept in a cold solution- to reduce enzyme activity to prevent the breakdown of cell components -solution must be isotonic to prevent any movements of water by osmosis which could result in organelles shrivelling or bursting -solution must be buffered to resist pH changes. This is to prevent damage to organelles and enzymes. once the cell has been broken open the solution must be filtered to remove larger pieces of debris.